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Channel Estimation for Double-RIS-Assisted Multi-User MIMO System in the Presence of Obstructed Links Using Deep Learning
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New organic–inorganic bromides [(C3H7)4N]2MBr4 (M=Hg and Cd): Synthesis, crystal structure and vibrational characterization
No full textInternational audienceTwo new quaternary ammonium mercury bromide and cadmium bromide crystals [(C3H7)4N]2HgBr4 and [(C3H7)4N]2CdBr4 have been synthesized by slow evaporation method at room temperature. Their crystal structure was determined at room temperature by single crystal X-ray diffraction. Both structures consist of three symmetrically inequivalent tetrapropylammonium cations and one discrete tetrahedral [MBr4]2- (M=Hg and Cd) anions. The compounds are isomorphous and crystalize in monoclinic system with C 2/c space group. The purity of each preparation was confirmed by X-ray powder diffraction measurements at room temperature. Internal vibration modes of both crystals have been studied at room temperature using Raman spectroscopy. The structural phase transitions in [(C3H7)4N]2HgBr4 and [(C3H7)4N]2CdBr4 are studied by differential scanning calorimetry (DSC) and two reversible structural phase transitions are detected at 341/330 K and 402/375 K for [(C3H7)4N]2HgBr4 and at 345/333 K and 404/377 K for [(C3H7)4N]2CdBr4 on heating/cooling process. Electrical measurements showed that both compounds were good semiconductors. The thermal evolution of their conductivity shows two regime changes at the temperatures at which structural transitions occur. The thermal evolution of the dielectric constant shows that the second phase transition for the [(C3H7)4N]2CdBr4 compound is ferroelectric in nature
La pratique de la pleine conscience au service d’une gouvernance comportementale des organisations
No full textInternational audienceEn 2020, Gérard Charreaux invitait à construire un « nouveau modèle du comportement humain qui intègre les résultats des travaux des économistes, des psychologues et des spécialistes des neurosciences afin de comprendre les comportements rationnels (calculés) et non rationnels » (Charreaux, 2000b), et ce faisant, « d’entreprendre au niveau de l’individu, le même effort que celui qui a été entrepris au niveau de l’organisation, c’est-à-dire de faire éclater la “boîte noire” individuelle de façon à mieux théoriser le comportement ». Le chapitre propose une voie d’opérationnalisation de cette perspective comportementale en tentant de montrer en quoi la pratique de la méditation de pleine conscience (traduction française de mindfulness meditation), objet d’études des neuroscientifiques et des psychologues, peut constituer un dispositif permettant aux organisations de diminuer les biais comportementaux et de réduire les « coûts d’agence avec soi-même » cités précédemment
Constraints on the neon isotopic composition of the lower mantle by single vesicle analyses in Icelandic glasses
No full textInternational audienceThe origin of volatile elements on Earth is still debated. Noble gases, due to their chemical inertness, can serve as powerful proxies to study planetary formation processes and mantle evolution. Neon is particularly relevant for tracing the source of volatile elements of our planet as its isotopic composition varies greatly between reservoirs in the Solar System. The existence of a preserved (over 4.45 Ga), relatively undegassed, reservoir in the mantle has been inferred from noble gas isotopic systematics [1]. This reservoir is tapped by deeply rooted mantle plumes, namely Galapagos, Hawaii and Iceland plumes. Analysis of quenched glass, preserving magmatic gases, from these locations, revealed that the neon isotopic composition of the lower mantle is different to that of the upper mantle (source of the MORBs), particularly for the 21Ne/22Ne ratio. In both cases however, neon has a20Ne/22Ne ratio over 12, akin to a solar, primitive source, distinct from the atmospheric ratio of 9.8. Two models may explain Earth's mantle neon isotopic compositions: (1) the capture and dissolution of a primordial atmosphere in an early magma ocean, or (2) solar wind irradiation of pre-planetary dust yielding different 20Ne/22Ne ratios in a preserved reservoir. The exact neon isotopic compositions of the lower mantle is still unclear, however. Indeed, the step-heating or step-crushing analytical techniques leads to a mixing curve for neon isotopic ratios between air contained in cracks and open vesicles (20Ne/22Ne = 9.8) and the mantellic value, contained in closed vesicles. To address this, we analyzed single vesicles from undegassed Icelandic subglacial lavas and developed a statistical approach to determine the 20Ne/22Ne of the Icelandic source. This technic has been shown to be efficient to obtain the neon isotopic composition devoid of shallow atmospheric contamination Our findings support solar wind irradiation of protoplanetary disk dust as the mechanism for Earth's light volatile accretion, aligning with Péron et al. [2] for the Galapagos mantle source
Hydrological and temperature controls on CO2 and CH4 exchange between a mid-altitude mountain peatland and the atmosphere
No full textInternational audienceThe aim of the present study is to understand the variability and the environmental factors controlling the fluxes of carbonaceous greenhouse gases (GHGs), methane (CH4) and carbon dioxide (CO2) between a temperate Sphagnum-dominated mid-altitude mountain peatland and the atmosphere. We conducted monthly measurements of GHG fluxes over 20 months using the chamber method. Specifically, we assessed the effects of (1) air temperature and (2) water level (WL) on GHG emissions. Open Top Chambers (OTC) were used to simulate a warming effect by passive heating of the air above the soil. To assess the effect of WL, we studied a hydrological gradient along a 35 m long transect from a near-surface "WET" area, through an "INTER" area with an intermediate WL, to a "DRY" area with a lower WL. The WET area featured a higher cover of Sphagnum species while the vegetation cover in the DRY area contained more vascular plants. Although all plots showed the same seasonality of GHG fluxes, considerable variability was observed among them. Raising the temperature using OTCs, which increased annual average air temperature by 0.2 °C to 0.6 °C, did not significantly affect CH4 and CO2 respiration (Reco) fluxes. In contrast, hydrological conditions played an important role in explaining flux variability. CH4 fluxes were significantly higher in the WET and INTER areas (median [95 % CI] values: 17.5 [14.2, 29.0] and 20.0 [14.8, 30.4] nmol m -2 s -1 ) compared to the DRY area (3.4 [1.9, 9.4] nmol m -2 s -1 ) during all hydrological periods, i.e., humid spring, humid summer and dry summer. Reco did not vary significantly along the hydrological gradient overall, but the fluxes were lower in the WET area under humid spring (0.4 [0.3, 0.6] µmol m -2 s -1 ) and summer (1.7 [1.25, 2.75] µmol m -2 s -1 ) conditions compared to the DRY area (1.6 [1.3, 2.0] µmol m -2 s -1 in spring and 3.8 [2.7, 4.6] µmol m -2 s -1 in summer). Conversely, greater fluxes (by ~ 0.5 µmol m -2 s -1 ) were observed in the WET area during summer drought. Given that Reco emissions are expected to be higher during droughts in the DRY area, we hypothesise a possible threshold effect, such as inhibition of phenoloxidase activity and/or other enzymatic activities, which would limit organic matter decomposition. Moreover, increasing WL in the WET and INTER areas led to a drastic drop in gross primary production (GPP) corresponding to Sphagnum immersion
Compréhension de la formation de l'Interface Electrolyte Solide (IES) et de la solvatation des ions sodium au sein de nouveaux systèmes d'électrolyte via la spectroscopie RMN pour des applications de batteries
No full textSodium-ion and sodium-metal batteries are emerging as more sustainable alternatives to current lithium-based systems. These technologies have the potential to deliver high energy density at lower cost. However, their development requires the design of safe and stable electrolytes capable of facilitating the transport of sodium ions within the electrolyte. One of the main challenges lies in the high reactivity of metallic sodium, which can pose safety concerns, reduce battery lifespan, and lead to the formation of undesirable interfacial layers between the electrolyte and the electrode, commonly referred to as the Solid Electrolyte Interphase (SEI) layer. In this thesis, we investigated novel solidand liquid electrolytes using solid-state Nuclear Magnetic Resonance (NMR) spectroscopy, a powerful technique that provides detailed atomic-level insights into material structure and dynamics. We focused on two types of solid electrolytes : block copolymers containing polymerized ions and zwitterionic plastic crystals, both doped with sodium salts to enhance their ionic conductivity. We also analysed the various phases present in the SEI layer when metallic sodium is employed as the electrode in combination with ionic liquid-based electrolytes. Our results indicate that the molecular structure, as well as the interactions between the different conformations adopted by the electrolyte solvent and sodium ions, significantly influence the conductivity of our electrolytes. For example, one solvent conformation facilitates ion transport due to its higher dynamics, whereas another exhibits very low mobility, promoting particularly strong interactions between this conformation and the sodium ions. Furthermore, at high concentrations of sodium salt mixed with the zwitterion, sodium ions bind excessively to their local environment, thereby reducing their effective mobility. Although the zwitterion exhibits local disorder, this effect is mitigated by the high concentration of sodium salt. Additionally, we identified key compounds in the SEI layer, such as sodium fluoride and various sulfur- and oxygen-based species. Some of these compounds are known to be highly stable and thus beneficial for the SEI, while others are entirely novel, raising new questions regarding the electrolyte decomposition mechanism during battery operation.This work improved understanding of local structure, solvation, and sodium-ion interactions, achieved through advanced solid-state NMR spectroscopy, will guide the design of new electrolytes based on ionic liquids, zwitterions, and ion-containing polymers, with the goal of achieving even higher performance.Les batteries sodium-ion et sodium-métal offrent une alternative plus durable à celles à base de lithium. Ces technologies présentent le potentiel de fournir une densité énergétique élevée à moindre coût. Toutefois, leur développement requiert la conception d’électrolytes sûrs et stables, capables de faciliter le transport des ions sodium au sein de l’électrolyte. L’un des principaux défis réside dans la forte réactivité du sodium métallique, qui peut engendrer des problèmes de sécurité, réduire la durée de vie des batteries et conduire à la formation de couches interfaciales indésirables entre l’électrolyte et l’électrode, communément appelées couches d’interface électrolyte solide (Solid Electrolyte Interphase, SEI). Dans le cadre de cette thèse, nous avons étudié de nouveaux électrolytes, solides et liquides, à l’aide de la spectroscopie de Résonance Magnétique Nucléaire (RMN) à l’état solide, une technique puissante offrant une compréhension fine, à l’échelle atomique, de la structure et de la dynamique des matériaux. Nous nous sommes concentrés sur deux types d’électrolytes solides : des copolymères blocs contenant des ions polymérisés et des cristaux plastiques zwitterioniques, tous deux dopés avec des sels de sodium afin d’améliorer leur conductivité ionique. Nous avons également analysé les différentes phases présentes dans la couche SEI lorsque le sodium métallique est employé comme électrode en combinaison avec des électrolytes à base de liquides ioniques. Nos résultats montrent que la structure moléculaire, ainsi que les interactions entre les différentes conformations adoptées par le solvant électrolytique et les ions sodium, influencent de manière significative la conductivité de nos électrolytes. Par exemple, une certaine conformation du solvant favorise le transport ionique en raison de sa dynamique plus élevée, tandis qu’une autre, caractérisée par une mobilité très faible, induit des interactions particulièrement fortes entre cette conformation et les ions sodium. Par ailleurs, à des concentrations élevées de sel de sodium mélangé avec le zwitterion, les ions sodium se lient de manière excessive à leur environnement local, ce qui réduit leur mobilité effective. Bien que le zwitterion présente un désordre local, cet effet est atténué par la forte concentration en sel de sodium. Nous avons également identifié des composés clés dans la couche SEI, tels que le fluorure de sodium ainsi que diverses espèces soufrées et oxygénées. Certains de ces composés sont connus pour leur grande stabilité, et sont ainsi bénéfiques pour la SEL, tandis que d’autres, totalement inédits, soulèvent de nouvelles questions concernant le mécanisme de décomposition de l’électrolyte lors du fonctionnement de la batterie. Ce travail a permis d’approfondir la compréhension de la structure locale, de la solvatation et des interactions entre les ions sodium grâce à la spectroscopie RMN à l’état solide avancée. Il contribuera à orienter la conception de nouveaux électrolytes fondés sur les liquides ioniques, les zwitterions et les polymères porteurs d’ions, dans la perspective d’atteindre des performances encore meilleures
Un géographe du Limousin : Aimé Perpillou (1902-1976)
No full textNational audienceL’origine familiale explique-t-elle les écrits ou recherches d’un universitaire ou d’un scientifique ? De quelle manière oriente-t-elle le choix de ses terrains d’étude ? Pour répondre à ces deux questions, les deux auteurs ont collaboré à une étude académique sur Aimé Perpillou, éminent géographe natif du Limousin, région dont il a fait un lieu privilégié pour ses travaux de recherche. L’article présente la généalogie de ce dernier, qui se concentre dans le val de Briance, et montre de quelle manière elle explique sa vocation et sa démarche de travaux. Pour cela est retracée la remarquable carrière de ce géographe du 20e siècle, enseignant et chercheur, dont les manuels scolaires de géographie sont peut-être toujours dans le souvenir de certains d’entre nous
No evidence of an effect of the M184I/V on the doravirine/lamivudine/tenofovir switch efficacy in people living with HIV
No full textInternational audienceObjectives: The effect of the M184I/V mutation on the rate of virological failure (VF) in people living with HIV (PLWHIV) with plasma HIV RNA viral load (VL) <50 copies/mL switching to a triple-therapy regimen of doravirine+lamivudine+ tenofovir or abacavir has not been evaluated. Design: A retrospective national study of antiretroviral-experienced PLWHIV who were switched to a doravirine plus lamivudine and abacavir or tenofovir regimen in the context of maintenance (VL<50 copies/mL) was conducted. Virological failure (VF) was characterized by either two consecutive plasma viral loads (VL) ≥ 50 copies/mL or a single VL ≥ 200 copies/mL. Viral blip (VB) was defined as an isolated VL 50_200 copies/mL at any time up to month 6 after switching to the doravirine-containing regimen. Results: Among the 338 PLWHIV, doravirine was mainly associated with tenofovir+lamivudine (311/338, 92.0%). Of these, 45 had a M184I/V mutation before switching. VF at M6 was 14.0% and 17.8% in the absence and presence of M184I/V, respectively, with an adjusted odds ratio (aOR) of 2.409, 95%CI 0.574–10.113, p=0.21. The risk of VF at M6 was associated with the level of zenith plasma HIV VL, with an aOR of 1.646, 95% CI 1.163–2.328, p = 0.0049, per additional log 10 unit. The proportion of VB at M6 was 2.4% and 6.7% in PLWHIV in the absence and presence of M184I/V, respectively, with an aOR of 0.818, 95%CI 0.187–3.587, p = 0.7897. Conclusions: Among PLWHIV with antiretroviral experience, there was no evidence that switching to doravirine + lamivudine plus tenofovir affected short-term treatment response in individuals harboring HIV M184I/V mutations
Model reduction strategy for the dynamic analysis of plates with a nearly periodic array of circular acoustic black holes
No full textInternational audienceThe concept of acoustic black hole (ABH) refers to bending stiffness decrease and added damping to localize and efficiently dissipate flexural vibrations in thin structures. For plate-like structures, a ABH typically takes the form of a circular pit whose thickness decreases as a power-law with the distance to the center. The central region has a very small residual thickness, and it is covered by a damping layer. While being inefficient at low frequencies, ABHs can drastically lowered the resonant behavior of a host structure at high frequencies (after a certain cut-on frequency). 2D-periodic arrays of circular ABHs embedded in a host structure can be involved, where the periodicity property is used to create low frequency band gaps. For instance, a small mass can be added to the center of each circular ABH to create resonant band gaps. Besides the analysis of structures with periodic arrays of ABHs, nearly periodic structures will be explored in this paper to see whether the lack of periodicity can be detrimental to create band gaps, or, on the contrary, if this can be used to enlarge band gaps. In the case of a periodic array of circular ABHs with central masses, near-periodicity can result from manufacturing imperfections of the ABH thicknesses, or slight variations of the central masses. Those nearly periodic structures can be seen as assemblies of different substructures (i.e., structure cells encompassing an ABH) subjected to parametric changes. For nearly-periodic structures built from finite element models of substructures with many degrees of freedom, parametric model order reduction strategies can be used to reduce the computational costs of the forced response simulations. In this paper, an interpolation strategy will be explored to approximate the reduced matrices of substructures over parametric spaces. This circumvents the need for computing the component mode bases, and the reduced matrices, many times for investigating different parametric changes. An enhanced version of this strategy is proposed here, which includes interface reduction and basis enrichment techniques. Numerical experiments are carried out on a plate with circular ABHs
Adaptive Local Maxima Windows for Tree Segmentation: A Point Process Perspective
No full textThe growing accessibility of Light Detection And Ranging (LiDAR) data brings out novel perspectives that are crucial for tracking forest growth and enhancing resource management amid climate change. Utilizing these data to propose decision-support tools involves a vital step of segmenting individual trees. Although most of the segmentation algorithms in the literature are designed to be unsupervised, some hyperparameters, which are likely to be site-or species-specific, need to be set by the users, thus increasing the risk of bias. In this direction, based on point process theory, we introduce formal implementation guidelines to refine the window size selection for the class of Local Maxima algorithms, a widely adopted class of methods for tree segmentation. This methodology can also be applied to incomplete plot measurements. We apply this methodology to an open dataset to ensure the reproducibility of the results. The method achieves an F 1 -score in the 55 -90% range, depending on the positioning of the tree within the canopy relative to its neighboring trees, i.e., its dominance status.</div