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Bidirectional communication between nucleotide and substrate binding sites in a type IV multidrug ABC transporter
No full textInternational audienceATP-binding cassette (ABC) transporters use ATP to transport substrates across membranes. In type IV ABC transporters, which include many multidrug resistance (MDR) pumps, communication between nucleotide-binding domains (NBDs) and transmembrane domains (TMDs) is mediated via large intracellular domains containing ‘coupling helices’. However, how ATP hydrolysis and substrate transport are functionally coordinated remains unclear. In the bacterial type IV MDR transporter BmrA, we identify a conserved residue cluster at the NBD/TMD interface centered on W413. Mutation of this tryptophan uncouples ATP hydrolysis from transport activity. Mutagenesis, functional assays, nuclear magnetic resonance spectroscopy, hydrogen-deuterium exchange mass spectrometry, and photo-induced electron-transfer fluorescence correlation spectroscopy show that the cluster forms a bidirectional communication hinge that relays signals between the NBD and TMD via coupling helix 2. Hinge mutations affect both local and global dynamics thereby influencing transporter activity. These findings uncover an allosteric pathway critical for functional coupling in multidomain ABC transporters
Dévoiler la naissance des premères galaxies massives avec le Télescope Spatial James Webb
No full textOver the past few decades, our understanding of galaxy evolution has been greatly enhanced by multiwavelength observations. In particular, the combined capabilities of the Spitzer Space Telescope (Spitzer) and the Atacama Large Millimeter/submillimeter Array (ALMA), has shed light on a population of galaxies extremely faint from the rest-frame ultraviolet (UV) up to the optical because of their high dust content, making them undetectable, even in the reddest and deepest images of the Hubble Space Telescope. This population has been shown to make a significant contribution to the star formation rate density of the z > 3 Universe, exceeding that of equivalently massive Lyman Break Galaxies (LBGs) by more than an order of magnitude. This makes them ideal candidates for being the ancestors of the first Quiescent Galaxies (QGs) in the Universe, supposing a scenario in which galaxies tend to undergo a morphological transformation when transitioning to passivity. This morphological change is thought to happen in an extremely dust-obscured phase, thus being only observable in the infrared (IR). However, the limited angular resolution of Spitzer in the near-infrared (NIR) has prevented detailed morphological analyses of this population at these redshifts, thus making it impossible to test this scenario.In this thesis, I used the unprecedentedly deep and high angular-resolution NIR imaging capabilities of the James Webb Space Telescope to study, for the first time, the spatially resolved properties of large samples of highly-obscured galaxies across cosmic time, with the aim to unveil the critical role of dust-shrouded star-formation in the morphological evolution of galaxies. In my first project, I assembled a mass-complete sample of 188 sources with log(M/M⋆) > 9.6 at z=3-4 in the CEERS field containing typical blue star-forming galaxies (BlueSFGs), red (and therefore heavily dust-obscured) star-forming galaxies (RedSFGs), and QGs. I investigated and compared their radial distribution in stellar mass, star-formation rate (SFR), and dust attenuation (Av), and was able to show that RedSFGs and QGs exhibit similar stellar surface density profiles, while RedSFGs have a significantly higher central concentration of dust attenuation compared to BlueSFGs across all stellar mass ranges. Since RedSFGs outnumber BlueSFGs at high mass log(M/M⋆) > 10.4, similarly to QGs outnumbering BlueSFGs in the local Universe, these results confirm the morphological connection between BlueSFGs, RedSFGs, and QGs in which the RedSFG phase is the ultimate contraction of the star-forming region preceding quenching. This work suggests that this color and morphological bimodality between extended BlueSFGs and compact and strongly attenuated RedSFGs is at the origin of the local bimodality between BlueSFGs and QGs, which I refer to as a "primeval bimodality."In my second project, I investigated dust-obscured star formation across cosmic time. I extended my sample by working on the PRIMER survey, which is a ~4 times bigger survey in area, and worked on mass-complete samples from z =1-5. While this is still a work in progress, this new study shows that there are two distinct regimes of star formation as traced by dusty SFGs at all cosmic times, hinting toward a universal quenching mechanism. Entering this second regime of star formation is correlated with the total stellar mass, but when the latter is fixed, compactness of both the stellar and the dust content are the main drivers of this transition. I showed that the most massive and compact galaxies at low redshift had already entered this regime early in the history of the Universe, and at lower stellar masses, suggesting that the underlying mechanism may depend on the initial conditions in which galaxies form. Galaxies can remain in this star-formation regime for extended periods, but they tend to eventually transition into quiescence.Au cours des dernières décennies, les observations multi-longueurs d'onde ont considérablement enrichi notre compréhension de l'évolution des galaxies. En particulier, les capacités combinées du télescope spatial Spitzer et du réseau millimétrique et submillimétrique ALMA ont révélé une population de galaxies extrêmement faibles en émission du repos-UV à l'optique, en raison d'une forte obscuration par la poussière. Indétectables, même dans les images les plus profondes du télescope Hubble, ces galaxies contribuent pourtant de manière significative à la densité de formation d'étoiles à z > 3, dépassant celle des galaxies Lyman Break massives d'un ordre de grandeur. Elles apparaissent ainsi comme les meilleures candidates au rôle d'ancêtres des premières galaxies quiescentes (QGs), selon un scénario où la transition vers la passivité s'accompagne d'une transformation morphologique. Celle-ci surviendrait durant une phase de forte obscuration, uniquement accessible dans le proche-infrarouge (NIR). Toutefois, la faible résolution angulaire de Spitzer dans cette gamme n'a jusqu'ici pas permis de tester ce scénario.Dans cette thèse, j'ai utilisé les capacités inédites d'imagerie NIR profonde et haute résolution du télescope James Webb pour étudier, pour la première fois, les propriétés résolues spatialement de grands échantillons de galaxies très obscurcies par la poussière à travers le temps cosmique, afin de mettre en lumière le rôle fondamental de la formation stellaire enfouie dans l'évolution morphologique des galaxies.Dans le premier projet, j'ai constitué dans le champ CEERS un échantillon complet en masse de 188 galaxies avec log(M/M⋆) > 9.6 à z = 3-4, incluant des galaxies bleues à formation d'étoiles (BlueSFGs), rouges et très obscurcies (RedSFGs), ainsi que des galaxies quiescentes. J'ai comparé leurs profils radiaux en masse stellaire, SFR et atténuation (Av), et montré que les RedSFGs et QGs partagent des densités stellaires similaires, tandis que les RedSFGs présentent une concentration centrale en poussière bien plus marquée que les BlueSFGs, quel que soit leur masse. Les RedSFGs devenant dominantes à haute masse (log(M/M⋆) > 10.4), tout comme les QGs dans l'Univers local, ces résultats indiquent qu'il existe un lien évolutif entre BlueSFGs, RedSFGs et QGs, où la phase RedSFG incarne l'ultime contraction de la région de formation stellaire précédant l'arrêt de l'activité. Ce travail suggère que la bimodalité locale entre BlueSFGs étendues et QGs compactes trouve son origine dans une bimodalité plus ancienne, entre BlueSFGs et RedSFGs, que je désigne comme « bimodalité primitive ».Dans le second projet, j'ai étudié la formation stellaire obscurcie à travers le temps cosmique en exploitant le relevé PRIMER, environ quatre fois plus étendu, pour constituer des échantillons complets en masse de z = 1 à 5. Bien qu'encore en cours, cette étude révèle déjà deux régimes distincts de formation stellaire pour les galaxies poussiéreuses, suggérant l'universalité d'un mécanisme d'arrêt de la formation d'étoiles, le « quenching ». L'entrée dans ce second régime est corrélée à la masse stellaire totale, mais, à masse fixée, la compacité des composantes stellaires et poussiéreuses en sont les moteurs principaux. J'ai montré que les galaxies les plus massives et compactes à bas redshift étaient déjà entrées dans ce régime très tôt dans l'histoire de l'Univers, et ce à des masses stellaires plus faibles, suggérant que le mécanisme sous-jacent pourrait dépendre des conditions initiales dans lesquelles les galaxies se forment. Les galaxies peuvent rester dans ce régime de formation d'étoile pendant des périodes prolongées, mais ont tendance à évoluer pour devenir passives
Global climate: monitoring drought using the self-calibrating Palmer drought severity index
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Optimisation de la sensibilité de capteurs AMR La1-xSrxMnO3 sur substrat vicinal SrTiO3 par intégration de concentrateurs de flux magnétique
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Nanoscale structural and chemical studies of the modifications induced by swift heavy ion irradiation in SrTiO3 at grazing incidence
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Iron Phosphate-Based Oxide Glasses as Cathode Materials for Lithium-Ion Batteries
No full textInternational audienceRechargeable lithium-ion batteries (LIBs) are a key alternative to reduce our reliance on fossil fuels. LIBs utilize cathode materials based on polycrystalline oxides or polyanionic compounds. However, some of these materials have limited performance due to their crystalline structure with restricted energy and power density, as well as poor cycling life. To address these issues, the use of glasses as cathode materials appears to be a promising approach. High specific capacities can be achieved depending on the composition of the glass1). Glasses have a structure with a high free volume, allowing them to accommodate a significant amount of lithium and easily undergo structural changes during lithium ion extraction/insertion. Furthermore, glass production is a scalable process and may be easier to implement commercially than most synthesis processes for conventional cathode materials. Phosphate glasses have been explored as promising cathode materials for lithium-ion batteries 2).In this study, we focused on iron phosphate oxide glasses. The impact of synthesis conditions and the iron content proportion on the amorphous nature of the as-prepared glasses, as well as their electrical properties, was investigated. The electronic and ionic conductivities of the bulk glasses were measured as a function of temperature using Electrical Impedance Spectroscopy (EIS). The electrochemical properties, including specific capacity, redox potentials vs Li+/Li, first cycle capacity loss, and coulombic and energy efficiencies, were examined in a coin cell through Galvanostatic Cycling. To clarify the reaction mechanisms of the electrochemical processes involved in these materials, Mössbauer Spectroscopy at room temperature was coupled and performed on the as-prepared glasses, as well as on the electrodes before and after cycling, at different electrochemical states of charge. This new study will provide valuable insights to optimize both the glass composition and its fabrication conditions, aiming to achieve high-performance cathode materials without the use of critical elements.1) K. Kercher et al., J. Electrochem. Soc., vol. 163, no 2, p. A131‑A137, 2016.2) Delanoë, A et al. S., Mater. Lett., 382, 137879, 2025
Distributed RIS-based sensing of mobile passive obstacles in dense mmWave networks
No full textInternational audienceThe millimeter-wave (mmWave) technology offers unprecedented potential to meet the growing demand for high-speed data communications. However, it is also highly sensitive to radio obstructions, which can significantly degrade the quality of service and require frequent handover operations. Anticipating such blockages through environment sensing is therefore critical for efficient radio resource management and improved network performance. In this context, this paper proposes an opportunistic and cooperative sensing approach based on spatially distributed dual-beam reflective Reconfigurable Intelligent Surfaces (RISs). These surfaces scan the environment and reflect toward sensing nodes the ambient signal power from a plurality of non-coherent sources. By analyzing the power fluctuations eventually caused by transient shadowing, the presence of a mobile blocker is first detected in angular sectors centered around the RISs. This information can then be shared and fused to position the blocker in 2D. As passive surfaces can suffer from significant power losses and irregular beam patterns leading respectively to false alarms and missed detections, we thus consider selecting and/or weighting the RIS-wise detection observations that feed the final cooperative positioning stage, relying on empirical reliability indicators inspired by image processing. Simulation results in a dense mmWave scenario illustrate benefits from selective multi-RIS cooperation
Smart Cut™ Transfer of Wide Bandgap Materials: The Case of Diamond
No full textInternational audienceThe ability to transfer a thin layer of high-quality wide-bandgap (WBG) material onto a substrate that is either more cost-effective or offers functional advantages (e.g. thermal, electrical, or insulating properties) is of significant interest. The Smart Cut™, which combines ion implantation with wafer bonding, enables the fabrication of material structures that cannot be achieved using conventional deposition techniques. Recent advances in direct covalent bonding methods have also relaxed stringent surfaces and substrate requirements, expanding the range of materials that can be assembled and opening new possibilities for heterogeneous integration. We develop the transfer of IIa diamond films onto larger and less expensive substrates
Search for light pseudoscalar bosons, pair-produced in Higgs boson decays in the four-electron final state in proton-proton collisions at = 13 TeV
No full textInternational audienceA search for pairs of light neutral pseudoscalar bosons (A) resulting from the decay of a Higgs boson is performed. The search is conducted using LHC proton-proton collision data at = 13 TeV, collected with the CMS detector in 20162018 and corresponding to an integrated luminosity of 138 fb. The A boson decays into a highly collimated electron-positron pair. A novel multivariate algorithm using tracks and calorimeter information is developed to identify these distinctive signatures, and events are selected with two such merged electron-positron pairs. No significant excess above the standard model background predictions is observed. Upper limits on the branching fraction for H AA 4e are set at 95% confidence level, for masses between 10 and 100 MeV and proper decay lengths below 100 m, reaching branching fraction sensitivities as low as 10. This is the first search for Higgs boson decays to four electrons via light pseudoscalars at the LHC. It significantly improves the experimental sensitivity to axion-like particles with masses below 100 MeV
Search for Higgsinos in final states with low-momentum lepton-track pairs at 13 TeV
No full textInternational audienceWe present a search for the pair production of Higgsinos in final states with large missing transverse momentum and either two reconstructed muons or a reconstructed lepton (muon or electron) and an isolated track. The analyzed data correspond to proton-proton collisions with an integrated luminosity of 137 fb, collected by the CMS experiment at = 13 TeV in 2016, 2017, and 2018. The signal scenario assumes two neutralino states, and , with a small mass difference in the range 110 GeV and a chargino with an intermediate mass. The analysis focuses on the decay of the heavier neutralino into the lighter one and a virtual Z boson, which decays into two same-flavor leptons. The leptons have small transverse momentum and/or a small opening angle between the identified muons. An isolated track is used to recover events in which only one of the two leptons is identified. Multivariate discriminants are used to enhance the sensitivity by efficiently rejecting backgrounds from SM processes or misreconstructed tracks and/or leptons. The search explores a unique phase space and probes a previously unexplored region of the signal model parameter space. Mass differences between the two neutralinos are probed down to 1.5 GeV, assuming a Higgsino mass of 100 GeV. The maximum excluded Higgsino mass is 115 GeV