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Magic-Angle Spinning NMR in a manganese sodium-ion cathode material and in surface-treated lithium titanate
No full textInternational audience1. AbstractHigh-resolution Magic Angle Spinning NMR can be performed on a wide variety of materials and providea wide range information on many atoms such as 6Li, 7Li or 23Na and correlation or relaxation experimentscan provide information on the localization of lithium or sodium ions and eventually probe phase separationin battery materials. [1,2]Moreover, in favorable systems such as lithium titanates, it has been shown that surface fluorination withXeF2 greatly improves the electrochemical properties. In such systems, high resolution MAS-NMR at highmagnetic field can help quantify the amount of fluorine in the structure, and the 19F chemical shift analysisyields information on the fluorine environment. Moreover, spin counting strategies based on HeteronuclearMultiple-Quantum Correlation experiments can provide the number of fluorine atoms which are coordinatedto lithium ions and help understand what kind of structures are created locally upon fluorination.[3]2. ExperimentalMost experiments on paramagnetic samples were realized at moderate magnetic field (4.7 T or 200 MHzfor 1H) with 1.3 mm rotor spinning around 60 kHz under N2 in Bruker spectrometers. For diamagneticsamples such as LTO, high magnetic fields (20 T or 850 MHz for 1H) provided a better signal-to-noise ratioand allowed spin counting experiments to be performed in 1.3 mm rotors.[1] B.Li, G.Rousse, L.Zhang, M.Avdeev, M.Deschamps, A.M.Abakumov, J.-M.Tarascon,Constructing “Li-rich Ni-rich” oxide cathodes for high-energy-density Li-ion batteriesEnergy Env. Sci. 16, 1210-1222 (2023)[2] Q.Wang, S.Mariyappan, G.Rousse, A.V.Morozov, B.Porcheron, A.Iadecola, R.Dedryvère, J.Wu, W.Yang,L.Zhang, M.Chakir, M.Deschamps, M.-L.Doublet, A.M.Abakumov, J.-M.TarasconUnlocking anionic redox activity in O3-type sodium 3d layered oxides via Li substitutionNat. Mater. 20, 353–361 (2021)[3] Y.Charles-Blin, D.Flahaut, J.B.Ledeuil, K.Guérin, M.Dubois, M.Deschamps, A.M.Perbost,L.Monconduit, H.Martinez, N.LouvainAtomic Layer Fluorination of the Li4Ti5O12 Surface: A Multiprobing SurveyACS Appl. Energy Mater. 2(9), 6681-6692 (2019
Light-Activated Artificial CO2-Reductase: Structure and Activity
No full textInternational audienceLight-dependent reduction of carbon dioxide (CO 2 ) into value-added products can be catalyzed by a variety of molecular complexes. Here we report a rare example of a structurally characterized artificial enzyme, resulting from the combination of a heme binding protein, heme oxygenase, with cobalt-protoporphyrin IX, with good activity for photoreduction of CO 2 to carbon monoxide (CO). Using a copper-based photosensitizer, thus making the photosystem free of noble metals, a large turnover frequency value of ~ 616 h -1 , a turnover value of ~ 589, after 3 h reaction, and a CO vs H 2 selectivity of 72 % were obtained, establishing a record among previously reported artificial CO 2 reductases. Thorough photophysical studies allowed tracking reaction intermediates and provided insights into the reaction mechanism. Thanks to a high-resolution crystal structure of the artificial enzyme, both in the absence and in the presence of the protein-bound CO 2 substrate, a rational sitedirected mutagenesis approach was used to study the effect of some modifications of the active site on the activity.</p
Le patriarche Germain II et les pouvoirs judiciaires de l’Église (XIIIe–XVe siècles).: Une influence juridique du Patriarcat de Constantinople sur l’Église de Kiev?
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Resolving double-peaked emission line galaxies using MaNGA: I. Mechanisms of star formation quenching
No full textInternational audienceUnderstanding the relationship between quenching mechanisms that transform star-forming galaxies into quiescent ones and galaxy properties remains a challenge. We investigate the gas and stellar properties of 69 double-peaked galaxies selected from the Sloan Digital Sky Survey (SDSS) and observed as part of the Mapping Nearby Galaxies at APO (MaNGA) survey to elucidate the mechanisms driving star formation quenching within these systems. We study their star formation activity along with their physical properties: colour, morphology, environment, stellar age, and gas ionisation diagnostics. We find that these 69 double-peaked MaNGA galaxies encompass a higher fraction of galaxies in the green valley, based on the corrected NUV − r colour, compared to our defined control samples of single-peaked emission line galaxies. This green colour traces intermediate stellar populations compared to blue and red galaxies, as indicated by the Dn(4000) index. These green galaxies show no recent star formation bursts within the last 2 Gyr. They exhibit emission line ratios that are suggestive of both ongoing star formation and nuclear activity. They are predominantly located in isolated or small group environments, indicating that internal processes rather than external factors drive their quenching. Moreover, optical emission lines detected throughout a significant area of these systems suggest that gas depletion is unlikely to be the primary quenching mechanism. These findings support a scenario where quenching is instead caused by reduced star formation efficiency
Entre lisible et scriptible : utopie et métafiction dans Projection privée d'Abe Kazushige
No full textInternational audienceElaborating on Barthes' famous distinction, this article examines the relationship between the writerly and the readerly in Abe Kazushige's novel Individual Projection (Indivijuaru purojekushon). The "writerly" (scriptible) designates an open-ended, playful narrative, giving free rein to the interpretation of the reader who thus becomes a co-writer of the text. The readerly (lisible), by contrast, implies authority and redundancy: it imposes a meaning or message, thus turning the reader into a consumer rather than producer of the text. I argue that Abe's novel is built upon an internal tension between the openness of the writerly and the more assertive and ethical message of the readerly. The first two parts of this essay focus on the writerly side of the text. Individual Projection could be first described as a parody (1. Political Utopia and Genre fiction as Parody in Individual Projection): through its unreliable narrator, the novel toys with stereotypes associated with political utopia and genre fiction. Such distancing with clichés destabilises the text and opens a free space of interpretation for the reader (2. Metafiction as Writerly Text: When the Reader Writes). Yet, the novel ends with a final metatextual reversal which reshapes our understanding of the story and redefines the reader's own relationship to the text (3. Metafiction: Revenge of the Author?). This end illustrates the paradoxical nature of metafiction in its relationship to the reader: its apparent semantic openness can also be a means to assert the author's authority over the text to convey a theoretical or philosophical message. Here, my own understanding of Individual Projection challenges Azuma Hiroki's interpretation of Abe's novel. Azuma saw in the openness of Individual Projection another illustration of his own theory both describing and advocating a free consumption of fiction, relying much more on the logic of recycling and recombination than on the linear path of the plot. If Azuma's interpretation sheds interesting light on the agency devoted to the reader in Individual Projection, it yet fails to apprehend the potentially critical message of the text: Abe's novel also suggests a pessimistic view of contemporary's hyperreality which seems quite antithetical to Azuma's own eulogy of postmodernity
Un rôle des microtubules astraux dans l’orientation de la division cellulaire: Quand la longueur compte… aussi !
No full textInternational audienceNo abstract availabl
Polaron formation in insulators and the key role of hole scattering processes: Band insulators, charge density waves and Mott transition
No full textInternational audienceA mobile impurity immersed in a non-interacting Fermi sea is dressed by the gapless particle-hole excitations of the fermionic medium. This conventional Fermi-polaron setting is well described by the so-called ladder approximation, which consists in neglecting impurity-hole scattering processes. In this work, we analyze polaron formation in the context of insulating states of matter, considering increasing levels of correlation in the medium:~band insulators originating from external periodic potentials, spontaneously-formed charge density waves, and a Fermi-Hubbard system undergoing a metal-Mott insulator transition. The polaron spectral function is shown to exhibit striking signatures of the underlying fermionic background, such as the single-particle band gap, particle-hole symmetry and the transition to the Mott state. These signatures are identified within the framework of the Chevy ansatz, i.e. upon restricting the Hilbert space to single particle-hole excitations. Interestingly, we find that the ladder approximation is inaccurate in these band systems, due to the fact that the particle and hole scattering phase spaces are comparable. Our results provide a step forward in the understanding of polaron formation in correlated many-body media, which are relevant to both cold-atom and semiconductor experiments
A shared pattern of midfacial bone modelling in hominids suggests deep evolutionary roots for human facial morphogenesis
No full textInternational audienceMidfacial morphology varies between hominoids, in particular between great apes and humans for which the face is small and retracted. The underlying developmental processes for these morphological differences are still largely unknown. Here, we investigate the cellular mechanism of maxillary development (bone modelling, BM), and how potential changes in this process may have shaped facial evolution. We analysed cross-sectional developmental series of gibbons, orangutans, gorillas, chimpanzees and present-day humans ( n = 183). Individuals were organized into five age groups according to their dental development. To visualize each species's BM pattern and corresponding morphology during ontogeny, maps based on microscopic data were mapped onto species-specific age group average shapes obtained using geometric morphometrics. The amount of bone resorption was quantified and compared between species. Great apes share a highly similar BM pattern, whereas gibbons have a distinctive resorption pattern. This suggests a change in cellular activity on the hominid branch. Humans possess most of the great ape pattern, but bone resorption is high in the canine area from birth on, suggesting a key role of canine reduction in facial evolution. We also observed that humans have high levels of bone resorption during childhood, a feature not shared with other apes
Carroll-invariant propagating fields
No full textInternational audienceWe construct Carroll-invariant theories with fields propagating outside the Carroll light cone, i.e., at a speed strictly greater than zero (“Carroll swiftons”). We first consider models in flat Carroll spacetime in general dimensions, where we present scalar and vector Carroll swifton field theories. We then turn to the coupling to gravity and achieve in particular in two dimensions a Carroll-invariant scalar swifton by coupling it suitably to Carroll dilaton gravity. Its backreaction on the geometry generates dynamical torsion
Trillium: Higher-Order Concurrent and Distributed Separation Logic for Intensional Refinement
No full textExpressive state-of-the-art separation logics rely on step-indexing to model semantically complex featuresand to support modular reasoning about imperative higher-order concurrent and distributed programs. Step-indexing comes, however, with an inherent cost: it restricts the adequacy theorem of program logics to a fairlysimple class of safety properties.In this paper, we explore if and how intensional refinement is a viable methodology for strengtheninghigher-order concurrent (and distributed) separation logic to prove non-trivial safety and liveness properties.Specifically, we introduce Trillium, a language-agnostic separation logic framework for showing intensionalrefinement relations between traces of a program and a model. We instantiate Trillium with a concurrentlanguage and develop Fairis, a concurrent separation logic, that we use to show liveness properties of concurrentprograms under fair scheduling assumptions through a fair liveness-preserving refinement of a model. We alsoinstantiate Trillium with a distributed language and obtain an extension of Aneris, a distributed separationlogic, which we use to show refinement relations between distributed systems and TLA+ models