DEMO - Portrait

Publications récentes

• HAL : Dernières publications

  • [hal-01680977] Morphology and surface reactivity relationship in the Li1+xMn2–xO4 spinel with x = 0.05 and 0.10: a combined first-principle and experimental study

    15 déc. 2018 02:44

    This article focuses on the surface reactivity of two spinel samples with different stoichiometries and crystal morphologies, namely Li1+xMn2–xO4 with x = 0.05 and 0.10. LiMn2O4 compounds are good candidates as positive electrode of high-power lithium-ion batteries for portable devices. The samples were investigated using both experimental and theoretical approaches. On the experimental point of view, they were characterized in depth from X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy (XPS) analyses. Then, the reactivity was investigated through the adsorption of (SO2) gaseous probes, in controlled conditions, followed by XPS characterization. First-principle calculations were conducted simultaneously to investigate the electronic properties and the reactivity of relevant surfaces of an ideal LiMn2O4 material. The results allow us to conclude that the reactivity of the samples is dominated by an acido-basic reactivity and the formation of sulfite species. Nonetheless, on the x = 0.05 sample, both sulfite and sulfate species are obtained, the later, in lesser extent, corresponding to a redox reactivity. Combining experimental and theoretical results, this redox reactivity could be associated with the presence of a larger quantity of Mn4+ cations on the last surface layers of the material linked to a specific surface orientation.

  • [hal-01840432] Integrative multi‐omics analysis of intestinal organoid differentiation

    11 déc. 2018 02:22

    Intestinal organoids accurately recapitulate epithelial homeostasis in vivo, thereby representing a powerful in vitro system to investigate lineage specification and cellular differentiation. Here, we applied a multi-omics framework on stem cell-enriched and stem cell-depleted mouse intestinal organoids to obtain a holistic view of the molecular mechanisms that drive differential gene expression during adult intestinal stem cell differentiation. Our data revealed a global rewiring of the transcriptome and proteome between intestinal stem cells and enterocytes, with the majority of dynamic protein expression being transcription-driven. Integrating absolute mRNA and protein copy numbers revealed post-transcrip-tional regulation of gene expression. Probing the epigenetic landscape identified a large number of cell-type-specific regulatory elements, which revealed Hnf4g as a major driver of enterocyte differentiation. In summary, by applying an integrative systems biology approach, we uncovered multiple layers of gene expression regulation, which contribute to lineage specification and plasticity of the mouse small intestinal epithelium.

  • [hal-00764350] Assessing ocean-model sensitivity to wind forcing uncertainties

    19 sept. 2018 03:22

    In this paper, we assess the short-term forecast error of a mesoscale primitive-equation open-ocean model, induced by uncertainties in wind forcing. Statistics calculated from an ensemble of ocean states show that temperature forecast error is strongest at the top of the ensemble-mean thermocline, as a consequence of vertical displacement of the mixed-layer base around its ensemble mean. Horizontal pattern of the temperature error in the mixed-layer is mainly explained by horizontal advection and surface heat flux fluctuations. These two mechanisms and entrainment through the mixed-layer bottom are presented as the three processes responsible for thermal forecast error growth in the modeled upper ocean.

  • [hal-01670660] Surface reactivity of Li2MnO3: first-principles and experimental study

    19 juil. 2018 12:46

    The present paper deals with the surface reactivity of (001) oriented Li2MnO3 crystals investigated from a multi-techniques approach combining, material synthesis, X-ray photoemission spectroscopy (XPS), Scanning Electron Microscopy (SEM), Auger Electron Spectroscopy (AES) and first-principle calculations. Li2MnO3 is considered as a model compound suitable to go further in the understanding of the role of tetravalent manganese atoms in the surface reactivity of layered lithium oxides. The knowledge of the surface properties of such materials is essential in order to understand the mechanisms involved in parasitic phenomena responsible for early aging or poor storage performances of lithium-ion batteries. The surface reactivity was probed through the adsorption of SO2 gas molecules on large Li2MnO3 crystals in order to be able to focus the XPS beam on the top of the (001) surface. A chemical mapping and XPS characterization of the material before and after the SO2 adsorption show in particular that the adsorption is homogeneous at the micro and nanoscale and involves Mn reduction, while first-principle calculations on a slab model of the surface allow us to conclude that the most energetically favorable species formed is a sulfate with charge transfer implying reduction of Mn.

  • [hal-00787088] Extensions of the Siesta DFT Code for Simulation of Molecules

    15 juin 2018 15:51

    We describe extensions to the siesta density functional theory (dft) code [30], for the simulation of isolated molecules and their absorption spectra. The extensions allow for: - Use of a multi-grid solver for the Poisson equation on a finite dft mesh. Non-periodic, Dirichlet boundary conditions are computed by expansion of the electric multipoles over spherical harmonics. - Truncation of a molecular system by the method of design atom pseudo- potentials of Xiao and Zhang[32]. - Electrostatic potential fitting to determine effective atomic charges. - Derivation of electronic absorption transition energies and oscillator stren- gths from the raw spectra produced by a recently described, order O(N3), time-dependent dft code[21]. The code is furthermore integrated within siesta as a post-processing option.