Portail HAL de l'Université Picardie Jules Verne
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BPS algebras and generalised Kac-Moody algebras from 2-Calabi-Yau categories
No full textWe determine the structure of the BPS algebra of 2-Calabi-Yau Abelian categories for which the stack of objects admits a good moduli space. We prove that this algebra is isomorphic to the positive part of the enveloping algebra of a generalised Kac-Moody Lie algebra generated by the intersection cohomology of certain connected components (corresponding to roots) of the good moduli space. Some major examples include the BPS algebras of (1) the category of semistable coherent sheaves of given slope on a K3 surface or, more generally, quasiprojective symplectic surface, (2) semistable Higgs bundles on a smooth projective curve, (3) preprojective algebras of quivers, (4) multiplicative preprojective algebras and (5) fundamental groups of (quiver) Riemann surfaces. We define the BPS Lie algebras of 2-Calabi-Yau categories and prove that they coincide with the ones obtained by dimensional reduction from the critical cohomological Hall algebra in the case in which the 2-Calabi-Yau category is the category of representations of a preprojective algebra. Consequences include (1) A proof in full generality of the Bozec-Schiffmann positivity conjecture for absolutely cuspidal polynomials, a strengthening of the Kac positivity conjecture (2) A proof of the cohomological integrality conjecture for the category of semistable coherent sheaves on local K3 surfaces (3) A description of the cohomology (in all degrees) of Nakajima quiver varieties as direct sums of irreducible lowest weight representations over the BPS Lie algebra
A new era of bioclimatic extremes in the terrestrial Arctic
No full textInternational audienceThe Arctic climate is rapidly warming, but long-term changes in extreme weather events that cause major ecosystem disturbances are not well understood. Here, by using a state-of-the-art atmospheric reanalysis spanning the past seven decades, we show that, in many parts of the terrestrial Arctic, the frequency of extreme weather events has increased sharply. We found pronounced spatial variability in bioclimatic extremes during the past 30 years, including more droughts in the high-Arctic and greater area affected by winter-warming and rain-on-snow events, especially in the European Arctic region. Across one-third of the Arctic domain, such extreme events have only recently begun to occur. Thus, the Arctic is entering a novel era of bioclimatic extremes with likely severe consequences on cold ecosystems
Coarse-grained physics-based modelling for tape casting of fuel-electrode supports in Solid Oxide Cells
No full textInternational audienceOptimising the tape casting process for fabricating NiO/YSZ cermet-based fuel-electrode supports in Solid Oxide Cells remains a resource-intensive challenge. Improving the green tape properties are often reliant on trial-and-error procedures or proprietary knowledge that is inaccessible to the broader scientific community. In this work, we use computational simulations as a powerful tool to link the manufacturing process to the final microstructure of the tape. A novel three-dimensional physics-based model is presented to simulate the slip preparation and the homogeneous drying process of the tape casting producing the fuel electrode support in Solid Oxide Cells. Our model is well-calibrated to experimental data, and we investigate the dried microstructure of the simulated support
Bacterial alginate-based hydrogels reinforced with polysaccharide nanocrystals for water and wastewater decontamination
No full textInternational audienc
A purity theorem for Mahler equations
No full textInternational audienceThe principal aim of this paper is to establish a purity theorem for Mahler functions that is reminiscent of famous purity theorems for G-functions by D. and G. Chudnovsky and for E-functions (and, more generally, for holonomic arithmetic Gevrey series) by Y. André. Our approach is based on a preliminary study of independent interest of the nature of the solutions of Mahler equations. Roughly speaking, we prove a reduction result for Mahler systems, implying that any Mahler equation admits a complete basis of solutions formed of what we call generalized Mahler series. These are sums involving Puiseux series, Hahn series of a very special type and solutions of inhomogeneous equations of order 1 with constant coefficients. In the light of B. Adamczewski, J. P. Bell and D. Smertnig's recent height gap theorem, we introduce a natural filtration on the set of generalized Mahler series according to the arithmetic growth of the coefficients of the Puiseux series involved in their decomposition. This filtration has five pieces. Our purity theorem states that the membership of a generalized Mahler series to one of the three largest pieces of this filtration propagates to any other generalized Mahler series solution of its minimal Mahler equation. We also show that this statement does not extend to the smallest two pieces.</div
Addressing Bottlenecks to Achieve High‐Energy Sodium‐Ion Cells Using Tin Anodes
No full textInternational audienceSodium‐ion batteries (NIBs), as a complementary energy storage device for Li‐ion batteries, are swiftly making their way into high‐power applications market. However, further progress in NIBs requires high energy density. This requires a shift from commonly used hard carbon (HC) anodes to alloy anodes such as Bi, Sn, Sb, etc., while overcoming the problems these materials pose, with regard to volume changes and interfacial reactivity. Although ether‐ and glyme‐based electrolytes mitigate anode reactivity, their poor oxidative stability limits compatibility with high‐voltage cathodes such as Na 3 V 2 (PO 4 ) 2 F 3 (NVPF). Here, we identify glyme oxidation by‐products and detail their cross‐talk–induced poisoning in NVPF|Sn‐HC cells using operando, ex situ, and post‐mortem (electro)chemical characterizations. Based on these insights, we explore mitigation strategies (i) by reducing the Sn‐poisoning via protective SnO coating and (ii) arresting the cross‐talk phenomenon using a chemical trap such as Na‐metal, Na 15 Sn 4, or Na x C between the separators. Both approaches improve cell performance, albeit not fully suppressing electrolyte oxidation, with later enabling to reach near 100% capacity retention over 200 cycles at C/5, also giving some hope for achieving anode‐free Na‐ion cells. Although still present some shortcomings, these strategies offer promising directions for materials design, cell engineering, and electrolyte development toward high‐energy sodium‐ion batteries
Nosocomial invasive Aspergillus calidoustus infection in a CAR-T cell-treated patient with concomitant Aspergillus fumigatus respiratory infection
No full textInternational audienc
Characterization of Arterial and Sinus Blood Flow Dynamics in the Rat Brain Using Phase-Contrast MRI
No full textInternational audiencePhase-contrast magnetic resonance imaging (PC-MRI) is a widely used technique for measuring cerebral blood flow dynamics in humans. However, the application of this technique for velocity mapping of cerebral blood flow in rats has been very limited thus far. This study aimed to determine the accuracy of PC-MRI flow measurements and to establish reference flow values for the main intracerebral feeding and draining vessels in rats. PC-MRI velocimetry was conducted on a flow phantom and 12 adult Sprague Dawley rats. A semi-automatic segmentation was applied to the velocity images to enable the quantification of flows and the calculation of pulsatility index. PC-MRI flow measurements showed good agreement with the reference flow from the pump. The main findings of the in vivo measurements were as follows: the mean blood flow values in the internal carotid artery (ICA), external carotid artery (ECA), basilar artery (BA), and transverse sinuses were 9.6 ± 3.4, 5.7 ± 2.4, 2.0 ± 0.6, and 10.5 ± 3.6 ml/min, respectively. Mean ICA flow was higher than ECA flow, while the ICA pulsatility index was lower than the ECA pulsatility index. There was no significant difference in the mean cerebral inflow (combined ICA and BA flows) and cerebral outflow (left and right transverse sinus flows) measures. No differences in arterial or sinus flow were observed between the left and right sides of the brain. These reference flow values and pulsatility index may be useful for understanding flow dynamics in healthy and pathological conditions in rats
