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An alternative elastoplastic model for ductile fracture with graded plasticity
No full textInternational audienceThe prediction of failure modes in metallic structures is a crucial step in the safety analysis of industrial components subjected to significant mechanical loads (e.g., nuclear power plant components, pipelines, etc.). To perform such analyses, it is essential to accurately simulate the propagation of a defect in the ductile regime, characterized by large plastic deformations before and during propagation. Predictive numerical simulation of ductile fracture remains an open scientific and technicalchallenge, despite significant progress in recent years. The so-called local approach to fracture is widely used to model ductile fracture; however, like all softening models, it exhibits dependency on spatial discretization. The objective of this work is to propose a robust approach for modeling and simulating ductile fracture at the structural scale. It introduces an elastoplastic model with a bounded gradient of accumulated plastic strain and an associated set of internal constraints. This method aims to eliminate mesh dependency, without increasing the number of degrees of freedom of the numerical problem as it can be the case for most of non-local models. So, the proposed model strives for fast and efficient numerical computations at the structural scale. The feasibility of this approach is demonstrated through the resolution of problems on simple geometries, such as cylinders or spheres made of composite elastoplastic materials. Tests on 316L steel specimens are also conducted to further validate the robustness of this method
Mechanism of lateral cell-wall expansion at a constant diameter in Bacillus subtilis
No full textInternational audienceIn Escherichia coli, lateral cell-wall expansion during growth occurs by cross-linking of new glycan strands to the existing peptidoglycan network. However, it is unclear whether the same mechanism applies to other rod-shaped bacteria. Here, we use cell imaging and mass spectrometry analysis of isotopically labeled peptidoglycan to study this process in the Gram-positive bacterium Bacillus subtilis. We show that new glycan strands are cross-linked exclusively to other newly synthesized glycan chains, and not to the existing peptidoglycan network. We propose that new peptidoglycan meshes, assembled at the membrane surface, impose a shift on older meshes toward the bacterial surface, where they sustain the cytoplasmic turgor pressure, before their eventual degradation. This outward movement would result in preferential lateral expansion due to the large difference in the strain tensors of the peptidic and glycosidic peptidoglycan components
Nitrite Causes Nitrosative Stress to Iron Sulfur Clusters
No full textInternational audienceNitric oxide (NO), produced by nitrite reductases or nitric oxide synthases, performs vital roles in signaling and the immune response. Iron sulfur (FeS) clusters are known targets for NO induced degradation, serving as sensors to trigger cellular responses. However, this FeS reactivity is proposed as NO specific, with no demonstrated reactivity toward nitrite, a soluble NO storage molecule. We demonstrate that synthetic FeS clusters supported by various ligands undergo facile nitrosylation by nitrite in the presence of a reductant, evidencing the nitrite reductase reactivity for FeS clusters. Moreover, a mononitrosylated Fe4S4 cluster, [tempS3Fe4S4(NO)]2-, can be readily synthesized by this approach, enabling further investigation into the FeS cluster repair and decomposition under NO induced oxidative stress
Eco-extraction de plantes tinctoriales pour la conception d'ingrédients cosmétiques
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LeYOLO, nouvelle architecture embarquée pour la détection d'objets
No full textInternational audienceLa réduction du coût de calcul des réseaux neuronaux profonds est essentielle pour la détection d'objets en temps réel. Pourtant, les récents progrès reposent surtout sur le matériel plutôt que sur l'optimisation des modèles. Cela se remarque notamment dans les dernières architectures YOLO, où la vitesse prime sur la légèreté. Pour répondre à ce dé, nous introduisons deux contributions majeures. D'abord, LeNeck, un cadre de détection rapide et précis, réduisant le nombre de paramètres. Ensuite, LeYOLO, un modèle optimisé pour YOLO, combinant compacité et haute précision. Ces solutions sont idéales pour les dispositifs à faible consommation, y compris les microcontrôleurs
The magnetic and spin-down properties of slowly rotating fully convective M dwarfs
No full textInternational audienceThe evolution of the magnetism, winds and rotation of low-mass stars are all linked. One of the most common ways to probe the magnetic properties of low-mass stars is with the Zeeman-Doppler imaging (ZDI) technique. The magnetic properties of partially convective stars has been relatively well explored with the ZDI technique, but the same is not true of fully convective stars. In this work, we analyse a sample of stars that have been mapped with ZDI. Notably, this sample contains a number of slowly rotating fully convective M dwarfs whose magnetic fields were recently reconstructed with ZDI. We find that the dipolar, quadrupolar and octupolar field strengths of the slowly rotating fully convective stars do not follow the same Rossby number scaling in the unsaturated regime as partially convective stars. Based on these field strengths, we demonstrate that previous estimates of spin-down torques for slowly rotating fully convective stars could have been underestimated by an order of magnitude or more. Additionally, we also find that fully convective and partially convective stars fall into distinct sequences when comparing their poloidal and toroidal magnetic energies
Depth-first: A deterministic and scalable NoC routing protocol for 3.5D packaged architectures
No full textInternational audienceNew high-volume commercial products combine 2.5D silicon-interposer based assemblies with 3D monolithic stacks of chiplets. This combination is called 3.5D packaging and makes it possible to assemble dense compute solutions. Components communicate via a Network-On-Chip, but current solutions do not support 3.5D Network-On-Chip topologies. To this end, this work proposes Depth-First, the first Deterministic, Virtual Channel based, Network-On-Chip routing protocol supporting 3.5D network topologies. The protocol prevents deadlocks using additional Virtual Channels only in the upper chiplets, while imposing no VC constraints on the base interposer. Depth-First also features an efficient node naming scheme, enabling highly compact routing tables. Since vertical links must be assigned to routers, we present a Mixed-Integer Linear Programming formulation that greatly speeds up execution time compared to a reference implementation from prior work, which was based on an exhaustive search. We formally prove that the protocol is deadlock-free, study its performance using an open-source cycle-accurate simulator, and compare it with other protocols (on a comparable topology). A partial implementation of Depth-First in an open-source router results in a small 4.9% area impact (7nm process) compared to an implementation without our routing algorithm
40 Hz light stimulation restores early brain dynamics alterations and associative memory in Alzheimer’s disease model mice
No full textInternational audienceAbstract Visual gamma entrainment using sensory stimuli (vGENUS) is a promising non-invasive therapeutic approach for Alzheimer’s disease (AD), showing efficacy in improving memory function. However, its mechanisms of action remain poorly understood. Using young AppNL-F/MAPT double knock-in (dKI) mice, a model of early AD, we examined brain dynamics alterations before amyloid plaque onset. High-density EEG recordings and metrics from fields outside neuroscience were used to assess brain dynamics fluidity—a measure of the brain’s ability to transition between activity states. We revealed that dKI mice exhibit early, awake state-specific reductions in brain dynamics fluidity associated with cognitive deficits in complex memory tasks. Daily vGENUS sessions over 2 weeks restored brain dynamics fluidity and rescued memory deficits in dKI mice. Importantly, these effects built up during the stimulation protocol and persisted after stimulation ended, suggesting long-term modulation of brain function. Based on these results, we propose a “brain dynamics repair” mechanism for vGENUS that goes beyond current amyloid-centric hypotheses. This dual insight—that brain dynamics are both a target for repair and a potential diagnostic tool—provides new perspectives on early Alzheimer’s disease pathophysiology
Separation of Calendula officinalis L lipophilic compounds using ultra-high efficiency / low-pressure supercritical fluid chromatography (UHE-LP/SFC)
No full textInternational audienceAs a result of the decreased usage of organic solvents, and to great chromatographic efficiencies, supercriticalfluid chromatography (SFC) successfully replaced in recent years non-aqueous reverse phase liquid chromatography(NARP-LC) for the separation of non-polar compounds. High relative amounts of various triterpenoidesters are present in the Calendula officinalis flowers, offering interesting bioactive properties. Because thesetriterpenoids present subtle structural differences on the aglycone moiety, their separation is challenging. Thispaper presents a method development to separate these compounds using ultra-high-performance low pressuresupercritical chromatography (UHP/LP-SFC). The lipophilic fractions were obtained by supercritical fluidextraction (SFE), in accordance to the safety required from the cosmetic industry. Five coupled C18 columnswere used, and an experimental design was applied to optimize their separation. The effects of temperature andmobile phase composition, i.e. the modifier percentage and the modifier composition (methanol/acetonitrilemixtures) were studied. Five criteria were considered: analysis duration, two discrimination factors of majortriterpenoid esters, peak number and fully resolved peaks. The modelling from the experimental correlated to thestudied analytical factors only shows significant results for the analysis duration. Therefore, derringer functionswere employed to the criteria to select an optimal separation. Resulting in an optimized separation; in less than20 min at 20 ◦C, with 30 % of a mixture MeOH/ACN 75/25 as modifier mixed with carbon dioxide. Centrifugalpartitioning chromatography (CPC) fractionation and NMR analysis of fractions collected by CPC allowed toconfirm identification of the two main peaks as faradiol myristate and faradiol palmitate. Other minor triterpenoidesters are well separated and based on NMR analysis and retention order an attempt of identificationand proportion was done