HAL Portal ESPCI (Ecole Supérieure de Physique et de Chimie Industrielles)
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Modèles homogénéisés de metainterfaces acous.ques à base de résonateurs de Helmholtz 3D.
No full textInternational audienceWe investigate the behaviour of metainterfaces composed of three-dimensional subwavelength Helmholtz resonators (HRs), that are open at both ends and may have distinct neck geometries, using a homogenized model derived from a three-scale asymptotic approach. This model reduces such metainterfaces to homogenized boundary conditions that incorporate a resonant pressure field, providing a continuous representation of the discrete pressure field within the cavities that constitute the metasurface. Notable special cases include mirror-symmetric metainterfaces and metasurfaces that operate solely in reflection. The model, developed in the time domain, is validated and discussed in the harmonic regime through comparisons with direct numerical simulations.Nous étudions le comportement d’une méta-interface composée de résonateurs de Helmholtz tridimensionnels sub-longueur d’onde, ouverts aux deux extrémités et pouvant présenter des géométries de col distincts, à l’aide d’un modèle homogénéisé asymptotique. La méthode appliquée implique l’utilisation de 3 échelles géométriques, et est conduite jusqu’à des ordres d’analyse élevés. Le modèle effectif obtenu encapsule les effets de telles méta-interfaces dans des conditions aux limites homogénéisées rendant compte des effets de résonance, et des effets des couches limite. Des cas particuliers remarquables, incluant des méta-interfaces à symétrie miroir et des métasurfaces reflectives sont présentés. Le modèle, développé dans le domaine temporel, est validé et discuté en régime harmonique au moyen de comparaisons avec des simulations numériques obtenues sur Comsol Multiphysics, et quelques interprétations physiques des résultats sont proposées
Integration of a Ruthenium-based Alcohol Dehydrogenation Catalyst in an all-Molecular CO2 Electrolyzer
No full textThe electrification of chemical processes using renewable feedstocks and energy sources represents a key strategy toward a sustainable chemical industry. Coupling CO2 electroreduction (CO2RR) with anodic alcohol oxidation offers an interesting route to reduce energy consumption and increase product value while circumventing the limitations of water oxidation. Here, we report a fully molecular co-electrolysis platform employing a well-defined ruthenium pincer-based alcohol dehydrogenation catalyst immobilized on carbonaceous support. The system enables the selective electrooxidation of ethanol to acetate with exceptional mass activities exceeding 2 A mg-1, thus outperforming previously reported molecular anode catalysts and competing with state-of-the- art materials. When paired with cathodic CO2-to-CO conversion using a molecular cobalt phthalocyanine catalyst, the integrated electrolyzer achieves co-production of acetate and CO at high rates. While long-term operational stability remains limited (<1 h), detailed electrochemical and spectroscopic analyses reveal main degradation pathways of the molecular anode, offering guidance for future improvements. These results establish a performance benchmark for molecular anodic electrocatalysis and underscore the potential of integrated electrosynthetic approaches based on well- defined active site
Quasi-amorphous crystal
No full textBrittle plastic yielding is a salient feature of well-annealed glassy materials. Here we show that the same behavior is characteristic of perfect crystals after they experience mechanically driven elastic instability leading to massive nucleation of dislocations. We argue that such 'preparation' effectively converts an atomic configuration from crystalline to quasi-amorphous. To understand the nature of the subsequent mechanical response, which is reminiscent of quasi-brittle yielding we study an athermal model 2D crystal subjected to quasistatic loading. We show that the intermittent pre- and post-yield dislocation avalanches exhibit power law statistics with matching exponents. The computed value of these exponents is indicative of marginal stability
Abnormal Connectivity of the Head Neural Integrator in Cervical Dystonia
No full textInternational audienceBackgroundCervical dystonia is characterized by abnormal neck and head movements, possibly related to a dysfunction of the interstitial nucleus of Cajal (INC) and the head neural integrator, a system responsible for the control of head and eye movements. However, neuroanatomical evidence of alterations in the head neural integrator in cervical dystonia is sparse.ObjectivesWe investigated structural and functional integrity of the INC and its connections in cervical dystonia.MethodsThis cross-sectional, observational study compared 19 cervical dystonia patients and 21 healthy controls, using anatomical, diffusion-weighted, and resting-state functional images. We reconstructed tracts converging on the INC, and involved in the control of head movements. We evaluated group differences in microstructural integrity using fixel-based analysis, and effective connectivity using dynamic causal modeling.ResultsCompared with controls, patients showed microstructural abnormalities within the INC and cerebral peduncle. Effective connectivity showed abnormal self-inhibition in the INC, substantia nigra, and vermis in patients, with decreased excitation from the substantia nigra to the INC, increased inhibition from the deep cerebellar nuclei and primary sensorimotor cortex, and decreased excitation from the INC to the cerebellar vermis.ConclusionsA dysfunction of the INC might contribute to altered sensorimotor integration in cervical dystonia, and abnormal feedback from its afferent connections could alter its integrative function, resulting in a disturbed head and neck posture. © 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society
WNK-Dependent Phosphorylation of Gephyrin Tunes GABA A Receptors at Inhibitory Synapses and Modulates Anxiety Behavior
No full textThe role of the chloride-sensitive kinase WNK1 and its effector SPAK in the brain remains poorly understood. Here, we identify a regulatory mechanism involving WNK signaling that directly controls the synaptic diffusion and clustering, as well as the membrane stability and endocytosis of inhibitory GABA A receptors (GABA A Rs). We show that activation of WNK signaling stabilizes GABA A Rs at inhibitory synapses, while inhibition enhances receptor internalization. This regulation depends on the phosphorylation state of two previously uncharacterized residues in the central linker region of the gephyrin scaffold protein. Modulating WNK activity alters neuronal activity and the kinetics of GABAergic currents. In vivo , expression of a phospho-mimetic form of gephyrin at WNK-targeted sites produces anxiolytic effects. By orchestrating the recruitment of GABA A Rs at inhibitory synapses, the WNK pathway emerges as a master regulator of GABAergic transmission and establishes chloride as a bona fide second messenger in inhibitory synaptic signaling. Significance Synaptic transmission relies on signaling pathways that control how neurotransmitter receptors move and stabilize at synapses. Many of these pathways use calcium as a second messenger. In contrast, how chloride might regulate synapses has remained unclear. In this study, we identify a chloride-sensitive pathway involving the WNK1 kinase and its partner SPAK, which controls the movement and stability of inhibitory GABA A receptors at synapses. This occurs through the phosphorylation of gephyrin, a key scaffolding protein, at two newly identified sites. Our results show that intracellular chloride can act as a second messenger, reshaping inhibitory synapses and altering behavior in mice, including reducing anxiety-like responses
Locally activated semisynthetic fluorescent biosensors for imaging cellular biochemistry
No full textInternational audienceBiosensors based on fluorescent proteins are widely used as genetically encoded indicators due to their capacity to target various biological analytes (metal ions, reactive oxygen species, biomolecules, etc.) within cells with precise localization. However, their complex development associated with the lack of photophysical versatility constrains the scope of their application in biosensing. Alternatively, semisynthetic fluorescent biosensors that combine a small chemical indicator with a self-labeling protein tag benefit from the versatility of molecular engineering and from the selectivity of genetic encoding of the recombinant protein. The variations in photophysical properties of the chemical indicator upon analyte recognition provide high sensitivity and rapid response time, making them attractive alternatives for biosensing. Fluorogenic semisynthetic biosensors that are fluorescent only upon local activation by reaction with a genetically encoded self-labeling protein tag provide an additional level of selectivity, allowing wash-free imaging experiments. This minireview focuses on the latter class of hybrid sensors and provides an outlook on the different small molecular probe design strategies and self-labeling protein tag combinations (mostly SNAP-tag and HaloTag) for their construction. The authors expect to present new clues and ideas to researchers for further advances in this field
Elastic, strong and tough ionically conductive elastomers
No full textInternational audienceStretchable elastic materials with high strength, toughness, and good ionic conductivity are highly desirable for wearable devices and stretchable batteries. Unfortunately, limited success has been reported to attain all of these properties simultaneously. Here, we report a family of ionically conductive elastomers (ICEs) without compromise between mechanical properties (high stiffness, reversible elasticity, fracture resistance) and ionic conductivity, by introducing a multiple network elastomer (MNE) architecture into a low polymer. The ICEs with the MNE architecture exhibit a room temperature ionic conductivity of the order of and stress at break of ~8 MPa, whereas the simple networks without an MNE architecture show two orders magnitude lower ionic conductivity () and comparably low strength (<1.5 MPa) at 25 °C than their MNE architecture based counterparts. The MNE architecture with a low monomer combines the stiffness and fracture toughness given by sacrificial bond breakage while improving ionic conductivity through increased segmental mobility
Evolutionary features in a minimal physical system: Diversity, selection, growth, inheritance, and adaptation
No full textInternational audienceWe present a simple physical model that recapitulates several features of biological evolution, while being based only on thermally driven attachment and detachment of elementary building blocks. Through its dynamics, this model samples a large and diverse array of nonequilibrium steady states, both within and between independent trajectories. These dynamics exhibit directionality with a quantity that increases in time, selection, and preferential spatial expansion of particular states, as well as inheritance in the form of correlated compositions between successive states, and environment-dependent adaptation. The model challenges common conceptions regarding the requirements for life-like properties: It does not involve separate mechanisms for metabolism, replication, and compartmentalization; stores and transmits digital information without template replication or assembly of large molecules; exhibits selection both without and with reproduction; and undergoes growth without autocatalysis. As the model is based on generic physical principles, it is amenable to various experimental implementations
Génération de modes de Lamb ZGV dans une plaque de silicium
No full textUltrasons laser, interaction son-lumière; GAPSUS - Acoustique Physique, Sous-Marine et Ultra-SonoreNational audienceLa mesure des ondes élastiques guidées permet d'évaluer les paramètres élastiques d'un échantillon donné. Une évaluation locale et plus précise peut être réalisée grâce aux modes de Lamb à vitesse de groupe nulle (ZGV pour Zero-Group-Velocity). Leur énergie étant confinée sous la source d'excitation, cela assure une résonance fine avec un très bon facteur de qualité. Les techniques d’ultrasons laser, sans contact, offrent une méthode unique pour observer ces résonances qui ont été mesurées dans divers guides d'ondes (plaques, tubes, rubans, …), divers matériaux (duralumin, zircaloy, verre, …) et pour différentes applications (comme la mesure du coefficient de Poisson ou de l'épaisseur locale d’un échantillon). Dans le silicium, dont l’anisotropie est cubique, on observe les modes ZGV dans les directions principales (100) et (110) correspondant respectivement aux minima et aux points selles de la surface de dispersion (1). Dans le cas d’un matériau semiconducteur avec une bande interdite indirecte, tel que le silicium, les ondes acoustiques peuvent être engendrées par l’absorption d’une impulsion laser conduisant à la fois à une expansion thermique (effet thermoélastique) et une contraction électronique, deux mécanismes qui s’opposent et dont la primauté dépend de l’intensité et de la longueur d’onde du laser (2). La compétition entre ces deux mécanismes pour la génération des ondes acoustiques et la différence de distribution volumique des contraintes qui leur sont associées ont des conséquences sur la génération de ces modes ZGV. Nous observerons ces effets pour les modes ZGV dans les plaques de silicium. (1) D. A. Kiefer, S. Mezil, C. Prada, Sci. Adv. 9, eadk6846 (2023) (2) B. Audoin, H. Meri, and C. Rossignol, Phys. Rev. B 74, 214304 (2006)
Exploring the limits to quantitative elastography: supersonic shear imaging in stretched soft strips
No full textUltrasons biomédicaux - Élasticité et visco-élasticité; GAPSUS - Acoustique Physique, Sous-Marine et Ultra-SonoreNational audienceL'élastographie par ondes de cisaillement a enrichi l'imagerie médicale par ultrasons en permettant la mesure quantitative de rigidité des tissus. Cependant, des limitations persistent concernant la viscoélasticité (1), le guidage (2) ou la déformation statique (3). Pour pallier ces limitations, nous introduisons des paramètres mécaniques dépendant de la fréquence et nous prenons en compte la dispersion et la pré- déformation lors de l'utilisation d'un scanner à ondes de cisaillement. Nous analysons la propagation de ces ondes dans un ruban en élastomère mou dont la quasi-incompressibilité permet d'obtenir des comportements similaires à un tissu déformé (4,5). En répétant l'expérience pour différentes orientations du ruban et différentes déformations de celui-ci, nous obtenons des vitesses de propagation variées allant de 2 à 6 m/s. Afin d'expliquer ces différences de vitesse et unifier les différents diagnostics possibles en fonction des vitesses obtenues, nous étudions les diagrammes de dispersion obtenus lors de l'expérience. Nous introduisons un modèle théorique permettant de prendre en compte à la fois l'effet de guidage géométrique des ondes, la rhéologie du tissu ainsi que sa réponse à une déformation statique. Nous extrayons ainsi les paramètres de rigidité de l'échantillon. Nous dépassons donc les limitations actuelles en élastographie en caractérisant simultanément les propriétés viscoélastiques et hyperélastiques des tissus mous, permettant d'envisager une élastographie quantitative des tissus étirés. Références: (1) Sinkus, Elasticity of the Heart, Problems and Potentials, Current Cardiovascular Imaging Reports, 2014. (2) Kirby, Pelivanov, Song, Ambrozinski, Yoon, Gao, Li, Shen, Wang, O’Donnell. Optical coherence elastography in ophthalmology, Journal of Biomedical Optics, 2017. (3) Elgeti, Sack. Magnetic Resonance Elastography of the Heart, Current Cardiovascular Imaging Reports, 2014. (4) Delory, Lemoult, Lanoy, Eddi, Prada. Soft Elastomers: a playground for guided waves, JASA, 2022. (5) Delory, Kiefer, Lanoy, Eddi, Prada, Lemoult. Viscoelastic dynamics of a soft strip subject to a large deformation, Soft Matter, 2024