HAL Portal ESPCI (Ecole Supérieure de Physique et de Chimie Industrielles)
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Lifelong evolution of autoreactive plasma cell numbers, affinity and anatomical location in arthritic K/BxN mice
No full textInternational audienceObjectiveThe spontaneous K/BxN mouse model of rheumatoid arthritis has been used extensively to study chronic inflammation, contribution of immune cells, and the primordial role of autoreactive antibodies in disease initiation and severity. Only the ubiquitous enzyme glucose-6-phosphate isomerase (GPI) is the target of IgG autoantibodies secreted by autoreactive plasma cells and plasmablasts in K/BxN mice. Strikingly, the appearance and evolution of these autoreactive IgG-secreting cells remain unstudied.MethodsHere, we quantitatively and qualitatively investigated the plasmablast and plasma cell responses by measuring the affinity of their secreted antibody for GPI from single cells in cohorts of K/BxN mice from 3 to 87 weeks of age.ResultsAnalysis of more than 36,000 individual IgG-secreting cells from spleen, popliteal lymph nodes, and bone marrow revealed high intercellular variability in affinity for GPI, with variations over 3 logs, with stable secretion rates over the life of the mice. Autoreactive IgG-secreting cells were detectable at 3-4 weeks and reached peak proportions of IgG-secreting cells at 35 weeks before stabilizing. High-affinity anti-GPI IgG-secreting cells appeared only transiently in the 6–9-weeks postnatal window, whereas low-affinity IgG-secreting cells represented more than 80% of the response at all time points. Serum anti-GPI IgG antibodies evolved in a similar kinetic fashion, peaking in proportion to total IgG and in affinity for GPI at 35 weeks.ConclusionOur results report the dynamic nature of the autoimmune B-cell response in the K/BxN model, revealing a transient phase of antibody affinity maturation early in disease that allows high-affinity antibody responses
How rigidity percolation and bending stiffness shape colloidal gel elasticity
No full textDispersed colloidal particles within a suspension can aggregate and spontaneously self-organize into a robust, percolating structure known as a gel. These network-like structures are prevalent in nature and play a critical role in many industrial processes, including those involving batteries, food products, and pharmaceutical formulations. In this paper, we examine the emergence of elasticity in colloidal gels. We show that gelation is governed by a rigidity percolation transition. We identify a characteristic correlation length that quantifies the extent of elastic and structural inhomogeneities, which diverges at the critical point. Our findings reveal that, regardless of the interaction types, the particle concentration, or the specific route to non-ergodicity i.e. the preparation protocol, the elastic moduli and vibrational properties of gels can be accurately predicted within a unifying framework, in which the bending modes of fractal clusters -approximately the size of this correlation length-dominate under small deformations
Characterization of temporal aiming for water waves with an anisotropic metabathymetry
No full textInternational audienceThe deflection of waves by combining the effects of time modulation with anisotropy has been recently proposed in the context of electromagnetism. In this work, we characterize this phenomenon, called temporal aiming, for water waves using a time-varying metabathymetry. This metabathymetry is composed of thin vertical plates that are periodically arranged at the fluid bottom and which act as an effective anisotropic medium for the surface wave in the long-wavelength approximation. When this plate array is vertically lifted at the fluid bottom at a given time, the medium switches from isotropic to anisotropic, causing a wave packet to scatter in time and deflect from its initial trajectory. Following a simple modeling, we obtain the scattering coefficients of the two waves generated due to the sudden medium change as well as the angle of deviation with respect to the incident angle. We then numerically evaluate this scattering problem with simulations of the full two-dimensional effective anisotropic wave equation, with a time-dependent anisotropy tensor. Finally, we provide experimental evidence of the temporal aiming, using space-time resolved measurement techniques, demonstrating the trajectory shift of a wave packet and measuring its angle of deviation
Stationary and transient correlations in driven electrolytes
No full textInternational audienceParticle–particle correlation functions in ionic systems control many of their macroscopic properties. In this work, we use stochastic density functional theory to compute these correlations, and then we analyze their long-range behavior. In particular, we study the system’s response to a rapid change (quench) in the external electric field. We show that the correlation functions relax diffusively toward the non-equilibrium stationary state and that in a stationary state, they present a universal conical shape. This shape distinguishes this system from systems with short-range interactions, where the correlations have a parabolic shape. We relate this temporal evolution of the correlations to the algebraic relaxation of the total charge current reported previously
Wavefront shaping enhanced nano-optomechanics down to the quantum precision limit
No full textInternational audienceWe introduce wavefront shaping as a tool for optimizing the sensitivity in nano-optomechanical measurement schemes. We perform multimode output analysis of an optomechanical system consisting of a focused laser beam coupled to the transverse motion of a tapered cantilever, and demonstrate that wavefront shaping enables a 350-fold enhancement of the measurement signal-to-noise (+25.5 dB) compared to standard split-detection, close to the quantum precision limit. Our results open new perspectives in terms of sensitivity and control of the optomechanical interaction
Responsive properties and triggered disassembly of supramolecular microgels: a key role of the structure
No full textInternational audienceAlthough understanding structure–property relationships in microgels is crucial, it remains limited due to the challenges associated with both controlling and quantitatively characterizing the distribution of crosslinkers within the network. Here, multi-responsive supramolecular poly(N-isopropylacrylamide) (PNIPAM) microgels have been synthesized with either “ultra” core-shell (via batch synthesis) or quasi-homogeneous (via continuous feeding) distributions of a metallosupramolecular charged crosslinker (SC), while maintaining a constant size. The SC presents two main advantages. First, its color and its high electronic contrast allow an easy and precise quantification of both its final content and its spatial distribution in the microgel network respectively. It is found that microgels with a quasi-homogeneous SC distribution exhibit a lower swelling ratios upon decreasing the temperature and/or the salt concentration. Second, the triggered SC cleavage through chemical oxidation allows the microgel disassembly. Both the SC cleavage kinetics and the resulting microgel disassembly are faster when the initial SC distribution is quasi-homogeneous. Furthermore, the molar mass of the disassembled polymer chains can be closely correlated to the initial microgel structure. Overall, this work highlights that the microgel structure is a key parameter in understanding their behavior and optimizing their applications
Doping dependence of the dipolar correlation length scale in metallic SrTiO3
No full textInternational audienceSuperconducting domes, ubiquitous across a variety of quantum materials, are often understood as a window in which pairing is favored, opened by the fluctuations of competing orders. Yet, the understanding of how such a window closes is missing. Here, we show that inelastic neutron scattering, by quantifying a length scale associated with the dipoles correlation, ℓ0, addresses this issue. We find that, within the experimental precision, the end of the superconducting dome coincides with the end of a highly polarizable state (in which ℓ0 is longer than the interatomic distance). Thus, the superconducting dome is driven by the competition between the increase in the density of states and the inevitable collapse of the quantum paraelectric phase. This is compatible with a crucial role played by the soft ferroelectric mode in driving superconductivity. Such a scenario may also be at work in other quantum paraelectric materials, either bulk or at interfaces
Anticorrelation between excitations and locally favored structures in glass-forming systems
No full textInternational audienceDynamics that are microscopic in space and time, where particles commit to a new position, referred to as excitations, are considered the elementary unit of relaxation in the dynamic facilitation theory of the glass transition. Meanwhile, geometric motifs known as locally favored structures are associated with vitrification in many glassformers. Recent work indicates that the probability of particles being found in both locally favored structures (LFS) and excitations decreases significantly upon supercooling, suggesting an anticorrelation between them [Ortlieb et al., Nat. Commun. 14, 2621 (2023)]. However, the spatial relationship between excitations and LFS remains unclear. By employing state-of-the-art GPU computer simulations and colloid experiments, we analyze this relationship in model glassformers. We reveal a strong anti-correlation between long-lived LFS and excitations, along with a spatial separation between the two in deeply supercooled liquids. This strong anticorrelation likely arises because well-packed LFS resist local rearrangements, and thus hindering the formation of excitations
Diffusion et dissipation des ondes ultrasonores dans les roches fissurées : schistes mouillés
No full textOndes en milieu hétérogène; GAPSUS - Acoustique Physique, Sous-Marine et Ultra-SonoreNational audienceNous avons mené des expériences ultrasonores sur des schistes secs et mouillés. Les schistes, composés de grains de sable et d’argile, sont caractérisés par leur porosité et perméabilité extrêmement faibles, ainsi que leur aspect feuilleté. Après mouillage, une forte diffusion des ondes de cisaillement a été observée, accompagnée d’un ramollissement de leur vitesse, probablement dû aux microfissures créées par le gonflement des argiles. Nous avons pu séparer les parcours moyens de diffusion et d'absorption des ondes en les comparant à une solution de l'équation de transfert radiatif obtenue par la méthode de Monte Carlo pour un échantillon de taille finie. La dépendance du parcours moyen de diffusion à la fréquence a révélé que le schiste mouillé peut être modélisé comme un milieu aléatoire dit exponentiel avec une longueur de corrélation inférieure à la longueur d'onde. Cette observation a été confirmée par des simulations 2D de la diffusion des ondes de cisaillement à travers des microfissures réparties de manière aléatoire (en position et en orientation). Lorsque la pression de confinement augmente, le schiste devient plus homogène, avec la fermeture des microfissures, entraînant une augmentation de la vitesse des ondes et du parcours moyen de diffusion. Un phénomène intéressant observé est l'augmentation de la dissipation intrinsèque, contrairement à la dépendance observée dans les grès (ex. le squirt flow). Ce comportement rappelle celui des milieux granulaires faiblement mouillés, où l’eau est piégée par des aspérités de surface. Nous proposons un modèle heuristique prenant en compte l'effet de liaison des argiles intergranulaires pour expliquer la dissipation du schiste en fonction de la pression et de la fréquence, ainsi que le ramollissement de la rigidité de cisaillement dû au mouillage