HAL Portal ESPCI (Ecole Supérieure de Physique et de Chimie Industrielles)
Not a member yet
13939 research outputs found
Sort by
Modeling conductive thermal transport in three-dimensional fibrous media with fiber-to-fiber contacts
No full textInternational audienceUnderstanding heat transfers in fibrous materials, particularly conduction, is a major challenge due to their heterogeneous and multiscale nature, and the unknown contribution of fiber-to-fiber contacts. In most previous modeling studies, the existence of thermal contact resistance is not considered, and the computational complexity limits the size of simulated samples, which often leads to imprecise or inaccurate predictions. The same problem arises when considering electrical conduction through fibrous materials. In this work, we describe a computationally efficient simulation approach based on a multinodal representation to analyze the steady-state heat conduction through the solid structure in numerically generated three-dimensional fibrous networks, including contact resistance. We show that the solid conductivity in these networks is governed by a master curve that depends on a single parameter: a characteristic ratio representing the interplay between the intrinsic fiber conductivity and contact resistance as well as the influence of other geometric parameters, which numerically validates previous theoretical studies. However, we observe a deviation to this established theory for poorly connected networks. We derive an expression for a correction factor, considering the influence of correlations between fiber temperatures, and we then find good agreement with our simulation data. Our results demonstrate that the solid conductivity can be fully predicted based on geometric quantities, regardless of the extent of network connectivity, thus generalizing previous studies on this topic. This work, contributing to improve our understanding of conductive heat transport in fibrous media, may prove useful in the development of accurate predictive models and optimization strategies for fibrous insulation materials
Probing the speckle to estimate the effective speed of sound, a first step towards quantitative ultrasound imaging
No full textIn this paper, we present a mathematical model and analysis for a new experimental method [Bureau and al., arXiv:2409.13901, 2024] for effective sound velocity estimation in medical ultrasound imaging. We perform a detailed analysis of the point spread function of a medical ultrasound imaging system when there is a mismatch between the effective sound speed in the medium and the one used in the backpropagation imaging functional. Based on this analysis, an estimator for the speed of sound error is introduced. Using recent results on stochastic homogenization of the Helmholtz equation, we provide a representation formula for the field scattered by a random multi-scale medium (whose acoustic behavior is similar to a biological tissue) in the time-harmonic regime. We then prove that statistical moments of the imaging function can be accessed from data collected with only one realization of the medium. We show that it is possible to locally extract the point spread function from an image constituted only of speckle and build an estimator for the effective sound velocity in the micro-structured medium. Some numerical illustrations are presented at the end of the paper.</div
Analog phase-sensitive time-reversal of optically-carried radiofrequency signals
No full textInternational audienceAchieving low-latency time-reversal of broadband radiofrequency signals is crucial for reliable communications in dynamic, uncontrolled environments. However, existing approaches are either digitally assisted -- making broadband extension challenging -- or limited to amplitude modulation. In this work, we report the very first experimental realization of a fully analog, phase-preserving time-reversal architecture for optically-carried radiofrequency signals. The method exploits the exceptional coherence properties of rare-earth ion-doped materials, and leverages the well-established photon echo mechanism, widely used in quantum technologies. While our demonstration is conducted with a modest bandwidth, we identify the fundamental cause of this limitation and propose solutions for future scalability
Probing the colloidal behavior of a cell wall polysaccharides-degrading enzyme in a highly constrained model system
No full textInternational audienceUnderstanding the specific interaction of cell wall polysaccharides degrading-enzymes with their substrates is of fundamental and practical interest for the fine grasp of their activity. Such interactions are difficult to unveil in real-life conditions due to the structural complexity of the plant cell wall. In this work, we present complex and highly confined model systems of cholesteric cellulose nanocrystal suspensions reaching dimensions close to those found in the plant cell wall. Cellulose-xyloglucan (XG) assemblies of various surface chemistries were studied, allowing to probe the interactions and diffusion behavior of a glucanase both in diluted dynamic conditions and in an organized and concentrated (110–140 g/L) cholesteric environment. QCM-D and synchrotron source-deep UV analyses showed that XG adsorbed in a flat and extended conformation changed the glucanase interaction with the polysaccharides from attractive to repulsive, making it prone to spontaneously migrate to regions with lower solid content. Furthermore, it strongly increased the enzyme diffusion kinetics. Our results confirm the preferential interaction of both enzyme and XG on the cellulose hydrophobic crystalline plane. This work provides new insights on the influence of the interaction of a protein with a substrate on its transport in a constrained environment
Microtubule-driven cell shape changes and actomyosin flow synergize to position the centrosome
No full textInternational audienceThe regulation of centrosome position is critical to the alignment of intracellular structures with extracellular cues. The exact nature and spatial distribution of the mechanical forces that balance at the centrosome are unknown. Here, we used laser-based nanoablations in adherent cells and found that forces along microtubules were damped by their anchoring to the actin network, rendering them ineffective in moving the microtubule aster. In contrast, the actomyosin contractile network was responsible for the generation of a centripetal flow that robustly drives the centrosome toward the geometrical center of the cell, even in the absence of microtubules. Unexpectedly, we discovered that the remodeling of cell shape around the centrosome was instrumental in aster centering. The radial array of microtubules and cytoplasmic dyneins appeared to direct this reorganization. This revised view of the respective roles of actin and microtubules in centrosome positioning offers a new perspective for understanding the establishment of cell polarity
The clean and hydrated low-index Rb2Ti2O5 surfaces
No full textInternational audienceDespite the remarkable dielectric properties of Rb2Ti2O5 upon exposure to a humid atmosphere, its surfaces are still poorly known, to date. Here we study the atomic-scale structure of the clean (100), (010) and (001) surfaces, and the onset of water adsorption via density functional theory. Among them, the clean (001) surface has a very low surface energy, much smaller than most terminations of other perovskites or titania. Rb2Ti2O5 (001) is also very reactive towards water, which adsorbs as a molecule, forming regular water arrays on the surface. From the calculations, we conclude that Rb2Ti2O5 could very easily cleave under ambient conditions, forming (001) planes with ordered adsorbed water and almost null surface stress. Although Rb2Ti2O5 is a three-dimensional crystal, it behaves in this respect as a two-dimensional compound, such as graphite or layered perovskites.Malgré les propriétés diélectriques remarquables du Rb2Ti2O5 lorsqu'il est exposé à une atmosphère humide, ses surfaces sont encore mal connues à ce jour. Nous étudions ici la structure à l'échelle atomique des surfaces propres (100), (010) et (001), ainsi que le début de l'adsorption d'eau par le biais de la théorie de la fonctionnelle de la densité. Parmi ces surfaces, la surface (001) présente une énergie de surface très faible, bien inférieure à la plupart des terminaisons d'autres pérovskites ou du titane. Rb2Ti2O5 (001) est également très réactif vis-à-vis de l'eau, qui s'adsorbe sous forme moléculaire, formant des réseaux d'eau réguliers sur la surface. Ces résultats nous permettent de conclure que le Rb2Ti2O5 pourrait très facilement se cliver dans des conditions ambiantes, formant des plans (001) avec des molécules d'eau adsorbées ordonnées et des contraintes de surface quasiment nulles. Bien que le Rb2Ti2O5 soit un cristal tridimensionnel, il se comporte à cet égard comme un composé bidimensionnel, tel que le graphite ou les pérovskites en couches
Metal‐Organic Frameworks for the Therapy of Inflammatory Diseases
No full textInternational audienceInflammation is a natural immune response triggered by harmful external or internal stimuli. However, when inflammation fails to resolve and restore basal homeostasis, it can lead to various inflammatory diseases such as rheumatoid arthritis (RA), inflammatory bowel disease (IBD), and diabetic chronic wound (DCW). The modulation of inflammation follows a highly complex mechanism, and monotherapy is often insufficient for treating such conditions. Therefore, developing next‐generation nanocarriers for anti‐inflammatory drug delivery and multi‐target combination therapies is critical. Metal‐organic frameworks (MOFs), a class of porous coordination polymers with large surface areas and adaptable porosity, have emerged as promising drug delivery systems (DDS) due to their biodegradability, high drug loading capacity, stimuli‐responsive drug release, and ease of functionalization. Over the past five years, MOFs have shown significant promise in treating inflammatory diseases, either as DDS or as intrinsic anti‐inflammatory and anti‐oxidative agents. Additionally, hybrid MOFs, which combine MOFs with nanozymes, offer a multifunctional anti‐inflammatory platform with great potential. This review intends to provide a comprehensive review of the recent development of MOF‐based nanomedicines for the therapy of inflammatory diseases. The challenges and future directions of research into the use of MOFs in the treatment of these diseases will also be discussed
99 / 5 000Commutation d'état de spin contrôlée par la lumière et induite par solvant dans un réseau hétérobimétallique hexagonal 3D
No full textInternational audienceA cyanide bridged {4d-3d} heterobimetallic assembly of MoV-FeII with formula {[MoV(CN)8][FeII(v-im)4]2·BF4}n 2DMF·H2O (1·2DMF·H2O) was achieved by the self-assembly of [Mo(CN)8]3− and iron(II) with monodentate nitrogen donor ligand v-im (v-im = 1-Vinylimidazol). The complex was fully characterized by single-crystal X-ray diffraction analyses, spectroscopic and (photo)magnetic studies. Single crystal X-ray analyses revealed that the complex exhibits a three-dimensional (3D) hexagonal network structure of molybdenum(V) and iron(II) centers bridged by the cyanide ligands. The partially desolvated form 1·2DMF exhibit thermo-induced spin crossover (SCO) between LS Fe(II) and HS Fe(II) center over a wide range of temperature and light-controlled spin-state switching phenomenon at low temperature under light irradiation with TLIESST = 70 K whereas the fully solvated complex 1·2DMF·H2O remains in the HS state. This complex represents the first 3D coordination complex consists of iron(II) and [MoV(CN)8]3− units exhibiting reversible and complete SCO phenomenon and photo-magnetic effect.Un assemblage hétérobimétallique {4d-3d} ponté par cyanure de MoV-FeII de formule {[MoV(CN)8][FeII(v-im)4]2·BF4}n 2DMF·H2O (1·2DMF·H2O) a été obtenu par l'auto-assemblage de [Mo(CN)8]3− et de fer(II) avec un ligand donneur d'azote monodentate v-im (v-im = 1-vinylimidazol). Le complexe a été entièrement caractérisé par des analyses de diffraction des rayons X sur monocristal, des études spectroscopiques et (photo)magnétiques. Les analyses des rayons X sur monocristal ont révélé que le complexe présente une structure de réseau hexagonal tridimensionnelle (3D) de centres de molybdène(V) et de fer(II) pontés par les ligands cyanure. La forme partiellement désolvatée 1·2DMF présente un croisement de spin thermo-induit (SCO) entre le centre Fe(II) LS et le centre Fe(II) HS sur une large plage de températures et un phénomène de commutation d'état de spin contrôlé par la lumière à basse température sous irradiation lumineuse avec TLIESST = 70 K, tandis que le complexe entièrement solvaté 1·2DMF·H2O reste dans l'état HS. Ce complexe représente le premier complexe de coordination 3D composé d'unités fer(II) et [MoV(CN)8]3− présentant un phénomène SCO réversible et complet et un effet photomagnétique
Factors shaping vaginal microbiota long-term community dynamics in young adult women
No full textInternational audienceThe vaginal microbiota is known to affect women's health. Yet, there is a notable paucity of highresolution follow-up studies lasting several months, which would be required to interrogate the longterm dynamics and associations with demographic and behavioural covariates. Here, we present a high-resolution longitudinal cohort study of 125 women, followed for a median duration of 8.6 months, with a median of 11 samples collected per woman. Using a hierarchical Bayesian Markov model, we characterised the patterns of vaginal microbiota community persistence and transition, simultaneously estimated the impact of 16 covariates and quantified individual variability among women. We showed that "optimal" (Community State Type (CST) I, II, and V) and "sub-optimal" (CST III) communities are more stable over time than "non-optimal" (CST IV) ones. Furthermore, we found that some covariates -most notably alcohol consumption -impacted the probability of shifting from one CST to another. We performed counterfactual simulations to confirm that alterations of key covariates, such as alcohol consumption, could shape the prevalence of different microbiota communities in the population. Finally, our analyses indicated that there is a relatively canalised pathway leading to the deterioration of vaginal microbiota communities, whereas the paths to recovery can be highly individualised among women. In addition to providing one of the first insights into vaginal microbiota dynamics over a year, our study showcases a novel application of a hierarchical Bayesian Markov model to clinical cohort data with many covariates. Our findings pave the way for an improved mechanistic understanding of microbial dynamics in the vaginal environment and the development of novel preventative and therapeutic strategies to improve vaginal health
Exploring the influence of wild silks composition on dyeing with turmeric and indigo: spectroscopic insights
No full textInternational audience"Wild" silks, produced by various silkworm species, are often valued in textile production, but present greater challenges in dyeing compared to the "domestic" mulberry silk from Bombyx mori. This study investigates the reasons behind these challenges, focusing on key components such as fibroin, sericin proteins, and calcium oxalate crystals. The degumming process, which removes sericin, generally enhances dye penetration; however, its efficiency varies with the type of silk and its chemical composition. Using Fourier-transform infrared (FTIR), Raman spectroscopy, and UV-Visible spectroscopy, we characterized the composition of cocoon samples from 11 different silkworms, both with and without a preliminary degumming step, and assessed their dyeing behavior with turmeric and indigo dyes. FTIR provided insights into the molecular structure and physico-chemical interactions within the silk fibers, while UV-Visible spectroscopy quantified dye sorption. Our findings demonstrate that effective degumming is crucial for dye uptake, with greater degumming loss often leading to a higher and more homogenous dye sorption. In some cases, the degumming procedure did not completely remove sericin, the latter of which not only physically impedes dye penetration into the silk mass but also forms physicochemical interactions with the dye, influencing the overall sorption capacity. Additionally, the presence of calcium oxalate crystals - particularly in wild silks like Antheraea paphia - can further impede dye sorption. Corroborating images obtained using optical digital microscopy supported these findings