Quantitative characterization of the ribbons and elastic vortices in viscoelastic Taylor-Couette flow with Boger fluids

International audienceInstabilities modes in viscoelastic Taylor-Couette flow are investigated using space-time diagrams and particle image velocimetry (PIV) of flow patterns in the meridional cross-section. The working solution is an aqueous mixture of the polymer solution of Polyethylene oxide (PEO) and Polyethylene glycol (PEG). The concentrations of the PEG and the POE are chosen in such a way to obtain solutions with constant shear viscosities (characteristic of Boger fluids) and a wide spectrum of values of the molecular elastic number in a single Taylor-Couette system. The interplay between the elasticity of the polymer solution and the inertia forces induced by the rotation of the cylinders leads to different critical modes: stationary Taylor vortices for very small values of the elasticity, ribbons i.e. superposition of spirals of opposite helicity for intermediate values of the elasticity and elastic vortices for large values of the elasticity and weak inertia forces. The elasto-rotational Rayleigh discriminant and linear stability analysis show the role of elasticity in the destabilization of the base flow and on the threshold of critical modes. The elastic vortices are characterized by regions of strong inflows separated by outflows; they form flame patterns in the spatiotemporal diagrams. The amplitude of the radial velocity at the centre of vortices is used as the order parameter of the ribbons dynamics. The Ginzburg-Landau theory offers a framework to describe the destabilization of regular ribbons with the introduction of a dissymmetry parameter. Spatiotemporal properties of elastic vortices (such as the drift velocity, the fraction, the size and the lifetime of inflows) are measured for different values of the criticality. The scaling exponents of energy spectra for inertio-elastic turbulence are determined for viscoelastic Taylor-Couette flow with the inner or outer sole rotating cylinder; the obtained values are compared with those from other experiments and from numerical simulations. PIV measurements have allowed to determine the power of the radial force at the inflow which shows that the driving mechanism of the elastic instability is active from the outer cylinder toward the inner cylinder

Femmes et sociabilité associative dans les campagnes de l’Ouest de la France (1830-1939). Le chemin de la discrimination ?

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Le lobby du sucre français entre dans les écoles. L'exemple des publications pédagogiques du Cédus (années 1950-années 1990)

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Dynamic Impedance Spectrum: A Novel Metric for Lithium-Ion Batteries Overcharging Diagnosis

International audienceDiagnosis of overcharging in lithium-ion batteries (LIBs) is crucial to guaranteeing the long-term thermal stability and operational lifespan of a battery system. Compared with conventional diagnosis methods that rely on cell temperature and voltage measurements, the dynamic impedance spectrum (DIS) provides novel insights into assessing battery charging and overcharging processes. In this article, the perturbation signals are superimposed onto the charging current for the real-time monitoring of the dynamic impedance variation. A quantitative analysis is conducted to examine the applicability of the characteristic parameters, which are extracted by fitting the DIS with an equivalent circuit model (ECM), in assessing the overcharging in LIBs. Experimental investigations confirm the validity of the DIS measurements by performing the Kramers-Kronig (K-K) tests, where the maximum absolute residuals are lower than 0.5%. The proposed method is capable of reliably warning the battery overcharge when the batteries are charged up to 98% state of charg

Configuración y tecnología de elementos geométricos en Coves del Fem: una aproximación cronoestratigráfica (6000-4500 CAL ane)

International audienceThe current study presents the analysis of previously unpublished lithic geometric artefacts recovered from the Coves dels Fem site. The analysis is conducted on the entire sample of geometric artefacts recovered from various chrono-stratigraphic levels documented in the cave, allowing the construction of a sequence spanning from 6000 cal ANE to 4500 cal ANE. Using a techno-morphological approach, the study examines the working processes performed on siliceous materials. The research focuses on the retouching work applied to configure the artefacts, highlighting the techniques used in their production. This comprehensive approach not only contributes to the understanding of the technological dynamics of the human groups that occupied the shelter but also provides a broader perspective on the evolution of productive practices during the Early Neolithic, facilitating comparisons with other sites of similar characteristics.El presente estudio expone el análisis de artefactos líticos geométricos inéditos recuperados en el yacimiento de Coves dels Fem. El análisis se realiza sobre la muestra total de elementos geométricos recuperados en distintos niveles cronoestratigráficos documentados en la cueva, permitiendo la construcción de una secuencia que abarca desde el 6000 cal ANE hasta el 4500 cal ANE. A partir de una aproximación tecnomorfológica, se abordan los procesos de trabajo realizados sobre la materia silícea. La investigación se centra en el trabajo de retoque aplicado para configurar los artefactos, destacando las técnicas utilizadas en su producción. Este enfoque integral no solo contribuye a la comprensión de las dinámicas tecnológicas de los grupos humanos que ocuparon el abrigo, sino que también ofrece una perspectiva más amplia sobre la evolución de las prácticas productivas a lo largo del Neolítico antiguo, permitiendo la comparación con otros yacimientos de características similare

3D Concrete Printing: State of the Art and Applications

International audienceThis book presents a comprehensive overview of the state of the art in additive manufacturing in the world of concrete construction. 3D Concrete Printing tackles its subject from several angles, including issues relating to concrete materials (such as their formulation or fresh-state behavior), the various printing processes that have been developed, and how to describe the mechanical behavior and architectural and structural designs of printed structures. This book also considers the transition to application and industrialization, and the relevance of these new technologies in reducing the environmental impact of the construction sector. Finally, material characterization methodologies are presented with a view to describing the behavior of materials both before and after printing, and the modeling tools used to simulate the process are listed

An Improved Sensorless Method to Submodule Voltage Balancing in Grid‐Connected Modular Multilevel Converters

International audienceABSTRACT This article proposes an improved sensorless capacitor voltage balancing (CVB) method for modular multilevel converters (MMCs) for high‐voltage direct current applications. The suggested method prioritizes achieving precise, straightforward, and computationally efficient control of MMCs, eliminating the necessity for external sensors. Simultaneously, it guarantees effective management of capacitor voltage balance within the converter arms. Combining the proposed sensorless control technique and CVB methods improves converter performance, reduces complexity, and increases overall system reliability. To validate the effectiveness of the proposed strategy, full simulations are performed. The simulation setup includes the MMC structure, the control algorithm, and the sensorless CVB method. The simulation results demonstrate the accurate regulation of energy flow while maintaining balanced capacitor voltages between the arms of the MMC. In addition, experimental verification is carried out using a scaled‐down laboratory prototype of the MMC system. The experimental results validate the practical feasibility and reliability of the proposed control strategy

A comprehensive platform investigating thermal, mechanical and rheological properties for biocomposite based on poly (3-hydroxybutyrate-co-3-hydroxyvalerate) reinforced with biomass by-products

International audienceInterest in developing polyhydroxyalkanoates (PHAs) -based biocomposites with biomass fillers (biofillers), derived from local organic by-products, to mitigate global plastic pollution has increased significantly in the last decades. These biocomposites not only offer a more cost-effective solution but also contribute to reducing the carbon footprint, enhancing product circularity, and accelerating biodegradation kinetics. However, optimising their mechanical properties and processability to effectively replace conventional plastics remains a challenge. This study holistically investigates key factors influencing the thermal, mechanical, and rheological properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) -based biocomposites. The range of biofillers used in this work, including wood sawdust, macadamia / walnut nutshell flour, agave piña fibres, sorghum stem/leaf fibres, wheat bran flakes and treated wood flour, differ significantly in origin, composition and shape. Except for the wood, the addition of biofillers resulted in a decrease in T m by 1 to 3 • C, T c by 1 to 6 • C, and T g by 0.5 to 13.5 • C. The greatest reduction in T g was observed with the Walnut biofiller. A significant gap of 60 % in tensile stress and modulus was noted between the best and worst performing biofillers, highlighting the importance of carefully selecting the biomass for biocomposite manufacturing. Consistent correlations were found between mechanical properties and the cellulose content, crystallinity, and the hydrophilic surface of the biofillers. The findings suggest that superior PHBV-based biocomposite performance can be attributed to the presence of hydroxyl groups from carbohydrates on the biofillers' surface and a robust internal cellulose structure. Additionally, the shape of the biofillers, particularly the aspect ratio, shows a stronger correlation with rheological behaviour at low angular frequency than the interactions between biofillers and PHBV. At high angular frequencies, the addition of biofillers leads to a reduction in PHBV viscosity by 40 % to 80 %, depending on biofiller used. To support the development of a comprehensive platform for PHAs-based biocomposites, this study compares and validates various characterisation methods ( 13 C ssNMR, TGA, carbohydrate and lignin analysis) that more effectively assess the composition of reinforcing biofillers

3D printing strategies and mechanical performance assessment of continuous basalt-fibre/PA12 composites with high fibre volume fraction

International audienceThe continuous filament fabrication (CFF), based on the fused filament fabrication (FFF), is a technology enabling to produce 3D-printed composite parts with high mechanical performance. Basalt fibres remain rather unused in CFF among fibrous reinforcements, in spite of properties similar to glass fibres. In addition, in the context of in-situ resource utilization for out-of-earth manufacturing, basalt fibres stand as an excellent earth-based analogue material of lunar regolith.This study aims at bringing deeper insights on the effect of specific printing strategies, by tuning the slicing parameters and by using a customized printer for CFF, as well as on the thermo-elastic properties of a novel high-performance composite material consisting of continuous basalt fibres embedded into a PA12 matrix, with a fibre volume fraction of 55 %.Thermal and morphological properties of the filament are first characterized. Then, the optimal slicing parameters – layer height (LH) and interfilament distance (ID) – are explored through the prism of process-induced porosity; a pore volume content as low as 2.15 % is reported for LH = 0.2 mm and ID = 1.15 mm, testifying to the high material quality and process handling. Finally, the in-plane mechanical properties of PA12-basalt are measured in the quasi-static regime, including longitudinal (0°) tension and compression, transverse (90°) tension, in-plane shear (±45°) and out-of-plane three-point bending. An extreme anisotropic behaviour is revealed. Competitive mechanical properties in the fibre direction are reported, comparable to similar glass-fibre reinforced composites. Conversely, those in the transverse direction are relatively moderate. The latter are attributed to the localized porosity induced by the juxtaposition of adjacent filaments for the interfilament distance selected

From Laboratory to Practice: Characterizing Fresh and Cured Printed Materials

International audienceCompared with the cast concrete used in traditional construction methods, 3D concrete printing imposes new specifications in the fresh state (Roussel 2018; Nicolas et al. 2022) and induces a potentially more complex anisotropic mechanical behavior in the hardened state (Asprone et al. 2018; Mechtcherine et al. 2021, 2022; Bos et al. 2022). These new constraints require the implementation of a comprehensive characterization process throughout the lifecycle of the printed element and material. This process necessitates numerous tests at different phases of the printing project