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Structural and chemical characterization of polysaccharides from the red alga Plocamium cartilagineum (Linnaeus) P.S. Dixon 1967 with antiviral, anti-angiogenic, and anti-inflammatory activities
No full textInternational audienc
Bioinspired 4D Printed Tubular/Helicoidal Shape Changing Metacomposites for Programmable Structural Morphing
No full textInternational audienceBiological structures combine passive shape‐changing with force generation through intricate composite architectures. Natural fibers, with their tubular‐like structures and responsive components, have inspired the design of pneumatic tubular soft composite actuators. However, no development of passive structural actuation is available despite the recent rise of 4D printing. In this study, a biomimicry approach is proposed with inspiration from natural fiber architecture to create a novel concept of thermally active 4D printed tubular metacomposites. These metacomposites exhibit high mechanical performance and 3D‐to‐3D shape‐changing ability triggered by changes in temperature. A rotative printer is proposed for winding a continuous carbon fibers reinforced PolyAmide 6.I composite on a PolyAmide 6.6 polymer mandrel in a similar manner to the structure of cellulose microfibrils within the polysaccharide matrix of natural fiber cell‐walls. The resulting 4D printed tubular metacomposites exhibit programmable rotation and torque in response to thermal variations thanks to the control of their mesostructure and the overall geometry. Energy density values representing a trade‐off between the rotation and the torque are comparable to shape memory alloys when normalized by stiffness. Finally, a proof of concept for an autonomous solar tracker is presented, showcasing its potential for designing autonomous assemblies for structure morphing
Four contemporary problems in extreme value analysis
No full textThis article gives a summary of recent results on extreme value analysis that were presented at the Journées MAS 2024 in Poitiers. We first set the general background and motivation for these results, and we then discuss partial solutions to four contemporary problems in extreme value analysis: the construction of bias-reduced estimators of the Expected Shortfall (or Tail-Valueat-Risk) at extreme levels, extremal regression and inference in the presence of dependent data, multivariate inference about extreme quantiles using an analogue of the classical ANOVA method in regression, and improved estimation of tail risk measures using nonparametric resampling of multivariate Generalized Pareto distributions
Individual cell fate and population dynamics revealed by a mathematical model linking telomere length and replicative senescence
No full textInternational audienceProgressive shortening of telomeres ultimately causes replicative senescence and is linked with aging and tumor suppression. Studying the intricate link between telomere shortening and senescence at the molecular level and its population-scale effects over time is challenging with current approaches but crucial for understanding behavior at the organ or tissue level. In this study, we developed a mathematical model for telomere shortening and the onset of replicative senescence using data from Saccharomyces cerevisiae without telomerase. Our model tracks individual cell states, their telomere length dynamics, and lifespan over time, revealing selection forces within a population. We discovered that both cell genealogy and global telomere length distribution are key to determine the population proliferation capacity. We also discovered that cell growth defects unrelated to telomeres also affect subsequent proliferation and may act as confounding variables in replicative senescence assays. Overall, while there is a deterministic limit for the shortest telomere length, the stochastic occurrence of non-terminal arrests drive cells into a totally different regime, which may promote genome instability and senescence escape. Our results offer a comprehensive framework for investigating the implications of telomere length on human diseases
Configuración y tecnología de elementos geométricos en Coves del Fem: una aproximación cronoestratigráfica (6000-4500 CAL ane)
No full textInternational 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: Technologies, Applications and Classifications
No full textInternational audienceSince its initial development in the early 2000s, 3D printing has always been a polymorphic process, depending on the type of material used and the robotic system employed. Initial developments such as Prof. Koshnevis’ Contour Crafting concept (Khoshnevis 2004; Khoshnevis et al. 2006; Buswell et al. 2018), based on an extrusion system, or Enrico Dini’s D-Shape process, based on a selective particle bonding printing system (Colla et al. 2013), illustrate this diversity, which has continued to increase ever since. 3D concrete printing has almost as many variations as there are printers and companies working on the subject
Size effect of natural fibre reinforcement on mechanical performance for the development of thin bio-composite laminates: do fibre bundles represent a limitation?
No full textInternational audienceAs a consequence of the scale effect, thinner laminates generally exhibit fewer defects than thicker ones. However, the use of natural fibres in thinner composites (approximately 500 µm), such as composite membranes, remains limited due to the inherent geometric and mechanical variability of natural fibres, which significantly affect properties at reduced thicknesses.This study investigates the effect of laminate thickness on the longitudinal tensile properties of unidirectional flax/PPMA biocomposites, with thicknesses ranging from 220 µm to 1778 µm.Cross-sectional analyses examine changes in reinforcement distribution and the degree of flax fibre individualisation, specifically, whether fibres are dispersed as elementary fibres or retained in bundles. Strain fields are analysed using Digital Image Correlation (DIC) during tensile tests to localise high-strain regions.Results show that when flax fibre bundles dominate the microstructure, mechanical performance decline. In contrast to conventional expectations of the scale effect, there appears to be a critical thickness threshold (approximately 550 µm), below which tensile properties decline. At the lowest tested thickness, tensile performance decreased by up to 20 % relative to the maximum. Back-calculated laminate properties closely match those of the bundles, indicating that conventional scale effect theory does not adequately reflect the heterogeneous structure of flax fibre bundles, and must be reconsidered for natural fibre-reinforced biocomposites. This study highlights the relevance of mechanical characterisation at the final object scale rather than at the norm scale as it exhibits a different behaviour. Undermined by the increased heterogeneity in reinforcement structure mainly dependant on bundles for their mechanical behaviour
Pierre Paris ou la révolution des perspectives. De l’hellénisme à l’hispanisme archéologique
No full textInternational audienc
Limits of equilibrium states for coupled weakly interacting systems. Application to the measure of maximal entropy
No full textWe study metastability for symbolic dynamic. We prove that for a global system given by two independent sub-systems linked by a hole, and for a Lipschitz continuous potential, the global equilibrium state converges, as the hole shrinks, to a convex combination of the two independent equilibria in each component. Two kinds of convergence occur, depending on the assumptions on how long an orbit has to stay in each well.As a by-product, we show that this can be applied to a geometrical system inspired from [11] and for the measure of maximal entropy.</div
