HAL-Université de Bretagne Occidentale
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Food web structure in a rapidly changing coastal environment: the West Antarctic Peninsula.
No full textInternational audienceThe West Antarctic Peninsula (WAP) is one of the most rapidly changing regions in the world. Steep environmental gradients in sea ice cover and glacier melting are observed, but much remains to be documented regarding the impact of these differences on biological communities and ecosystem processes. Here, we study how environmental variability impacts trophic interactions and ecological habitats of benthic communities along the WAP. During the Belgica 121 expedition, dominant benthic mega- and macrofauna, as well as primary producers, were sampled in multiple stations featuring different environmental conditions around the Gerlache Strait. Stable isotope ratios of carbon, nitrogen, and sulfur were measured and combined in an isotope niche analysis (SIBER). Our results suggest that changes in environmental features, notably ice-related conditions, could alter food source availability and organic matter fluxes towards benthic organisms. Isotopic compositions of abundant species were more variable in stations with stronger ice-related disturbance. Besides variability in isotopic baseline, this result could possibly also be linked to the use of a wider diversity of food sources (niche expansion) in stations affected by different ice-related conditions. Overall, our findings provide important insights towards understanding the interplay between environmental conditions and ecological habits of benthic consumers along the WAP
Scout Monte Carlo: Preliminary Results of a Variance Reduction Technique for Photon Scattering Dose Calculation
No full textInternational audienc
Hierarchical Modeling of Archaeological and Modern Flax Fiber: From Micro- to Macroscale
No full textInternational audienceFlax fiber reinforcements weaken with aging and microstructural changes, limiting their applications. Here, we examine the effects of microstructure and aging on flax fiber elements' performance by using 4000-year-old and modern Egyptian flax as references through multi-scale numerical modeling. This study introduces a novel investigation into the tensile stress distribution behavior of archaeological and modern flax yarns. The finite element (FE) model is derived from 3D volumes obtained via X-ray microtomography and tensile testing in the elastic domain. At the microscale, fibers exhibit higher axial stress concentrations around surface defects and pores, particularly in regions with kink bands and lumens. At the mesoscale, fiber bundles show increased stress concentrations at inter-fiber voids and lumen, with larger bundles exhibiting greater stress heterogeneity, especially around pores and surface roughness. At the macroscale, yarns display significant stress heterogeneity, especially around microstructural defects like pores and fiber-fiber cohesion points. Aged fibers from ancient Egyptian cultural heritage in particular demonstrate large fiber discontinuities due to long-term degradation or aging. These numerical observations highlight how porosity, surface imperfections, and structural degradation increase stress concentration, leading to fiber rupture and mechanical failure. This insight reveals how aging and defects impact flax fiber performance and durability
Proposition d’une modalité prospective pour penser la coopération du futur entre l’agent humain et le jumeau numérique : application à l’activité de planification de la maintenance
No full textThe digital twin is a key technology in Industry 4.0, particularly for optimizing maintenance. The deployment of this technology at SPIE Industrie involves two major challenges. The initial specifications focus on technical expectations, giving less importance to cooperative aspects, which is a potential barrier to acceptance of the digital twin. In addition, maintenance managers are experiencing difficulties in projecting themselves into this future cooperation, and thus expressing their future needs. This CIFRE thesis mobilizes prospective ergonomics to enrich the SPIE Industrie specifications and support the projection into this future cooperation. The aim is to develop a prospective modality with support, enabling the explicit expression of future needs related to cooperation with the digital twin.The efficacy of the prospective modality with support was evaluated in three studies, by analyzing the future needs expressed in terms of fluency, diversity and completeness. The results show that the prospective modality with support improves fluency. In terms of diversity, future needs related more to cooperation with the digital twin. In addition, novice participants were able to express more complete future needs. We are thus encouraging the deployment of a digital twin adapted to the future needs of maintenance managers. The aim of this thesis is also to increase knowledge of prospective methods and to propose a new approach for evaluating their efficacy.Le jumeau numérique constitue une technologie clé de l'Industrie 4.0, notamment pour optimiser la maintenance. Dans le cadre de son déploiement chez SPIE Industrie, deux enjeux majeurs émergent. Le cahier des charges initial privilégie des attentes techniques, accordant une moindre importance aux aspects coopératifs, ce qui constitue un frein potentiel pour l’acceptation du jumeau numérique. De plus, les responsables de maintenance éprouvent des difficultés à se projeter dans cette coopération à venir, et ainsi exprimer leurs besoins futurs. Cette thèse CIFRE mobilise l’ergonomie prospective pour enrichir le cahier des charges SPIE Industrie et soutenir la projection dans cette coopération future. L'objectif est de développer une modalité prospective avec support, permettant d’expliciter les besoins futurs liés à la coopération avec le jumeau numérique.L'efficacité de la modalité prospective avec support a été évaluée au cours de trois études, en analysant les besoins futurs exprimés selon la fluence, la diversité et la complétude. Les résultats montrent que la modalité prospective avec support améliore la fluence. En termes de diversité, les besoins futurs concernent davantage la coopération avec le jumeau numérique. De plus, les participants novices parviennent à formuler des besoins futurs plus complets. Nous favorisons ainsi le déploiement d’un jumeau numérique adapté aux besoins futurs des responsables de maintenance. Les travaux de thèse ont également la volonté d’enrichir les connaissances sur les méthodes prospectives et de proposer une nouvelle approche pour l’évaluation de leur efficacité
Bast from the past: the fibre architectures and properties of Ancient Egyptian and Peruvian fishing nets
No full textInternational audienceBast fibres have been critical materials in the evolution of human history. In particular, their use in fishing technology as well as in maritime transport has enabled mobility, livelihoods, and the exchange of goods and transmission of cultures in human societies. Here, we compare fishing nets from two distant but contemporaneous groups at the end of the 4th millennium BCE: one from Neolithic period in Egypt and the other from the Middle Preceramic Peruvian Pacific coast. The fishing nets possess substantially similar textile architectures even though they use bast fibres from different species: domesticated cf. Linum usitatissimum L. (flax linen) by the Ancient Egyptians and cf. Asclepias . (milkweed) by the coastal Peruvian community. We examine these two fibre types and show that despite their distinct morphological and ultrastructural characteristics, their processing and manufacture share some similarities, both 2-ply with Z final torsion. Multiphoton, atomic force, and scanning electron microscopy are supplemented by 3D micro-computed X-ray phase-contrast tomography to investigate the unique architectures of the yarns and their fibres’ artefacts. We demonstrate the use of state-of-the-art micro-spectroscopy techniques for archaeobotanical studies and use fishing nets as a new lens to unravel the episteme and techne of fibre and textile production in the past
Exploring HP-LT records through time using inclusions of rutile grains
No full textInternational audienc
Optimizing reliability and safety of wind turbine systems through a hybrid control technique for low-voltage ride-through capability
No full textInternational audienceThis study addresses a significant challenge in reliability engineering and system safety, specifically the operation of wind turbines under fault conditions. It proposes an asymmetrical fault ride-through (AFRT) control method designed for the doubly fed induction generator (DFIG) rotor-side converter (RSC) used in wind turbines. The DFIG model is analyzed in both positive and negative rotating synchronous reference frames (PR-SRF and NR-SRF), incorporating four key components to prevent overcurrent in the RSC during AFRT conditions. The proposed control method is divided into two segments: first, reducing the four components based on boundary constraints and reference value configuration; and second, determining the control characteristic ‘ k ’ through an optimization loop using the particle swarm optimization (PSO) algorithm. The effectiveness of the PSO algorithm is compared with three other optimization methods genetic algorithm (GA), differential evolution (DE), and ant colony optimization (ACO). The dynamic performance of the proposed method is assessed under Line-to-Line (LL) and Line-to-Line-to-Ground (LLG) fault scenarios. Simulation results demonstrate that the method successfully mitigates fluctuations caused by asymmetrical faults (AFs), achieving a 7.2% higher efficiency in AFRT than similar approaches. Ultimately, this research enhances wind turbine system safety and reliability, ensuring more robust power generation during asymmetrical fault conditions
Biosynthesis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) using microalgae-derived starch and levulinic acid
No full textInternational audienceA microalgae cultivation process was developed in order to produce starch-rich biomass, which can be converted into glucose after starch extraction and hydrolysis. Associated to levulinic acid, biosynthesis processes were carried out with microalgae-derived starch glucose, resulting in the production of poly (3-hydroxybutyrate-co-3hydroxyvalerate)s (PHBHV) with different contents in HB and HV units, with HV units reaching up to 32 %. The thermal and mechanical characteristics were measured as a function of HV proportion and are discussed in terms of chemical structure/morphology/properties relationships, showing that these properties can be modulated by adjusting the ratio between HB and HV units. The crystallinity of PHBHV copolymers gradually decreases as HV unit content increases and tends to drastically increase the ductility of materials with an elongation at break equal to about 800 % for PHBHV with 32 % in HV units. This work emphasizes the possibility to precisely design tailor-made PHBHV with tunable functional properties, by playing on the mixture of substrates initially introduced. Moreover, it addresses crucial societal considerations by using raw materials that do not compete with the food industry.</div
Analysis of the tensile behaviour of flax fibre bundles as a function of the loaded volume
No full textInternational audienceAddressing the mechanical behaviour of flax bundles is a key point when used as reinforcements in composite materials. To determine their mechanical properties, the bundle cross-sectional area must be correctly assessed and has been estimated here using three types of models: elliptical, circular or polygonal. The circular model shows the higher disparity with twice the polygonal standard deviation. Innovatively, 3D rendering of bundles were carried out using microtomographic acquisitions, highlighting their partially cohesive unidirectional composite structure. Then, to analyse the phenomenon involved in the characterisation of bundles, mechanical properties were determined from a threshold value (first damage detected) and expressed as a function of the loaded volume (depends on the bundle cross-section area and the gauge length). To consider the dispersion of the bundles cross-sections, these properties were also weighted using the cross-section distribution curve. The results show their dependence on the volume and morphology of the tested bundles