Université Bretagne Sud
Recent publications
Seaweed surface provides a suitable substratum for the settlement of microorganisms (bacteria, viruses, and plankton). These microbial partners may have either beneficial or detrimental effects on the host since surface microbiota can act either as a protective layer to the macroalgae (symbiotic beneficial relations) or, under changing environmental conditions, the microbial equilibrium may shift to a detrimental, pathogenic state thus inducing diseases in the host. In commercial aquaculture, seaweed diseases feature a growing concern. Pathogenicity of microorganisms that infect algal hosts is closely related to the release of virulence factors and the formation of biofilms, both of which are regulated by Quorum Sensing (QS). The main focus of this study is to determine the pathogenicity of the surface-associated bacteria of Halymenia floresii, a carrageenophyte that originated from distinct habitats. Twenty-five bacterial species isolated from the surface of H. floresii were individually tested for tip bleaching assay to evaluate their potential pathogenicity. Ten isolates significantly reduced the risk of tip bleaching in H. floresii and were designated as ‘significantly non-pathogenic’. Vibrio owensii was identified as a ‘significant pathogen’ inducing bleaching disease in H. floresii. By using LC-MS, we here identified its HomoSerine Lactones (HSL) QS signal, as a C4-HSL (short-chain). This study thus suggests a possible involvement of QS signal (short-chain) in the disease-inducing bacterium from the aquaculture ponds (an integrated multitrophic aquaculture system). This study firstly reports on the surface-associated bacteria of a lambda-carrageenophyte. This study must contribute to the development of dedicated strategies for disease control based on HSL disruption in aquaculture. Keywords: Halymenia floresii, lambda-carrageenophyte, Vibrio owensii, bleaching, Quorum Sensing, homoserine lactones, LC-MS
Unintended evaporation of additive elements can be observed on alloys during processes involving high temperatures and fusion. Indeed, welding, casting and additive manufacturing of steels lead to temperatures sufficiently high to start the evaporation of some low boiling point element such as manganese. In this paper, both experimental and numerical approaches are developed to study and quantify this phenomenon. Experimentally, an ex-situ aerodynamic levitation apparatus is employed to apply varying temperatures or durations at liquid state to a 304L steel sample. These experiments are represented numerically with a multiphysics model solving heat transfer, fluid flow and evolution of concentration of manganese dynamically. Equations chosen to represent this poorly studied phenomena are presented and compared to experiments. A comparison highlights a good accuracy of the proposed model. This precision increases particularly when the melting duration is high. Order of magnitude of evaporation phenomena is precisely quantified with time and temperature dependencies.
Tensile properties of elementary flax fibres were investigated through in situ Synchrotron X-ray diffraction in order to understand the effect of tensile loading, on the internal reorganisation of crystalline cellulose; for the first time, these experiments were conducted for different RH conditions. Synchrotron radiation experiments were considered under reduced spot size and short acquisition times to quantify the variation of cellulose microfibril angle (MFA) in a single fibre during tensile loading, while limiting the fibre damage during X-ray exposure. The acquisitions were possible at various relative humidity (RH) conditions (from 25 % to 92 %) in order to quantify the effects of different hygro-mechanical actions upon elementary flax fibres. The results show that the MFA decreases with the increase of the applied loading, indicating a partial realignment of the cellulose microfibrils with the loading axis. The MFA at fracture point shows a decrease between − 11 and − 15 % compared to the initial MFA at all relative humidity conditions studied. The strain at break of the fibres increases with increasing relative humidity. This mechanical behaviour shows the plasticizing effect of water on the non-cellulosic amorphous matrix of cell wall.
Presented herein is a novel design framework for obtaining the optimal design of functionally graded lattice (FGL) structures that involve using a physical discrete structural model called the Hencky bar-grid model (HBM) and topology optimization (TO). The continuous FGL structure is discretized by HBM comprising rigid bars, frictionless hinges, frictionless pulleys, elastic primary and secondary axial springs, and torsional springs. A penalty function is introduced to each of the HBM spring’s stiffnesses to model non-uniform material properties. The gradient-based TO method is applied to find the stiffest structure via minimizing the compliance or elastic strain energy by adjusting the HBM spring stiffnesses subjected to prescribed design constraints. The optimal design of FGL structures is constructed based on the optimal spring stiffnesses of the HBM. The proposed design framework is simple to implement and for obtaining optimal FGL structures as it involves a relatively small number of design variables such as the spring stiffnesses of each grid cell. As illustration of the HBM-TO method, some optimization problems of FGL structures are considered and their optimal solutions obtained. The solutions are shown to converge after a small number of iterations. A Python code is given in the Appendix for interested readers who wish to reproduce the results.
This paper describes a novel voxel-based technique to accurately model 3D printed continuous yarns of fibre composites at printed filament scale. To cater for the constraints of continuous filament printing, the design strategy here makes use of a set of variables that fully define the printing path as input in the model. A voxel-based algorithm is developed to obtain the local orientations of the filaments and local quantities of yarns and matrix from a pixelated flat layout of the printed composite. This voxel-based representation is then translated into a Finite Element model to obtain the required structural properties. This approach simplifies and potentially shortens the design of the part, compared to other analytical techniques. The design space of the part is defined by the variables of the gcode used to print the composite. The voxel model is coupled with an evolutionary algorithm to explore the part of the design space related to the use of continuous yarns. The hygro expansion of the material was measured to determine the coefficients of moisture expansion serving as input in the model. Promising results are obtained from a test case related to a continuous flax fibres-reinforced polylactic acid (PLA) printed structure, mimicking the shape of a leaf. The proposed modelling strategy has the potential to characterise geometric, material, mechanical and actuation properties of general 3D printed structures with negligible out-of-plane (i.e., through thickness) printing.
Connected Vehicles (CVs) are the key enabling technology for Intelligent Transportation Systems (ITSs) that offer great opportunities for improving traffic safety and efficiency. They provide several innovative safety-related applications such as traffic management and monitoring, which involve the transmission of messages from all vehicles on the road. Basic Safety Messages (BSMs) constitute an essential type of control message. However, several critical issues affect the BSM messages’ reliability. In this paper, a model-based approach for detecting discordant BSMs is proposed, which allows to avoid the vehicle disturbance. This approach consists of detecting incoherence in communication metric values, where the detection is formulated as an anomaly detection problem that is solved using the Gaussian distribution. The detection process allows the vehicles to cross their prediction to achieve more precision in deciding whether to accept or reject a message from a vehicle. The efficiency of our model for detecting an anomaly has been evaluated through simulations using our generated dataset. The obtained results indicate that the proposed model provides high performance in terms of detection rate. Moreover, we evaluate and validate the proposed approach through formal evaluation, where it demonstrates promising performances, as compare it with a concurrent approach through simulations considering important metrics.
3D porous electrodes have been considered as a new paradigm shift for increasing the energy storage of pseudocapacitive micro-supercapacitors for on-chip electronics. However, the conformal deposition of active materials is still challenging when highly porous structures are involved. In this work, we have investigated the atomic layer deposition (ALD) of ruthenium dioxide RuO 2 on porous Au and Pt architectures prepared by hydrogen bubble templated electrodeposition, with area enlargement factors (AEF) ranging from 400 to 10000 cm ² /cm ² . Using proper ALD conditions, a uniform RuO 2 coverage has been successfully obtained on porous Au, with a specific electrode capacitance of 8.1 mF cm ⁻² and a specific power of 160 mW cm ⁻² for a minute amount of active material. This study also shows the importance of the chemical composition and reactivity of the porous substrate for achieving conformal deposition of a ruthenium oxide layer.
The Simple Ranking Method using Reference Profiles (or SRMP) is a Multi-Criteria Decision Aiding technique based on the outranking paradigm, which allows to rank decision alternatives according to the preferences of a decision maker (DM). Inferring the preference parameters of such a model can lead to a cognitive fatigue of the DM, who is often asked to express several preferential statements about pairs of alternatives during the elicitation process. To limit the DM’s effort, we propose in this work an incremental elicitation process to select informative pairs of alternatives to be presented to the DM sequentially with the aim of refining the SRMP model until a robust recommendation can be made. We study several different heuristics for selecting the pair of alternatives to be submitted to the DM at each step. Following extensive numerical experiments we identify one of the proposed heuristics as performing significantly better than the others and we provide several guidelines for its use in practice.
The creation and ultrastructure of kink-bands in flax fibres are key issues for developing more and more performing biobased composite materials. Nevertheless, despite many hypotheses and structural characterisation, the exact origin of kink-bands and the moment they appear remain unexplained. Here, by using cutting-edge techniques such as microtomography, a range of flax stems and fibres, from the green stem to stretched fibres, were morphologically explored. The study shows that all the extracted fibres, whether scutched, combed or stretched, contain significant amounts of kink-bands, which can be identified by the large pores they contain. On the other hand, at the scale of the green or retted stems, tomographic analysis does not reveal any kink-bands. These original observations suggest that the stress undergone by the plants during their growth is not sufficient, without major growth or lodging accidents, to generate these structural defects; the latter are only revealed after mechanical extraction of the fibres. Hypotheses regarding the kink-band appearance deformation levels are also given to complete the observations.
Currently, the effects of global warming are one of the most important topics on the agendas of all governments and international economic and scientific organisations on the planet. Temperatures and rainfall will be especially subjected to increasing deregulation, and thus crop yields will be affected according to geographic location. Cellulosic materials, such as bast fibres, are considered one solution to decrease human environmental impact: they are a renewable resource, biodegradable and have a lower carbon emission than synthetic materials. However, their quality, yield and mechanical properties depend on environmental conditions during plant growth. In this paper, we explored the possible impact of seasonal drought linked to future climate change on flax plants and fibre quality. Two batches of the same textile flax plant cultivar were grown under two different field environmental conditions in the same year, one taken as a control under regular climatic conditions and the second one grown under drought stress. Carbon isotopic discrimination reveal an increase in water stress plant of the fibre δ¹³C, reflecting that plants are indeed suffering from drought stress from a physiological point of view. We characterized the mechanical properties, biochemistry and morphology parameters at both the stem and technical fibre scales. Our results showed that the plants of the two batches were morphologically different and that the drought-stressed plants were smaller, mainly in terms of the height of the stem (−28%) and diameter (−16%). Biochemical analyses highlighted a contrasting lignin content between the two batches. A difference in protein content was also measured, with an increased amount in stressed flax plants, with contrasting distributions revealed by tyrosine and tryptophan monitored by synchrotron UV fluorescence. In addition, polysaccharide composition was also quantified with an increase in mannose and an important decrease in glucose in the drought-stressed technical fibres. Surprisingly, despite the difference in biochemistry composition and morphological parameters, the mechanical properties of elementary flax fibres extracted from the two batches were not significantly different. This suggests that drought can affect the yield and biochemistry of the extracted technical flax fibres but does not necessarily impact the longitudinal mechanical performance of single fibres.
Light earth is a natural insulating material composed of earth and vegetal fibres. It can be used to insulate existing and new buildings to reduce energy and resources consumption, and excavated earth generation by the construction sector. A pedological database is crossed with suitability thresholds in order to evaluate spatially the availability of earth resources. Then, the soil suitability is mapped, and suitable soil amounts metrics are estimated for Brittany territory. A sensitivity analysis is performed to understand the potential variability of the results. Study estimates that 48% of Brittany's soil horizons are suitable for light earth building. Every year, 1.3 Mt of suitable soil are excavated in Brittany. Using only these excavated earths, all existing and new buildings in Brittany could be insulated with light-earth in less than 8 years. This study shows that suitable earth availability is not a limiting factor to develop light earth insulation in Brittany.
3D-printing of biocomposites using continuous natural fiber composites is emerging as a relevant manufacturing method to develop highly tailorable materials. These are materials with high performance characteristics, whose capabilities have been achieved through the controlled design of the mesostructure via the 3D printing process. However, the development of 3D printing using continuous natural fiber composites is so recent that no geometric limitations have yet been investigated. The present article has established the printability and design window of several cellular lattice structures by investigating and discussing a comparative analysis of the difference between the programmed and actual trajectories of pure polylactic acid (PLA), short flax fiber biocomposite (FF/PLA) and continuous flax fiber/PLA biocomposites (cFF/PLA) for a specific set of printing and slicing parameters. It is expected that the presented findings will support the ongoing development of improved design methods and optimized technical deposition approaches that can expand the design space for cFF/PLA 3D printed biocomposites with multi-layered periodic cellular lattice patterns.
Natural language resources are essential for integrating linguistic engineering components into information processing suites. However, the resources available in French are scarce and do not cover all possible tasks, especially for specific business applications. In this context, we present a dataset of French newsletters and their use to predict their impact, good or bad, on readers. We propose an original representation of newsletters in the form of graphs that take into account the layout of the newsletters. We then evaluate the interest of such a representation in predicting a newsletter’s performance in terms of open and click rates using graph convolution network models.
Friction is one of the key factors in the manufacture of ropes, and has an important influence on the mechanical behavior of many fiber assemblies. For this reason, the understanding and the evaluation of the coefficients of friction between fibers is an essential step in the development of numerical rope models. This paper describes tests on a modified, upscaled version of the ASTM (American Society for Testing and Materials) standard yarn-on-yarn abrasion test device, which allows measurement of the friction coefficient between polyamide rope yarns. It is shown that the inter-fiber angle has a significant influence on the friction coefficient, and the direction of movement relative to the filament has to be considered in the determination of this coefficient. A normalized representation allows friction coefficients measured for a range of test conditions to be plotted on a single curve. The abrasion test device allows the friction coefficient to be measured throughout abrasion tests. It is concluded that lower friction leads to higher abrasion resistance and longer lifetime.
In this work, the main objective is to investigate the effect of olive husk flour (OHF) used as a biofiller on the marine degradation of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) biocomposites up to 6 months of immersion in sea water at 25°C and 40°C. Film samples based on neat PHBV and PHBV are filled with 20 wt.% OHF is prepared by melt compounding. After 6 months of immersion in sea water, the study reveals a noticeable decrease in the absorption band intensity of ester groups of PHBV through Fourier transform infrared (FTIR-ATR) spectroscopy, even more in the presence of OHF in PHBV biocomposite due to hydrolytic degradation. This phenomenon is, however, more pronounced at 40°C. This also agrees with differential scanning calorimetry (DSC) data, which indicates a large increase in crystallinity index (X c) resulting from short chains reorganization. Moreover, scanning electron microscopic (SEM) analysis shows for both degraded samples, eroded and cracked surfaces, being however more pronounced for PHBV/OHF biocomposite at 40°C. This study highlights the role of OHF as a promotor of marine degradation of PHBV.
Background: Decontamination regimen decreases acquired infection (AI) incidence but remains controversial, mostly because it contained a course of intravenous antibiotic. Multiple site decontamination (MSD), that do not included systemic antibiotics, has been less studied but is associated with lower risk of ventilator associated pneumonia (VAP), bloodstream infection (BSI) and multidrug resistant micro-organisms (MDRO) acquisition. We aimed to confirm these favorable outcomes. Methods: A prospective pre/post-observational study was conducted in 5 ICUs in western France. Among them, 4 implemented MSD whereas the last one applied standard care (SC) during all study period. Patients who required intubation were eligible for study and divided into two groups: MSD group if they were admitted in an ICU that already implemented MSD and SC group otherwise. Primary objective was AI incidence. Results: 1346 patients were available for analysis (334 in the MSD and 1012 patients in the SC group). In a multivariable Poisson regression model, MSD was independently associated with a decreased incidence of AI (IRR = 0.33; 95%CI [0.18-0.60] p<0.001). A non-parsimonious propensity-score matching resulted in 334 patient-pairs with well-balanced baseline characteristics. There were a lower incidence of AI (6.3% vs 20.7% p<0.001), VAP (3.6% vs 16.2% p <0.001) and BSI (3.0% vs 7.2% p = 0.029) in the MSD group as compared with the SC group. Five patients (1.5%) and 11 (3.3%) acquired a MDRO respectively (p=0.206). Conclusion: MSD is associated with a decrease risk of AI, VAP and BSI with no increase in MDRO acquisition.
When a hydrogen or oxygen bubble is created on the surface of an electrode, a micro-convective vortex flow due to the Marangoni effect is generated at the bottom of the bubble in contact with the electrode. In order to study such a phenomenon numerically, it is necessary to be able to simulate the surface tension variations along with a liquid-gas interface, to integrate the mass transfer across the interface from the dissolved species present in the electrolyte to the gas phase, and to take into account the moving contact line. Eulerian methods seem to have the potential to solve this modeling. However, the use of the continuous surface force (CSF) model in the volume of fluid (VOF) framework is known to introduce non-physical velocities, called spurious currents. This paper presents an alternative model based on the height function (HF) approach. The use of this method limits spurious currents and makes the VOF methodology suitable for studying Marangoni currents along with the interface of an electrogenerated bubble.
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1,162 members
  • LBCM - Laboratoire de Biotechnologie et Chimie Marines
Thierry Morineau
  • Laboratoire Psychologie, Cognition, Communication, Comportement LP3C
Cedric Marchand
  • Lab-STICC - Laboratoire en sciences et techniques de l'information, de la communication et de la connaissance
Nathalie Bourgougnon
  • LBCM - Laboratoire de Biotechnologie et Chimie Marines
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