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The association of dextran sodium sulfate to the bioactive agent I-modulia® attenuates Staphylococcus aureus virulence expression and δ-toxin production
No full textInternational audienceAs a part of the human skin commensal bacterial community, Staphylococcus aureus contributes to the host's immune system education. Nevertheless, it is also considered as an opportunistic pathogen involved in cutaneous infections or skin pathologies, in particular atopic dermatitis. To switch to a pathogenic behavior, S. aureus uses regulatory mechanisms to collectively produce virulence factors. Deprivation of these factors has emerged as a promising way to prevent or treat Staphylococcal diseases in facilitating the role of the immune system, while preserving the protective one of the commensal communities. This study focuses on the anti-virulent effect of dextran sodium sulfate (DSS) and I-modulia ® , two natural products that have already proven their value in skincare. The anti-virulent capacity of DSS was first demonstrated by a dose-dependent inhibition of δ-toxin release, a virulence factor known to be a potent inducer of mast cell degranulation, on in vitro S. aureus cultures at high and low virulent states. A transcriptomic study was then implemented for a comprehensive overview of the anti-virulent impact. The results have shown the downregulation of many transcripts related to host immune evasion (scn, sbi), as well as exotoxins (α,γ-toxin) and adhesins production (map, emp), mostly under the control of SaeRS Two-Component System (TCS), one of the two major virulence regulators in S. aureus.Interestingly, genes related to secretion systems and the synthesis of exo-proteases were significantly downregulated when DSS was used in combination with I-modulia ® . The repression of these genes was not previously observed and reflects a broader inhibitory action.We have also demonstrated that the inhibition of virulence factors didn't affect S. aureus viability. Our findings suggest that combining DSS and I-modulia® could be a promising therapeutic strategy to counteract microbial dysbiosis in the treatment of S. aureus skin pathologies in re-empowering the host's natural immune defences.</div
Concevoir et intégrer des IA explicatives de confiance : conditions sociotechniques et d’usage pour des technologies centrées sur l’humain en contextes professionnels et domestiques
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Characterizing the onset and development of internal erosion in gap-graded soils under complex stress states
No full textInternational audienceThe complex phenomenon of suffusion is the selective erosion of the fine fraction under the effect of seepage flow within the matrix of coarser particles. Three processes are involved simultaneously: detachment, transport, and partial filtration of the fine particles. With the objective to characterize the influence of the stress state on suffusion-related parameters, downward seepage flow tests were conducted under hydraulic-gradient controlled conditions. Four stress states are investigated: triaxial isotropic, triaxial compression, triaxial extension and rigid vertical boundaries. Also, four different cohesionless gap-graded soils were tested, from underfilled to overfilled microstructures. The entire erosion process can be divided into four phases: onset, self-filtration, blow-out and steady state. The definitions of several suffusion-related parameters are given for each suffusion phase, in terms of hydraulic gradient, hydraulic conductivity variation, cumulative expended energy, erosion resistance index and Darcy velocity. The results demonstrate that the suffusion kinetics of soils in transition between underfilled and overfilled microstructures are more affected by the stress state than others
Current and Planned Activities of the FONESYS Network of System Code Developers in Collaboration with the SILENCE Network of Experimentalists
No full textInternational audienceFONESYS is an international network of system code developers created in 2010 to share informationon R&D, to benchmark codes, to discuss the Validation and Verification as well as the code scalabilityand uncertainty quantification. APROS, ARIANT, ATHLET, CATHARE, CATHENA, COSINE, ,LOCUST, MARS-KS, RELAP5, RELAP5-3D, SPACE, TRACE are the codes that were involved inthe FONESYS activities: updating the state of the art, identifying issues, discussing envisaged solutions,sharing experience in 3-field models, transport of interfacial area, numerical issues and well-posedness,code uncertainty evaluation. Code benchmarking were performed on boiling channel with CHF andPost-dryout, two-phase critical flow, flow regime transitions in horizontal flow, core interfacial friction,core 3D-mixing effects and two-phase singular pressure losses. Many code improvements wereimplemented in the various codes following the benchmark activities. When the need of newexperimental data was identified, FONESYS discussed with SILENCE experimentalists to definerequirements of new instrumentation and new experiments. Future activities will focus on codescalability, core 3D modelling and validation, two-phase pressure losses, use of system codes for scalinganalysis and applications to passive systems, SMRs and AMR. The present paper presents the majorachievements and the motivations for the future activities
Modélisation des transitoires multi-phasiques avec interaction fluide-structure
No full textIn certain operating or accidental situations, some undesirable multi-phase fast-transient events can occur in the piping systems of nuclear power plants such as Pressurized Water Reactor (PWR). These phenomena are characterized by high pressure variations. The generated pressure waves propagate and induce significant mechanical loads on some components which could impact the operation and the safety of industrial installations. In addition, due to the high pressure variation, the pressure amplitude can fall to its saturation value leading to the generation of vapor. This has a significant influence on the pressure waves propagation. In order to obtain realistic and representative computations, it is necessary to consider compressible two-phase flow modeling. The coupling between the fluid and the deformable structures has also to be taken into account in order to satisfactorily represent the mechanical consequences on some sensitive components. Moreover, the speed of sound within a compressible two-phase flow is known to undergo high variations as well as the Mach number as a function of the vapor volume fraction. Numerical methods able to capture the different flow regimes (incompressible and compressible) are thus required. Furthermore, most of the mentioned multi-phase fast-transient events occur in piping systems. As a consequence, dedicated mathematical models and numerical methods have to be developed for the achievement of industrial studies. The research summarized in the present document deals with the different topics, mentioned previously
Undoped and doped wurtzite GaAs probed by polarization- and time-resolved cathodoluminescence
No full textInternational audienceNanowires (NWs) offer unique possibilities to control semiconductor heterostructures and polytypes at the nanometer scale. The crystal structure of GaAs can be switched from bulk cubic zinc-blende (ZB) to hexagonal wurtzite (WZ) phase, but the properties and doping of WZ GaAs are still poorly known. Here, we grow high-quality GaAs NWs containing large segments of pure ZB and WZ phases using self-catalyzed, vapor-liquid-solid molecular beam epitaxy. Undoped, Be-doped and Si-doped WZ GaAs are investigated by high-resolution cathodoluminescence (CL) at low temperature (10K). The luminescence originating from the WZ region is unambiguously distinguished by its strong anisotropy evidenced by polarimetry.In undoped GaAs, the WZ CL peak is found ~1 meV higher than the free exciton energy in ZB. The recombination dynamics is probed by time-resolved CL and features a lifetime of 0.6 ns for the exciton recombination and 1.65 ns for the free-electron-to-acceptor transition. From Be-doped NWs, we infer an ionization energy of the Be acceptor of ~30 meV in GaAs WZ . The CL spectra broaden and redshift with increasing Be concentration due to the bandgap narrowing, following a trend similar to GaAs ZB.Si-doped WZ GaAs exhibits a low-energy CL peak (1.47 eV) attributed to the donor-acceptor pair recombination involving Si impurities.The degree of polarization of WZ luminescence decreases with higher doping level for both p-type and n-type. These results shed light on the properties and doping of WZ GaAs and show that time-resolved and polarimetry CL constitutes a powerful tool to characterize crystal phase, local defect, transport and recombination mechanism at the nanoscale
Modélisation et simulation CFD de l'affouillement local au pied d'une éolienne en mer
No full textScour is a process of erosion involving the displacement of solid particles under the influence of fluid flow. The presence of an obstacle, such as an offshore wind turbine structure placed on the seabed, causes a local modification of the flow: streamlines contract on the sides of the structure, lee-wake vortices are emitted at a certain frequency, and especially horseshoe vortices form in front of the structure's base and extend along its sides. These vortices excavate the seabed, creating additional, localized scour, leading to the exposure of the structure's foundations, which jeopardizes its stability. To reduce local scour, countermeasures (riprap, concrete mattresses, etc.) are implemented at the base of the offshore wind turbine structure to decrease sediment mobility. Today, these anti-scour protections require costly regular monitoring and maintenance. A better understanding of the scour phenomenon and its interaction with protections would allow for cost reductions.The objective of this thesis is to develop a CFD simulation tool to predict the dynamics of local scour at the base of a scaled-down offshore wind turbine model. The n-Euler approach developed in the multiphase code neptune_cfd was chosen because it allows for the representation of the complex diphasic flow located at the upper level of the bed, where sediment transport mainly occurs. Moreover, this approach is not limited in terms of CPU cost by the number of particles to be represented.Firstly, the simulation of 2D scour configurations was conducted and compared to experimental data to evaluate the capabilities of the neptune_cfd code. Qualitatively, the scour hole is reproduced. Quantitatively, we observe that the scour rate, initially consistent, decreases prematurely. Consequently, the final scour depth is underestimated. More academic configurations of dense and quasi-static liquid-solid flow were set up. These configurations, ranging from the formation of a static bed to its movement, first by a Couette flow in the laminar regime, then along an inclined plane in the turbulent regime, allowed for the validation of the Eulerian modeling of long contacts between particles, the implementation of an effective fluid viscosity model, and the adoption of a model for the dissipation of particle agitation by friction during particle collisions. Finally, the turbulent flow around an offshore wind turbine model, i.e., a vertical cylinder placed on the seabed, was studied. The URANS modeling of turbulence with a second-order model is satisfactory in terms of accuracy and CPU cost for the intended application. The simulation of scour around this cylinder revealed the same difficulties encountered during the initial scour simulations, where the scour depth is underestimated. The results are discussed, and improvement possibilities are proposed.L’affouillement est un processus d'érosion d'un ensemble de particules solides qui sont déplacées sous l'effet de l’écoulement d’un fluide. La présence d’un obstacle, tel que la structure d’une éolienne en mer posée sur le fond marin, provoque une modification locale de l’écoulement : les lignes de courant se contractent sur les côtés de la structure, des tourbillons de sillage (lee-wake vortices) sont émis à une certaine fréquence et surtout des tourbillons en fer à cheval (horseshoe vortices) se forment devant le pied de la structure et s'étendent sur ses côtés. Ces tourbillons creusent le fond marin, créant un affouillement supplémentaire, dit local, conduisant à l'exposition des fondations de la structure, ce qui met en péril sa stabilité. Pour réduire l’affouillement local, des contre-mesures (enrochements, matelas en béton, etc.) sont mises en place au pied de la structure de l’éolienne en mer afin de diminuer la mobilité des sédiments. Aujourd’hui, ces protections anti-affouillements nécessitent un suivi et un entretien régulier coûteux. Une meilleure compréhension du phénomène de l'affouillement et de son interaction avec les protections permettrait une réduction des coûts associés.L’objectif de cette thèse est de développer un outil de simulation CFD de prédiction de la dynamique de l’affouillement local au pied d’un modèle d'éolienne en mer à échelle réduite. L'approche n-Euler développée dans le code multiphasique neptune_cfd a été retenue car elle permet de représenter l'écoulement diphasique complexe situé au niveau supérieur du lit, où le transport de sédiments a principalement lieu. De plus, cette approche n'est pas limitée en termes de coût CPU par le nombre de particules à représenter.En premier lieu, la simulation de configurations d'affouillement 2D a été menée et comparée à des données expérimentales afin d'évaluer les capacités du code neptune_cfd. Qualitativement, la fosse d'affouillement est reproduite. Quantitativement, nous observons que le taux d'affouillement, initialement cohérent, diminue de façon prématurée. Par conséquent, la profondeur finale d'affouillement est sous-estimée. Des configurations plus académiques d'écoulement liquide-solide dense et quasi-statique ont été mises en place. Ces configurations, allant de la formation d'un lit statique à sa mise en mouvement, d'abord par un écoulement de Couette dans le régime laminaire, puis le long d'un plan incliné dans le régime turbulent, ont permis de valider la modélisation eulérienne des contacts longs entre particules, d'implémenter un modèle de viscosité effective fluide et d'adopter un modèle de dissipation de l'agitation des particules par friction lors de collisions entre particules. Enfin, l'écoulement turbulent autour d'un modèle d'éolienne en mer, c'est-à-dire un cylindre vertical posé sur le fond, a été étudié. La modélisation URANS de la turbulence avec un modèle du second ordre est satisfaisante en termes de précision et de coût CPU pour l'application visée. La simulation de l'affouillement autour de ce cylindre a révélé les mêmes difficultés rencontrées lors des premières simulations d'affouillement, où la profondeur d'affouillement est sous-estimée. Les résultats sont discutés et des possibilités d'amélioration sont proposées
Table ronde : Quelles expériences et connaissances sur la restauration trouveriez-vous intéressant de partager et de travailler entre le Rhin, le Rhône et d'autres cours d'eau ?
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INNOVATIVE SITE RESPONSE ANALYSIS ACCOUNTING FOR GROUND IMPROVEMENTS
No full textInternational audienceSite response analyses (SRA) are crucial for evaluating the behavior of sensitive structures, such as nuclear facilities, under seismic loads. Typically, SRA are conducted in the frequency domain using 1D wave propagation models to determine the linear equivalent soil profile and the input signal at the base of the structure. In order to consider the non-linear strain-dependent behavior of soil, an iterative approach is required to achieve a compatible strain profile. While this method is effective for horizontally layered soil profiles, it is not suitable for configurations with soil reinforcement elements such as deep soil-mixing (DSM) or rigid inclusions (RI), whose presence modifies the overall response of the soil profile and introduces anisotropy.Classic 1D wave propagation analyses are thus inadequate in the presence of reinforced soils due to the complex effects of the reinforcements on soil stiffness and wave propagation. Analytical homogenization formulae can give a preliminary estimate of the apparent shear stiffness of the reinforced medium but present several limitations such inadequacy to model the response near interfaces between soil layers or in the presence of important stiffness contrasts, and they are limited to specific reinforcement geometries. To address this question, the present study introduces a new iterative methodology combining 1D wave propagation analysis with 3D finite element (FE) modelling of the reinforced soil column to determine its equivalent shear modulus. This approach makes it possible to determine a strain-compatible soil profile suitable for SSI analyses, taking into account both strain-dependent soil behavior and the impact of soil improvements in terms of equivalent shear modulus.</div