HAL Portal UO (Université d'Orléans)
Not a member yet
48841 research outputs found
Sort by
The effect of micas on the strength of experimental granitoid fault gouge
No full textInternational audienceSheet silicates play an important role in shaping crustal rheology and shear localization at shallow depths through their low strength. However, their effect at deeper levels (>3 km) remains unclear. We conducted hydrothermal ring shear experiments on three simulated gouges with similar quartz content but varying mica types and contents. Applied temperatures T ranged from 20 to 650 • C, with sliding velocities V between 0.03 and 1 μm/s, and an effective normal stress and pore water pressure of 100 MPa. Shear strains up to 30 were attained.At 1 μm/s and 20 • C, granitoids exhibit a higher friction coefficient (μ = 0.81) than the muscovite-rich (μ = 0.47) and biotite-rich gouges (μ = 0.44). With increasing T at a fixed V of 1 μm/s, μ of granitoids decreases to 0.61 at 650 • C, whereas muscovite-and biotite-rich gouges strengthen (μ = 0.56-0.69) until T reaches 200-450 • C. At 650 • C, weakening is observed in granitoid and muscovite-rich gouges as V decreases, while biotite-rich gouge shows no change. Granitoids are weaker than the mica-rich gouges once V decreases to 0.03 μm/s and T reaches 650 • C. All gouges at 650 • C exhibit μm-wide principal slip zones, featuring microstructures consistent with dissolution-precipitation creep (DPC). These include truncated grain contacts, mineral precipitates, submicrometer grain size and low porosity. Muscovite breakdown and biotite formation occurs in muscovite-rich gouge as they weaken. Our results imply that mica enrichment in granitoid faults can lead to a weaker upper crust and stronger middle crusts as they weaken less than granitoids. The onset of DPC may trigger a frictional-viscous transition at greenschist facies depths.</div
Le mythe de la forge destructrice des forêts : un exemple ariégeois
No full textInternational audienceCette conférence invitée renverse le paradigme de la forge destructrice de la forêt en s'appuyant sur les recherches collectives menées en Ariège depuis plus de dix ans, intégrant des approches historiques, archéologiques, géographiques, paléoécologiques, anthracologiques et dendrochronologiques.En confrontant les sources écrites, les vestiges archéologiques et les archives naturelles (sédiments, charbons, bois), elle démontre que l’image d’une sidérurgie responsable d’une déforestation continue et irréversible ne résiste pas à l’analyse fine. L’activité métallurgique, loin d’être linéaire, apparaît fluctuante, marquée par des phases d’émergence, de ralentissement et de réorganisation. Les archives anthracologiques et dendrochronologiques révèlent une gestion sylvicole attentive, fondée sur l’exploitation de taillis de hêtre et de hêtraies-sapinières, avec des cycles de coupe relativement courts, une sélection des calibres et un séchage du bois avant carbonisation. Loin de toute anarchie, ces pratiques témoignent d’un véritable savoir-faire sylvo-métallurgique.Les données paléoenvironnementales montrent qu’au XVIIe siècle, alors même que la sidérurgie ariégeoise est florissante, les forêts sont encore fournies. Ce n’est qu’au XVIIIe-XIXe siècle, avec le boom démographique, l’intensification agropastorale et l’extension agricole, que s’opère une réduction drastique du couvert forestier — moment du « minimum forestier ». Dans ce contexte, la forge, par ses réglementations, ses approvisionnements extérieurs et ses pratiques de gestion, a pu jouer un rôle paradoxalement conservatoire en stabilisant certains espaces forestiers.L’étude du Haut-Vicdessos, laboratoire pyrénéen de ces recherches, met en évidence que la déforestation ne peut être imputée à la seule métallurgie, mais résulte d’une combinaison complexe de facteurs sociaux, économiques et environnementaux. Elle invite ainsi à reconsidérer les relations entre industrie et forêt sur le temps long, et à sortir du mythe d’une sidérurgie uniquement prédatrice pour la ressource forestière
Loi Duplomb, transition énergétique… et si les citoyens reprenaient la main ? Leçons du succès de la campagne « Décarbonons la France »
No full textInternational audienceEn résonance avec la récente mobilisation citoyenne contre la loi Duplomb, la campagne de financement participatif « Décarbonons la France » révèle une autre forme d’engagement, tournée vers l’élaboration de solutions et la mise en œuvre d’un projet collectif. Elle témoigne des mutations à l’œuvre dans les modalités de participation citoyenne et du rôle croissant des plateformes numériques. Décryptage du succès record de cette campagne
Bioluminescence Resonance Energy Transfer: A Powerful Technique in Neuropharmacology for Discovering New Ligands of G Protein-Coupled Receptors
No full textMasterThe Bioluminescence Resonance Energy Transfer (BRET) is a proximity-based assay used to study protein-protein interactions in living cells. The principle behind BRET involves resonance transfer of energy between bioluminescent enzymes and a fluorescent acceptors, resulting in measurable signals that indicate specific molecular interactions. BRET has been widely adopted in drug discovery as a high-throughput screening method to investigate the behavior of signaling proteins, such as G protein-coupled receptors (GPCRs). Due to its ability to operate under physiological conditions, BRET is a highly sensitive and well-suited tool for real-time, dynamic studies regarding diverse signaling pathways, their downstream messengers, receptor internalization and more
Optical depth characterization of superheated ammonia spray using a collimated laser illumination with Fourier filtering
No full textInternational audienceToday, the research on the direct injection of liquid ammonia remains limited, especially in internal combustion engines, even if it can improve the global efficiency. The liquid ammonia injection results in flash-boiling and provides a strong cooling effect due to the higher latent heat of vaporization. Generally, superheat degree (Rp) represents the level of flash boiling, given by the ratio of the saturated vapor pressure of the fuel and ambient pressure. It was found that the sprays show different extents of flash boiling and spray morphology for the same degree of superheating. This indicates the dependency of spray morphology on other criteria in addition to Rp. In flash-boiling conditions, the rapid breakup of liquid ammonia injection results in a high optically dense droplet cloud.Besides, the interference from the enormously produced vapor phase could be more problematic and challenging to perform droplet sizing. Therefore, doing it by using optical techniques is of significant interest, but it needs to remove multiple scattering to provide reliable data acquisition. Hence, to mitigate multiple scattering, the knowledge of the optical depth (OD), the average number of statistical scattering events occurring in the spray, is relevant. In this present experimental study, a novel Collimated Laser Illumination with Fourier Filtering (CLIFF) technique was considered. This imaging technique measures the spray evolution of an ECN Spray G multi-hole injector fed with ammonia at superheated conditions. Hence, this study extends our previous work and investigates the spray characteristics at a constant Rp = 9. The multi-hole GDI injector injects ammonia at a fuel injection pressure (FIP) of 75 bar in the constant volume spray chamber. The fuel temperature varies from -10 to 50 °C in increments of 10°C, while the ambient pressure is adjusted to maintain a constant Rp of 9. The setup consists of a continuous laser emitting light at 532 nm, which forms a homogeneous collimated beam as an illumination source. The transmitted light signals are collected by the positive lens and displayed on the sensor through a Fourier filter. This can be done by placing an iris diaphragm at the center of the focal plane of the positive lens.</p
One hydrothermal system may hide another: Insights from a geochemical exploration of Chaudes-Aigues and nearby springs (French Massif Central)
No full textInternational audienceGranitic-hosted hydrothermal systems offer valuable insight into deep fluid circulation mechanisms in amagmatic contexts. This study focuses on the Chaudes-Aigues hydrothermal system in the French Massif Central, which hosts one of the hottest natural springs in Europe (Par Spring, 80-82 • C). Our work aims to better constrain the functioning of the system, including reservoir temperature, recharge zone, and fluid pathways. A combined approach of water geochemistry (major elements, isotopes) and thermo-hydraulic numerical modelling was applied. Using 22 thermal springs distributed across the Margeride Granitic Complex (MGC) and the Cantal Volcanic Complex (CVC) the temperature of Chaudes-Aigues reservoir has been estimated and is thought to reach 190 ± 10 • C, validating and refining previous estimates. Isotopic and geochemical tracers point to a meteoric origin, with the recharge area most likely located along the southern edge of the MGC, connected to the emergence zone via a thick N150E fault zone. This study redefines the Chaudes-Aigues system as fully amagmatic and structurally controlled. Other geothermal reservoirs have also been identified within the Margeride Granitic Complex, with temperatures exceeding 100 • C, indicating a broader geothermal potential of the area. Furthermore, this study highlights the potential for identifying similar hidden geothermal systems in other fractured granites with limited surface manifestations, offering new perspectives for high-temperature geothermal exploration in Europe
Firewall boundaries and mixed phases of rotating quark matter in linear sigma model
No full textInternational audienceA rigidly rotating body in unbounded space is usually considered a pathological system since it leads to faster-than-light velocities and associated breaches of causality. However, numerical results on chiral symmetry breaking in rotating plasmas of interacting fermions reveal surprisingly close correspondence in predictions between rigorous bounded and formal unbounded approaches. To provide insight into this correlation, we consider the linear sigma model coupled to quarks, undergoing rigid rotation in unbounded Minkowski space-time. Within the mean-field approach, we adopt three consecutive levels of approximation to the ground state of the system that feature a uniform (model 1), weakly-inhomogeneous (model 2) and fully inhomogeneus (model 3) condensates. Models 1 and 2 that do not take into account spatial gradients of the condensate, show agreement with the Tolman-Ehrenfest law. Model 3 exhibits a deviation from the Tolman-Ehrenfest prediction due to the appearance of a new energy scale set by the inhomogeneity of the ground state. Its boundary conditions are fixed by imposing regularity at the rotation axis and by demanding the global minimization of the grand potential. We dub the latter as "firewall boundary conditions," translating into the requirement of vanishing condensate on the light cylinder, which follows from the fact that the system state formally diverges at the light cylinder. In all models, we present the phase diagram of the system and point out that in models 2 and 3, the system resides either in a chirally-restored phase, or in a mixed phase that possesses spatially-separated chirally-restored and chirally-broken phases
Effect of water saturation on the diffusive transport of water and solutes in compacted kaolinite, illite and vermiculite
No full textInternational audienceThrough-diffusion experiments were carried out under partially water saturated conditions and using uncharged tracers (HTO and HDO; water molecule with one tritium and deuterium atom, respectively), negatively charged tracers (125I− and 36Cl−) and positively charged tracer (22Na+) in two reference clayey materials: (i) illite, a negatively-charged clay mineral with only interparticle porosity and (ii) vermiculite, a negatively-charged clay mineral with both inter-particle and interlayer porosities. For both types of porous media, a sharp decrease in diffusive flux was observed for all three types of tracer when water saturation (Sw) was reduced from Sw = 0.95 to 0.88. The data were compared to those obtained previously with porous media made of kaolinite, a weakly-charged clay mineral having only inter-particle porosity, to quantify the relative influences of surface charge and pore geometry/pore size distribution on diffusion properties as a function of water saturation. The latter parameter had a prominent role on the diffusional properties in the investigated range of Sw, regardless of the type of clayey material. Then, a relationship predicting diffusivities of cation under partially water saturated conditions as a function of diffusivities of anion at the same level of water saturation is proposed for the reference clayey materials investigated
Rapport d'expertise sur le projet de fouille du site de Saint-Nicolas 2 (Steinbach, Haut-Rhin) - 2025
No full textA dynamical system approach to the Chandrasekhar-Hamilton-Jacobi equation
No full text48 pagesInternational audienceWe study the local properties of positive solutions of the equation -∆u = e^u -M |∇u|^q in a punctured domain Ω \ {0} of R^N in the range of parameters q> 1 and M>0. We prove a series of a priori estimates near a singular point. In the case of radial solutions we use various techniques inherited from the dynamical systems theory to obtain the precise behaviour of singular solutions. We prove also the existence of singular solutions with these precise behaviours