Portail HAL UNIV-RENNES
Not a member yet
180610 research outputs found
Sort by
Laser-induced breakdown spectroscopy (LIBS) imaging for carbon quantification in archaeological ferrous alloys
No full textInternational audienceThis study demonstrates that μ-LIBS imaging provides high-resolution, quantitative carbon distribution in archaeological ferrous alloys. Ancient ferrous alloys are characterized by a heterogeneous distribution of carbon and other elements within their metallic matrix. This study uses micro-Laser Induced Breakdown Spectroscopy (μ-LIBS) to analyze the characteristic elements in archaeological ferrous alloys, complementing classical metallographic methods. Typically, this latter approach relies on image analysis following optical microscopy observations, which has limitations in accurately quantifying carbon concentrations. The analytical approach using μ-LIBS imaging not only enhances carbon localization but also facilitates the study of other elements present in ferrous alloys, such as phosphorus and manganese. This article shows the potential of μ-LIBS imaging for future archaeometallurgical research
Maximum number of zeroes of polynomials on weighted projective spaces over a finite field
No full textWe compute the maximum number of rational points at which a homogeneous polynomial can vanish on a weighted projective space over a finite field, provided that the first weight is equal to one. This solves a conjecture by Aubry, Castryck, Ghorpade, Lachaud, O'Sullivan and Ram, which stated that a Serre-like bound holds with equality for weighted projective spaces when the first weight is one, and when considering polynomials whose degree is divisible by the least common multiple of the weights. We refine this conjecture by lifting the restriction on the degree and we prove it using footprint techniques, Delorme's reduction and Serre's classical bound
Multifunctional light-emitting materials based on hybrid copper iodide compounds
No full textInternational audienceTo develop materials for sustainable light-emitting technologies, materials science has to focus on low-cost and earth-abundant emitters. Copper-based materials displaying rich photophysical properties along with low cost and toxicity are able to meet these criteria. In this work, a series of multinuclear copper iodide complexes have been synthesized and characterized. Upon coordination with different phosphine ligands, solubility of the compounds has been achieved in common organic solvents. Structural characterization studies have been conducted using single crystal X-ray diffraction and solid-state NMR. Photoluminescence analyses showed that all materials exhibit yellow emission with high photoluminescence quantum yields. Rationalization of the optical properties is supported by density functional theory calculations. To design processable materials for light-emitting applications, these emitters have been successfully incorporated within polymer materials, thanks to their good solubility properties. In addition to display the room temperature emission properties of the complexes, the resulting composite materials present contrast luminescence thermochromism. The potential of these composites as multifunctional light-emitting materials has been demonstrated through their use as phosphors in light emitting diodes and as inks in anti-counterfeiting systems. This study illustrates the relevance of copper halide materials for the development of multifunctional materials with high potential, based on cost-effective emitters
Full Field Strain Measurements Uncover the Influence of External Far-Field Stresses on Fracturing During Cavity Expansion in Anisotropic Sandstone
No full textInternational audienceFailure of porous granular rocks by fluid overpressure encompasses both natural and artificial phenomena. To better comprehend the mechanisms behind the formation and propagation of the fractures leading to failure, we subject multiaxially confined Vosges sandstone specimens to cavity expansion until sample failure. The specimens are prevented from invasion of pressurizing fluid by an internal soft jacket covering the borehole. Interlaced radial and orthoradial deformation bands appear around the cylindrical injection hole during initial fluid pressure build-up; at later stages, tensile cracks appear from the boundary of the hole. The cracks are dominantly mode I, and propagate mostly in straight line as pressure is increased, thus following their initial trajectories, apart from some instances of crack coalescence. In the experiments with radial symmetry of loading (equal far-field stresses), crack propagation does not show preferential orientation (opposite cracks or star-shaped cracks) and the fractures propagate with a slight angle to the bedding planes toward the sample boundary. In the experiments with asymmetric loading, the emancipating cracks initiate near the top and bottom of the borehole wall (region of largest tensile stress). For a particular experiment where the applied axial load is parallel to the bedding plane of the specimen, cracks propagate initially with a slight angle to the bedding planes, and then, en echelon cracks parallel to the bedding are observed during later deformation stages. The experimental results indicate thatinitial crack patterns are mainly controlled by the deviatoric stress state, while at much later deformation stages, crack propagation is mostly influenced by material anisotropy. The observations with equal far-field stresses also suggest that the number of propagating cracks influences the breakdown pressure: the more cracks there are, the higher the pressure peak in the hole, which is consistent with theoretical analyses of fracture mechanics
Les systemes volcano-sedimentaires ediacariens dans l’Anti-Atlas – Enregistrement d’une transition rift – post-rift
No full textNational audienc
Differentiable wave propagation method for shape optimization of freeform optics beyond the paraxial approximation
No full textInternational audienceFreeform optics provides precise control of light for beam shaping and mode conversion, but designing volumetric micro-optical elements requires efficient, low-runtime simulation methods. The wave propagation method (WPM) offers a fast alternative to full-wave solvers for high-index-contrast and non-paraxial systems but lacks differentiability, preventing its use with gradient descent methods for inverse design. We propose a differentiable formulation of WPM using smoothstep functions to create a soft partition of the spatial domain, allowing for gradient-based optimization. This crucial modification enables a general and computationally efficient framework for solving inverse design problems in micro-optics. We demonstrate its effectiveness through the simulation of a freeform hologram exhibiting high diffraction angles, highlighting the limitations of traditional paraxial methods. (c) 2025 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved
Self-stabilizing multivalued consensus in the presence of Byzantine faults and asynchrony
No full textInternational audienc
Quantifying excess mortality attributable to tropical cyclones in South Korea: Insights from a generalized synthetic control approach
No full textInternational audienceEpidemiological evidence related to health impacts attributable to tropical cyclones, typhoons or hurricanes is growing, but evidence from Korea remains limited. Utilizing detailed cyclone routes and cause-specific mortality data in fine administrative unit resolution, this study was conducted to evaluate the effect of multiple cyclones in Korea on excess mortality counts using a natural experiment framework. Administrative unit specific mortality counts (all-cause, non-accidental, and cause-specific) and cyclone (size, moving route, and gale radius) data from 2002 to 2023 were obtained from governmental databases. The timing of each cyclone was treated as a natural experiment and a generalized synthetic control (GSC) analysis coupled with random effects meta-analysis was used to estimate pooled changes in daily average mortality counts over the 2 weeks following cyclone exposure. Stratification analyses according to gender, age group, educational level, and location of death were conducted. Of the 21 cyclones that made landfall on the Korean Peninsula between 2002 and 2023, nine in clearly defined exposed and non-exposed regions were selected for analysis. During the 2 weeks following tropical cyclone exposure, daily average increases of 0.084 (95% confidence interval [CI]: 0.020, 0.148), 0.075 (95% CI: 0.012, 0.137), and 0.007 (95% CI: -0.011, 0.025) in all-cause, non-accidental, and external injury-related mortality counts, respectively, were observed in each cyclone-exposed region when compared to synthetic control. Residents living closer to the route of the cyclone center, elderly individuals, and low-educated populations were more susceptible to the effects of cyclones. An average of 150 excess all-cause deaths were estimated for each tropical cyclone during the 2 weeks post-exposure in Korea. Therefore, it is essential to develop countermeasures to prevent excess mortality from tropical cyclone exposure
Multimaterial fibers interfaced with ZnO for photoelectrochemical detection
No full textInternational audienceThe development of miniaturized, remotely addressable sensing devices is crucial in a variety of fields, including healthcare, environmental monitoring, and security. This study introduces an optrode sensor comprising a multimaterial fiber composed of a phosphate glass cladding and a continuous Zn wire core, interfaced with a photoactive ZnO coating on its tip, deposited by anodization. It is shown that this optrode can promote photoelectrochemical reactions under illumination with UV light when immersed in an aqueous electrolyte. Proof-of-principle experiments demonstrate that these optrodes produce a glucose-responsive photocurrent, opening the way to biomedical applications. This optical sensor shows promise, as it would ultimately allow the decoupling of input stimuli, i.e., potential and light excitation, over a long distance. Due to its advantages in terms of integration, detection speed, and ease of use, these ZnO/Zn/phosphate optrodes hold significant potential for remote analysis and implantable sensors.</p
