Scientific Publications of the University of Toulouse II Le Mirail
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Self-written high-efficiency single-mode optical link using a single near-infrared photopolymerization step
No full textAccepté pour publication dans J. Lightwave Tech.International audienceWe present a method for fabricating a self-written waveguide (SWW) between two optical fibers that are single-mode (SM) at 850 nm (780HP/ core diameter: 4.4 µm). The basic principle consists in exposing an acrylic photopolymer formulation sensitive in the near-infrared range (NIR) to a laser beam transmitted simultaneously from both fibers placed face to face, to build a continuous, flexible and self-aligned optical link. The specificity of the presented process (NIR-SM-SWW) lies in the use of a writing wavelength identical to that intended for singlemode propagation in the fibers. This enables the creation in a single step of a SWW directly adapted to the fundamental mode to be transmitted. A precise pre-positioning stage is used to optimize the process. For best photochemical conditions, a coupling efficiency as high as 82 % (-0.86 dB loss) is demonstrated for a 300 µm-long link. The effect of fiber-to-fiber axial and lateral distances is also investigated to estimate the propagation loss and misalignment tolerance, respectively. In addition, measurements performed by quantitative phase optical microscopy indicate a homogeneous index profile in the guide. Using these data, optical modeling is performed and compared to experiments, confirming that a high efficiency SM link is actually fabricated, without the need for further fabrication of an external cladding. This method could therefore be easily applied to the SM connection of a SM VCSEL (vertical-cavity surface-emitting laser) to a SM fiber, which is of major interest for the development of compact optical communications and instrumentation systems
Directional light scattering in Mie-resonant Si particles with ultra-thin Au shells
No full textInternational audienceMetamaterial research has sought to create nanostructures with strong directional optical scattering to control light propagation at the nanoscale. Core–shell architectures comprised of both resonant cores and resonant shells are suggested as candidate particles in which the spectral overlap of the electric and magnetic dipoles is controlled to create strong directional scattering. In this study, Au-decorated Si core–shell (Si@Au) particles are presented, studying the role of the architecture (particulate, discontinuous shells vs continuous) and dimensions of the shell. The core–shell particles are synthesized by first creating Si particles, through the thermal disproportionation of hydrogen silsesquioxane (HSQ), which are then decorated with ≈4 nm diameter Au nanoparticles. The resonant behavior of the core–shell particles is characterized using electron energy-loss spectroscopy mapping and optical single-particle scatter spectroscopy. These observations are supported by T-matrix simulations and Mie-theory calculations of the scattering spectra, which show that, compared to Si, Si@Au particles demonstrate a dampened magnetic dipole resonance for smaller Si core diameters (100–130 nm) and an enhanced magnetic dipole resonance for larger Si core sizes (150–200 nm). The study indicates that the previously reported hybridized modes do not exist in particulate Au shells around a Si core and can only exist in continuous plasmonic shells. Thus, it is shown here how important it is to be as precise as possible regarding the nanomaterial architecture used in simulations. No configuration of Si@Au core–shell particles with a particulate shell could be found that strongly enhanced directional scattering, and a continuous shell may do so only modestly. However, the simulations show that the synthesis of thin, continuous Ag shells might represent an alternative route towards achieving good directional scattering properties.</p
Front-surface cooling of infrared thermophotovoltaic cells
No full textInternational audienceThis paper proposes a front-surface cooling method for thermophotovoltaic (TPV) cells utilizing microfluidic channels for efficient heat dissipation. Unlike conventional back-surface cooling, front-surface cooling minimizes thermal resistance by directly cooling the top surface of the cell. The microfluidic channel layer also functions as an antireflection layer through the gradual change in the refractive index. The proposed cooling method was evaluated using a thermo-fluid analysis, considering factors such as the emitter temperature, cell reflectance, thermal resistance, and fluid optical properties. We examined liquids with ideal absorption characteristics and actual liquids whose absorption coefficients were measured. The results showed that front-surface cooling significantly outperformed back-surface cooling in terms of the net power density. This method is particularly advantageous for high emitter temperatures or in cases where the thermal resistance between the cell and backsurface liquid is high. Moreover, this study highlights the potential application of the cooling method in bifacial TPV cells, which can generate electricity from thermal radiation incident on both sides. Bifacial cells offer higher power generation per unit area but face cooling challenges. The proposed cooling technique addresses these challenges, paving the way for innovative TPV system configurations and improved performance
The Phoenicians’ Impiety in the Narrative Process of Herodotus’ Work: The Theft of the Statue of Apollo as an Omen of Barbaric Defeat
No full textInternational audienceHerodotus regularly uses narrative processes in order to explain peace and war. In this framework, religious elements play an important role, especially in the course of the Persian Wars. The plain of Marathon in 490 BCE is one example of this that clearly explains the Persian defeat. The author uses an ethical composition: the defeat is symbolically the fault of the Phoenicians from the Persian fleet who stole a statue of Apollo on the island of Delos, but the Persians, who disturb the balance between men and gods with their act of pride, are also guilty. Herodotus chooses the Phoenicians as narrative mediators of the Persians’ downfall, because they are always present at cultural, moral or physical borders. From the Greeks’ point of view, the Phoenicians stealing the statue of Apollo is an omen of the barbaric defeat in the course of the First Persian War
Les savants du linéaire B, les machines à écrire et le Babel des caractères
No full textInternational audienc
Global Sensitivity Analysis for Engineering Design Based on Individual Conditional Expectations
No full textPublished in Aerospace Science and Technology, 2026International audienceExplainable machine learning techniques have gained increasing attention in engineering applications, especially in aerospace design and analysis, where understanding how input variables influence predictive models is essential. Partial Dependence Plots (PDPs) are widely used for interpreting black-box models by showing the average effect of an input variable on the prediction. However, their global sensitivity metric can be misleading when strong interactions are present, as averaging tends to obscure interaction effects. To address this limitation, we propose a global sensitivity metric based on Individual Conditional Expectation (ICE) curves. The method computes the expected feature importance across ICE curves, along with their standard deviation, to more effectively capture the influence of interactions. The proposed metrics are model-agnostic and can be applied to any predictive model, including but not limited to surrogate models. Furthermore, we provide a mathematical proof demonstrating that the PDP-based sensitivity is a lower bound of the proposed ICE-based metric under additive and multiplicative separability. In addition, we introduce an ICE-based correlation value to quantify how interactions modify the relationship between inputs and the output. Comparative evaluations were performed on three cases: a 5-variable analytical function, a 5-variable wind-turbine fatigue problem, and a 9-variable airfoil aerodynamics case, where ICE-based sensitivity was benchmarked against PDP, SHapley Additive exPlanations (SHAP), and Sobol' indices. The results show that ICE-based feature importance provides richer insights than the traditional PDP-based approach, while visual interpretations from PDP, ICE, and SHAP complement one another by offering multiple perspectives
Le mystère des pépites vertes (enfin résolu!) – A la source des matières colorantes des sites paléolithiques de la vallée de l’Ardèche
No full textNational audienceLes opérations archéologiques menées dans la vallée de l’Ardèche et du Chassezac ont livré un corpus remarquable de matières colorantes. Parmi elles, plusieurs fragments à inclusions vertes ont été identifiés à la grotte aux Points (30), à l’abri des Pêcheurs (07) et au Mas d’Aiguillon (07). Des matériaux similaires, mais sans inclusions, proviennent d’Huchard et de la Baume d’Oulen (07). L’étude pétrographique révèle une matrice argilo-ferrugineuse fine, associant hématite en feuillets et aluminosilicates, témoignant d’une origine probablement hydrothermale.Ces caractéristiques suggèrent qu’une stratégie de sélection a guidée la collecte des matières colorantes.Deux approches complémentaires ont été menées : la première, analytique (microscopie, Raman, DRX), pour déterminer la nature minéralogique des inclusions vertes ; la seconde, dans le cadre du PCR Pigmentothèque, pour rechercher des affleurements compatibles. Les prospections de 2024 ont abouti à la découverte, d’un affleurement présentant toutes les caractéristiques pétrographiques recherchées : matrice argilo-ferrugineuse et… pépites vertes
On the approximation of the von Neumann equation in the semiclassical limit. Part II : numerical analysis
No full textThis paper is devoted to the numerical analysis of the Hermite spectral method proposed in [14], which provides, in the semiclassical limit, an asymptotic preserving approximation of the von Neumann equation. More precisely, it relies on the use of so-called Weyl's variables to effectively address the stiffness associated to the equation. Then by employing a truncated Hermite expansion of the density operator, we successfully manage this stiffness and provide error estimates by leveraging the propagation of regularity in the exact solution
A literatura nacional brasileira em perspectiva transnacional: debates, conceitos, metodologias
No full textInternational audienceSébastien Rozeaux, brasilianista dedicado ao estudo da história e da história literária brasileiras, concedeu entrevista aos professores Valéria Bezerra, Raquel Campos, Lúcia Granja e Pedro Paulo Catharina, que ora publicamos. O material, transcrito, editado, anotado e revisado por Valéria Bezerra e por Raquel Campos, traz um debate acerca das pesquisas de Sébastien Rozeaux sobre a literatura brasileira oitocentista; do exame sociológico que fez das personalidades implicadas na construção da literatura nacional brasileira; de métodos e conceitos relevantes para o estudo da literatura em uma perspectiva histórica e ainda de suas incursões nos estudos das relações Brasil-Portugal
