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Persistent Nanophosphors: Poised to Outperform Bulk Counterparts?
No full textInternational audienceThe design of advanced materials often reveals how apparent imperfections, such as structural defects or impurities, can be transformed into functional advantages. In insulating oxide matrices, the controlled introduction of dopant ions is the first step toward efficient photoluminescence. Later, the engineering of additional defects, often detrimental for photoluminescence, gives rise to unique capabilities for optical energy storage and persistent luminescence. Initially driven by biomedical applications, nanomaterials currently occupy a central role in persistent phosphor research. However, elaboration processes allowing to preserve their nanoscale usually involve poor control over their crystallinity, leading to performance behind that of bulk materials. Developing nanophosphors with well‐defined morphology and energy levels engineered for tailor‐made and efficient energy storage presents a significant materials challenge. Yet once again, what seems a limitation may prove to be a powerful opportunity. By exploiting the nanoscale to engineer energy storage in an unprecedented manner, persistent nanophosphors can open a new era in advanced optical materials. This perspective highlights how emerging applications, progress in nanoscale synthesis, surface engineering, and integration into advanced architectures are opening the path toward multifunctional, application‐ready materials. Altogether, the nanoscale offers a transformative avenue that can enable persistent nanophosphors to outperform their bulk counterparts
Volcanic plume height during the 2021 Tajogaite eruption (La Palma) from two complementary monitoring methods – implications for satellite-based products
No full textInternational audienceAbstract. Volcanic emissions from the Tajogaite volcano, located on the Cumbre Vieja edifice on the island of La Palma (Canary Islands, Spain), caused significant public health and aviation disruptions throughout the eruption (19 September–13 December 2021, officially declared over on 25 December). Nonetheless, it is considered the most significant volcanic event in Europe over the past 75 years due to the substantial amount of SO2 released into the atmosphere. The Instituto Geográfico Nacional (IGN), the authority responsible for volcano surveillance in Spain, implemented extensive operational monitoring to track volcanic activity and to provide a robust estimation of the volcanic plume height using a video-surveillance network. In parallel, the State Meteorological Agency of Spain (AEMET), in partnership with other Spanish ACTRIS (Aerosol, Clouds, and Trace Gases Research Infrastructure) members and collaborating institutions, conducted an unprecedented instrumental deployment to evaluate the impacts of this volcanic event on atmospheric composition. This effort included a network of aerosol profilers surrounding the volcano. A total of four profiling instruments were installed on La Palma: one MPL-4B lidar and three ceilometers. Additionally, a pre-existing Raman lidar on the island contributed valuable data to this study. These efforts are undertaken due to the importance of monitoring volcanic plume height in terms of air quality (necessary for the implementation of effective civil protection policies), volcanic activity surveillance (for tracking and forecasting eruptive behaviour), and, from a scientific perspective, for improving our understanding of the climatic and radiative impacts of this type of aerosol. In this study, the eruptive process was characterised in terms of the altitude of the dispersive volcanic plume (hd), measured by both IGN and AEMET-ACTRIS, and the altitude of the eruptive column (hec), measured by IGN. Modulating factors such as seismicity and meteorological conditions were also analysed. The consistency between the two independent and complementary datasets (hd,IGN and hd,AEMET) was assessed throughout the eruption (mean difference of 258.6 m). Our results confirmed the existence of three distinct eruptive phases, encompassing a range of styles from Strombolian explosive to effusive activity. While these phases have been characterised in previous studies, the results of the present work provide complementary information and novel insights from an alternative observational approach, which may be of use in future volcanic crises and will be applied to operational surveillance during such events. A subsequent comparison of hd,AEMET with the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aerosol layer height product (ALHCALIOP) revealed a systematic underestimation by the satellite product, with a mean difference of 392.2 m. Finally, the impact of using hec in estimating SO2 emissions from the NASA MSVOLSO2L4 satellite-based product was evaluated. When a fixed (standard) plume altitude of 8 km was used instead of the observed hec, the total SO2 emission was significantly underestimated by an average of 56.2 %, and by up to 84.7 %. These findings underscore the importance of accurately determining the volcanic plume height when deriving SO2 emissions from satellite data
Comparison of Logical Execution Time Programming Languages
No full textInternational audienceLogical execution time (LET) paradigm received substantial emphasis from the real-time community due to its many benefits, specifically its time determinism guarantees. Therefore, many programming languages have made the choice to implement this paradigm. This raises the question of which language needs to be considered. Our paper tackles this question by exploring and comparing LET-based programming languages through a dual-lens approach: (1) global framing; which consists of chronological and contextual comparisons; and (2) the extent of pattern support capabilities. Our aim is to offer some guidance to developers in selecting the most suitable programming language based on system constraints
Flux vectoriels paramétriques pour le recalage en domaine borné et l’interpolation non linéaire d’écoulements à chocs
No full textWe present a registration procedure for parametric model order reduction (MOR) in two- and three-dimensional bounded domains. In the MOR framework, registration methods exploit solution snapshots to identify a parametric coordinate transformation that improves the approximation of the solution set through linear subspaces. For each training parameter, optimization-based (or variational) registration methods minimize a target function that measures the alignment of the coherent structures of interest (e.g., shocks, shear layers, cracks) for different parameter values, over a family of bijections of the computational domain . We consider diffeomorphisms that are vector flows of given velocity fields with vanishing normal component on ; we rely on a sensor to extract appropriate point clouds from the solution snapshots and we develop an expectation-maximization procedure to simultaneously solve the point cloud matching problem and to determine the velocity (and thus the bijection ); finally, we combine our registration method with the nonlinear interpolation technique of [Iollo, Taddei, J. Comput. Phys., 2022] to perform accurate interpolations of fluid dynamic fields in the presence of shocks. Numerical results for a two-dimensional inviscid transonic flow past a NACA airfoil and a three-dimensional viscous transonic flow past an ONERA M6 wing illustrate the many elements of the methodology and demonstrate the effectiveness of nonlinear interpolation for shock-dominated fields
Caractérisation de la porosité agglomérée dans des composites stratifié par interférométrie ultrasonore
No full textInternational audienceLocalized porosity in stratified carbon fiber-reinforced polymer (CFRP) composites can severely affect mechanical performance and structural integrity. Conventional ultrasonic attenuation methods can quantify residual porosity but cannot characterize clusters of voids. This work presents an ultrasonic interferometric approach for the quantitative assessment of localized porosity in laminated composites. CFRP specimens are manufactured in an autoclave under controlled conditions to introduce defined porosity levels. Through-transmission ultrasonic measurements are compared with an analytical multilayer propagation model including a degraded layer described by multiple scattering theory. Solving the inverse problem enabled estimation of both the location and concentration of void clusters. Results show good agreement with X-ray tomographies, confirming the capability of ultrasonic interferometry for accurate detection of localized porosity and its potential for non-destructive evaluation of laminated composites
Derivation of a new LES model approximated from exact two-point equations and evaluation in a Taylor-Green flow
No full textInternational audienceThe Kármán-Howarth-Monin-Hill equation has been used by various authors to quantify and understand the small scale turbulent energy cascade without assumptions and therefore even in the case of non-homogeneous turbulence. A complementary equation was introduced by Germano [1] to describe the large scales dynamics of the flow. In this publication, the links between the Germano equation and Large Eddy Simulation (LES) are examined and an approximation of an exact equation is used to design a new LES model which captures the physical energy transfer between filtered scales and residual subfilter scales. This new model, based on simple simplifications of exact equations, is tested both a priori and a posteriori in a Taylor-Green flow. The model is found to better represent the local energy transfers compared to a similar model introduced in [2] especially for both extreme forward and backscatter events. The Bardina et al. scale similarity model [3] over-performs our model in the a priori analysis, meaning that refining the mathematical approximations used for the derivation of our model could be useful, but our model's performance is comparable if not even better than the scale similarity model in a mixed configuration including a turbulent viscosity model. Therefore, our model, derived with simple simplifications of the exact two-point equations, already performs similarly to LES models classically used for simulations. This publication is a proof of concept that two-point equations can be used to develop new LES models and it may be the right direction to develop more efficient models derived from the Navier stokes equations
Transmission Operators Optimisation for the Iterative Solution of a Trefftz Method for Time-Harmonic Wave Propagation Problems
No full textWhen solving time-harmonic wave propagation problems in wide domains, memory considerations impose to resort to iterative solvers. Unfortunately, classic numerical methods (as Finite Element or Discontinuous Galerkin) are usually poorly adapted to these algorithms, in opposition to Trefftz methods: a natural preconditioner leads to a contracting system. Nevertheless, such an iterative convergence can be quite slow: inspired by the Domain Decomposition community, we propose to define generalised outgoing/incoming traces (on which relies an Ultra Weak Variational Formulation) by introducing transmission operators on each mesh face, intending to improve the iterative convergence. A generalised Trefftz formulation can then be obtained, and is described in a generic formalism issued from two-fields Friedrichs systems. In particular, these operators (and their matrix representation) are characterised so as to ensure the associated formulation satisfies the original weak-coercivity and contraction properties. Following DDM literature, the transmission operator is searched as an approximation of the Dirichlet-to-Neumann operator, through analytic forms and a data-driven approach, where the function linking local parameters to the operator is searched as a neural network. The iterative convergence of the associated Trefftz methods is then discussed for these choices, allowing to highlight robust gains in terms of iterations to convergence
A Quasi-Trefftz Method Based on Local Polynomial Impedance Boundary Conditions for Time-Harmonic Wave Propagation Problems
No full textFacing the need to solve time-harmonic wave problems in wide propagation domains, one needs to resort to iterative algorithms, to which classic numerical methods are usually poorly suited. The Trefftz method, based on the use of actual local solutions as basis functions, can then appear as a viable option for this kind of configurations. Thus, we first propose a general formalism allowing to gather different wave problems, so that a general Ultra Weak Variational Formulation can be defined for them at the same time. Yet, as its classic discretisation by plane waves is used to causing independence and accuracy limitations, we suggest to characterise local solutions by an impedance boundary conditions, which is discretised thanks to piecewise polynomial fields. Unfortunately, analytic expressions of such functions are not practically derivable, and we resort to a local numerical method so as to provide approximations: these quasi-solutions are finally chosen as basis functions in the Trefftz formulation, which is then referred as a quasi-Trefftz method. In the end, numerical experiments allow to highlight robust independence, convergence and iterative behaviour of this method, under calibration conditions of the local solver with respect to the polynomial BC discretisation
Extension of ACETONE C code generator for multi-core architectures
No full textInternational audienceAs the industry's interest in machine learning has grown in recent years, some solutions have emerged to safely embed them in safety-critical systems, such as the C code generator ACETONE. However, this framework is limited to generating sequential code, which cannot make most of the multi-core architectures.In this paper, we initiate an extension of ACETONE for the generation of parallel code by formally defining our processor assignment problem and surveying the state of the art on existing solutions. In the final paper, we will introduce the completed extension, including the implementation of the scheduling heuristic, the creation of templates implementing synchronization mechanisms, and an evaluation of the worst-case execution time of the framework's layers
