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Face à la fascisation de la société : l’antifascisme. D’une nécessité à la contradiction
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Linear and nonlinear crystal optics: phenomenology, symmetries, and angular distributions
No full textInternational audienceThis book provides both theoretical foundations and practical insights into linear and nonlinear crystal optics. It bridges the fundamental principles of light-crystal interactions with advanced applications in optics. Linear and Nonlinear Crystal Optics offers a thorough exploration of electric susceptibility—the cornerstone of optical properties through electric constitutive relations and Maxwell’s equations. Key features include comprehensive tensor representations, detailed angular distributions of optical parameters, complete mathematical demonstrations, and original research insights developed over decades. The book covers essential topics including phenomenological introduction to light-matter coupling, mathematical background in orientation and thermodynamic symmetries, electric susceptibility and field tensors, polarization calculations, linear optical effects linked to the real and imaginary parts of the refractive index, and both second-order and third-order interactions. Each chapter concludes with a summary and references, providing readers with clear learning pathways and resources for further exploration. This book is ideal for advanced undergraduate students, graduate students, and researchers in physics, optical engineering, materials science, and crystallography. It serves as an essential reference for professionals working in fields requiring deep understanding of crystal optics, including photonics, laser technology, telecommunications, and materials characterizatio
Assessing simplified approaches in modeling rainfall-induced landslides using Richards' equation with Biot poroelasticity
No full textInternational audienceCoupled Hydro-Mechanical (HM) models, which involve the interaction between fluid flow and mechanical processes in porous media, are essential for simulating rainfall-induced landslides (RILS). A common strategy to investigate RILS is through the Biot poroelasticity approach combined with the Local Factor of Safety concept. While the two-phase flow and mechanical equations are well-documented for modeling HM processes in variably saturated conditions, the use of Richards' Eq. (RE) in this context remains underexplored. This paper aims to address this gap by providing a comprehensive formulation for coupling RE with mechanical equations and evaluating the impact of various model simplifications on the reliability of RILS predictions. We present the theoretical development of the original mathematical model that leads to a strong coupling between flow and mechanical equations. We also review the different simplification approaches proposed in the literature to reduce the complexity of the original model. A straightforward implementation of these approaches in COMSOL is provided, with validation against established benchmarks. Through a comparative analysis of different approaches, using both hypothetical benchmark and real case study in Azerbaijan, this study provides new insights into the balance between model complexity and prediction accuracy. While simplified approaches are commonly used in literature, this study advocates for the fully coupled model, which delivers the most reliable results. The employment of advanced numerical techniques enhances the computational performance of the fully coupled model, making it competitive with simplified approaches
Hydrodynamic effects of ship passage in confined channels: A multi-parameter study
No full textInternational audienceThis study investigates the impact of inland navigation on inland. Two methods were used: experimental campaigns in the towing tank of the Pprime Institute and numerical simulations with the CFD software StarCCM+. These approaches allowed detailed analysis of the hydrodynamic effects caused by ship passage in confined channels. The experiments reproduced various navigation scenarios using adjustable banks. Flow velocities and surface elevations were measured with Stereo-PIV and stereo-refraction techniques. A numerical model was also developed using the SST k–ω turbulence model and mesh refinement near the free surface. It was validated against the experimental data. Four key parameters were studied: ship speed, initial water depth, channel width, and bank slope. Each had a strong influence on flow characteristics. Extreme conditions (high speed, shallow depth, narrow channels, and sloped banks) produced amplified effects. These included deeper surface depressions, stronger return currents, larger waves, more turbulent wakes, and sharper velocity gradients, especially near banks. This study highlights the need to control navigation conditions to protect riverbanks
Spillover from flower plantings benefits apple pollination on a small scale
No full textInternational audienceAnimal-mediated pollination is critical to support crop yields but is threatened by the decline of pollinator populations. The establishment of flower plantings in agricultural landscapes is a conservation strategy that aims to provide diverse floral resources for pollinators. Despite several studies on the effect of flower plantings on pollination, their effects remain unclear. In particular, the influence of the distance has been studied through theoretical approaches but field studies are scarce. We conducted field experiments over two years, 2023 and 2024, in the Provence-Alpes-Côte d'Azur region of France, to investigate how co-flowering plantings affect insect flower visitation and crop pollination in apple orchards. We found that the abundance of apple flower visitors, especially wild bees, decreased with the distance from flower plantings, thus suggesting a spillover of flower visitors from flower plantings into adjacent apple trees. Interestingly, we found a non-linear effect of the distance from flower planting on the initial fruit set, which suggests that flower plantings can improve apple pollination at close distances from the plantings (about 33 m). No effect of the distance from flower plantings was observed on the diversity of flower visitors, final apple fruit set or fruit quality. Overall, our results suggest that flower plantings are a promising strategy to support pollinators. Furthermore, as they can increase pollinator abundance in the adjacent apple flowers, flower plantings have the potential to enhance pollination and yield of the adjacent crops. Given the short distance of the observed facilitation effect, we recommend that flower plantings should be spread across farmland in order to promote crop pollination at farm level
Exploring Zero-Shot SLM Ensembles as an Alternative to LLMs for Sentiment Analysis
No full textInternational audienceSentiment analysis has become vital for understanding consumer attitudes, guiding product development, and informing strategic decisions. Although LLMs such as GPT-3.5 and GPT-4 deliver strong zero-shot performance, they can be cost prohibitive and raise privacy concerns. In contrast, Small Language Models (SLMs) provide a lighter and more deployable solution, but their ability to match LLM accuracy, especially in zero-shot scenarios, remains underexplored. In this experimental study , we examine whether ensembles of zero-shot SLMs can serve as a viable alternative to proprietary LLMs in sentiment classification tasks. We investigate five commonly used SLMs (Phi2 Mini, Mistral, Llama, Gemma, Aya) and compare them to GPT-based models (GPT-3.5, GPT-4, GPT-4 omni, GPT-4 omni mini) across seven English-language datasets. By automating prompt generation and filtering responses based on a strict output format, we maintain a purely zero-shot approach. We form SLM ensembles via majority voting and evaluate their performance on accuracy, weighted precision, and weighted F1. We also measure inference time to assess cost and scalability trade-offs. Results show that SLM ensembles as a form of decision fusion, consistently outperform single SLMs, significantly boosting metrics in zero-shot settings. In contrast with GPT models, the ensemble achieves accuracy comparable to GPT-3.5 and even rivals GPT-4 on certain prompts. However, GPT-4 retains a slight edge in both precision and F1 score. Moreover, local SLM ensembles incur higher latency yet offer potential advantages in data privacy and operational control. This experimental study’s findings illuminate the feasibility of employing lightweight, zero-shot SLM ensembles for sentiment analysis, providing organizations with an effective and more flexible alternative to exclusively relying on large proprietary models
Projets alimentaires territoriaux et stratégies alimentaires locales : une comparaison France -Brésil
No full textInternational audienceThis text compares civil society and national and local policy actions targeting the food system in Brazil and France. It shows how the two countries have adopted mirror strategies, with France relying on a multitude of local initiatives led by local authorities and civil society, with little national support, while Brazil first developed a powerful national policy influenced by organised citizen networks to disseminate it at regional and local levels.Ce texte, en version longue par rapport à l'ouvrage à paraître, compare les actions de la société civile et politiques nationales et locales visant le système alimentaire, entre le Brésil et la France. Il montre comment les deux pays ont adopté des stratégies en miroir, la France se basant sur une multitude d'initiatives locales portées par les collectivités et la société civile, avec un faible portage national, pendant que le Brésil a d'abord développé une puissante politique nationale influencée par les réseaux citoyens organisés pour la diffuser aux échelles régionale et locale
An Autoethnography on Visualization Literacy: A Wicked Measurement Problem
No full textInternational audienceWe contribute an autoethnographic reflection on the complexity of defining and measuring visualization literacy (i.e., the ability to interpret and construct visualizations) to expose our tacit thoughts that often exist in-between polished works and remain unreported in individual research papers. Our work is inspired by the growing number of empirical studies in visualization research that rely on visualization literacy as a basis for developing effective data representations or educational interventions. Researchers have already made various efforts to assess this construct, yet it is often hard to pinpoint either what we want to measure or what we are effectively measuring. In this autoethnography, we gather insights from 14 internal interviews with researchers who are users or designers of visualization literacy tests. We aim to identify what makes visualization literacy assessment a “wicked” problem. We further reflect on the fluidity of visualization literacy and discuss how this property may lead to misalignment between what the construct is and how measurements of it are used or designed. We also examine potential threats to measurement validity from conceptual, operational, and methodological perspectives. Based on our experiences and reflections, we propose several calls to action aimed at tackling the wicked problem of visualization literacy measurement, such as by broadening test scopes and modalities, improving test ecological validity, making it easier to use tests, seeking interdisciplinary collaboration, and drawing from continued dialogue on visualization literacy to expect and be more comfortable with its fluidity
Embrittlement after high-temperature exposure to air of a near-γ TiAl alloy
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Algebraic hierarchical partitioning to improve H-matrix compression
No full textInternational audienceSolving large dense problems is a challenging task in many industrial applications such as computational electromagnetics. H-matrices may solve these problems efficiently while significantly reducing storage requirements. The compression rate and efficiency of H-matrices depend on the partitioning of the unknowns. This partitioning must be hierarchical and should respect geometric criteria in order to maximize compression. A fixed block size constraint is added to accommodate load balancing and performance concerns on HPC runtime systems. Numerous partitioning schemes exist, but few meet all requirements. Some geometric methods such as recursive coordinates bipartition, space-filling curves and cobblestone sorting provide acceptable results whereas algebraic graph partitioner generally do not. We propose a method to build a graph from the mesh to combine geometric and physical properties, suited to provide adapted partitions reliably. We review fitting geometric partitioning methods and compare them to our algebraic approach using relevant metrics such as compression rates before and after factorization and execution time of H-matrix assembly, factorization and solving step. We also study resulting partitions based on their volume, overlap and distance. Our contribution shows significant improvements in compression rates and execution times for complex 3D objects with multiple materials which are representative of industrial applications.</div