Hal - Université Grenoble Alpes
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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
Diamond-based non-volatile memory
No full textInternational audienceThe digital age has brought unprecedented challenges in data storage, with exponential growth in data generation outpacing traditional storage solutions in capacity, speed, and reliability. Long-term data preservation is particularly concerning, as current technologies like semiconductor drives and hard disk drives struggle with data longevity beyond a few decades. Optoelectronic memories show promise among emerging storageclass memory technologies, but they face trade-offs between information retention time and fatigue cycles due to material limitations. Diamond, with its exceptional physical properties, especially its ultra-wide bandgap, emerges as a strong candidate for developing non-volatile memories capable of retaining information over extremely long periods. This paper explores the fundamental aspects and fabrication methods of diamond non-volatile memories, focusing on the information storage mechanisms and unique properties of the ultradeep nitrogen donor in diamond, as well as the associated junction field effect transistor. The study describes the physical concept of the memory effect and the transistor structure, details the fabrication and properties of the samples, and addresses key challenges in creating efficient devices. These findings establish diamond as a viable material for ultra-stable memory applications and provide key insights into its long-term performance.</div
A Noetherian approach to invariants for the statics and dynamics of elastic rods
No full textInternational audienceThe static-dynamic analogy discovered by Gustav Kirchhoff in 1859 shows that the statics of an elastic beam is equivalent to the dynamics of a spinning top. This analogy, where time and angular velocity are, for example, equivalent to arclength and curvatures,allows the use of Emmy Noether's 1918 theorem on continuous symmetries to unravel a quantity that is invariant along elastic rods at equilibrium. A spinning top having a Lagrangian independent of time will have its mechanical energy constant in time.In the same manner, an elastic rod with uniform elastic properties will have the sum of its curvature energy and its tension force uniform along the structure. This arclength invariance property is known in simple cases, but the present approach generalises it to more complex scenarios where extensibility, shear, conservative loads (\eg gravity), and contact are involved.Moreover, still using Noether's theorem and bringing to light the continuous symmetries of the Lagrangian of the variational approach, we recover all known invariants for the statics and dynamics of rods and ribbons, including configurational invariants. Furthermore, we show how the arclength invariant may be used to obtain pivotal information on some landmark elastic rod problems, including confinement buckling, sliding sleeves, or plectonemes.Finally, we extend the approach to vibrations.Overall, this paper is an attempt to explain, unify and extend all previous results on rod invariants thanks to the beautiful Noetherian formalism, and to show its practical use on a few relevant applications
Ranking Big Data Analytics Micro-Foundations for the Resilience of Agri-Food Retailers: A Multi-Criteria Decision-Analysis Study
No full textInternational audienceThe agriculture industry needs resilience beyond the traditional reactive measures due to increasing disruptions. This study investigates social-ecological resilience capabilities and big data analytics (BDA) micro-foundations in the agri-food supply chain (AFSC) using a multiple-criteria decision analysis approach. Relying on the dynamic capabilities view, first, a fuzzy DANP approach was employed to validate and weight 19 key resilience capabilities, and, second, fuzzy VIKOR was used to rank the 14 BDA micro-foundations that most effectively support them. By consulting resilience experts to evaluate resilience capabilities on three levels of organizational, supply chain, and industry and testing the final model in one large food retailers, this study provides a framework for managers to devise actionable plans to develop resilience using BDA. The findings suggest risk-aware culture, adaptability, and collaboration as the most important capabilities and agility, adaptability, and compliance flexibility as capabilities with the most influence on other capabilities. Finally, using BDA micro-foundations to sense the market and devise data-driven solutions were the most critical for the case of the large food retailer
Autoregressive Multiplier Bootstrap for In-situ Error Estimation and Quality Monitoring of Finite Time Averages in Turbulent Flow Simulations
No full textInternational audienceIn Computational Fluid Dynamics (CFD), and particularly within Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES), the computational cost is largely dictated by the effort required to obtain statistically converged quantities such as time-averaged fields and higher-order moments. Despite the importance of accurately quantifying statistical uncertainty in unsteady simulations, no continuous and cost-effective, on-line method currently exists for monitoring the convergence quality of such statistics during runtime. This work introduces a novel, fully on-line bootstrapping approach to estimate the variance of finite-time averages without requiring the estimation of the flows Auto-Correlation Function (ACF). Unlike existing methods that rely on ACF estimation, which are often impractical due to excessive storage demands in large-scale simulations, or require off-line processing or a priori modeling assumptions, our method operates entirely during the simulation and incurs minimal overhead. The proposed technique employs a recursive update of bootstrap replicates of the time average, using correlated random weights generated via an autoregressive model. This formulation is computationally efficient: the update cost scales linearly with the number of bootstrap replicates and the dimensionality of the flow field, and the autoregressive model is inexpensive to evaluate. The method only requires storage of a small number of fields, making it suitable for large-scale CFD applications. We demonstrate the effectiveness of the approach on synthetic data from the Ornstein-Uhlenbeck process and on two canonical LES cases: a turbulent pipe flow and a round jet. We further discuss the methods applicability to simulations with non-uniform time stepping, highlighting its flexibility and robustness
Precision cross-sections for advancing cosmic-ray physics and other applications: a comprehensive programme for the next decade
No full textInternational audienceCosmic-ray physics in the GeV-to-TeV energy range has entered a precision era thanks to recent data from space-based experiments. However, the poor knowledge of nuclear reactions, in particular for the production of antimatter and secondary nuclei, limits the information that can be extracted from these data, such as source properties, transport in the Galaxy and indirect searches for particle dark matter. The Cross-Section for Cosmic Rays at CERN workshop series has addressed the challenges encountered in the interpretation of high-precision cosmic-ray data, with the goal of strengthening emergent synergies and taking advantage of the complementarity and know-how in different communities, from theoretical and experimental astroparticle physics to high-energy and nuclear physics. In this paper, we present the outcomes of the third edition of the workshop that took place in 2024. We present the current state of cosmic-ray experiments and their perspectives, and provide a detailed road map to close the most urgent gaps in cross-section data, in order to efficiently progress on many open physics cases, which are motivated in the paper. Finally, with the aim of being as exhaustive as possible, this report touches several other fields -- such as cosmogenic studies, space radiation protection and hadrontherapy -- where overlapping and specific new cross-section measurements, as well as nuclear code improvement and benchmarking efforts, are also needed. We also briefly highlight further synergies between astroparticle and high-energy physics on the question of cross-sections
Speaking Face-to-Face with a Virtual Avatar to Reduce Anxiety in Students Who Stutter: Tool Development and Pilot Study Results
No full textInternational audiencePurpose: Speaking in class is challenging for students who stutter. Cognitive-behavioral therapy (CBT) with exposure in virtual reality (VR) emerges as a promising intervention for treating speaking anxiety in pediatric populations. This pilot study tested if real-time avatar-based VR can elicit anxiety responses while remaining acceptable to youth who stutter. Method: Twelve students who stutter (aged 9-18) were randomly assigned to a single training session conducted either (1) in VR with a realistic avatar controlled live by their SLP, or (2) in role-play with their SLP, before facing a real actor. We assessed system acceptability, anxiety levels and perceived self-efficacy. Results: The VR system was well accepted and elicited physiological arousal comparable to reallife interactions. Although participants reported experiencing less anxiety during VR, skin conductance level showed higher arousal; suggesting a divergence between the subjective report and physiological response. Finally, one training session (either in VR or with the SLP) did not produce gains in self-efficacy or decrease in anxiety related to the final real-actor conversation. Conclusion: This study demonstrates evidence that the potential use of immersive VR could represent an acceptable and viable complementary strategy for SLP treatment, that could control exposure parameters while evoking physiological responses similar to real-life contexts. The differences between subjective and physiological measures suggest that VR is inducing anxiety responses differently than it was perceived. Further research could investigate the use of VR as anxiety interventions for students who stutter and should be explored across multi-session studies to understand their therapeutic effect.</div
Osservare le condizioni politiche contemporanee: soggettività assistite, opinioni pubbliche approssimative e Stato algoritmico
No full textInternational audienceIn questo intervento cercheremo di rispondere alla domanda sul carattere potenzialmente post-politico del futuro alla luce delle nostre ricerche sulla trasformazione algoritmica delle società contemporanee. In particolare, vogliamo esaminare la situazione contemporanea alla luce di tre fatti che ipotizziamo essere « generativi » nel senso inteso da Tocqueville in De la démocratie en Amérique a proposito della dinamica dell'equalizzazione delle condizioni: hanno un notevole potere di trasformazione sia morale, sia sociale, sia politica. Si tratta (1) del rapporto individuale con se stessi assistito dall'IA generativa, che modifica le condizioni della soggettività e l'espressione della cittadinanza; (2) degli effetti di questo fenomeno sulla formazione dell'opinione pubblica che, a causa del carattere allucinatorio di questi sistemi algoritmici, diventa approssimativa e non può più valere come principio normativo, come sperava Kant con l’ « Öffentlichkeit »; (3) della competenza algoritmica per tutti i servizi dello Stato