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Probing Berry Curvature in Magnetic Topological Insulators through Resonant Infrared Magnetic Circular Dichroism
No full textInternational audienc
HISTORICAL PRIMERS ON HERITAGE AIRCRAFT: ANALYSIS OF THE ZINC-CHROMATE ANTICORROSION PIGMENTS
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Jeux non-locaux au travers de la complexité de la communication et de la cryptographie quantique
No full textThis thesis explores foundational aspects of quantum information theory and quantum cryptography. First, we investigate quantum correlations in interactive settings, including the CHSH and graph isomorphism games. We aim to distinguish quantum correlations from non-signaling correlations by leveraging the principle of communication complexity. To this end, we employ techniques such as distributed computation, majority-function-based distillation protocols, the algebraic and geometric properties of nonlocal box wirings, and variations of some graph properties such as isomorphism, transitivity, and equitable partitions. This inquiry advances our understanding of non-physical correlations. Second, we address a key open problem in cryptography: the feasibility of unclonable encryption. We aim to construct an encryption scheme that prevents two distant parties from simultaneously obtaining information about a shared encrypted message. We introduce a candidate for unclonable encryption in the plain model, i.e., without assumptions, in working towards an unconditional proof. Our protocol is based on Clifford algebra, utilizing complex Hermitian unitary matrices that anti-commute. For small key sizes, we rigorously prove security using sum-of-squares methods, while for larger key sizes, we provide strong numerical evidence via the NPA hierarchy.Cette thèse explore des aspects fondamentaux de la théorie de l'information quantique et de la cryptographie quantique. D'une part, nous étudions les corrélations quantiques dans des contextes interactifs, notamment les jeux de CHSH et d'isomorphisme de graphes. Notre objectif est de distinguer les corrélations quantiques des corrélations non-signalantes en nous appuyant sur le principe de complexité de la communication. Pour cela, nous utilisons des techniques telles que le calcul distribué, l'amplification de biais grâce à la fonction majorité, les propriétés algébriques et géométriques des câblages de boîtes non-locales, ainsi que des variantes de certaines propriétés de graphes comme l'isomorphisme, la transitivité et les partitions équitables. Cette étude fait progresser notre compréhension des corrélations non-physiques. D'autre part, nous abordons un problème ouvert majeur en cryptographie : la faisabilité du chiffrement non-clonable. Notre objectif est de construire un schéma de chiffrement qui empêche deux réceptionneurs distants l'un de l'autre d'obtenir simultanément de l'information sur un message chiffré partagé. Nous introduisons un candidat au chiffrement non-clonable dans le modèle standard, c'est-à-dire sans hypothèse, en vue d'obtenir une preuve inconditionnelle de la sécurité. Notre protocole repose sur l'algèbre de Clifford et utilise des matrices unitaires hermitiennes à coefficients complexes qui anti-commutent. Pour des tailles de clés réduites, nous prouvons rigoureusement la sécurité à l'aide de méthodes de sommes de carrés, tandis que pour des tailles de clés plus grandes, nous fournissons des validations numériques solides via la hiérarchie NPA
Silicon nanoantennas for tailoring the optical properties of MoS2 monolayers
No full textInternational audienceSilicon-based dielectric nanoantennas provide an effective platform for engineering light–matter interactions in van der Waals semiconductors. Here, we demonstrate near-field coupling between monolayer MoS2 and silicon nanoantennas arranged in hexagonal lattices with tunable geometric parameters, leading to a threefold enhancement in photoluminescence and an excitation-wavelength-dependent emission that aligns with Mie-resonant modes. Raman spectroscopy reveals an up to eightfold enhancement in the vibrational modes of MoS2, while second-harmonic generation exhibits a 20 to 30-fold increase in efficiency, closely correlating with the presence of the underlying nanoantennas. Our experiments and simulations quantify the tunable benefits of the near-field interactions, taking into account thin-film interference and strain-induced effects. Our findings present dielectric nanoantennas as a promising platform for tailoring linear and nonlinear optical properties in 2D materials, with potential applications in nanophotonic devices and integrated photonics
Surface-dependent reorganization of Chlorella vulgaris cell wall components revealed by AFM and SRS microscopy
No full textInternational audienceCharacterization of microalgae cell wall properties using Atomic Force Microscopy (AFM) depends critically on the immobilization strategy employed. In this study, we investigated how various immobilization surfaces influence the biophysical properties of the Chlorella vulgaris cell wall as probed by AFM. Cells were immobilized on three distinct surfaces, each leveraging different types of interactions with cells: polyoctyl-(PO)-Chitosan-coated glass slides promoting hydrophobic interactions, Superfrost™ positively charged glass slides that interact hydrophobically and electrostatically with cells, and PDMS chambers that immobilize cells through mechanical confinement. AFM imaging, nanoindentation, and force spectroscopy revealed that the biophysical properties of the Chlorella vulgaris cell wall strongly depend on the immobilization strategy. At the same time, all other experimental conditions were kept identical. Cells attached to PO-Chitosan through hydrophobic interactions displayed high surface roughness, higher rigidity, hydrophobic behavior, and positive surface charges. In contrast, cells immobilized on positively charged but less hydrophobic Superfrost™ slides exhibited smoother surfaces, lower rigidity, reduced hydrophobicity, and no detectable positive charges. Cells confined in PDMS chambers exhibited the smoothest and softest cell walls, characterized by hydrophilic and uncharged surfaces. Complementary Stimulated Raman Scattering (SRS) microscopy experiments confirmed distinct lipid rearrangements associated with each immobilization method.Together, these results support the hypothesis formulated in this study that immobilization surfaces can cause the reorganization of cell wall components-polysaccharides, proteins, and lipids-thereby reshaping the physico-chemical and mechanical surface properties. This study thus demonstrates the great significance of immobilization strategies to ensure the reliability of nanoscale biophysical measurements in microalgae research
Gas-Phase Synthesis of Ag Nanoparticles for Integration into Nanocapacitors and Operando Electron Holography Analysis
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L'eau et les Hommes, Mythes de toujours, périls d'aujourd'hui - Avant-propos
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Gaussian Processes: from knowledge-informed Machine Learning to optimization
No full textNational audienceMany situations lead to sparse data or uncertain data. Gaussian processes (GPs) offer a mathematically funded framework for learning, optimizing,and other decision-making activities. This poster, presented at the HCERES* audit of the LIMOS laboratory in 2025, summarizes several contributions of the St-Etienne applied mathematics team of the LIMOS made between 2023 and 2025. * HCERES : Haut Conseil de l'Evaluation de la Recherche et de l'Enseignement Supérieu
Analysis of quasi-periodic waves of cubic nonlinear Schrödinger equations
No full textWe study the quasi-periodic standing wave solutions of the focusing and defocusing cubic nonlinear Schrödinger equations in dimension one. In the defocusing case, we establish a diffeomorphic correspondence between the invariants of the ordinary differential equation of the wave profiles and the conserved quantities of the evolution equation. We introduce a numerical scheme to compute the minimizers of the energy at fixed mass and momentum for both focusing and defocusing cases. The scheme is based on a gradient flow approach with discrete renormalization at each time step. The novelty of our scheme is that the renormalization step deals at the same time with the mass and the momentum constraints. In numerical experiments, we observe that a given solution of the profile ordinary differential equation is also a minimizer of the energy at corresponding mass and momentum
Génération de mondes virtuels pour tester des robots autonomes en simulation
No full textThe research leading to these results has received funding from the EuropeanUnion’s Horizon 2020 research and innovation programme under the MarieSkłodowska-Curie grant agreement No. 812.788 (MSCA-ETN SAS).National audienceThis thesis addresses the challenges of automated test case generation for autonomous systems using simulation-based testing. The manuscript tackles three primary research questions: (1) how to generate structured test data with constraints, (2) how to integrate automated test generation frameworks into existing industrial testing platforms, and (3) how to apply pairwise testing to hierarchical data structures like XML and JSON. To address the first question, the manuscript introduces TAF (not a contribution of this thesis), a testing tool for generating test cases from complex declarative models with structure and constraints. For the second question, the integration of TAF into two industrial simulation-based platforms is discussed, highlighting practical considerations and lessons learned from real-world applications. The main contribution of this work, addressing the third question, is a formalization for applying pairwise testing to hierarchical data structures with constraints. This formalization redefines concepts such as test parameters, choices, and pairs to accommodate structured data, considering data instance multiplicity, access paths, and common ancestors. Various strategies for selecting the lowest common ancestor (LCA) are presented, along with XPath queries for coverage checking. The thesis also reports on the implementation of a framework that combines pairwise strategies with TAF. Results from two case studies demonstrate the framework's ability to minimize test suite size while maximizing coverage, outperforming the baseline approach. Future research directions include exploring closed-loop testing, integrating search-based and combinatorial algorithms, modeling more complex scenarios with dynamic agents, and extending the pairwise formalization to handle recursive definitions and n-way testing.Cette thèse aborde les défis de la génération automatisée de cas de test pour les systèmes autonomes à l'aide de tests basés sur la simulation. Le manuscrit aborde trois questions de recherche principales : (1) comment générer des données de test structurées avec des contraintes, (2) comment intégrer des cadres de génération de tests automatisés dans des plates-formes de tests industrielles existantes et (3) comment appliquer des tests par paires à des structures de données hiérarchiques comme XML et JSON. Pour répondre à la première question, le manuscrit présente TAF (qui n'est pas une contribution de cette thèse), un outil de test permettant de générer des cas de test à partir de modèles déclaratifs complexes avec structure et contraintes. Pour la deuxième question, l'intégration de TAF dans deux plates-formes industrielles basées sur la simulation est discutée, mettant en évidence les considérations pratiques et les leçons tirées d'applications du monde réel. La principale contribution de ce travail, abordant la troisième question, est une formalisation permettant d'appliquer pairwise testing à des structures de données hiérarchiques avec contraintes. Cette formalisation redéfinit des concepts tels que les paramètres de test, les choix et les paires pour s'adapter aux données structurées, en tenant compte de la multiplicité des instances de données, des chemins d'accès et des ancêtres communs. Diverses stratégies de sélection du plus petit ancêtre commun (LCA) sont présentées, ainsi que des requêtes XPath pour la vérification de la couverture. La thèse rend également compte de la mise en œuvre d'un framework combinant des stratégies par paires avec TAF. Les résultats de deux études de cas démontrent la capacité du framework à minimiser la taille de la suite de tests tout en maximisant la couverture, surpassant l'approche de base. Les futures orientations de recherche comprennent l'exploration des tests en boucle fermée, l'intégration d'algorithmes basés sur la recherche et combinatoires, la modélisation de scénarios plus complexes avec des agents dynamiques et l'extension de la formalisation par paires pour gérer les définitions récursives et les tests n-way