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No-go theorem for quantum realization of extremal correlations
No full textThe study of quantum correlations is central to quantum information and foundations. The paradigmatic case of Bell scenarios considers product measurements implemented on a multipartite state. The more general case of contextuality scenarios--where the measurements do not have to be of product form or even on a composite system--has been studied for the case of projective measurements. While it is known that in any Bell scenario extremal indeterministic correlations (e.g., Popescu-Rohrlich or PR boxes) are unachievable quantumly, the case of general contextuality scenarios has remained open. Here we study quantum realizations of extremal correlations in arbitrary contextuality scenarios and prove that, for all such scenarios, no extremal indeterministic correlation can be achieved using projective quantum measurements, i.e., there exists no quantum state and no set of projective measurements, for any contextuality scenario, that can achieve such correlations. This no-go result follows as a corollary of a more general no-go theorem that holds when the most general set of quantum measurements (i.e., positive operator-valued measures, or POVMs) is taken into account. This general no-go theorem entails that no non-trivial quantum realization of an extremal indeterministic correlation exists, i.e., any "quantum" realization must be simulable by classical randomness. We discuss implications of this no-go theorem and the open questions it raises
Nutrient estimation in the Peruvian upwelling system based on a neural network approach
No full textInternational audienceThis study presents a regionally trained version of the “CArbonate system and Nutrients concentration from hYdrological properties and Oxygen using a Neural network” (CANYON) method, named CANYON-PU, for estimating primary macronutrients (phosphates, silicates, and nitrates) in the Peruvian Upwelling System (PUS). Using a neural network approach, the model was trained using extensive biogeochemical data spanning between 2003 and 2021, collected by the Peruvian Institute of Marine Research (IMARPE). Variables representing the low-frequency variability related to ENSO were introduced in the training and significantly improved the performance of the algorithm. The performance of CANYON-PU was validated against independent datasets and demonstrated an improvement in accuracy over the global CANYON model that struggled to represent the nutrient distribution in the PUS mainly due to the lack of samples in its training. Therefore, CANYON-PU successfully captured nutrient variability across different spatial and temporal scales, showcasing its applicability to diverse datasets, including high-frequency data such as profiling floats or gliders. This work highlights the effectiveness of neural networks for representing the nutrient distribution within highly variable ecosystems like the PUS
Incubation Experiments, Observations, and Modeling Highlight the Key Role of Dimethylmercury on Seawater Methylmercury Distributions
No full textInternational audienceThe origin of the bioaccumulative neurotoxin methylmercury (MeHg) in the ocean remains elusive. The current paradigm suggests that microbial methylation of inorganic Hg within the oceanic water column produces monomethylmercury (MMHg) and potentially dimethylmercury (DMHg). Reaction rates and main drivers governing MeHg levels (sum of MMHg and DMHg) are poorly constrained. We conducted ambient Hg species measurements and enriched isotopic tracer experiments in waters of two contrasting marine environments, the oligotrophic Mediterranean Sea (MED) and the mesotrophic Atlantic Ocean (ATL). Maximum subsurface MeHg levels were ~2 times higher in the MED compared to the ATL, essentially driven by higher DMHg concentrations (0.45 ± 0.06 vs 0.16 ± 0.02 pM).Methylation was only detectable in unfiltered subsurface waters and presumably biotically driven. The highest methylation rate (MMHg to DMHg) was observed in subsurface MED waters while reduction and demethylation rates were highest in surface waters of both environments. Experimental reaction rates and the potential microbial activity (based on 16S rDNA) aligned with ambient Hg species distributions.Assuming high DMHg stability and applying our fast experimental DMHg formation rates, a newly developed 1D water column model (MED) successfully reproduced MeHg species distribution, suggesting DMHg plays a key role in the global marine Hg cycle
First data on dissolved black carbon in the coastal Northwestern Mediterranean Sea
No full textInternational audienc
L'État de droit face aux crises. L'État de droit en crise
No full textInternational audienceLe concept d’État de droit, pilier de la démocratie libérale, est aujourd’hui fragilisé par une inflation sémantique, reflet d’attaques politiques et juridiques qui risquent de le vider de sa substance. Né au xixe siècle en Allemagne, sous le nom de Rechtsstaat, et incarné dans le monde anglo-saxon par le Rule of Law, il désigne un ordre juridique dans lequel le pouvoir est limité par le droit, les droits fondamentaux protégés et l’action de l’État soumise à un contrôle juridictionnel. Cette idée s’est progressivement imposée comme référence constitutionnelle et internationale, notamment après la Seconde Guerre mondiale et, plus encore, à partir de années 1990, après la chute des régimes communistes et la mise en place des politiques d’élargissement de l’Union européenne. L’État de droit devient alors un critère d’adhésion et d’appartenance à l’Europe et un pilier de la démocratie libérale.Toutefois, depuis une vingtaine d’années, ce consensus est mis à mal. La montée des régimes populistes, l’affaiblissement des contre-pouvoirs, l’instrumentalisation du droit et du juge, l’essor de nouvelles formes de domination, dû au développement des nouvelles technologies, au renforcement de la puissance d’entreprises privées, sont des phénomènes qui contribuent à une érosion réelle de l’État de droit. Celui-ci est également menacé par les effets conjugués de la mondialisation, des crises migratoires, sanitaires, sécuritaires et environnementales. Le colloque organisé les 7 et 8 décembre 2023, à l’origine du présent ouvrage, propose une analyse pluridisciplinaire de ces mutations, en explorant les causes profondes de la crise de l’État de droit et en s’interrogeant sur les voies possibles de refondation ou d’adaptation du concept dans un monde en transformation
On Hyperexponential Stabilization of Perturbed Unicycle Dynamics
No full textInternational audienceThe problem of hyperexponential stabilization for a mobile robot is addressed by leveraging its kinematic model with external perturbations. To this end, a robust nonlinear control law is designed, and several state and time transformations are introduced, reformulating the system model to an interconnection of integrators. A novel fixed-time stabilization strategy is developed for an uncertain double-integrator system. The whole closed-loop system's convergence rate is rigorously analyzed, demonstrating hyperexponential behavior. The obtained results are compared with existing analogues in numeric experiments.</div
System Feature Awareness and Retrieval Strategies in the Use of System Feature Awareness and Retrieval Strategies in the Use of Voice-Activated Devices Voice-Activated Devices
No full textInternational audienceUsers rarely take full advantage of the unprecedented possibilities offered by IT in the post-adoptive stage of use, creating a feature-use paradox. This paradox is particularly pronounced in the context of voiceactivated devices (VADs), such as smart voice assistants, as VADs require users to rely entirely on memory when interacting with them. In this setting, we theorize that users' ability to recall which system features are available is crucial for effectively engaging with VADs and can thus shed light on the feature-use paradox. We define IT Feature Awareness in the context of VADs by adapting the brand awareness concept from marketing research, and we develop a conceptual model rooted in adaptive system use theory that captures the expected impact of IT feature awareness on innovative use behaviors. We conclude this workin-progress by outlining our data collection plans and expected contribution to the post-adoptive IT use stream of the IS literature.</div
Entry and exit of Fragilariopsis cylindrus diatoms from the polar night: evidence for chromatin-mediated genome control
No full textRegulation of the epigenome landscape plays a crucial role in adaptation to environmental changes. However, the molecular mechanisms by which epigenome landscapes are established and tuned to adjust the cellular status to environmental cues remain poorly understood, especially in unicellular photosynthetic eukaryotes. Polar microalgae must adapt to extreme variations in light and temperature for survival and therefore represent excellent models to understand the diversity of gene regulatory mechanisms, yet chromatin-based mechanisms have never been explored in these organisms. In this study, we combined genome-wide profiling of histone and DNA modifications with transcriptomic analyses of the marine polar diatom Fragilariopsis cylindrus upon entry and exit of a 3-month-long polar night. We show that, in agreement with its established role in transcription facilitation, histone H2B monobiquitination (H2Bub) is modulated at active genes upon prolonged darkness to light re-exposure. In contrast, histone H3 lysine 27 trimethylation (H3K27me3) and DNA cytosine methylation (CG methylation), two modifications typically associated with the silencing of genes or transposable elements (TEs), remained stable throughout the transitions, reinforcing their role in transcriptional repression, particularly at TEs but also at a few genes. We further demonstrate that H3K27me3 and DNA methylation are physically associated at TEs, probably reflecting a dual locking system enabling F.cylindrus cells to cope with the invasive nature of these genetic elements under extreme environmental conditions. These findings enhance our understanding of genome and epigenome regulation in diatoms in response to environmental variability and open new avenues for exploring the role played by chromatin-level regulation in the unique evolutionary history of polar unicellular eukaryotes
La fabrication additive pour les drones sous-marins : Etat actuel et challenges
No full textInternational audienceLa fabrication additive pour les drones sous-marins : Etat actuel et challenge
Fonds d'investissements immobilier et production de la ville : les complexes urbains multifonctionnels privés au Mexique
No full textInternational audienceSince 2010, new types of urban projects in Mexico - privately-owned multifunctional urban complexes - have marked a turning point in the logic of city closure. These projects concentrate residential and commercial buildings, offices, and leisure activities, all within a delimited, secure perimeter aimed at the affluent social classes. This article mobilizes the figure of the multifunctional urban complex as a revelation of transformations in the modes of production of the private city in Mexico. The creation of a database of over 79 projects reveals a continuity in the production logics of closed neighborhoods, but a rupture in terms of the scale and urban form they imply, and their location. The novelty of these buildings, which are intended to be true urban centralities, lies in the combination of functional diversity, enclosure and verticalization of residential spaces, but at the service of a specific category of population. A field study shows how the mobilization of financial capital by an exclusive social network becomes a lever of power in urban governance and management.Managed by investment funds, these spatial entities appear to be a tool and a support for the financial development of the country's metropolises, also reinforcing the socio-spatial polarity of the metropolises.Au Mexique, l'émergence de complexes urbains multifonctionnels privés marque un tournant dans les logiques de privatisation et de fermeture de la ville depuis 2010. Ces projets concentrent des édifices résidentiels et commerciaux, des bureaux et des activités de loisir, le tout dans un périmètre délimité et sécurisé à destination des classes sociales aisées. Cet article mobilise la figure du complexe urbain multifonctionnel privé en tant que révélateur des transformations des modes de production de la ville privée au Mexique. La création originale d’une base de données recensant 79 projets associée à une enquête de terrain permet de comprendre comment la mobilisation de capitaux financiarisés par un réseau social exclusif devient un levier de pouvoir dans la gouvernance et la gestion urbaine. Gérés par des fonds d’investissements mexicains, les complexes urbains multifonctionnels privés apparaissent comme un outil et un support du développement financier des métropoles, renforçant également la polarité socio-spatiale des métropoles