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Cycloadditions of 5-Vinyloxazolidine-2,4-diones: A Straightforward Access to the (Thio)hydantoin Scaffold
No full textInternational audienc
Propagation acoustique en milieu fluctuant : des phénomènes océanographiques au traitement du signal
No full textOcean fluctuations affect acoustic propagation and reduce the performance of SONAR arrays. In particular, internal waves can lead to a loss of coherence in incident signals, reducing the efficiency of classical processing. Precise knowledge of the environment is necessary to predict the degradation it causes. However, it is impossible to know the exact state of the ocean, especially in the operational context of a boat at sea. It is therefore necessary to use statistical methods to study the ocean and acoustic propagation, and model their relationship. A statistical method, canonical correlation analysis (CCA), is used to find linear relationships between sets of statistical variables. In this work, we propose to use it to link acoustic variables of interest with oceanographic measurements. In some experimental cases, the method alone can simply explain the underlying physics. In other, more complex cases, such as reception on a highfrequency antenna, it enables us to define a linear model between environmental and acoustic variables, which can be integrated as an a-priori in an array processing. More specifically, we propose to use subarray processing parameterized by the acoustic coherence length. This approach makes it possible to assume a coherent field on each sub-array, and thus to use more conventional processing. In this work, the coherence radius is thus deduced from environmental measurements using the model learned by CCA. To compensate for the loss of angular resolution inherent in sub-arrays, we introduce the use of a Bayesian algorithm exploiting ℓ0 norm regularization. We show on experimental data from the ALMA 2017 campaign that the proposed processing improves detection when signal coherence is low.Les fluctuations océaniques affectent la propagation acoustique et réduisent les performances des antennes SONARs. Les ondes internes, notamment, peuvent entraîner une perte de cohérence des signaux incidents et ainsi réduire l’efficacité des traitements classiques. Une connaissance précise de l’environnement est nécessaire afin de prévoir les dégradations qu’il engendre. Cependant il est impossible de connaître l’état exact de l’océan, surtout dans un contexte opérationnel d’un navire en mer. Il devient nécessaire d’utiliser des méthodes statistiques afin d’étudier océan et propagation acoustique et modéliser leur lien. Une méthode statistique, l’analyse des corrélations canoniques (CCA), est utilisée pour trouver des relations linéaires entre des ensembles de variables statistiques. Dans ces travaux, nous proposons de l’envisager pour lier les variables acoustiques d’intérêt et des mesures océanographiques. Dans certains cas expérimentaux, la méthode permet, seule, d’expliciter simplement la physique sous-jacente. Dans d’autres, plus complexes, notamment de réception sur une antenne à haute fréquence, elle permet de définir un modèle linéaire entre variables environnementales et acoustiques, pouvant être intégré comme a-priori dans un traitement d’antenne. En particulier, nous proposons de recourir à un traitement par sous-antennes paramétré par la longueur de cohérence acoustique. Cette approche permet de supposer un champ cohérent sur chaque sous-antenne, et donc d’utiliser des traitements plus classiques. Dans ce travail, le rayon de cohérence est ainsi déduit de mesures environnementales à partir du modèle appris par CCA. Pour compenser la perte de résolution angulaire inhérente aux sous-antennes, nous introduisons l’utilisation d’un algorithme bayésien exploitant une régularisation en norme ℓ0. Nous montrons sur des données expérimentales de la campagne ALMA 2017 que le traitement proposé améliore les performances de détection lorsque la cohérence du signal est faible
Influence de l'équation d'état pour les systèmes gazeux à moyenne et haute pression
No full textInternational audienceFor transportation and defense systems, equations of state describe the thermodynamical behavior of gases, as a function of pressure, density, and temperature and are often used to close systems of equation (such as Navier–Stokes for fluid mechanics). For low pressure system (under a few dozen MPa), the ideal gas equation can be used, whereas for high pressure system (above 1000 MPa), dedicated equations of state are used (Jones-Wilkins-Lee: JWL or Becker-Kistiakowsky-Wilson: BKW). For intermediate pressure systems, such as interior ballistics or pyromechanisms, where the pressure is around a few hundreds MPa and many phenomena interact closely and simultaneously (multiphysics system: combustion, fluid dynamics, thermics, fluid-structure interaction, thermodynamics…), the ideal gas equation is not valid anymore and nor are the JWL or BKW equations. A dedicated equation of state is then necessary for intermediate level of pressures, and its choice is not obvious. This paper presents a comparison of equations of state for this range of pressure (Noble-Abel, Van der Waals, virial), details the calculations of the involved coefficients and their effects on uncertainties, and studies the influence of the equation of state on the predictions of pressure, density, pressure coefficient, and heat transfer, with both analytical and numerical approach. The results highlight the importance of the choice of the equation of state, especially for a multiphysics system, as the equation of state influences not only thermodynamical properties (pressure, density, temperature) but also thermical properties of a system, such as heat transfer
Cultural evolution in populations of Large Language Models
No full textResearch in cultural evolution aims at providing causal explanations for the change of culture over time. Over the past decades, this field has generated an important body of knowledge, using experimental, historical, and computational methods. While computational models have been very successful at generating testable hypotheses about the effects of several factors, such as population structure or transmission biases, some phenomena have so far been more complex to capture using agent-based and formal models. This is in particular the case for the effect of the transformations of social information induced by evolved cognitive mechanisms. We here propose that leveraging the capacity of Large Language Models (LLMs) to mimic human behavior may be fruitful to address this gap. On top of being an useful approximation of human cultural dynamics, multi-agents models featuring generative agents are also important to study for their own sake. Indeed, as artificial agents are bound to participate more and more to the evolution of culture, it is crucial to better understand the dynamics of machine-generated cultural evolution. We here present a framework for simulating cultural evolution in populations of LLMs, allowing the manipulation of variables known to be important in cultural evolution, such as network structure, personality, and the way social information is aggregated and transformed. The software we developed for conducting these simulations is open-source and features an intuitive user-interface, which we hope will help to build bridges between the fields of cultural evolution and generative artificial intelligence
Physics and technology of Laser Lightning Control
No full textInternational audienceThe recent development of high average, high peak power lasers has revived the effort of using lasers as a potential tool to influence natural lightning. Although impressive, the current progress in laser lightning control technology may only be the beginning of a new area involving a positive feedback between powerful laser development and atmospheric research. In this review paper, we critically evaluate the past, present and future of Laser Lightning Control (LLC), considering both its technological and scientific significance in atmospheric research
Austenite-martensite interfacial patterns and energy dissipation of phase transformation in Ni-Mn-Ga single crystal
No full textInternational audienceThe martensitic phase transformation occurs in Shape Memory Alloys (SMA) via the nucleation/propagation of the Austenite-Martensite interface (A-M interface), which is a transition region (domain) between the two coexisting phases. For providing compatibility, the transition region consists of various martensitic twin structures (laminates), forming different interfacial patterns, such as parallel laminates and branching laminates. Due to the energy accumulation in the interfacial structures (e.g., elastic mismatch and twin-boundary surface energy), the interfacial patterns should be relevant to the driving force (energy dissipation) and the associated kinetics of the phase transformation. In this paper, we adopt a special thermal loading, small-temperature-gradient "heatingcooling-reheating", to control the A-M interface's forward and reverse propagation to generate different interfacial patterns in a Ni-Mn-Ga single crystal SMA with the observation on the twin structures (by optical microscope and SEM) and the InfraRed measurement on the temperature hysteresis of the interface propagation (for characterizing the thermal driving force). Simple energetic analysis indicates that the thermal driving force (energy dissipation) is directly related to the stored energy in the interfacial structure, particularly the large mismatch elastic energy near the habit plane. This study not only provides the details of the various interfacial patterns and their dependence on the 2 / 34 loading path, but also indicates the driving force and the associated mechanism about the pattern evolution to understand the phase transformation process
10 years of Model Federation with Openflexo: Challenges and Lessons Learned
No full textBest Paper Award, Practice TrackInternational audienceIn the context of complex system development, heterogeneous modeling responds to the need to integrate several domains. This need requires the use of the most appropriate formalism and tooling for each domain to be efficient. Model federation promotes the semantic interoperability of heterogeneous models by providing the means to reify correspondences between different model elements, add custom behaviors and bridge the gap between technological spaces. As such, it can be used as an infrastructure to address many different software engineering problems. We have been doing so for over a decade in a tight collaboration between a small software engineering startup and academia. This paper reports on this experience.Concretely, we discuss the context, ambitions, and challenges that led to the inception of our practice of model federation, and we present five use cases experiences, stemming from real industrial and academic needs, and elaborate on lessons learned. In addition, we also report on challenges and lessons learned regarding the development and maintenance of a model-driven model federation tool, the Openflexo framework. Finally, we set up a road map for the future of model federation and Openflexo
Fading regularization method for an inverse boundary value problem associated with the biharmonic equation
No full textInternational audienceIn this paper, we propose a numerical algorithm that combines the fading regularization method with the method of fundamental solutions (MFS) to solve a Cauchy problem associated with the biharmonic equation. We introduce a new stopping criterion for the iterative process and compare its performance with previous criteria. Numerical simulations using MFS validate the accuracy of this stopping criterion for both compatible and noisy data and demonstrate the convergence, stability, and efficiency of the proposed algorithm, as well as its ability to deblur noisy data
Notes de cours sur les méthodes variationnelles pour l'analyse et la résolution de problèmes non coercifs
No full textMaste
Capacité portante sismique des fondations sur sol renforcé par inclusions rigides
No full textInternational audienceThe kinematic exterior approach, in the framework of the yield design theory, is widely utilised for assessing foundation bearing capacity. This study aims at extending this approach to shallow foundations on reinforced soil by rigid inclusions. The interaction diagram in the (V, H, M) space is obtained by combining the interaction curves derived from different failure mechanisms. The resisting forces provided by the rigid inclusions are evaluated using a multicriterion approach and are considered at the intersection of the inclusions with the failure surface. Furthermore, the soil inertia due to the horizontal seismic excitation is also considered in the analysis. The results reveal that the bearing capacity under seismic load is unaffected in the zone of interest for foundations with a sufficient safety factor under static loading.L’approche cinématique par l’extérieur, dans le cadre de la théorie de calcul à la rupture, est largement utilisée pour évaluer la capacité portante des fondations. Cette étude vise à étendre cette approche aux fondations renforcées par inclusions rigides. Pour ce faire, le diagramme d’interaction dans l’espace (H, V, M) est obtenu en combinant les diagrammes d’interaction issus de différents mécanismes de rupture. L’effet de renforcement apporté par les inclusions rigides est pris en compte au moyen des forces résistantes développées à l’intersection de l’inclusion avec la surface de rupture, et sont évaluées à l’aide d’un multicritère. De plus, cette étude prend en compte les effets d’inertie du. Les résultats révèlent que la capacité portante sous charge sismique n'est pas impactée dans la zone d'intérêt pour les fondations présentant un facteur de sécurité suffisant sous charge statique