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Analysis of variational formulations and low-regularity solutions for time-harmonic electromagnetic problems in complex anisotropic media
No full textInternational audienceWe consider the time-harmonic Maxwell's equations with physical parameters, namely the electric permittivity and the magnetic permeability, that are complex, possibly non-Hermitian, tensor fields. Both tensor fields verify a general ellipticity condition. In this work, the well-posedness of formulations for the Dirichlet and Neumann problems (i.e. with a boundary condition on the electric field or its curl, respectively) is proven using well-suited functional spaces and Helmholtz decompositions. For both problems, the a priori regularity of the solution and the solution's curl is analysed. The regularity results are obtained by splitting the fields and using shift theorems for second-order divergence elliptic operators. Finally, the discretization of the formulations with a H(curl)-conforming approximation based on edge finite elements is considered. An a priori error estimate is derived and verified thanks to numerical results with an elementary benchmark
Have We Ever Been Planetary?
No full textInternational audienceIn response to the rise of interest in the notion of the planetary among environmental historians and philosophers, and likewise reacting to the current wave of interest in returning to space and the proclaimed birth of Space 2.0, this essay considers the somewhat provocative question as to whether we have indeed ever been planetary. The answer that we offer is no. We support this claim based on historical considerations on the inseparability of our current understanding of the planet with the human expansion into outer space. Stated rather more precisely, but also somewhat paradoxically: humankind only became aware of itself as a planetary species by becoming a post-planetary species. Our argument then is that the current rhetoric proclaiming that we live in a planetary age needs to be revised to take into account the extra-planetary dimension in our supposedly planetary existence. The remainder of the essay attempts to rapidly sketch what it might mean to begin to think critically about our current historical situation in post-planetary terms, with a particular focus on culture, ecology, economics, and politics. Many philosophers, historians, and critical theorists are now telling us that we live in a planetary age, characterized by a planetary consciousness and a need to confront planetary challenges such as global climate change. 1 Arguably, the birth of this planetary age, what Alexander Geppert has 1 The number of texts articulating this perspective is literally overwhelming. An incomplete selection might include
A Palladium-Catalyzed Oxa-(4+4)-Cycloaddition Strategy Towards Oxazocine Scaffolds
No full textInternational audiencePd-catalyzed oxa-(4+4)-cycloaddition between 1-azadienes and (2-hydroxymethyl)allyl carbonates is described. Aurone-derived azadienes furnished polycyclic 1,5-oxazocines in good yields. Interestingly, linear azadienes have also been involved and yielded monocyclic heterocycles with complete regioselectivity. DFT calculations were carried out to gain insight on this observation
Model Predictive Control as an Industrially Applicable Approach for Power Control of Solid Oxide Fuel Cells
No full textInternational audienceIn this paper, a model predictive control (MPC) combined with a discrete-time stationary Kalman filter as an observer for non-measureable states and input disturbances is presented as a simple and industrially applicable approach for controlling the electric power of a solid oxide fuel cell (SOFC). The developed controller was tested in a simulation in terms of its robustness under consideration of model uncertainties and measurement noise. The results were compared with a PI output-feedback controller combined with a feedforward control and an internal model control (IMC). For the MPC the framework conditions are equal to the PI controller and the IMC. Since these conditions can be reproduced by simulations, we can omit a rerun of the experiments. As a result, the MPC provides comparable results and presents as the better of the two alternative controllers
Confidence-based Contractor, Propagation and Potential Clouds for Differential Equations
No full textInternational audienceA novel interval contractor based on the confidence assigned to a random variable is proposed in this paper. It makes possible to consider at the same time an interval in which the quantity is guaranteed to be, and a confidence level to reduce the pessimism induced by interval approach. This contractor consists in computing a confidence region. Using different confidence levels, a particular case of potential cloud can be computed. As application, we propose to compute the reachable set of an ordinary differential equation under the form of a set of confidence regions, with respect to confidence levels on initial value
Inducing strong convergence of trajectories in dynamical systems associated to monotone inclusions with composite structure
No full textInternational audienceAbstract In this work we investigate dynamical systems designed to approach the solution sets of inclusion problems involving the sum of two maximally monotone operators. Our aim is to design methods which guarantee strong convergence of trajectories towards the minimum norm solution of the underlying monotone inclusion problem. To that end, we investigate in detail the asymptotic behavior of dynamical systems perturbed by a Tikhonov regularization where either the maximally monotone operators themselves, or the vector field of the dynamical system is regularized. In both cases we prove strong convergence of the trajectories towards minimum norm solutions to an underlying monotone inclusion problem, and we illustrate numerically qualitative differences between these two complementary regularization strategies. The so-constructed dynamical systems are either of Krasnoselskiĭ-Mann, of forward-backward type or of forward-backward-forward type, and with the help of injected regularization we demonstrate seminal results on the strong convergence of Hilbert space valued evolutions designed to solve monotone inclusion and equilibrium problems
SocialAI: Benchmarking Socio-Cognitive Abilities in Deep Reinforcement Learning Agents
No full textBuilding embodied autonomous agents capable of participating in social interactions with humans is one of the main challenges in AI. Within the Deep Reinforcement Learning (DRL) field, this objective motivated multiple works on embodied language use. However, current approaches focus on language as a communication tool in very simplified and non-diverse social situations: the "naturalness" of language is reduced to the concept of high vocabulary size and variability. In this paper, we argue that aiming towards human-level AI requires a broader set of key social skills: 1) language use in complex and variable social contexts; 2) beyond language, complex embodied communication in multimodal settings within constantly evolving social worlds. We explain how concepts from cognitive sciences could help AI to draw a roadmap towards human-like intelligence, with a focus on its social dimensions. As a first step, we propose to expand current research to a broader set of core social skills. To do this, we present SocialAI, a benchmark to assess the acquisition of social skills of DRL agents using multiple grid-world environments featuring other (scripted) social agents. We then study the limits of a recent SOTA DRL approach when tested on SocialAI and discuss important next steps towards proficient social agents. Videos and code are available at https://sites.google.com/view/socialai
Optimization of Acoustic Communication Links for a Swarm of AUVs: The COMET and NEMOSENS Examples
No full textInternational audienceUnderwater acoustic communication is a key point for performance improvement in an autonomous underwater vehicle (AUV) swarm. The communication process is essential for improving the AUVs localization accuracy for navigation and is a convenient way for sharing information among the AUVs in a network. The objective of this work, which was developed in the COMET and NEMOSENS projects, is to address the communication process required in a mobile underwater wireless network, with a focus on the proposal of an adaptive physical layer methodology. We discuss about the employed channel access method, the frame structure, and we propose the usage of an adaptive guard interval in order to ameliorate the network usage rate. We explain the physical layer aspect of the communication: the data processing at the transmitter and receiver side. In addition to that, we propose the usage of smart communications among AUVs. We design a method for adapting some physical layer parameters. The proposed approach relies only on the knowledge of the transmission geometry, and it optimizes the number of subcarriers and the cyclic-prefix length of the Orthogonal Frequency-Division Multiplexing (OFDM) system. The obtained results show a performance improvement in terms of bit-error rate when compared with the case of random parameters selection. These results corroborate the benefits of our adaptive parameters approach
Analysis, improvement and limits of the multiscale Latin method
No full textInternational audienceThis work studies the convergence properties of the mixed non-overlapping domain decomposition method (DDM) commonly named "Latin method". As all DDM, the Latin method is sensitive to nearinterface heterogeneity and irregularity. Using a simple yet fresh point of view, we analyze the role of the Robin parameters as well as of the second level (coarse space) correction-which are a characteristic of the method. In particular, we show how to build a spectrum-motivated coarse space aiming at ensuring fast convergence. 2D and 3D linear elasticity problems involving highly heterogeneous materials confirm the robustness of the spectral coarse space and provide evidence of the scalability of the multiscale Latin method
A continuation method for building invisible obstacles in waveguides
No full textInternational audienceWe consider the propagation of acoustic waves at a given wavenumber in a waveguide which is unbounded in one direction. We explain how to construct penetrable obstacles characterized by a physical coefficient ρ which are invisible in various ways. In particular, we focus our attention on invisibility in reflection (the reflection matrix is zero), invisibility in reflection and transmission (the scattering matrix is the same as if there were no obstacle) and relative invisibility (two different obstacles have the same scattering matrix). To study these problems, we use a continuation method which requires to compute the scattering matrix S(ρ) as well as its differential with respect to the material index dS(ρ). The justification of the method also needs for the proof of abstract results of ontoness of well-chosen functionals constructed from the terms of dS(ρ). We provide a complete proof of the results in monomode regime when the wavenumber is such that only one mode can propagate. And we give all the ingredients to implement the method in multimode regime. We end the article by presenting numerical results to illustrate the analysis