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Experimental Procedures for Mixed-Mode Fracture Testing of Bonded Beams Using a Dual-Actuator Load Frame
No full textInternational audienceExperimental Procedures for Mixed-Mode Fracture Testing of Bonded Beams Using a Dual-Actuator Load Fram
Comportement des plaques minces en aluminium 2024-T3 sous l'effet du souffle
No full textInternational audienceComportement des plaques minces en aluminium 2024-T3 sous l'effet du souffl
Radar Echo Simulation of Offshore Wind Turbines at X-Band
No full textInternational audienceOffshore wind turbines are problematic for radar detection due to their large Radar Cross Section (RCS) and micro-Doppler signature, and the multiple scattering path caused by the sea surface. These problems hinder the growth of wind farms and thus our ability to combat climate change. In this paper, we build a model based on Physical Optics (PO) and an improved four-path model, which takes the sea surface randomness into account, using the K-distribution. These methods are chosen as a compromise between model realism and computational efficiency. The proposed model is then applied to an offshore wind turbine observed by an X-band radar: its monostatic RCS and its micro-Doppler signature are computed and analyzed. The obtained results are compared to similar ones obtained at lower frequencies, and show good agreement with both measurements and simulation results at lower frequencies. Emphasis is placed on the impact of the sea surface on the signal scattered by the wind turbine, and on the impact of the high frequency on the model
Vers une version verifiable de l'algorithme SCVx fondé sur la programmation linéaire
No full textInternational audienceINTRODUCTIONMany solutions for real-time embedded trajectory generation rely on model predictive control (MPC) and so various optimization solvers, including linear programming (LP), quadratic programming (QP),and second-order cone programming (SOCP). Recent developments have introduced lightweight first-order methods, like proportional integral projected gradient (PIPG) method [1, 2], which are suitable for embedded systems but face challenges related to projection functions. Other approaches leverage second-order properties, such as the SOCP embedded conic solver (ECOS) [3], which performs well for small to medium-sized problems. However, in both cases, formal verification remains a concern due to the complex mathematical proofs required for convergence.Recent advancements in formal verification and optimization techniques facilitate the development of safe algorithms. Cohen et al.[4] introduced a formal verification framework for optimization algorithms using the interior point method (IPM) and the Ellipsoid algorithm in case of linear programming. In trajectory generation, where problems can often be reduced to convex forms, linear programming-based methods are particularly relevant.The Frank-Wolfe algorithm [5] is a notable projection-free first-order optimization method that iteratively engages with a linear minimization oracle-based (LMO) on the objective function's gradient. Using Frank-Wolfe algorithm in SCVX algorithm may make possible to apply formal verification. This would be relevant only if the efficiency of the result FW-SCVX algorithm is preserved.</div
A discrete dual finite volume method for the convection-diffusion equation: toward cold-plasma modeling
No full textInternational audienceTo model cold plasma one needs to solve a system of convection-diffusion and Poisson equations as [3]. In [1], we proposed a discrete dual finite volume (DDFV) method to solve the Poisson equation with non-homogeneous jump conditions. This work is thus devoted to solving the convection-diffusion equation, in the framework of [2], using a self-consistent DDFV scheme to then apply it to cold-plasma modeling. Contrary to [2], mixed boundary conditions, and both the steady-state and time varying equations are studied. Numerical tests are proposed to show the convergence rate of the method in different configurations
On the structuration and composition of decision problems: a systemic approach to rollbacks
No full textInternational audienceFollowing Maier principles, system of systems are composed of constituent systems that exhibit together emergent behaviors which cannot be exposed using individually the constituent systems. All constituent systems chosen to realize emergent behaviors are themselves composed of thousands of system elements, which were selected also as a result of decision processes. However, decision making based on specific criteria and decision gates in ISO/IEC 15288:2023 is based on management assumptions rather than formal mathematical formulations. The present paper proposes a mathematical formulation of decision aid composition in systems of systems. Based on the observation that state-of-the-art in decision aid applied mathematics domain could be tackled with system engineering process. Using decision aid, we expose the big picture in architecture selection as a composition of decisions. Through a simple example of a choice to introduce a new technology in an existing air-defence system-ofsystem, a sketch of a decision algebra in system-of-system design holds keys to validation of GO/No GO with quantifyable interests of multiple external stakeholders. Our definitions and axioms are presented as a solid foundation for shaping design spaces in systems with respect to dedicated large industrial consortiums.</div
The algebraic structures of social organizations: the operad of cooperative games
No full textThe main goal of this paper is to settle a conceptual framework for cooperative game theory in which the notion of composition/aggregation of games is the defining structure. This is done via the mathematical theory of algebraic operads: we start by endowing the collection of all cooperative games with any number of players with an operad structure, and we show that it generalises all the previous notions of sums, products and compositions of games considered by Owen, Shapley, von Neumann and Morgenstern, and many others. Furthermore, we explicitly compute this operad in terms of generators and relations, showing that the Möbius transform map induces a canonical isomorphism between the operad of cooperative games and the operad that encodes commutative triassociative algebras. In other words, we prove that any cooperative game is a linear combination of iterated compositions of the 2-player bargaining game and the 2-player dictator games. We show that many interesting classes of games (simple, balanced, capacities a.k.a fuzzy measures and convex functions, totally monotone, etc) are stable under compositions, and thus form suboperads. In the convex case, this gives by the submodularity theorem a new operad structure on the family of all generalized permutahedra. Finally, we focus on how solution concepts in cooperative game theory behave under composition: we study the core of a composite and describe it in terms of the core of its components, and we give explicit formulas for the Shapley value and the Banzhaf index of a compound game.</div
Tropospheric water vapor retrievals by Ground-Based GNSS in Africa: A systematic review
No full textInternational audienceAbstract Tropospheric water vapor is a complex parameter due to its spatial and temporal variability, but it is essential for meteorology and study of climate. Faced with high operating costs and traditional low resolutions, Ground-Based Global Navigation Satellite System (GNSS) is increasingly used for tropospheric water vapor retrieval. From databases and several query strings, this study examines in different ways the evidence-based studies of water vapor retrieval from African Ground-Based GNSS using the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) protocol and specific criteria. 30 articles of empirical studies published between 2000 and June 2024 were analysed in depth vis-a-vis research questions. This Systematic Review (SR) includes a mapping of the selected literature, highlighting the distribution and focus of research efforts across Africa. This SR provides new insights by consolidating the evidence on the various approaches used with African Ground Stations. Water vapor time series obtained from GNSS data show consistency with traditional data sources, particularly for seasonal and diurnal cycles. It also highlights the under-exploited potential of GNSS networks in Africa, limited by uneven geographical coverage and a lack of standardization of methodologies, despite significant progress in atmospheric studies, as well as it highlights the advanced techniques that are under-exploredand proposes future research directions, while calling for closer collaboration between scientists and decision-makers to improve access to GNSS data, promote network interoperability, and explore methodological approaches adapted to Africa’s specific climatic conditions, in order to maximise the applications of GNSS techniques for water vapor retrieval
