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Relaxed-inertial proximal point algorithms for problems involving strongly quasiconvex functions
No full textInternational audienceIntroduced in the 1970's by Martinet for minimizing convex functions and extended shortly afterward by Rockafellar towards monotone inclusion problems, the proximal point algorithm turned out to be a viable computational method for solving various classes of optimization problems, in particular with nonconvex objective functions.We propose a relaxed-inertial proximal point type algorithm for solving optimization problems consisting in minimizing strongly quasiconvex functions whose variables lie in finitely dimensional linear subspaces, that can be extended to equilibrium problems involving such functions. We also discuss possible modifications of the hypotheses in order to deal with quasiconvex functions. Numerical experiments confirm the theoretical results, in particular, that the relaxed-inertial algorithms outperform their ``pure'' proximal point counterparts
High-Harmonic Generation and Correlated Electron Emission from Relativistic Plasma Mirrors at 1 kHz Repetition Rate
No full textInternational audienceWe report evidence for the first generation of XUV spectra from relativistic surface high-harmonic generation (SHHG) on plasma mirrors at a kilohertz repetition rate, emitted simultaneously with energetic electrons. SHHG spectra and electron angular distributions are measured as a function of the experimentally controlled plasma density gradient scale length L_g for three increasingly short and intense driving pulses: 24 fs and a_0 = 1.1, 8 fs and a_0 = 1.6, and finally 4 fs and a_0 ≈ 2.1, where a_0 is the peak vector potential normalized by m_e c/e with the elementary charge e, the electron rest mass m_e , and the vacuum light velocity c. For all driver pulses, we observe correlated relativistic SHHG and electron emission in the range L_g ∈ [λ/20, λ/4], with an optimum gradient scale length of L_g ≈ λ/10. This universal optimal L_g-range is rationalized by deriving a direct intensity-independent link between the scale length L_g and an effective similarity parameter for relativistic laser-plasma interactions
Inconsistent and Incomplete Datasheet: The case for systematic use of requirement engineering
No full textInternational audienceThe lifecycle of a system is extended from its early conception to its retirement of service. The lifespan of Unmanned Ground Vehicles (UGVs) can be expected to last over 50 years in the defense market. In this context, the rising complexity of UGV systems imposes engineering steps that would ensure both capabilities of the system and resilience to its future inclusion in a system-ofsystem context. During its operational usage, the UGV is supposed to be maneuvered for specifically designed purposes following user manual datasheet of the components off-the-shelf (COTS) that were integrated. This paper exposes the public user datasheet relevance compared to the system engineering requirements that are the artifacts of system design architecture. The use of connecting COTS user manual to system requirements is discussed, all the more if the systems are to be re-used in a system production line. This article is intended to explore system of system conception methods for future robotized battlefield
Do Academic Recruitment Policies Under Represent Teaching and Learning Competences?
No full textInternational audienceCDIO standards 9 and 10 focus on the technical and teaching competences of staff delivering engineering education programmes. For most Universities, whether CDIO or otherwise teaching and learning are the key financial and reputational activities which ensure the institution can thrive. To ensure academic degrees can be delivered in a progressive, student centered and active manner such as that championed by CDIO it is essential that staff with the capabilities to deliver and develop strong teaching and learning approaches are recruited and trained. This paper looks at recruitment practices for Engineering academics in the UK and France. It examines how research and teaching criteria are framed in the hiring process examining recruitment advertisements and job details to examine both the numbers and types of terms used to describe these two types of core academic activities. This tends to show that, while anecdotally it has always been reported, for many of the more established Universities there is a significantly greater emphasis on research over teaching competences though the picture is not uniform and while the picture in France and the UK overall is similar the degree of emphasis of research over teaching in France appears lower
Relaxed-Inertial Proximal Point Type Algorithms for Quasiconvex Minimization
No full textInternational audienceWe propose a relaxed-inertial proximal point type algorithm for solving optimization problems consisting in minimizing strongly quasiconvex functions whose variables lie in finitely dimensional linear subspaces. A relaxed version of the method where the constraint set is only closed and convex is also discussed, and so is the case of a quasiconvex objective function. Numerical experiments illustrate the theoretical results
Lie symmetries applied to interval integration
No full textInternational audienceIn this paper, we propose a new approach for improving significantly existing guaranteed integration methods for state equations with uncertain initial conditions. We first find a tube that encloses the solution of the differential equation assuming that the initial state is known. Then, using Lie symmetries, we inflate the tube in order to contain the uncertainty associated with the initial state. The method is shown to be efficient on examples coming from reachability analysis and robotics
Une nouvelle implémentation de la méthode perturbative itérative pour la propagation de fissures en fatigue.
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Convergence d'un couplage élastique-acoustique FEM-BEM itératif, global en temps
No full textInternational audienceUne méthode itérative convergente pour le couplage FEM-BEM élastodynamique-acoustique global en temps, permettant de traiter un problème d’interaction fluide-structure est proposée. Les équations structures sont résolues en éléments finis (FEM), tandis que la partie fluide est traitée par éléments de frontière (BEM), formulée en temps discrets par Convolution Quadrature method (CQM). Le couplage présenté se base sur la formulation de conditions de transmission de Robin. La convergence est démontrée et illustrée. Un deuxième couplage itératif en temps à convergence garantie est proposé
Plasticity and evolvability under environmental variability: the joint role of fitness-based selection and niche-limited competition
No full textInternational audienceThe diversity and quality of natural systems have been a puzzle and inspiration for communities studying artificial life. It is now widely admitted that the adaptation mechanisms enabling these properties are largely influenced by the environments they inhabit. Organisms facing environmental variability have two alternative adaptation mechanisms operating at different timescales: \textit{plasticity}, the ability of a phenotype to survive in diverse environments and \textit{evolvability}, the ability to adapt through mutations. Although vital under environmental variability, both mechanisms are associated with fitness costs hypothesized to render them unnecessary in stable environments. In this work, we study the interplay between environmental dynamics and adaptation in a minimal model of the evolution of plasticity and evolvability. We experiment with different types of environments characterized by the presence of niches and a climate function that determines the fitness landscape. We empirically show that environmental dynamics affect plasticity and evolvability differently and that the presence of diverse ecological niches favors adaptability even in stable environments. We perform ablation studies of the selection mechanisms to separate the role of fitness-based selection and niche-limited competition. Results obtained from our minimal model allow us to propose promising research directions in the study of open-endedness in biological and artificial systems
Méthode split-step wavelet pour la propagation troposphérique en 3D
No full textInternational audiencePour des systèmes électromagnétiques, comme le radar, il est important de modéliser précisément la propagation sur de longues distances en tenant compte des effets de l'environnement. Une méthode répandue dans ce contexte est basée sur la résolution de l'équation parabolique par split-step Fourier (SSF). Cependant, pour des scénarios 3D elle est limitée par son temps de calcul et sa taille mémoire. Récemment, une méthode efficace en temps et mémoire en ondelettes a été proposée en 2D. Dans cet article, nous généralisons la méthode à des scénarios 3D. Nous montrons également qu'elle est de complexité plus faible que SSF. Des tests numériques sont également proposés pour montrer les avantages de la méthode en comparaison de SSF