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Natural product total synthesis, a step toward biological applications
No full textInternational audienc
Imagerie d’interface barrage-fondation par inversion de forme d'onde complète
No full textInternational audienceIn the context of studying the stability of dams, imaging the interface between the dam and the rock is of great importance. Geophysical techniques can provide additional information to geotechnical measurements. Here, a method for processing seismic measurements is presented. The objective is to obtain an image of the interface between the concrete of the dam and the rock of the foundation with metric resolution. The proposed technique is based on "Full Waveform Inversion" with a shape optimization approach. Numerical results using synthetic measurements demonstrate the method's ability to accurately recover the interface with a limited number of measurement points and in the presence of noise.Dans le cadre de l’étude de la stabilité des barrages, la connaissance de l’interface entre le barrage et la roche revêt une grande importance. Le recours à des techniques géophysiques peut apporter des informations complémentaires par rapport aux mesures géotechniques. Nous proposons ici une méthode de traitement des mesures sismiques, l’objectif étant d'obtenir une image de l'interface entre le béton du barrage et le rocher de la fondation avec une résolution métrique. Il s’agit d’une technique de type « Full Waveform Inversion » avec optimisation de forme. Des résultats numériques utilisant des mesures synthétiques montrent la capacité de la méthode à retrouver l'interface avec une précision satisfaisante, pour un nombre limité de points de mesure et en présence de bruit
Generalized impedance boundary conditions with vanishing or sign-changing impedance
No full textInternational audienceWe consider a Laplace type problem with a generalized impedance boundary condition of the form ∂_νu = −∂_x(g∂_xu) on a flat part Γ of the boundary. Here ν is the outward unit normal vector to ∂Ω, g is the impedance function and x is the coordinate along Γ. Such problems appear for example in the modelling of small perturbations of the boundary. In the literature, the cases g=1 or g=−1 have been investigated. In this work, we address situations where Γ contains the origin and g(x)=1_{x>0}(x)x^\alpha or g(x)=−sign(x)|x|^\alpha with \alpha≥ 0. In other words, we study cases where g vanishes at the origin and changes its sign. The main message is that the well-posedness in the Fredholm sense of the corresponding problems depends on the value of \alpha. For \alpha∈ [0,1), we show that the associated operators are Fredholm of index zero while it is not the case when \alpha=1. The proof of the first results is based on the reformulation as 1D problems combined with the derivation of compact embedding results for the functional spaces involved in the analysis. The proof of the second results relies on the computation of singularities and the construction of Weyl's sequences. We also discuss the equivalence between the strong and weak formulations, which is not straightforward. Finally, we provide simple numerical experiments which seem to corroborate the theorems
Synthesis of photoactivatable molecules for the spatiotemporal control of cell motility with light
No full textInternational audienc
The experience of albinism in France: a qualitative study on dyads of parents and their adult child with albinism
No full textInternational audienceTo date, almost no research on the psychosocial implications of albinism has been conducted in France and an exploration of albinism-related experiences could be beneficial, in order to better understand this condition. The aim of this study was to examine how French people with albinism and their parents live with and adapt to this condition in all the areas of their lives. Semi-structured phone interviews were conducted with 9 parent-child dyads, each participating separately. Participants were recruited by convenience sampling, thanks to the combined efforts of a patient association (Genespoir) and professionals from the partner medical referral centers involved in the project. Dyads in which the individual with albinism had any comorbidity were excluded. The interviews were then transcribed and subjected to in-depth thematic analysis. Two codebooks were constructed in a mirrored process: one for people with albinism; the other for their parents. They were finally merged at the end of the coding step. Four main categories were identified: personal perceptions and social representations of albinism, difficulties and obstacles encountered by people with albinism, resources and facilitators, and the importance of parent-child functioning. The results indicated that experiences of stigmatization during childhood and adolescence are common and that people with albinism face challenges in adapting to certain obstacles related to their visual impairments (VI) (e.g., inability to drive a car; eye strain...). Parents emerged as one, if not as the main, source of support for people with albinism throughout their development. Although external support systems exist to assist them in various aspects of their lives, some of them primarily rely on their own personal resources to cope. This research highlights the importance of a systemic and transdisciplinary approach to make sure families receive the support that best meets their needs
Bi-objective finite horizon optimal control problems with Bolza and maximum running cost
No full textIn this paper, we investigate optimal control problems with two objective functions of different nature that need to be minimized simultaneously. One objective is in the classical Bolza form and the other one is defined as a maximum running cost. Our approach is based on the Hamilton-Jacobi-Bellman framework. In the problem considered here the existence of Pareto solutions is not guaranteed. So first, we consider the bi-objective problem to be minimized over the convexified dynamical system. We show that if a vector is (weak) Pareto optimal solution for the convexified problem, then there exists an (weak) ε-Pareto optimal solution of the original problem that is in the neighborhood of this vector. After we define an auxiliary optimal control problem and show that the weak Pareto front of the convexified problem is a subset of the zero level set of the corresponding value function. Moreover, with a geometrical approach we establish a characterization of the Pareto front. It is also proved that the (weak) ε-Pareto front is contained in the negative level set of the auxiliary optimal control problem that is less or equal ε. Some numerical examples are considered to show the relevance of our approach
VISCOSITY SOLUTIONS OF HAMILTON-JACOBI EQUATIONS IN PROPER CAT(0) SPACES
No full textInternational audienceIn this article, we develop a novel notion of viscosity solutions for first order Hamilton-Jacobi equations in proper CAT(0) spaces. The notion of viscosity is defined by taking test functions that are directionally differentiable and can be represented as a difference of two semiconvex functions. Under mild assumptions on the Hamiltonian, we recover the main features of viscosity theory for both the stationary and the time-dependent cases in this setting: the comparison principle and Perron's method. Finally, we show that this notion of viscosity coincides with classical one in R N and we give several examples of Hamilton-Jacobi equations in more general CAT(0) spaces covered by this setting
Improved Performances and Motivation in Intelligent Tutoring Systems: Combining Machine Learning and Learner Choice
No full textLarge class sizes pose challenges to personalized learning in schools, which educational technologies, especially intelligent tutoring systems, aim to address. In this context, the ZPDES algorithm, based on the Learning Progress Hypothesis (LPH) and multi-armed bandit AI techniques, sequences exercises that maximize learning progress for each student. Previous field studies showed its learning efficacy compared to a hand-designed curriculum. However, its motivational impact was not assessed. Also, ZPDES did not allow students to express choices: this limitation in agency conflicts with LPH as a model of curiosity-driven learning. We study here how introducing choice (on dimensions orthogonal to exercise difficulty, acting as gamification) impacts both learning efficiency and motivation. We present an extensive field study (265 7-8 years old children, RCT design) showing that ZPDES indeed improves learning performance but also produces a positive learning experience. Combining choice with ZPDES triggers intrinsic motivation and reinforces the learning effectiveness of the LP-based personalization. Conversely, adding choice possibilities to a handdesigned linear pedagogical paths produces deleterious effects on learning. Thus, the intrinsic motivation elicited by choice (gamification) is beneficial only if the curriculum is personalized efficiently for the learner. This deserves attention due to increased use of playful features in educational technologies
Relaxed-Inertial Proximal Point Algorithms for Nonconvex Equilibrium Problems with Applications
No full textInternational audienceWe propose a relaxed-inertial proximal point algorithm for solving equilibrium problems involving bifunctions which satisfy in the second variable a generalized convexity notion called strong quasiconvexity, introduced by Polyak in 1966. The method is suitable for solving mixed variational inequalities and inverse mixed variational inequalities involving strongly quasiconvex functions, as these can be written as special cases of equilibrium problems. Numerical experiments where the performance of the proposed algorithm outperforms the one of the standard proximal point methods are provided, too
Radial perfectly matched layers and infinite elements for the anisotropic wave equation
No full textWe consider the scalar anisotropic wave equation. Recently a convergence analysis for radial perfectly matched layers (PML) in the frequency domain was reported and in the present article we continue this approach into the time domain. First we explain why there is a good hope that radial complex scalings can overcome the instabilities of PML methods caused by anisotropic materials. Next we discuss some sensitive details, which seem like a paradox at the first glance: if the absorbing layer and the inhomogeneities are sufficiently separated, then the solution is indeed stable. However, for more general data the problem becomes unstable. In numerical computations we observe instabilities regardless of the position of the inhomogeneities, although the instabilities arise only for fine enough discretizations. As a remedy we propose a complex frequency shifted scaling and discretizations by Hardy space infinite elements or truncation-free PMLs. We show numerical experiments which confirm the stability and convergence of these methods