Absence of superconductivity in iron polyhydrides at high pressures

Recently, C. M. Pépin et al. [Science 357, 382 (2017)] reported the formation of several new iron polyhydrides FeHx at pressures in the megabar range and spotted FeH5, which forms above 130 GPa, as a potential high-Tc superconductor because of an alleged layer of dense metallic hydrogen. Shortly after, two studies by A. Majumdar et al. [Phys. Rev. B 96, 201107 (2017)] and A. G. Kvashnin et al. [J. Phys. Chem. C 122, 4731 (2018)] based on ab initio Migdal-Eliashberg theory seemed to independently confirm such a conjecture. We conversely find, on the same theoretical-numerical basis, that neither FeH5 nor its precursor, FeH3, shows any conventional superconductivity and explain why this is the case. We also show that superconductivity may be attained by transition-metal polyhydrides in the FeH3 structure type by adding more electrons to partially fill one of the Fe-H hybrid bands (as, e.g., in NiH3). Critical temperatures, however, will remain low because the d-metal bonding, and not the metallic hydrogen, dominates the behavior of electrons and phonons involved in the superconducting pairing in these compounds

Developing an enterprising spirit among engineering college students : what are the educational factors ?

The purpose of this chapter is to further what can be called the Entrepreneurial Spirit. Indeed these words, although widely used, have not yet been properly defined in the literature as to how it is created, and what precise aspects can be enhanced through teaching activities. It is a matter of suggesting hypotheses in order to build up a model of how an Entrepreneurial Spirit is engendered among newly trained engineers. Our chapter is divided into four section. The first deals with the question of the definition of the Entrepreneurial Spirit: How does it arise prior to the decision to set up a business? How can the components of an Entrepreneurial Spirit be defined? We suggest a dynamic model. The second section deals with the factors leading to an Entrepreneurial Spirit among young engineers: What is the relevance of the educational background ? What are the possible teaching method variables within engineering college training? The third section presents methodological features of our research. The fourth section presents early results about the projective dimensions of our model of engineering students in 2004. As a conclusion, we present theoretical and practical implications of our research.entreprising spirit, entrepreneurship education

SIDRA: a blind algorithm for signal detection in photometric surveys

We present the Signal Detection using Random-Forest Algorithm (SIDRA). SIDRA is a detection and classification algorithm based on the Machine Learning technique (Random Forest). The goal of this paper is to show the power of SIDRA for quick and accurate signal detection and classification. We first diagnose the power of the method with simulated light curves and try it on a subset of the Kepler space mission catalogue. We use five classes of simulated light curves (CONSTANT, TRANSIT, VARIABLE, MLENS and EB for constant light curves, transiting exoplanet, variable, microlensing events and eclipsing binaries, respectively) to analyse the power of the method. The algorithm uses four features in order to classify the light curves. The training sample contains 5000 light curves (1000 from each class) and 50000 random light curves for testing. The total SIDRA success ratio is $\geq 90\%$. Furthermore, the success ratio reaches 95 - 100$\%$ for the CONSTANT, VARIABLE, EB, and MLENS classes and 92$\%$ for the TRANSIT class with a decision probability of 60$\%$. Because the TRANSIT class is the one which fails the most, we run a simultaneous fit using SIDRA and a Box Least Square (BLS) based algorithm for searching for transiting exoplanets. As a result, our algorithm detects 7.5$\%$ more planets than a classic BLS algorithm, with better results for lower signal-to-noise light curves. SIDRA succeeds to catch 98$\%$ of the planet candidates in the Kepler sample and fails for 7$\%$ of the false alarms subset. SIDRA promises to be useful for developing a detection algorithm and/or classifier for large photometric surveys such as TESS and PLATO exoplanet future space missions.Comment: 8 pages, 9 figures, 2 Table

Designing Expression Templates with Concepts

International audienceConcepts are likely to be introduced in a future C++ standard. They can be used for constraining template parameters, which enables checking requirements on template parameters sooner in the compilation process, and thus providing more intelligible error messages to the user.They can also be used in the specialization of templates, thus leading to a better control over the selection of the most appropriate version of a template for a given instantiation. This latter aspect offers new possibilities in the design of template libraries, as it enhances the specialization mechanism of templates, and set it up as a solid alternative to inheritance when static binding can replace dynamic binding.This report addresses the design of expression templates (i.e. templates that represent expressions and are usually built through operator overloading) that are useful to develop an embedded domain specific language (EDSL), and can speed up the evaluation of an expression by delaying the evaluation of intermediate operations to avoid unnecessary temporary objects.We propose to use concept-based template specialization to parse expression templates in order to ease the design of an EDSL. This approach is a static variant of the well-known visitor design pattern that replaces the overridden methods in the double dispatch of the original design pattern by template specializations based on concepts. An example of EDSL for linear programming developed with our solution demonstrates that a concept-based design helps producing concise and reliable code

L'acquisition du vocabulaire à l'école maternelle

À l'école maternelle, en petite et moyenne sections, les élèves doivent acquérir un bagage lexique minimal. Comment favoriser cette acquisition du vocabulaire chez les P.S. et M.S. ? Et, plus précisément, est-ce que les nombreuses réitérations, le lien avec le vécu quotidien des élèves et la diversité des activités spécifiques proposées sont des paramètres qui facilitent l'acquisition du vocabulaire des vêtements en petite et moyenne sections ? Telles sont notre problématique et notre hypothèse. Au cours de ce dossier, nous nous efforcerons de répondre à ces questions à travers une séquence sur le vocabulaire des vêtements. En effet, notre dispositif d'apprentissage met en œuvre des séances spécifiques et des réinvestissements transversaux tout en variant les situations de travail pour favoriser l'implication des élèves. Cette séquence d'enseignement est encadrée par deux évaluations dont la comparaison des résultats a permis de valider globalement notre hypothèse tout en montrant certaines limites