Le moteur de recherche et les collégiens : quelles représentations, quels obstacles, quelle didactisation ?

Search engines are nowadays one of the daily tools used by secondary-school pupils in need for information. Still, this notion remains poorly managed and very few pupils are actually able to explain what a search engine is and how it works. This lack of clarity may find its roots in the lack of time granted in the curriculums, along with the wrong pictures pupils may have in mind about it. Once those wrong pictures are identified, we can have a better view of the difficulties pupils are confronted with. Using those difficulties as a starting point, a work on a teaching approach can thus be initiated. To this end, we collected data thanks to a field study consisting of a survey completed by 96 pupils and eight semi-guided interviews. Conceptual confusion, a lack of critical distance regarding the tool as well as the inability to explain how it works and strong but wrong beliefs about the topic were brought to light. Once those difficulties in the understanding of the concept of search engines were clearly identified, we were able to build up and propose teaching strategies supported by the theoretical contributions of researchers in the fields of information and communication science and experts in information and documentation.Les moteurs de recherche font désormais partie des outils informationnels utilisés quotidiennement par les collégiens. Cependant, cette notion reste mal maîtrisée et très peu d’élèves sont en fait capables d’expliquer ce qu’est un moteur de recherche et comment il fonctionne. Ce flou conceptuel trouve ses origines dans le peu de place qu’accorde l’institution scolaire à cette notion dans les programmes mais également dans les conceptions que les élèves ont construites sur ce sujet. Celles-ci sont particulièrement intéressantes car une fois identifiées, elles permettent de repérer les obstacles auxquels les élèves sont confrontés. Un travail de didactisation peut alors s’engager en partant de ces obstacles. Dans cette optique, nous avons collecté des données lors d’une enquête de terrain auprès de 96 collégiens à travers un questionnaire et huit entretiens semi-directifs. Des confusions conceptuelles, un manque de recul critique face à l’outil, une incapacité à expliquer son fonctionnement et la présence de fortes conceptions explicatives erronées ont ainsi été mises au jour. Une fois ces difficultés dans l’appropriation de la notion « moteur de recherche » clairement mises en lumière, nous avons pu élaborer une proposition de didactisation en nous appuyant sur les apports théoriques de chercheurs en Sciences de l’information et de la communication et de spécialistes de l’information-documentation

Prediction of thermal radiative properties (300–1000 K) of La2NiO4+δ ceramics.

A multiscale numerical model is developed to predict the thermal radiative properties (TRP) of rough La2NiO4+δ coatings. The model integrates intrinsic and extrinsic contributions related to the chemical composition and the texture, respectively. High-temperature infrared reflectivity and thermogravimetric measurements on a La2NiO4+δ single crystal make it possible to understand the role of the excess oxygen in the intrinsic TRP. We show that dense ceramics with thicknesses higher than 4 μm are optically thick, and that one can adjust the surface roughness parameters to predict their TRP

Bridging the gap between particle-scale forces and continuum modelling of size segregation: application to bedload transport

Gravity-driven size segregation is important in mountain streams where a wide range of grain sizes are transported as bedload. More particularly, vertical size segregation is a multi-scale process that originates in interactions at the scale of particles with important morphological consequences on the reach scale. To address this issue, a volume-averaged multi-phase flow model for immersed bidisperse granular flows was developed based on an interparticle segregation force (Guillard et al. 2016) and a granular Stokesian drag force (Tripathi and Khakhar 2013). An advection-diffusion model was derived from this model yielding parametrisations for the advection and diffusion coefficients based on the interparticle interactions. This approach makes it possible to bridge the gap between grain-scale physics and continuum modelling. Both models were successfully tested against existing Discrete Element Model (DEM) simulations of size segregation in bedload transport (Chassagne et al. 2020). Through a detailed investigation of the granular forces, it is demonstrated that the observed scaling of the advection and diffusion coefficients with the inertial number can be explained by the granular drag force dependency on the viscosity. The drag coefficient was shown to be linearly dependent on the small particle concentration. The scaling relationship of the segregation force with the friction coefficient is confirmed and additional non-trivial dependencies including the inertial number and small particle concentration are identified. Lastly, adding a size ratio dependency in the segregation force perfectly reproduces the DEM results for a large range of small particle concentrations and size-ratios

Probing DNA conformational changes with high temporal resolution by Tethered Particle Motion

The Tethered Particle Motion (TPM) technique informs about conformational changes of DNA molecules, e.g. upon looping or interaction with proteins, by tracking the Brownian motion of a particle probe tethered to a surface by a single DNA molecule and detecting changes of its amplitude of movement. We discuss in this context the time resolution of TPM, which strongly depends on the particle-DNA complex relaxation time, i.e. the characteristic time it takes to explore its configuration space by diffusion. By comparing theory, simulations and experiments, we propose a calibration of TPM at the dynamical level: we analyze how the relaxation time grows with both DNA contour length (from 401 to 2080 base pairs) and particle radius (from 20 to 150~nm). Notably we demonstrate that, for a particle of radius 20~nm or less, the hydrodynamic friction induced by the particle and the surface does not significantly slow down the DNA. This enables us to determine the optimal time resolution of TPM in distinct experimental contexts which can be as short as 20~ms.Comment: Improved version, to appear in Physical Biology. 10 pages + 10 pages of supporting materia

Global Perturbation of Initial Geometry in a Biomechanical Model of Cortical Morphogenesis

Cortical folding pattern is a main characteristic of the geometry of the human brain which is formed by gyri (ridges) and sulci (grooves). Several biological hypotheses have suggested different mechanisms that attempt to explain the development of cortical folding and its abnormal evolutions. Based on these hypotheses, biomechanical models of cortical folding have been proposed. In this work, we compare biomechanical simulations for several initial conditions by using an adaptive spherical parameterization approach. Our approach allows us to study and explore one of the most potential sources of reproducible cortical folding pattern: the specification of initial geometry of the brain.Comment: 4 pages 2 columns (IEEE style), 41st EMB Conferenc

Spatial variability of soil lipids reflects vegetation cover in a French peatland

International audienceThe purpose of this study was to show how current vegetation in a peatland is imprinted in the lipid fraction of the underlying soil. La Guette is a fen peatland in Central France dominated by Sphagnum spp. and ericaceous shrubs, colonized by sedges (Molinia caerulea) and trees since the 1970s (Betula pendula and Pinus sylvestris). Lipid were identified and quantified in the most abundant plants and in samples collected at the base of M. caerulea tussocks. Among relevant biomarkers, tricyclic diterpenes and methoxy-serratenes stood out as specific for P. sylvestris, betulin derivatives as specific for B. pendula, and some pentacyclic triterpene ketones and acetates as biomarkers of Ericaceae. Multivariate analysis applied to biomarker concentration in soil samples from several sites permitted distinguishing three different vegetation types: vegetation cover: (i) closed vegetation dominated by P. sylvestris; (ii) closed vegetation dominated B. pendula and (iii) open vegetation or semi-open vegetation (early colonization by trees) constituted mainly by Ericaceae, Sphagnum and graminoids. Comparison of tree-specific biomarker concentrations with estimates of tree biomass allowed establishing of quantitative relationships that were valid over at least 80 m2 around the sampling site. Although preliminary, the results are promising in attempting to relate biomarker concentrations in geological archives to paleo-biomass

SPECTRAL CLUSTERING BASED PARCELLATION OF FETAL BRAIN MRI

Many neuroimaging studies are based on the idea that there are distinct brain regions that are functionally or micro-anatomically homogeneous. Obtaining such regions in an au-tomatic way is a challenging task for fetal data due to the lack of strong and consistent anatomical features at the early stages of brain development. In this paper we propose the use of an automatic approach for parcellating fetal cerebral hemi-spheric surfaces into K regions via spectral clustering. Unlike previous methods, our technique has the crucial advantage of only relying on intrinsic geometrical properties of the corti-cal surface and thus being unsupervised. Results on a data-set of fetal brain MRI acquired in utero demonstrated a convinc-ing parcellation reproducibility of the cortical surfaces across fetuses with varying gestational ages and folding magnitude

Simulation de travail en hauteur en réalité mixte : étude de la présence et de l'anxiété

Dans cet article, nous proposons d'évaluer la performance d'un simulateur immersif de travail en hauteur en réalité mixte, en termes de sentiment de présence et de répercussion sur le sentiment d'anxiété liée à la hauteur. Le simulateur consiste en une échelle réelle fixée sur un support et synchronisée en position avec une échelle virtuelle placée à 11 mètres de hauteur sur un poteau électrique. La visualisation de l'environnement virtuel se fait à travers un casque immersif. Deux modalités ont été intégrées et comparées : l'une avec affichage de pieds et mains virtuels synchronisés en position avec les pieds et mains réels des utilisateurs, l'autre sans affichage des pieds et mains virtuels. Vingt-six sujets âgés de 22 à 55 ans ont pris part à une étude utilisateur pour la réalisation d’une simulation de tâche en hauteur, séparés en deux groupes, l'un avec la première modalité visuelle, l'autre avec la seconde. Le niveau d'anxiété est mesuré par leur activité électrodermale, tandis que la présence est mesurée à travers un questionnaire. Les résultats montrent que le simulateur est performant en termes de présence et d'anxiété qu'il génère chez des personnes ayant le vertige. L'apport visuel des mains et pieds virtuels dans ce contexte n'apparaît pas significatif sur le sentiment de présence. Ce simulateur ouvre des perspectives intéressantes pour une utilisation comme outil de prévention, de détection d’acrophobie de futurs travailleurs en hauteur ou de formation.Enedis Bourgogn

A Virtual Reality Simulator to Detect Acrophobia in Work-at-Height Situations

We propose to demonstrate a novel immersive virtual reality simulator aimed at detecting whether potential workers at height are able to climb high up for dangerous operations. Our simulator consists in a dynamic platform that simulates the vibrations of an aerial device during elevation, a real ladder synchronized in position with a virtual one placed on top of a virtual electric pole, a harness that allows users safely climbing the ladder and a head-mounted display (HMD) for visualization. Our demonstration invites users to experience a high fidelity work-at-height situation triggering fear of heights.Enedis Bourgogn