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Analysis of Students' Attempts Trajectories in Learning Programming
No full textInternational audienceThe aim of this paper is to provide tools to teachers for monitoring student work and understanding practices in order to help student and possibly adapt exercises in the future. In the context of an online programming learning platform, we propose to study the attempts (i.e., submitted programs) of the students for each exercise by using trajectory visualisation and clustering. To track the progress of students while performing exercises, we build numerical representations (embeddings) of their programs, generate the trajectories of these attempts (i.e., the sequence of their attempts) and provide an intuitive visualization of them. The advantage of these representations is to capture syntactic and semantic information that can be used to identify similar practices. In order to describe these practices, we perform a clustering of these attempts and generate a description of each cluster based on the common instructions of the underlying programs. By studying a student's trajectory for an exercise, the teacher can detect if the student is in difficulty and help him. Our approach can also highlight atypical solutions such as alternative solutions or unwanted solutions. In the experiments, we study the impact of using embeddings to identify common practices on two real datasets. We also present a comparison of different dimension reduction methods (PCA, t-SNE, and PaCMAP) for the purpose of visualization. The experimental results show that code embeddings improve results compared to a classical approach, and that PCA and t-SNE are the most suitable for visualization
Assessing spin-flip time-dependent density-functional-based tight-binding for describing Z/E photoisomerization reactions
No full textInternational audiencePhotoisomerisation of molecular systems are important as building blocks for light driven molecular motors. Understanding the effect of chemical substitution on the underlying mechanisms and the isomerisation quantum yields is crucial for optimizing their functionality. In this study, we develop, implement and evaluate the performance of the spin-flip time-dependent density-functional based tight-binding (SF-TDDFTB) as a cost-effective approach for simulating the excited-state potential energy surfaces of several photoisomerising chromophores. By comparing the results with SF-TDDFTB with all-electron MRSF-TDDFT, we investigate the accuracy of the tight-binding formalism in capturing the correct potential energy surface leading to the photoisomerization pathways for well-known photoisomerisation reactions of a protonated Schiff base, an oxidondole molecular motor, the green fluorescent protein chromophore and a photodrug. Our findings demonstrate that the SF-TDDFTB method offers a balanced trade-off between computational efficiency and accuracy. These results pave the way for more efficient computational models for studying the photoisomerisation reactions of complex molecular systems.</div
Отклик Эрнеста Ренана в стихотворении «Отравлен хлеб и воздух выпит» Мандельштама
No full textInternational audienceIn his poem “The bread is poisoned and the air’s drunk dry” Mandelstam proceeds from Biblical antiquity (Joseph sold by his brothers) to the description of the most ancient poetry of Pre-Islamic Arabs, which the poet mentions as an archetype of circumstances poetry. In this metapoetic description of the primeval Arabic poetry even before the Jāhiliyyah, it is possible to perceive a reminiscence of what Ernest Renan wrote about the Arabic poetry in his Histoire générale et système comparé des langues sémitiques. As a result of a free association of ideas the young Osip Mandelstam identified himself with the eponymic figure of Joseph. Likewise the relation between the Madianite caravan to which Joseph was sold and Pre-Islamic Beduins is based on the fact that in Genesis 37:28 the Madianites are described as “Ismaelites”, an ethnonym that can also refer to the ancient Arabs. In this way, Mandelstam represents his poetic I not only as a paradigmatic Joseph but also as a beduin poet
Hypnose et Neurosciences. Volume I : les fondamentaux (fiche de lecture)
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Microbial biomass – not diversity – drives soil carbon and nitrogen mineralization in Spanish holm oak ecosystems
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System Design Using Sensor Compression and Grey Wolf Optimizer for AI-based Security Applications
No full textInternational audienceThe security of public spaces is a major concern. In particular, there is a need for compact and non invasive concealed threat detection systems. In this paper, we investigate the reduction of the number of sensors using a joint design scheme involving the number of antennas and the Support Vector Machine (SVM) classification algorithm. We have developed a joint optimization that combines a bio-inspired optimized method, called Grey Wolf Optimizer, and the Run-Length Encoding (RLE) compression method. Results are compared to a reference case using 22,801 sensors. The classification performance reaches 75%, with specificity and sensitivity (that account for lethal objects) values of 66% and 83%, respectively. The optimized system reduces the number of sensors to 2,818 with an overall detection performance of 79%. A sub-sampling method further reduces the system to 1,038 sensors, achieving 100% sensitivity, guaranteeing detection of all concealed threats
Etude expérimentale de la convection dans une fine couche de gaz cylindrique avec flux imposés en bas et en haut et une température latérale fixée.
No full textInternational audienceWe investigate convection in a thin cylindrical gas layer with an imposed flux at the bottom and a fixed temperature along the side, using a combination of direct numerical simulations and laboratory experiments. The experimental approach allows us to extend by two orders of magnitude the explored range in terms of flux Rayleigh number. We identify a scaling law governing the root-mean-square horizontal velocity and explain it through a dimensional analysis based on heat transport in the turbulent regime. Using particle image velocimetry, we experimentally confirm, for the most turbulent regimes, the presence of a drifting persistent pattern consisting of radial branches, as identified by Rein et al. (2023, J. Fluid Mech. 977 , A26). We characterise the angular drift frequency and azimuthal wavenumber of this pattern as functions of the Rayleigh number. The system exhibits a wide distribution of heat flux across various time scales, with the longest fluctuations attributed to the branch pattern and the shortest to turbulent fluctuations. Consequently, the branch pattern must be considered to better forecast important wall heat flux fluctuations, a result of great relevance in the context of nuclear safety, the initial motivation for our study.Nous étudions la convection dans une fine couche cylindrique de gaz soumise à un flux imposé à la base et une température fixée sur le côté, en combinant des simulations numériques directes et des expériences en laboratoire. L’approche expérimentale nous permet d’étendre de deux ordres de grandeur la gamme explorée en termes de nombre de Rayleigh basé sur le flux. Nous identifions une loi d’échelle gouvernant la vitesse horizontale quadratique moyenne, que nous expliquons par une analyse dimensionnelle fondée sur le transport de chaleur en régime turbulent. Grâce à la vélocimétrie par image de particules, nous confirmons expérimentalement, pour les régimes les plus turbulents, la présence d’un motif persistant dérivant, constitué de branches radiales, comme identifié par Rein et al. (2023, J. Fluid Mech. 977, A26). Nous caractérisons la fréquence angulaire de dérive ainsi que le nombre d’onde azimutal de ce motif en fonction du nombre de Rayleigh. Le système présente une large distribution des flux de chaleur sur différentes échelles temporelles, les fluctuations les plus longues étant attribuées au motif en branches et les plus courtes aux fluctuations turbulentes. Par conséquent, le motif en branches doit être pris en compte afin de mieux prévoir les fluctuations importantes du flux de chaleur aux parois, un résultat particulièrement pertinent dans le contexte de la sûreté nucléaire, motivation initiale de notre étude
How can X-ray computed tomography help improve the performances of a preferential water flow model in soils?
No full textInternational audiencePreferential flow pathways in soil macropores allow fast, gravity-driven water transfer that can bypass most of the soil matrix. Still, some water, and the contaminants it contains, transfer from the macropores to the matrix. This water exchange is accounted for in 1D compartment models by coupling preferential and matrix flow with simplified, physics-based equations. Still, some parameters of these exchange terms need to be calibrated, often with unrealistic values. We propose a new macropore-matrix exchange term that considers the horizontal distribution of water in the soil matrix and overcomes this shortcoming. This term was defined as the product of a macropore-matrix specific wetted interfacial area and the water flux density from macropores. The former was estimated using X-ray Computed Tomography images. The latter was obtained by solving the Richards' equation in a horizontal representation of the soil matrix. A water transfer model equipped with this exchange term performed better, when compared to experimental data, than a version using an exchange term based on the average pressure head in the soil matrix. It significantly improved the modeled temporal evolution of drained and stored water in the soil. Water exchange was maximum after the start of a rainfall and decreased towards zero before the soil matrix was saturated. This new pseudo-2D exchange term opens up the possibility of improving the modeling of water and contaminant retention at the macropore-matrix interface and of using values of the transfer-term parameters determined experimentally or calculated by another model.</div
D’Antony aux Chittagong Hill Tracts : itinéraire et péripéties d’une mission de Lucien Bernot
No full textInternational audienceIn 1959, Lucien Bernot, an anthropologist specializing in Southeast Asia, obtained funding from SEATO and spent five months in the Chittagong Hill Tracts, then in East Pakistan, to complete his study of the Marma people begun in 1951. A file of correspondence and miscellaneous documents found in his archives enables us to reconstruct the entire mission, from the application for funding to his return to France. While the scientific results of this mission are well known and published by L. Bernot, it is the organization of the mission, the various hassles he had to face and the course of his stay that are discussed here. These archival documents show how anthropological research was created and administered in the 1960s.En 1959, Lucien Bernot, anthropologue spécialiste de l’Asie du Sud-Est, obtient un financement de l’OTASE et part pour cinq mois dans les Chittagong Hill Tracts, alors au Pakistan oriental, afin de compléter son étude sur les Marma entamée en 1951. Un dossier de correspondances et documents divers trouvé dans ses archives permet de reconstituer l’ensemble de cette mission, de la demande de financement jusqu’à son retour en France. Les résultats scientifiques de cette mission sont bien connus et publiés par L. Bernot ; ce sont ici l’organisation de la mission, les divers tracas auxquels il doit faire face et le déroulement de son séjour dont il est question. Ces documents d’archive nous permettent de montrer comment se créait et s’administrait la recherche en anthropologie dans les années 1960
