Atomistic Simulations of Basal Dislocations Interacting with Mg17_{17}Al12_{12} Precipitates in Mg

The mechanical properties of Mg-Al alloys are greatly influenced by the complex intermetallic phase Mg$_{17}$Al$_{12}$, which is the most dominant precipitate found in this alloy system. The interaction of basal edge and 30$^\text{o}$ dislocations with Mg$_{17}$Al$_{12}$ precipitates is studied by molecular dynamics and statics simulations, varying the inter-precipitate spacing ($L$), and size ($D$), shape and orientation of the precipitates. The critical resolved shear stress $\tau_c$ to pass an array of precipitates follows the usual $\ln((1/D + 1/L)^{-1})$ proportionality. In all cases but the smallest precipitate, the dislocations pass the obstacles by depositing dislocation segments in the disordered interphase boundary rather than shearing the precipitate or leaving Orowan loops in the matrix around the precipitate. An absorbed dislocation increases the stress necessary for a second dislocation to pass the precipitate also by absorbing dislocation segments into the boundary. Replacing the precipitate with a void of identical size and shape decreases the critical passing stress and work hardening contribution while an artificially impenetrable Mg$_{17}$Al$_{12}$ precipitate increases both. These insights will help improve mesoscale models of hardening by incoherent particles.Comment: 13 pages with 9 figures and 2 tables. Supplementary materia

Influence of intrinsic strain on irradiation induced damage: the role of threshold displacement and surface binding energies

International audienc

A Transformer Architecture for Online Gesture Recognition of Mathematical Expressions

The Transformer architecture is shown to provide a powerful framework as an end-to-end model for building expression trees from online handwritten gestures corresponding to glyph strokes. In particular, the attention mechanism was successfully used to encode, learn and enforce the underlying syntax of expressions creating latent representations that are correctly decoded to the exact mathematical expression tree, providing robustness to ablated inputs and unseen glyphs. For the first time, the encoder is fed with spatio-temporal data tokens potentially forming an infinitely large vocabulary, which finds applications beyond that of online gesture recognition. A new supervised dataset of online handwriting gestures is provided for training models on generic handwriting recognition tasks and a new metric is proposed for the evaluation of the syntactic correctness of the output expression trees. A small Transformer model suitable for edge inference was successfully trained to an average normalised Levenshtein accuracy of 94%, resulting in valid postfix RPN tree representation for 94% of predictions.Comment: 12 pages, 3 Figures, 4 Table

Evaluation of large-scale unsupervised classification of New Caledonia reef ecosystems using Landsat 7 ETM+ imagery

The capacity of the Landsat 7 Enhanced Thematic Mapper Plus sensor to classify the shallow benthic ecosytems of New Caledonia (South Pacific) is tested using a novel unsupervised classification method. The classes are defined by using a set of multiple spectral decision rules based on the image spectral bands. A general model is applied to the entire Southwest lagoon (5500 km(2)) and tested on three representative sites: a section of the barrier reef, a cay reef flat rich in corals, and a cay reef flat rich in algae and seagrass beds. In the latter one, the classification results are compared with a locally optimized model, with aerial color photographs and extensive ground-truthed observations. Results show that a reconnaissance of the main benthic habitats in shallow areas (<5 m depth) is possible, at a geomorphological scale for coral reef structure and at a habitat scale for seagrass beds. However, results directly issued from the model must be cautiously interpreted according to empirical spatial rules, especially to avoid confusion between coral slopes and shallow dense seagrass.Le but de cette étude est de tester la capacité des images Landsat 7 Enhanced Thematic Mapper Plus à discriminer les principales classes d’habitats benthiques rencontrées dans les parties peu profondes du système récifal et lagonaire de Nouvelle-Calédonie (Pacifique Sud). Une méthode originale de classification non-supervisée est proposée. Les habitats benthiques correspondent à une combinaison de plusieurs règles de décision établies à partir des bandes radiométriques Landsat. Cette modélisation statistique des habitats benthiques est appliquée au lagon sud-ouest de Nouvelle-Calédonie (5500 km2). Les résultats sont testés sur trois sites témoins contrastés: un platier de récif barrière, un platier d’îlot riche en corail et un platier d’îlot riche en herbiers/algueraies. Pour ce dernier, le résultat est comparé à celui d’un modèle optimisé, construit à échelle locale et validé à partir de photographies aériennes et d’observations de terrain. Les résultats montrent qu’une reconnaissance des différentes classes benthiques est possible pour des fonds peu profonds (< 5 m de profondeur), à l’échelle géomorphologique pour les structures récifales et à l’échelle des habitats pour les herbiers. Toutefois, les résultats bruts du modèle doivent être interprétés en fonction de critères spatiaux pour corriger les confusions entre certaines classes, notamment entre les pentes coralliennes et les herbiers denses

Atomistic simulations of focused ion beam machining of strained silicon

International audienc

Evaluate Fine-tuning Strategies for Fetal Head Ultrasound Image Segmentation with U-Net

Fetal head segmentation is a crucial step in measuring the fetal head circumference (HC) during gestation, an important biometric in obstetrics for monitoring fetal growth. However, manual biometry generation is time-consuming and results in inconsistent accuracy. To address this issue, convolutional neural network (CNN) models have been utilized to improve the efficiency of medical biometry. But training a CNN network from scratch is a challenging task, we proposed a Transfer Learning (TL) method. Our approach involves fine-tuning (FT) a U-Net network with a lightweight MobileNet as the encoder to perform segmentation on a set of fetal head ultrasound (US) images with limited effort. This method addresses the challenges associated with training a CNN network from scratch. It suggests that our proposed FT strategy yields segmentation performance that is comparable when trained with a reduced number of parameters by 85.8%. And our proposed FT strategy outperforms other strategies with smaller trainable parameter sizes below 4.4 million. Thus, we contend that it can serve as a dependable FT approach for reducing the size of models in medical image analysis. Our key findings highlight the importance of the balance between model performance and size in developing Artificial Intelligence (AI) applications by TL methods. Code is available at https://github.com/13204942/FT_Methods_for_Fetal_Head_Segmentation.Comment: 4 pages, 2 figure

Vivre une métaphore : écritures anglo-saxonnes du voyage en mer au viiie siècle

Revisitant la question des origines du pèlerinage, des publications récentes ont rappelé qu’aux yeux des contemporains les premiers voyages religieux relevaient plutôt de l’expression d’une forme particulière de monachisme que d’une pratique de dévotion caractérisée par des rites et un réseau de destinations fermement institués. En examinant les sources du corpus des « Vies missionnaires », nous nous efforçons ici de montrer que les voyageurs religieux anglo-saxons des viie et viiie siècles concevaient encore la peregrinatio pro Deo comme cette recherche d’un renoncement au monde matériel par le mouvement physique réel. La nécessité de justifier cette forme de dévotion, trop proche de l’errance des moines dénoncée par la Règle bénédictine, favorisa le recours au thème littéraire du voyage sur la mer, susceptible de décourager les critiques stigmatisant l’immoralité du genre de vie mené par les moines errants dans le monde séculier. L’aptitude du motif de la traversée maritime à se fondre dans la métaphore du chrétien-voyageur s’ajouta à une lecture « missionnaire » de l’histoire du peuple des Angles pour faire d’un voyage maritime initial une condition nécessaire de ce qui pouvait être considéré comme une pérégrination légitime. Ce thème littéraire, délaissé par l’hagiographie continentale au siècle suivant, imprima pourtant sa marque sur l’historiographie, et peut-être aussi sur la littérature, de la Bretagne insulaire.While re-examining the questions of the origins of pilgrimage, recent publications suggested that contemporary observers considered the earliest religious travels more as another form of monasticism than as a religious practice characterized by a cluster of definite rituals and a network of distinct holy places. In this essay, using Ian Wood’s work on missionary hagiography, we will argue that Anglo-Saxon religious travellers from the seventh and eighth centuries still considered the peregrinatio pro Deo as the pursuit of withdrawal from the material world through physical movement. In order to justify this particular kind of religious devotion, which was, to many extents, too close to the kind of wandering monasticism denounced by the Benedictine Rule, authors used and developed the literary theme of travel by water, which could discourage criticism of the corrupting way of life lived by wandering monks within the secular world. The matching of the sea travel theme with the metaphor of the Christian as a traveller added to a “missionary” conception of the gens Anglorum’s history in establishing initial maritime journey as a necessary pre-condition of what could be properly considered as a peregrinatio by contemporary authors. The topic of water travel was comparatively neglected by continental authors of later missionary Lives. Nonetheless, it stamped its mark on early medieval Britain’s historiography, and also, maybe, on its literature