Efficient Exploration of Microstructure-Property Spaces via Active Learning

In materials design, supervised learning plays an important role for optimization and inverse modeling of microstructure-property relations. To successfully apply supervised learning models, it is essential to train them on suitable data. Here, suitable means that the data covers the microstructure and property space sufficiently and, especially for optimization and inverse modeling, that the property space is explored broadly. For virtual materials design, typically data is generated by numerical simulations, which implies that data pairs can be sampled on demand at arbitrary locations in microstructure space. However, exploring the space of properties remains challenging. To tackle this problem, interactive learning techniques known as active learning can be applied. The present work is the first that investigates the applicability of the active learning strategy query-by-committee for an efficient property space exploration. Furthermore, an extension to active learning strategies is described, which prevents from exploring regions with properties out of scope (i.e., properties that are physically not meaningful or not reachable by manufacturing processes)

Connections and dynamical trajectories in generalised Newton-Cartan gravity I. An intrinsic view

The "metric" structure of nonrelativistic spacetimes consists of a one-form (the absolute clock) whose kernel is endowed with a positive-definite metric. Contrarily to the relativistic case, the metric structure and the torsion do not determine a unique Galilean (i.e. compatible) connection. This subtlety is intimately related to the fact that the timelike part of the torsion is proportional to the exterior derivative of the absolute clock. When the latter is not closed, torsionfreeness and metric-compatibility are thus mutually exclusive. We will explore generalisations of Galilean connections along the two corresponding alternative roads in a series of papers. In the present one, we focus on compatible connections and investigate the equivalence problem (i.e. the search for the necessary data allowing to uniquely determine connections) in the torsionfree and torsional cases. More precisely, we characterise the affine structure of the spaces of such connections and display the associated model vector spaces. In contrast with the relativistic case, the metric structure does not single out a privileged origin for the space of metric-compatible connections. In our construction, the role of the Levi-Civita connection is played by a whole class of privileged origins, the so-called torsional Newton-Cartan (TNC) geometries recently investigated in the literature. Finally, we discuss a generalisation of Newtonian connections to the torsional case.Comment: 79 pages, 7 figures; v2: added material on affine structure of connection space, former Section 4 postponed to 3rd paper of the serie

Recognition of 2D modelized objects by a discrete relaxation method

In this paper, a discrete relaxation method is described . The aim of this method is the recognition of 2D objects, a model of which having prealably be established. The model is based on two kinds of features : straight segments and circles . The approach is both forward and backward ; so, it is not necessary to detect all the primitives at the beginning of the procedure new primitives may be detected, if necessary, during the relaxation procedure .L'article présente une méthode de relaxation discrète pour la reconnaissance d'objets plans dont on a effectué une modélisation préalable . Cette modélisation est réalisée à l'aide de primitives du type segments de droite ou cercles . L'approche est descendante et ascendante, permettant, par un retour au niveau de l'image pour détecter de nouvelles primitives, d'éviter un prétraitement exhaustif de l'image

Dental Shape Variation and Phylogenetic Signal in the Rattini Tribe Species of Mainland Southeast Asia

We would like to thank Pierre-Henri Fabre for providing the phylogeny for this study. The collection of specimens used was funded by the French ANR Biodiversity, grant ANR 07 BDIV 012 CERoPath project (www.ceropath.org), and by the French ANR CP&ES, grant ANR 11 CPEL 002 BiodivHealthSEA project (www.biodivhealthsea.org). We also thank Madoudou Garba and Gauthier Dobigny (CBGP-IRD) for providing additional specimens. We greatly thank all local communities and their leaders for permission and invaluable help during field trapping. Special thanks to the CERoPath and BiodivHealthSEA teams and the drivers for their invaluable help during fieldwork. We would also like to thank Maeve McMahon for help with manuscript editing and preparation.Peer reviewedPublisher PD

Etude expérimentale d'un arc impulsionnel entre des contacts Ag et Ag-C

International audienc

Extracellular Bacterial Pathogen Induces Host Cell Surface Reorganization to Resist Shear Stress

Bacterial infections targeting the bloodstream lead to a wide array of devastating diseases such as septic shock and meningitis. To study this crucial type of infection, its specific environment needs to be taken into account, in particular the mechanical forces generated by the blood flow. In a previous study using Neisseria meningitidis as a model, we observed that bacterial microcolonies forming on the endothelial cell surface in the vessel lumen are remarkably resistant to mechanical stress. The present study aims to identify the molecular basis of this resistance. N. meningitidis forms aggregates independently of host cells, yet we demonstrate here that cohesive forces involved in these bacterial aggregates are not sufficient to explain the stability of colonies on cell surfaces. Results imply that host cell attributes enhance microcolony cohesion. Microcolonies on the cell surface induce a cellular response consisting of numerous cellular protrusions similar to filopodia that come in close contact with all the bacteria in the microcolony. Consistent with a role of this cellular response, host cell lipid microdomain disruption simultaneously inhibited this response and rendered microcolonies sensitive to blood flow–generated drag forces. We then identified, by a genetic approach, the type IV pili component PilV as a triggering factor of plasma membrane reorganization, and consistently found that microcolonies formed by a pilV mutant are highly sensitive to shear stress. Our study shows that bacteria manipulate host cell functions to reorganize the host cell surface to form filopodia-like structures that enhance the cohesion of the microcolonies and therefore blood vessel colonization under the harsh conditions of the bloodstream