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Semantic Web-Mining and Deep Vision for Lifelong Object Discovery
No full textInternational audienceAutonomous robots that are to assist humans in their daily lives must recognize and understand the meaning of objects in their environment. However, the open nature of the world means robots must be able to learn and extend their knowledge about previously unknown objects on-line. In this work we investigate the problem of unknown object hypotheses generation, and employ a semantic web-mining framework along with deep-learning-based object detectors. This allows us to make use of both visual and semantic features in combined hypotheses generation. Experiments on data from mobile robots in real world application deployments show that this combination improves performance over the use of either method in isolation
Slope tomography based on eikonal solvers and the adjoint-state method
No full textInternational audienceVelocity macromodel building is a crucial step in the seismic imaging workflow as it provides the necessary background model for migration or full waveform inversion. In this study, we present a new formulation of stereotomography that can handle more efficiently long-offset acquisition, complex geological structures and large-scale data sets. Stereotomography is a slope tomographic method based upon a semi-automatic picking of local coherent events. Each local coherent event, characterized by its two-way traveltime and two slopes in common-shot and common-receiver gathers, is tied to a scatterer or a reflector segment in the subsurface. Ray tracing provides a natural forward engine to compute traveltime and slopes but can suffer from non-uniform ray sampling in presence of complex media and long-offset acquisitions. Moreover, most implementations of stereotomography explicitly build a sensitivity matrix, leading to the resolution of large systems of linear equations, which can be cumbersome when large-scale data sets are considered. Overcoming these issues comes with a new matrix-free formulation of stereotomography: a factored eikonal solver based on the fast sweeping method to compute first-arrival traveltimes and an adjoint-state formulation to compute the gradient of the misfit function. By solving eikonal equation from sources and receivers, we make the computational cost proportional to the number of sources and receivers while it is independent of picked events density in each shot and receiver gather. The model space involves the subsurface velocities and the scatterer coordinates, while the dips of the reflector segments are implicitly represented by the spatial support of the adjoint sources and are updated through the joint localization of nearby scatterers. We present an application on the complex Marmousi model for a towed-streamer acquisition and a realistic distribution of local events. We show that the estimated model, built without any prior knowledge of the velocities, provides a reliable initial model for frequency-domain FWI of long-offset data for a starting frequency of 4 Hz, although some artefacts at the reservoir level result from a deficit of illumination. This formulation of slope tomography provides a computationally efficient alternative to waveform inversion method such as reflection waveform inversion or differential-semblance optimization to build an initial model for pre-stack depth migration and conventional FWI
VizieR Online Data Catalog: Gaia DR1 open cluster members (Gaia Collaboration+, 2017)
No full textVizieR On-line Data Catalog: J/A+A/601/A19. Originally published in: 2017A&A...601..A19GWe have determined and examined the astrometric data for 19 open clusters, ranging from the Hyades at just under 47pc to NGC 2422 at nearly 440pc. The clusters are : the Hyades, Coma Berenices, the Pleiades, Praesepe, alpha Per, IC 2391, IC 2602, Blanco 1, NGC 2451, NGC 6475, NGC 7092, NGC 2516, NGC 2232, IC 4665, NGC 6633, Collinder 140, NGC 2422, NGC 3532 and NGC 2547. (2 data files)
A new family of exponential-based high order DGTD methods for modelling 3D transient multiscale electromagnetic problems
No full text—The accurate and efficient simulation of 3D transient multiscale electromagnetic problems is extremely challenging for conventional numerical methods. Assuming a splitting of the underlying tetrahedral mesh in coarse and fine parts and using the Lawson procedure, we derive a family of exponential-based time integration methods for the time-domain Maxwell's equations discretized by a high order discontinuous Galerkin (DG) scheme formulated on locally refined unstructured meshes. These methods remove the stiffness on the time explicit integration of the semi-discrete operator associated to the fine part of the mesh, and allow for the use of high order time explicit scheme for the coarse part operator. They combine excellent stability properties with the ability to obtain very accurate solutions even for very large time step sizes. Here, the explicit time integration of the Lawson-transformed semi-discrete system relies on a Low-Storage Runge-Kutta (LSRK) scheme, leading to a combined Lawson-LSRK scheme. In addition, efficient techniques are also presented to further improve the efficiency of this exponential-based time integration. For the efficient calculation of matrix exponential, we employ the Krylov subspace method. Numerical experiments are presented to assess the stability, verify the accuracy and numerical convergence of the Lawson-LSRK scheme. They also demonstrate that the DGTD methods based on the proposed time integration scheme can be much faster than those based on classical fully explicit time stepping schemes, with the same accuracy and moderate memory usage increase on locally refined unstructured meshes, and are thus very promising for modelling three-dimensional multiscale electromagnetic problems
Neighbour-Sum-2-Distinguishing Edge-Weightings: Doubling the 1-2-3 Conjecture
No full textThe 1-2-3 Conjecture asks whether every graph with no connected component isomorphic to K2 can be 3-edge-weighted so that every two adjacent vertices u and v can be distinguished via the sum of their incident weights, that is the incident sums of u and v differ by at least 1. We here investigate the consequences on the 1-2-3 Conjecture of requiring a stronger distinction condition. Namely, we consider two adjacent vertices distinguished when their incident sums differ by at least 2. As a guiding line, we conjecture that every graph with no connected component isomorphic to K2 admits a 5-edge-weighting permitting to distinguish the adjacent vertices in this stronger way. We verify this conjecture for several classes of graphs, including bipartite graphs and cubic graphs. We then consider algorithmic aspects, and show that it is NP-complete to determine the smallest k such that a given bipartite graph admits such a k-edge-weighting. In contrast, we show that the same problem can be solved in polynomial time for a given tree
Antenna Q Bounds for Given Directivity: a Case Study of a Directive Parasitic Element Antenna
No full textInternational audienc
Decay dynamics in the coupled-dipole model
No full textCooperative scattering in cold atoms has gained renewed interest, in particular in the context of single-photon superradiance, with the recent experimental observation of super-and subradiance in dilute atomic clouds. Numerical simulations to support experimental signatures of cooperative scattering are often limited by the number of dipoles which can be treated, well below the number of atoms in the experiments. In this paper, we provide systematic numerical studies aimed at matching the regime of dilute atomic clouds. We use a scalar coupled-dipole model in the low excitation limit and an exclusion volume to avoid density-related effects. Scaling laws for super-and subradiance are obtained and the limits of numerical studies are pointed out. We also illustrate the cooperative nature of light scattering by considering an incident laser field, where half of the beam has a π phase shift. The enhanced subradiance obtained under such condition provides an additional signature of the role of coherence in the detected signal
Peuplement d'une base de connaissance par annotation automatique de textes relatifs à la cosmétique
No full textNational audienceDans cet article, nous proposons une approche pour construire une base de connaissances à partir de textes dans le domaine de la cosmétique. Il s’agit d’un cas particulier pour un domaine fixé du problème de l’extraction de relations à partir de textes. Dans le but de résoudre ce problème, nous proposons une approche semi-supervisée pour l’extraction des relations en combinant deux méthodes : (i) la construction de patrons d’extraction à partir des résumés présents dans les pages de DBpedia, (ii) l’annotation manuelle d’un ensemble de textes pour définir des patrons syntaxiques pour extraire les relations. Nous avons évalué notre approche sur deux types de corpus : (i) un premier corpus est composé d’articles de journaux spécialisés, tels que au féminin. com et Cosmétique Hebdo, (ii) un deuxième corpus est constitué d’un ensemble de phrases collectées sur sur le Web
Colouring graphs with constraints on connectivity
No full textInternational audienceA graph G has maximal local edge-connectivity k if the maximum number of edge-disjoint paths between every pair of distinct vertices x and y is at most k. We prove Brooks-type theorems for k-connected graphs with maximal local edge-connectivity k, and for any graph with maximal local edge-connectivity 3. We also consider several related graph classes defined by constraints on connectivity. In particular, we show that there is a polynomial-time algorithm that, given a 3-connected graph G with maximal local connectivity 3, outputs an optimal colouring for G. On the other hand, we prove, for k ≥ 3, that k-colourability is NP-complete when restricted to minimally k-connected graphs, and 3-colourability is NP-complete when restricted to (k − 1)-connected graphs with maximal local connectivity k. Finally, we consider a parameterization of k-colourability based on the number of vertices of degree at least k + 1, and prove that, even when k is part of the input, the corresponding parameterized problem is FPT