A Projection Approach to the Numerical Analysis of Limit Load Problems

International audienceThis paper proposes a numerical scheme to approximate the solution of (vectorial) limit load problems. The method makes use of a strictly convex perturbation of the problem, which corresponds to a projection of the deformation field under bounded deformation and incompressibility constraints. The discretized formulation of this perturbation converges to the solution of the original landslide problem when the amplitude of the perturbation tends to zero. The projection is computed numerically with a multi-steps gradient descent on the dual formation of the problem

A priori analysis of subgrid-scale models for shock wave / boundary layer interaction

This study addresses the subgrid-scale modeling issue for large eddy simulation of shock wave / boundary layer interaction. By using a reference flow database, obtained by direct numerical simulation, a priori testing of the most prominent LES models is carried out. The various modelling and filtering approaches are discussed and compared, leading to suggest a priori the most appropriate closure strategy

Statistical Evaluation of the Shock Wave Boundary Layer Interaction Phenomenon

Turbulent velocity and thermal correlations from direct numerical simulation data of a spatially growing compressible turbulent boundary layer interacting with an impinging shock are discussed. The cross-stream variation of the velocity second-moments and the thermal fluxes one boundary layer thickness upstream of the shock impingement point are discussed. Other correlations are examined to further statistically quantify the effect of the oblique shock-turbulence interaction

Aevol-4b: Toward a new simulation platform to benchmark phylogenetic tools

National audienceAevol (www.aevol.fr) is a computational platform that allows for the study and manipulation of populations of digital organisms evolving under different conditions. Using Aevol simulations, one can better understand evolutionary forces and mechanisms leading to specific genome and transcriptome structures, as well as indirect selection pressures involved in the evolution of cooperation and genetic information transfer. Recently, we used aevol as a benchmarking tool. Indeed, Molecular evolutionary methods and tools are difficult to validate, as we have almost no direct access to ancient molecules. Inference methods may be tested with simulated data but this requires that the inference methods and the simulation be design independently (Biller et al., Computation in Europe 2016; Biller et al., Jobim 2016). Using aevol we can simulate perfectly characterized phylogenies and obtain a final population that evolved accordingly. Then we can use this final population to try to recover the initial phylogeny using various tools and assess their efficiency in doing so. This approach has recently been applied to test various estimators of inversion distance, revealing their limits and suggesting important improvement directions (Biller et al., Genome Biology and Evolution 2016). However, current aevol structure – more specifically the use of a binary representation for the genomic sequence – strongly limits its usability as a benchmarking tool. That is why we recently started the development of a new version of the software in which the genome sequence will use a four-nucleotides code and the translation from genetic sequence to polypeptide sequences will use the extant genetic code to map the 4-bases alphabet to the 20-amino-acids one. Although the development of this new version is in its infancy a first prototype has been developed and we would like to discuss the main modelling choices with the Alphy community that will be the potential users of the generated benchmarks. In particular, in this prototype the genotype-to-phenotype map is be based a mathematical description of traits under selection and on A.D. Solis (Proteins, 2015) classification of amino-acids, two crucial modelling choices that deserve discussion before we start final software implementation

Post-shock downstream evolution of turbulent boundary layer based on quadrant analysis

Quadrant analysis is one of the technique that commonly used to detect and to quantify the composition of occurrence of different turbulent events (e.g. ejections and sweeps) in a turbulent boundary layer. In the present communication the post-shock behaviour of the supersonic turbulent boundary layer will be presented on the basis of above mentioned analysis. In addition the effect of two different wall-temperature conditions will also be investigated

Controlling spatial distributions of molecules in multicomponent organic crystals, with quantitative mapping by confocal Raman microspectrometry

We report four experimental strategies for controlling the three-dimensional arrangement of molecules in multicomponent organic crystals, exploiting confocal Raman microspectrometry to quantify the three-dimensional spatial distributions. Specifically, we focus on controlling the distribution of two types of guest molecule in solid organic inclusion compounds to produce composite core–shell crystals, crystals with a homogeneous distribution of the components, crystals with continuous compositional variation from the core to the surface, and crystals with alternating shells of the components. In this context, confocal Raman microspectrometry is particularly advantageous over optical microscopy as it is nondestructive, offers micrometric spatial resolution, and relies only on the component molecules having different vibrational properties

Many-body theory of pump-probe spectra for highly excited semiconductors

We present a unified theory for pump-probe spectra in highly excited semiconductors, which is applicable throughout the whole density regime including the high-density electron-hole BCS state and the low-density excitonic Bose-Einstein condensate (BEC). The analysis is based on the BCS-like pairing theory combined with the Bethe-Salpeter (BS) equation, which first enables us to incorporate the state-filling effect, the band-gap renormalization and the strong/weak electron-hole pair correlations in a unified manner. We show that the electron-hole BCS state is distinctly stabilized by the intense pump-light, and this result strongly suggests that the macroscopic quantum state can be observed under the strong photoexcitation. The calculated spectra considerably deviate from results given by the BCS-like mean field theory and the simple BS equation without electron-hole pair correlation especially in the intermediate density states between the electron-hole BCS state and the excitonic BEC state. In particular, we find the sharp stimulated emission and absorption lines which originate from the optical transition accompanied by the collective phase fluctuation mode in the electron-hole BCS state. From the pump-probe spectral viewpoint, we show that this fluctuation mode changes to the exciton mode with decreasing carrier densityComment: RevTeX 11 pages, 10 figures. To appear in Phys.Rev.B1

Similarity learning for person re-identification and semantic video retrieval

Many computer vision problems boil down to the learning of a good visual similarity function that calculates a score of how likely two instances share the same semantic concept. In this thesis, we focus on two problems related to similarity learning: Person Re-Identification, and Semantic Video Retrieval. Person Re-Identification aims to maintain the identity of an individual in diverse locations through different non-overlapping camera views. Starting with two cameras, we propose a novel visual word co-occurrence based appearance model to measure the similarities between pedestrian images. This model naturally accounts for spatial similarities and variations caused by pose, illumination and configuration changes across camera views. As a generalization to multiple camera views, we introduce the Group Membership Prediction (GMP) problem. The GMP problem involves predicting whether a collection of instances shares the same semantic property. In this context, we propose a novel probability model and introduce latent view-specific and view-shared random variables to jointly account for the view-specific appearance and cross-view similarities among data instances. Our method is tested on various benchmarks demonstrating superior accuracy over state-of-art. Semantic Video Retrieval seeks to match complex activities in a surveillance video to user described queries. In surveillance scenarios with noise and clutter usually present, visual uncertainties introduced by error-prone low-level detectors, classifiers and trackers compose a significant part of the semantic gap between user defined queries and the archive video. To bridge the gap, we propose a novel probabilistic activity localization formulation that incorporates learning of object attributes, between-object relationships, and object re-identification without activity-level training data. Our experiments demonstrate that the introduction of similarity learning components effectively compensate for noise and error in previous stages, and result in preferable performance on both aerial and ground surveillance videos. Considering the computational complexity of our similarity learning models, we attempt to develop a way of training complicated models efficiently while remaining good performance. As a proof-of-concept, we propose training deep neural networks for supervised learning of hash codes. With slight changes in the optimization formulation, we could explore the possibilities of incorporating the training framework for Person Re-Identification and related problems.2019-07-09T00:00:00

Theory of Luminescence Spectra of High-Density Electron-Hole Systems: Crossover from Excitonic Bose-Einstein Condenstation to Electron-Hole BCS State

We present a unified theory of luminescence spectra for highly excited semiconductors, which is applicable both to the electron-hole BCS state and to the exciton Bose-Einstein condensate. The crossover behavior between electron-hole BCS state and exciton Bose-Einstein condensate clearly manifests itself in the calculated luminescence spectra. The analysis is based on the Bethe-Salpeter equation combined with the generalized random-phase-approximation, which enables us to consider the multiple Coulomb scattering and the quantum fluctuation associated with the center-of-mass motion of electron-hole pairs. In the crossover regime, the calculated spectra are essentially different from results obtained by the BCS-like mean-field theory and the interacting Boson model. In particular, it is found that the broad spectrum, arising from the recombination of electron-hole BCS state, splits into the P- and P_2-luminescence bands with decreasing the particle density. The dependence of these bands on the carrier density is in good agreement with experiments for highly excited semiconductors.Comment: 9 pages, 4 figures, To appear in Solid State Communication

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