École des ponts ParisTech

About: École des ponts ParisTech is a education organization based out in Paris, France. It is known for research contribution in the topics: Finite element method & Nonlinear system. The organization has 1512 authors who have published 3357 publications receiving 93497 citations. The organization is also known as: Ecole Nationale des Ponts et Chaussées & École des Ponts et Chaussées.

Unsupervised Representation Learning by Predicting Image Rotations

Abstract: Over the last years, deep convolutional neural networks (ConvNets) have transformed the field of computer vision thanks to their unparalleled capacity to learn high level semantic image features. However, in order to successfully learn those features, they usually require massive amounts of manually labeled data, which is both expensive and impractical to scale. Therefore, unsupervised semantic feature learning, i.e., learning without requiring manual annotation effort, is of crucial importance in order to successfully harvest the vast amount of visual data that are available today. In our work we propose to learn image features by training Con-vNets to recognize the 2d rotation that is applied to the image that it gets as input. We demonstrate both qualitatively and quantitatively that this apparently simple task actually provides a very powerful supervisory signal for semantic feature learning. We exhaustively evaluate our method in various unsupervised feature learning benchmarks and we exhibit in all of them state-of-the-art performance. Specifically, our results on those benchmarks demonstrate dramatic improvements w.r.t. prior state-of-the-art approaches in unsupervised representation learning and thus significantly close the gap with supervised feature learning. For instance, in PASCAL VOC 2007 detection task our unsupervised pre-trained AlexNet model achieves the state-of-the-art (among unsupervised methods) mAP of 54.4% that is only 2.4 points lower from the supervised case. We get similarly striking results when we transfer our unsupervised learned features on various other tasks, such as ImageNet classification, PASCAL classification, PASCAL segmentation, and CIFAR-10 classification. The code and models of our paper will be published on: https://github.com/gidariss/FeatureLearningRotNet.

The IEF version of the PCM solvation method: an overview of a new method addressed to study molecular solutes at the QM ab initio level

Abstract: The integral equation formalism (IEF) is a recent method (the grounds have been elaborated at the beginning of 1997) addressed to solve the electrostatic solvation problem at the QM level with the aid of apparent surface charges (ASC). IEF uses a new formalism of this problem, based on integral operators never used before in the chemical community and it manages to treat on the same footing linear isotropic solvent models, as well as anisotropic liquid crystals and ionic solutions. In this overview we emphasize the good performances of IEF at the lowest level of its potentialities, i.e. for isotropic solvents, as a new approach to compute solvation free energies and properties (dipole hyperpolarizabilities) of molecular solutes, as well as energy gradients for geometry optimization procedures. Finally we present a new IEF implementation of the nonequilibrium problem for electronic spectra which appears to be decidedly competitive with the previous more standard ASC formulations.

Evaluation of Solvent Effects in Isotropic and Anisotropic Dielectrics and in Ionic Solutions with a Unified Integral Equation Method: Theoretical Bases, Computational Implementation, and Numerical Applications

Abstract: We present the full implementation of the integral equation formalism (IEF) we have recently formulated to treat solvent effects. The method exploits a single common approach for dielectrics of very different nature: standard isotropic liquids, intrinsically anisotropic media like liquid crystals, and ionic solutions. We report here an analysis of its both formal and technical details as well as some numerical applications addressed to state the achieved generalization to all kinds of molecular solutes and to show the equally reliable performances in treating such different environmental systems. In particular, we report, for isotropic liquids, data of solvation free energies and static (hyper)polarizabilities of various molecular solutes in water, for anisotropic dielectrics, a study of an SN2 reaction, and finally, for ionic solution, a study of some structural aspects of ion pairing.

Finite Volume Methods

Abstract: Publisher Summary This chapter focuses on finite volume methods. The finite volume method is a discretization method that is well suited for the numerical simulation of various types (for instance, elliptic, parabolic, or hyperbolic) of conservation laws; it has been extensively used in several engineering fields, such as fluid mechanics, heat and mass transfer, or petroleum engineering. Some of the important features of the finite volume method are similar to those of the finite element method: it may be used on arbitrary geometries, using structured or unstructured meshes, and it leads to robust schemes. The finite volume method is locally conservative because it is based on a “balance" approach: a local balance is written on each discretization cell that is often called “control volume;” by the divergence formula, an integral formulation of the fluxes over the boundary of the control volume is then obtained. The fluxes on the boundary are discretized with respect to the discrete unknowns.

Chicken and egg: competition among intermediation service providers

Abstract: We analyze a model of imperfect price competition between intermediation service providers. We insist on features that are relevant for informational intermediation via the Internet: the presence of indirect network externalities, the possibility of using the nonexclusive services of several intermediaries, and the widespread practice of price discrimination based on users' identity and on usage. Efficient market structures emerge in equilibrium, as well as some specific form of inefficient structures. Intermediaries have incentives to propose non-exclusive services, as this moderates competition and allows them to exert market power. We analyze in detail the pricing and business strategies followed by intermediation services providers. Copyright 2003 by the RAND Corporation.