INRIA a CCSD electronic archive server

    Heterogeneous Face Recognition with CNNs

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    International audienceHeterogeneous face recognition aims to recognize faces across different sensor modalities. Typically, gallery images are normal visible spectrum images, and probe images are infrared images or sketches. Recently significant improvements in visible spectrum face recognition have been obtained by CNNs learned from very large training datasets. In this paper, we are interested in the question to what extent the features from a CNN pre-trained on visible spectrum face images can be used to perform heterogeneous face recognition. We explore different metric learning strategies to reduce the discrepancies between the different modalities. Experimental results show that we can use CNNs trained on visible spectrum images to obtain results that are on par or improve over the state-of-the-art for heterogeneous recognition with near-infrared images and sketches

    Traçage Wi-Fi: Attaques par Prise d'Empreinte et Contre-Mesures

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    The recent spread of everyday-carried Wi-Fi-enabled devices (smartphones, tablets and wearable devices) comes with a privacy threat to their owner, and to society as a whole. These devices continuously emit signals which can be captured by a passive attacker using cheap hardware and basic knowledge. These signals contain a unique identifier, called the MAC address. To mitigate the threat, device vendors are currently deploying a countermeasure on new devices: MAC address randomization. Unfortunately, we show that this mitigation, in its current state, is insufficient to prevent tracking.To do so, we introduce several attacks, based on the content and the timing of emitted signals. In complement, we study implementations of MAC address randomization in some recent devices, and find a number of shortcomings limiting the efficiency of these implementations at preventing device tracking.At the same time, we perform two real-world studies. The first one considers the development of actors exploiting this issue to install Wi-Fi tracking systems. We list some real-world installations and discuss their various aspects, including regulation, privacy implications, consent and public acceptance. The second one deals with the spread of MAC address randomization in the devices population.Finally, we present two tools: an experimental Wi-Fi tracking system for testing and public awareness raising purpose, and a tool estimating the uniqueness of a device based on the content of its emitted signals even if the identifier is randomized.Le récent développement des appareils portatifs possédant une interface Wi-Fi (smartphones, tablettes et « wearables ») s'accompagne d'une menace sur la vie privée de leurs utilisateurs, et sur la société toute entière. Ces appareils émettent en continu des signaux pouvant être capturés par un attaquant passif, à l'aide de matériel peu coûteux et de connaissances basiques. Ces signaux contiennent un identifiant unique appelé l'adresse MAC. Pour faire face à cette menace, les acteurs du secteur déploient actuellement une contre-mesure sur les appareils récents: le changement aléatoire de l'adresse MAC. Malheureusement, nous montrons que cette mesure, dans son état actuel, n'est pas suffisante pour empêcher le traçage des appareils.Pour cela, nous introduisons plusieurs attaques basées sur le contenu et la répartition temporelle des signaux. En complément, nous étudions les implémentations du changement aléatoire de l'adresse MAC sur des appareils récents, et trouvons un certain nombre de manquements limitant l'efficacité de ces implémentations à prévenir le traçage.En parallèle, nous effectuons deux études de terrain. La première s'attaque au développement des acteurs exploitant les problèmes cités plus haut afin d'installer des systèmes de traçage basés sur le Wi-Fi. Nous listons certaines de ces installations et examinons plusieurs aspects de ces systèmes : leur régulation, les implications en terme de vie privée, les questions de consentement et leur acceptation par le public. La seconde étude concerne la progression du changement aléatoire d'adresse MAC dans la population des appareils.Finalement, nous présentons deux outils : le premier est un système de traçage expérimental développé pour effectuer des tests et sensibiliser le public aux problèmes de vie privée liés à de tels systèmes. Le second estime l'unicité d'un appareil en se basant sur le contenu des signaux qu'il émet, même si leur identifiant est modifié

    Data-driven stochastic inversion under functional uncertainties

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    In this paper, we propose a new methodology to deal with an uncertain functional input in inversion problems through computer experiments. This study is motivated by an automotive application. In this context, the simulator code takes a double set of simulation inputs : deterministic control variables and functional random variables. This framework is characterized by two features. The first feature is the high computational cost of simulations, which makes the inversion in the presence of uncertainties unaffordable. The second feature is that the probability density of the functional input V is only known through a sample of realizations. The proposed method involves two imbricated tasks. A first task based on a bayesian approach aims at wisely choosing the new evaluations of the code in order to estimate the excursion set with a limited number of costly simulations. The second task targets on efficiently estimating the expectation over the functional random variable. As the uncertain variable is observable through a finite training sample, we present three ways to infer the distribution from data. Our method is illustrated and calibrated on an analytical example. It is then applied on the automotive industrial test case where the objective is to identify the set of control parameters leading to meet the pollutant emissions standards of a vehicle

    Une formalisation en Coq de l'intégrale de Lebesgue des fonctions positives

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    Integration, just as much as differentiation, is a fundamental calculus tool that is widely used in many scientific domains. Formalizing the mathematical concept of integration and the associated results in a formal proof assistant helps providing the highest confidence on the correction of numerical programs involving the use of integration, directly or indirectly. By its capability to extend the (Riemann) integral to a wide class of irregular functions, and to functions defined on more general spaces than the real line, the Lebesgue integral is considered as perfectly suited for use in mathematical fields such as probability theory, numerical mathematics, and real analysis. In this article, we present the Coq formalization of σ\sigma-algebras, measures, simple functions, and integration of nonnegative measurable functions, up to the full formal proofs of the Beppo Levi (monotone convergence) theorem and Fatou's lemma. More than a plain formalization of known literature, we present several design choices made to balance the harmony between mathematical readability and usability of Coq theorems. These results are a first milestone towards the formalization of LpL^p spaces such as Banach spaces.Le calcul intégral, tout comme le calcul différentiel, est un outil fondamental utilisé largement dans de nombreux domaines scientifiques. La formalisation de la notion mathématique d'intégrale et de ses propriétés dans un assistant de preuve aide à donner la plus grande confiance sur la correction de programmes numériques utilisant l'intégration, directement ou indirectement. De part sa capacité à étendre l'intégrale (de Riemann) à une large classe de fonctions irrégulières, et à des fonctions définies sur des espaces plus généraux que la droite réelle, l'intégrale de Lebesgue est considérée comme parfaitement adaptée aux domaines mathématiques tels que la théorie des probabilités, les mathématiques numériques et l'analyse réelle. Dans cet article, nous présentons la formalisation en Coq des tribus (ou σ\sigma-algèbres), des mesures, des fonctions étagées et de l'intégrale des fonctions mesurables positives, jusqu'aux preuves formelles complètes du théorème de convergence monotone de Beppo Levi et du lemme de Fatou. Plus qu'une simple formalisation de la littérature connue, nous présentons plusieurs choix de design menés pour équilibrer l'harmonie entre la lisibilité mathématique et l'ergonomie des théorèmes Coq. Ces résultats sont un premier jalon vers la formalisation des espaces LpL^p comme espaces de Banach

    Convergence of a finite volume scheme for a parabolic system with a free boundary modeling concrete carbonation

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    International audienceIn this paper we define and study a finite volume scheme for a concrete carbonation model proposed by Aiki and Muntean in [1]. The model consists in a system of two weakly coupled parabolic equations in a varying domain whose length is governed by an ordinary differential equation. The numerical sheme is obtained by a Euler discretisation in time and a Scharfetter-Gummel discretisation in space. We establish the convergence of the scheme. As a by-product, we obtain existence of a solution to the model. Finally, some numerical experiments show the efficiency of the scheme

    Small-world networks and RNA secondary structures

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    International audienceLet SnS_n denote the network of all RNA secondary structures of length nn, in which undirected edges exist between structures ss, tt such that tt is obtained from ss by the addition, removal or shift of a single base pair. Using context-free grammars, generating functions and complex analysis, we show that the asymptotic average degree is O(n)O(n) and that the asymptotic clustering coefficient is O(1/n)O(1/n), from which it follows that the family SnS_n, n=1,2,3,n = 1, 2, 3,\ldots of secondary structure networks is not small-world

    Construction of a two-phase flow with singular energy by gradient flow methods

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    We prove the existence of weak solutions to a system of two diffusion equations that are coupled by a pointwise volume constraint. The time evolution is given by gradient dynamics for a free energy functional. Our primary example is a model for the demixing of polymers, the corresponding energy is the one of Flory, Huggins and deGennes. Due to the non-locality in the equations, the dynamics considered here is qualitatively different from the one found in the formally related Cahn-Hilliard equations. Our angle of attack is from the theory of optimal mass transport, that is, we consider the evolution equations for the two components as two gradient flows in the Wasserstein distance with one joint energy functional that has the volume constraint built in. The main difference to our previous work [6] is the nonlinearity of the energy density in the gradient part, which becomes singular at the interface between pure and mixed phases

    High-Order Time Discretization Of The Wave Equation By Nabla-P Scheme

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    International audienceHigh-order Discontinuous Galerkin Methods (DGM) are now routinely used for simulationof wave propagation, especially for geophysical applications. However, to fully take full advantage of thehigh-order space discretization, it is relevant to use a high-order time discretization. Hence, DGM arecurrently coupled with ADER schemes, which leads to high-order explicit time schemes, but requiresthe introduction of auxiliary unknowns. The memory can thus be considerably cluttered up. In thiswork, we propose a new high order time scheme, the so-called Nabla-p scheme. This scheme doesnot increase the storage costs since it is a single step method which does not require introducingauxiliary unknowns. Numerical results show that for a given accuracy, the new scheme requires lesscomputational burden regarding both the memory and the computational costs than the DG-ADERschemeLes méthodes de Galerkin Discontinues (DGM) d’ordre élevé sont maintenant couramment utilisées pour la simulation de la propagation des ondes, en particulier pour les applicationsgéophysiques. Cependant, pour profiter pleinement d’une discrétisation en espace d’ordre élevé, ilest pertinent d’utiliser une discrétisation en temps d’ordre élevé. C’est pourquoi les DGM sont souvent associées à des schémas ADER, ce qui conduit à des formulations en temps explicites et d’ordreélevé. Toutefois, les méthodes DG-ADER nécessitent d’introduire des inconnue auxiliaire, ce qui peutencombrer considérablement la mémoire. Dans ce travail, nous proposons un nouveau schéma temporel d’ordre élevé, le schéma Nabla-p. Ce schéma n’augmente pas les coûts de stockage car il s’agitd’une méthode à un pas, sans utilisation d’inconnues auxiliaires. Les résultats numériques montrentqu’il nécessite moins d’espace mémoire et qu’il coûte moins cher que la méthode DG-ADER pour uneprécision donnée

    Cell Pairings for Ascidian Embryo Registration

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    International audienceRecent microscopy techniques allow imaging temporal 3D stacks of developing organs or embryos with a cellular level of resolution and with a sufficient acquisition frequency to accurately track cell lineages. Imaging multiple organs or embryos in different experimental conditions may help decipher the impact of genetic backgrounds and environmental inputs on the developmental pro-gram. For this, we need to precisely compare distinct individuals and to compute population statistics. The first step of this procedure is to develop methods to register individuals. From a previous work of cell segmentation from microscopy im-ages, we here demonstrate how to extract the symmetry plane of em-bryos at early stages, and how to use this information as a geometri-cal constraint to both register these embryos and obtain a cell-to-cell mapping

    Extension de la Complexité Implicite et des Machines Abstraites aux Langues avec Contrôle

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    The Curry-Howard isomorphism is the idea that proofs in natural deduction can be put in correspondence with lambda terms in such a way that this correspondence is preserved by normalization. The concept can be extended from Intuitionistic Logic to other systems, such as Linear Logic. One of the nice consequences of this isomorphism is that we can reason about functional programs with formal tools which are typical of proof systems: such analysis can also include quantitative qualities of programs, such as the number of steps it takes to terminate. Another is the possibility to describe the execution of these programs in terms of abstract machines.In 1990 Griffin proved that the correspondence can be extended to Classical Logic and control operators. That is, Classical Logic adds the possibility to manipulate continuations. In this thesis we see how the things we described above work in this larger context.L'isomorphisme de Curry-Howard est l'idée que les preuves en déduction naturelle peuvent être mises en correspondance avec lambda-termes de telle manière que cette correspondance est préservée par la normalisation. Le concept peut être étendu à partir intuitionniste Logique à d'autres systèmes, tels que la logique linéaire. Une des belles conséquences de cet isomorphisme est que nous pouvons raisonner sur des programmes fonctionnels avec des outils formels qui sont typiques des systèmes de preuve: une telle analyse peut également inclure qualités quantitatives de programmes, tels que le nombre d'étapes nécessaires pour la terminaison. Un autre est la possibilité de décrire l'exécution de ces programmes en termes de machines abstraites.En 1990, Griffin a prouvé que la correspondance peut être étendue à des opérateurs logiques et de contrôle classiques. Ce est à dire, la logique classique ajoute la possibilité de manipuler des continuations. Dans cette thèse, nous voyons comment les choses que nous décrites ci-dessus travail dans ce contexte plus large
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