L'archive ouverte pluridisciplinaire HAL , est destinée au dépôt et à la diffusion d'articles scientifiques de niveau recherche, publiés ou non, et de thèses, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Derniers Dépôts
Chimie
Économie et finance quantitative
Informatique
Mathématiques
Physique
Planète et Univers
Science non linéaire
Sciences cognitives
Sciences de l'environnement
Sciences de l'Homme et Société
Sciences de l'ingénieur
Sciences du Vivant
Statistiques
Amélioration des propriétés des couches minces de carbone amorphe (appelé Diamond Like Carbon, DLC) et recherche de nouvelles fonctionnalités pour ce type de couches minces en dopant les films DLC par des métaux comme le nickel et le tantale.
La cinétique de la décomposition thermique de Co3O4 a été étudiée sur des échantillons pulvérulent ou monocristallins. La formation d'une couche compacte de monoxyde de cobalt ainsi que la forme de l'équation décrivant les courbes degré de décomposition-temps ont abouti au développement d'un modèle dans lequel la cinétique est limitée par la diffusion de l'oxygène à travers la couche. Ce modèle dérive de celui de Ginstling et Brounshtein tient compte de la variation de l'énergie d'activation avec le degré de décomposition. Une interprétation des propriétés électriques de Co3O4 pur et dopé est également proposée.
Ultrafiltration polyethersulfone membranes were modified covalently by chemical reduction of aryl diazonium salts. Functionalizations were performed with four aryl diazonium salts bearing different functional groups (4-benzyltriphenylphosphonium diazonium, 4-nitrophenyl diazonium, 4-benzonitrile diazonium and 4-phenylacetic acid diazonium) so as to demonstrate the versatility of the method. The efficiency of the different functionalizations was checked with various characterization techniques. Attenuated Total Reflectance Fourier Transform Infra Red spectroscopy revealed the presence of 4-nitrophenyl, 4-benzonitrile and 4-phenylacetic acid groups at the surface of the different modified membranes but no characteristic vibration band was detected on the surface of the membrane modified with 4-benzyltriphenylphosphonium diazonium. The presence of 4-benzyltriphenylphosphonium, however, could be demonstrated by both Energy Dispersive X-ray spectroscopy (detection of the Kα ray of phosphorous at 2.015 keV) and streaming current measurements (shift of the membrane isoelectric point). Finally, dead-end filtration of an antibiotic (tylosin) was carried out with the unmodified membrane and the membrane modified by 4-benzyltriphenyl-phosphonium diazonium. Experiments revealed that the transport properties of the grafted membrane were significantly modified, with a significant increase in rejection mainly due to electrostatic repulsions between the surface of the modified membrane and tylosin.
In this paper we build a method to optimize Multi-Year Prospective Budgets. First we present a systemic model of Local Community Finances. Then, from two acceptable Multi-Year Prospective Budgets the method implements a Genetic Algorithm to generate a collection of admissible Multi-Year Prospective Budgets among which Decision-Makers can choose. The method is tested on simplified cases and on in operational situation and gives satisfactory results.
Cette these propose un cadre mathematique pour la modelisation du risque endogene dans les marches financiers. Le risque endogene designe le risque genere, et amplifie, au sein du systeme financier lui-meme, par les differents acteurs economiques et leurs interactions, par opposition au risque exogene, genere par des chocs exterieurs au systeme financier. Notre etude est motivee par l'observation des differentes crises financieres passees, qui montre le role central du risque endogene dans les marches financiers. Ainsi, les periodes de crises sont souvent associees a des phenomenes de liquidation/ventes 'eclair ('fire sales'), qui g'en'erent, de mani'ere endog'ene, une importante volatilit'e pour les actifs financiers et des pics inattendus de corr'elations entre les rendements de ces actifs, entraˆınant de fortes pertes pour les investisseurs. Alors que la structure de d'ependance entre les rendements d'actifs financiers est traditionnellement mod'elis'ee de mani'ere exog'ene, les faits d'ecrits pr'ec'edemment sugg'erent qu'une telle mod'elisation exog'ene ne peut rendre compte du risque endog'ene observ'e dans les march'es financiers. L'id'ee principale de cette th'ese est de distinguer entre deux origines pour la corr'elation entre actifs. La premi'ere est exog'ene et refl'ete une corr'elation fondamentale. La seconde est endog'ene et trouve son origine dans l'offre et la demande syst'ematiques g'en'er'ees par les grandes institutions financi'eres. Nous mod'elisons la dynamique en temps discret des prix d'actifs financiers d'un march'e multi-actifs par une chaˆıne de Markov dans lequel le rendement de chaque actif, 'a chaque p'eriode k, se d'ecompose en un terme al'eatoire - qui repr'esente les fondamentaux de l'actif et est independant du passe - et un terme d'offre/demande syst'ematique, genere de maniere endogene. Dans chaque chapitre, nous caracterisons mathematiquement cette offre endog'ene et son impact sur les prix d'actifs financiers. Nous exhibons des conditions sous lesquelles la chaıne de Markov converge faiblement, lorsque le pas de temps du modele discret tend vers zero, vers la solution d'une equation differentielle stochastique dont nous donnons le drift et la volatilite multi-dimensionnels. L''etude du processus de covariation quadratique de la limite diffusive nous permet de quantifier l'impact de l'offre et demande endogenes systematiques sur la structure de dependance entre actifs. Enfin, nous developpons des outils statistiques et econometriques visant a resoudre le probleme inverse d'identification et d'estimation des parametres de notre modele a partir de donnees de prix d'actifs financiers. Le Chapitre 1 'etudie le risque endogene genere par un fonds sujet a des ventes forcees en raison d'investisseurs qui sortent de leurs positions lorsque le fonds sous-performe et que sa valeur passe en-dessous d'un seuil. Nous modelisons l'offre et la demande provenant de telles ventes forcees en introduisant une 'fonction de liquidation' f qui mesure la vitesse 'a laquelle les investisseurs sortent de leurs positions dans le fonds. Nous supposons que l'offre en exces due au fonds sur chaque actif impacte le rendement de l'actif de maniere lineaire et nous explicitons les conditions pour que la dynamique de prix en temps discret soit une chaˆıne de Markov dans (R∗ )n, ou' n est le nombre d'actifs dans le marche. Nous exhibons des conditions sous lesquelles le modele discret converge faiblement vers une diffusion en temps continu et calculons les drifts et volatilites multi- 7 dimensionnels de la dynamique de prix en temps continu. L'etude de la covariation quadratique de la limite diffusive permet d'expliciter l'impact des ventes forcees dans le fonds sur la structure de d'ependance entre les actifs financiers. En particulier, nous montrons que la matrice de covariance realisee s''ecrit comme la somme d'une matrice de covariance fondamentale et une matrice de covariance en exces, qui depend des positions du fonds, de la liquidite des actifs et de la trajectoire passee des prix et qui est nulle lorsqu'il n'y a pas de ventes forcees. Nous prouvons alors que cet impact endogene augmente la volatilite du fonds en question, exactement dans les scenarios ou' le fonds subit des pertes. Nous calculons 'egalement son impact sur la volatilit'e d'autres fonds investissant dans les memes actifs et prouvons l'existence d'une relation d'orthogonalite entre les positions du fonds de reference et d'un autre fonds telle que, si cette relation d'orthogonalite est verifiee, des ventes forcees dans le fonds de reference n'affectent pas la volatilit'e de l'autre fonds. Le Chapitre 2 etend les resultats du Chapitre 1 au cas de plusieurs fonds et d'un impact quelconque (pas necessairement lineaire) de l'offre aggregee en exces provenant de ventes forcees dans ces fonds, sur les rendements de prix d'actifs. Nous exhibons des conditions sous lesquelles le mod'ele discret converge faiblement vers une diffusion en temps continu. La fonction de volatilite de la limite diffusive ne depend de la fonction de d'impact qu''a travers sa derivee premiere en zero, montrant qu'un modele de d'impact lineaire capture completement l'impact des effets de retroaction dus aux ventes forcees dans les differents fonds sur la structure de dependance entre actifs. Nous calculons la matrice de covariance realisee, en fonction des positions liquid'ees, en particulier dans un cas simple ou' les liquidations ont lieu 'a vitesse constante, dans un intervalle de temps fix'e et nous donnons des conditions assurant que cette relation peut etre inversee et les volumes de liquidations identifi'es. Nous construisons alors un estimateur du volume de liquidation dans chaque actif, dont nous prouvons la consistance, et pour lequel nous d'erivons un th'eor'eme central limite, qui nous permet de construire un test statistique testant si, pendant une periode donnee, des liquidations ont eu lieu. Nous illustrons notre procedure d'estimation avec deux exemples empiriques: le 'quant event' d'aouˆt 2007 et les liquidations suivant la faillite de Lehman Brothers en Automne 2008. Le Chapitre 3 etudie l'impact d'un investisseur institutionnel investissant une portion constante de sa richesse dans chaque actif (strategie fixed-mix). Pour un vecteur d'allocations donne, nous prouvons l'existence d'une unique strategie fixed-mix autofinancante. A chaque p'eriode, le prix des n actifs et la valeur du fonds fixed-mix sont obtenus comme la solution d'un probl'eme de point fixe. Nous montrons que, sous certaines conditions que nous explicitons, le modele discret converge vers une limite diffusive, pour laquelle nous calculons la covariance et la correlation realisee 'a l'ordre un en liquidit'e. Nos r'esultats montrent que la presence d'investisseurs institutionnels peut modifier les correlations de facon significative. Nous calculons les vecteurs propres et valeurs propres de la matrice de correlation realisee (a' l'ordre un en liquidite). L''etude des drifts de la limite continue nous permet de calculer les rendements esperes des actifs et montre qu'en raison de la presence de l'investisseur institutionnel, les rendements esp'er'es des actifs avec grand (resp. faible) drift fondamental, compares au rendement fondamental du fonds, diminuent (resp. augmentent). Nous calculons, dans un exemple simple, la strategie efficiente pour un critere moyenne-variance et montrons qu'elle est differente de la strategie optimale fondamentale (sans le fonds). L''etude de la frontiere optimale dans cet exemple montre qu'un investisseur prenant en compte l'impact de l'investisseur institutionnel peut ameliorer son rendement pour un niveau de risque donne.
We formalize the randomization procedure undertaken to discriminate players in real option games with Stackelberg leadership advantage. This is done by introducing a random arbitrator with specific parameterizations, and allows to propose a unified treatment of both Cournot and Stackelberg competition in real option games. We extend the study to a partial arbitrator, which leads to competitive advantages in various asymmetrical situations. We fully characterize strategic interactions. We then apply the procedure to risk-neutral and risk-averse firms in a stochastic preemptive real option game in complete market under regulation. The risk-averse case gives us the opportunity to study a new phenomenon we call aversion for confrontation, and its impact on the asymmetrical game.
Majorization-minimization algorithms consist of iteratively minimizing a majorizing surrogate of an objective function. Because of its simplicity and its wide applicability, this principle has been very popular in statistics and in signal processing. In this paper, we intend to make this principle scalable. We introduce and study a stochastic majorization-minimization scheme, which is able to deal with large-scale or possibly infinite data sets. When applied to convex optimization problems under suitable assumptions, we show that it achieves an expected convergence rate of O(1/\sqrt{n}) after n iterations, and O(1/n) for strongly convex functions. Equally important, our scheme almost surely converges to stationary points for a large class of non-convex problems. We derive from our framework several efficient algorithms. First, we propose a new stochastic proximal gradient method, which experimentally matches state-of-the-art solvers for large-scale l1-logistic regression. Second, we develop an online DC programming algorithm for non-convex sparse estimation. Finally, we demonstrate the effectiveness of our technique for solving large-scale structured matrix factorization problems.
Cet article étudie la robustesse aux bruits de type outlier dans le cadre de la super-résolution. On utilise l'équivalence entre reconstruction parcimonieuse et robustesse aux outliers pointée par Candès et Tao. Elle permet de déduire des bornes sur le nombre d'images acquises en fonction de la quantité d'outliers qui garantissent une reconstruction parfaite par minimisation L1.
Nous présentons dans ce papier un capteur de stéréovision à base de caméras fisheyes coaxiales, capables d'observer jusqu'à 2x3 voies de circulation et destiné à des applications autoroutières. En s'appuyant sur une modélisation sphérique des vues fisheyes, nous proposons une approche d'estimation de carte de disparité directe sans dépliage suivie d'une reconstruction 3D. La méthode proposée est entièrement basée sur l'interprétation des données de disparité / 3D. Le système élaboré permet d'acquérir, reconstruire et classifier automatiquement des véhicules dont les 2 Roues Motorisés (2RM). Les résultats expérimentaux montrent l'efficacité de la méthode, testée jusqu'à 133km/h sur voie rapide.
Majorization-minimization algorithms consist of iteratively minimizing a majorizing surrogate of an objective function. Because of its simplicity and its wide applicability, this principle has been very popular in statistics and in signal processing. In this paper, we intend to make this principle scalable. We introduce and study a stochastic majorization-minimization scheme, which is able to deal with large-scale or possibly infinite data sets. When applied to convex optimization problems under suitable assumptions, we show that it achieves an expected convergence rate of O(1/\sqrt{n}) after n iterations, and O(1/n) for strongly convex functions. Equally important, our scheme almost surely converges to stationary points for a large class of non-convex problems. We derive from our framework several efficient algorithms. First, we propose a new stochastic proximal gradient method, which experimentally matches state-of-the-art solvers for large-scale l1-logistic regression. Second, we develop an online DC programming algorithm for non-convex sparse estimation. Finally, we demonstrate the effectiveness of our technique for solving large-scale structured matrix factorization problems.
We propose an iterative approximate reconstruction algorithm for non-overdetermined inverse scattering at fixed energy E with incomplete data in dimension d >= 2. In particular, we obtain rapidly converging approximate reconstructions for this inverse scattering for E --> +infinity.
This article deals with a numerical solution of combined radiation and conduction heat transfer in gray participating (non-scattering) medium in a two-dimensional domain using triangular meshes. The radiative transfer equation is solved using the high order Discontinuous Galerkin method with an upwind numerical flux. The energy balance equation is discretized with a high finite order element method. A stability and error analysis are performed for the numerical methods to solve the two-equations. The radiative - conductive heat transfer problem is examined under different types of boundary conditions. High performances of the proposed technique, in terms of computational requirements, accuracy and stability, are shown through numerical examples.
L'étude in situ des relations Soleil-Terre et plus généralement des environnements ionisés du système solaire, nécessite la mesure d'ondes qui se propagent dans un plasma magnétisé. A bord des observatoires spatiaux, la composante magnétique de ces ondes est obtenue à l'aide de magnétomètres à induction. La mesure des hautes fréquences (de quelques Hz à quelques 100 kHz) est réalisée par des magnétomètres Searchcoil tandis que celles des basses fréquences (de quelques 10 mHz à quelques Hz) et de la composante continue sont confiées aux magnétomètres Fluxgate. Cette thèse porte sur le développement d'un magnétomètre dont la bande de mesure s'étend du continu à plusieurs kiloHertz. On y présente un concept instrumental innovant reposant sur la mise en œuvre simultanée d'une mesure inductive et magnétorésistive du champ magnétique. Nous nous intéressons d'abord à la conception et à l'étude de capteurs à magnétorésistance anisotrope (AMR) et à magnétorésistance tunnel (TMR) dont les propriétés d'anisotropie sont contrôlées par couplage d'échange. Nous montrons ensuite comment ces magnétorésistances peuvent être intégrées à un magnétomètre Searchcoil dont le noyau ferromagnétique est mis à profit pour réaliser un concentrateur magnétique performant. Nous détaillons alors les différents aspects de la conception d'un magnétomètre hybride Searchcoil/Magnétorésistance répondant aux contraintes environnementales associées aux expériences spatiales ainsi que d'un outil original d'optimisation des performances, alliant un modèle par éléments finis à un algorithme de type génétique. Nous prouvons enfin la faisabilité du concept proposé en réalisant un premier prototype de magnétomètre hybride Searchcoil/Capteur PHE tri-axes et de son électronique de préamplification faible bruit. La sensibilité de ce prototype, testé en conditions réelles lors d'un tir de fusée scientifique, avoisine les 200 fT/sqrt (Hz) à 1 kHz et les 400 pT/sqrt (Hz) à 1 Hz.
Life is a discrete, stochastic phenomena : for a biological organism, the time of the two most important events of its life (reproduction and death) is random and these events change the number of individuals of the species by single units. These facts can have surprising, counter-intuitive consequences. I review here three examples where these facts play, or could play, important roles : the spatial distribution of species, the biodiversity and the (Darwinian) evolution of altruistic behavior.
Dans cette thèse, nous étudions le problème de la localisation de sources sismo-volcanique, à partir des données enregistrées par des r\'{e}seaux de capteurs composés de nouveaux sismomètres à trois composantes (3C). Nous nous concentrerons sur le volcan Ubinas, l'un des plus actifs au Pérou. Nous développons une nouvelle approche (MUSIC-3C) basée sur la méthode MUSIC permettant de retourner les 3 paramètres utiles (lenteur, azimut et incidence). Pour valider notre méthodologie, nous analysons des sources synthétiques propagées en tenant compte de la topographie du volcan Ubinas. Dans cette expérience, les données synthétiques ont été générées pour plusieurs sources situées à différentes profondeurs sous le cratère Ubinas. Nous utilisons l'algorithme MUSIC-3C pour les relocaliser. Nous traitons également des données réelles provenant d'une expérience de terrain menée sur le volcan Ubinas (Pérou) en 2009 par les équipes de recherche de l'IRD-France (Institut de Recherche pour le Développement), UCD l'Irlande (projet VOLUME) et l'Institut de Géophysique du Pérou (IGP). Nous utilisons l'algorithme MUSIC-3C pour localiser les évènements explosifs (type vulcanien), ce qui nous permet d'identifier et d'analyser les processus physiques de ces évènements. Dans la suite de cette analyse, nous avons trouvé deux sources pour chaque explosion situées à 300 m et 1100 m en dessous du fond du cratère actif. Basé sur les mécanismes éruptifs proposés pour d'autres volcans du même type, nous interprétons la position de ces sources ainsi que les limites du conduit éruptif impliqué dans le processus de fragmentation.
The continental margin of southeast Brazil is elevated. Onshore Tertiary basins and Late Cretaceous/Paleogene intrusions are good evidence for post breakup tectono-magmatic activity. To constrain the impact of post-rift reactivation on the geological history of the area, we carried out a new thermochronological study. Apatite fission track ages range from 60.7 1.9 Ma to 129.3 4.3 Ma, mean track lengths from 11.41 0.23 mm to 14.31 0.24 mm and a subset of the (U-Th)/He ages range from 45.1 1.5 to 122.4 2.5 Ma. Results of inverse thermal history modeling generally support the conclusions from an earlier study for a Late Cretaceous phase of cooling. Around the onshore Taubaté Basin, for a limited number of samples, the first detectable period of cooling occurred during the Early Tertiary. The inferred thermal histories for many samples also imply subsequent reheating followed by Neogene cooling. Given the uncertainty of the inversion results, we did deterministic forward modeling to assess the range of possibilities of this Tertiary part of the thermal history. The evidence for reheating seems to be robust around the Taubaté Basin, but elsewhere the data cannot discriminate between this and a less complex thermal history. However, forward modeling results and geological information support the conclusion that the whole area underwent cooling during the Neogene. The synchronicity of the cooling phases with Andean tectonics and those in NE Brazil leads us to assume a plate-wide compressional stress that reactivated inherited structures. The present-day topographic relief of the margin reflects a contribution from post-breakup reactivation and uplift.
Adding to the on-going debate regarding vegetation recolonisation (more particularly the timing) in Europe and climate change since the Lateglacial, this study investigates a long sediment core (LL081) from Lake Ledro (652ma.s.l., southern Alps, Italy). Environmental changes were reconstructed using multiproxy analysis (pollen-based vegetation and climate reconstruction, lake levels, magnetic susceptibility and X-ray fluorescence (XRF) measurements) recorded climate and land-use changes during the Lateglacial and early-middle Holocene. The well-dated and high-resolution pollen record of Lake Ledro is compared with vegetation records from the southern and northern Alps to trace the history of tree species distribution. An altitudedependent progressive time delay of the first continuous occurrence of Abies (fir) and of the Larix (larch) development has been observed since the Lateglacial in the southern Alps. This pattern suggests that the mid-altitude Lake Ledro area was not a refuge and that trees originated from lowlands or hilly areas (e.g. Euganean Hills) in northern Italy. Preboreal oscillations (ca. 11 000 cal BP), Boreal oscillations (ca. 10 200, 9300 cal BP) and the 8.2 kyr cold event suggest a centennial-scale climate forcing in the studied area. Picea (spruce) expansion occurred preferentially around 10 200 and 8200 cal BP in the south-eastern Alps, and therefore reflects the long-lasting cumulative effects of successive boreal and the 8.2 kyr cold event. The extension of Abies is contemporaneous with the 8.2 kyr event, but its development in the southern Alps benefits from the wettest interval 8200-7300 cal BP evidenced in high lake levels, flood activity and pollen-based climate reconstructions. Since ca. 7500 cal BP, a weak signal of pollen-based anthropogenic activities suggest weak human impact. The period between ca. 5700 and ca. 4100 cal BP is considered as a transition period to colder and wetter conditions (particularly during summers) that favoured a dense beech (Fagus) forest development which in return caused a distinctive yew (Taxus) decline.We conclude that climate was the dominant factor controlling vegetation changes and erosion processes during the early and middle Holocene (up to ca. 4100 cal BP).
L'étude in situ des relations Soleil-Terre et plus généralement des environnements ionisés du système solaire, nécessite la mesure d'ondes qui se propagent dans un plasma magnétisé. A bord des observatoires spatiaux, la composante magnétique de ces ondes est obtenue à l'aide de magnétomètres à induction. La mesure des hautes fréquences (de quelques Hz à quelques 100 kHz) est réalisée par des magnétomètres Searchcoil tandis que celles des basses fréquences (de quelques 10 mHz à quelques Hz) et de la composante continue sont confiées aux magnétomètres Fluxgate. Cette thèse porte sur le développement d'un magnétomètre dont la bande de mesure s'étend du continu à plusieurs kiloHertz. On y présente un concept instrumental innovant reposant sur la mise en œuvre simultanée d'une mesure inductive et magnétorésistive du champ magnétique. Nous nous intéressons d'abord à la conception et à l'étude de capteurs à magnétorésistance anisotrope (AMR) et à magnétorésistance tunnel (TMR) dont les propriétés d'anisotropie sont contrôlées par couplage d'échange. Nous montrons ensuite comment ces magnétorésistances peuvent être intégrées à un magnétomètre Searchcoil dont le noyau ferromagnétique est mis à profit pour réaliser un concentrateur magnétique performant. Nous détaillons alors les différents aspects de la conception d'un magnétomètre hybride Searchcoil/Magnétorésistance répondant aux contraintes environnementales associées aux expériences spatiales ainsi que d'un outil original d'optimisation des performances, alliant un modèle par éléments finis à un algorithme de type génétique. Nous prouvons enfin la faisabilité du concept proposé en réalisant un premier prototype de magnétomètre hybride Searchcoil/Capteur PHE tri-axes et de son électronique de préamplification faible bruit. La sensibilité de ce prototype, testé en conditions réelles lors d'un tir de fusée scientifique, avoisine les 200 fT/sqrt (Hz) à 1 kHz et les 400 pT/sqrt (Hz) à 1 Hz.
We report an experimental study of a dilute ''gas'' of magnetic particles subjected to a vertical alternating magnetic field in a 3D container. Due to the torque exerted by the field on the magnetic moment of each particle, a spatially homogeneous and random forcing is reached where only rotational motions are driven. This forcing differs significantly from boundary-driven systems used in most previous experimental studies on non equilibrium dissipative granular gases. Here, no cluster formation occurs, and the equation of state displays strong analogy with the usual gas one apart from a geometric factor. Collision statistics is also measured, and shows an exponential tail for the particle velocity distribution. Most of these observations are well explained by a simple model, and enable to better understand out-of-equilibrium systems uniformly ''heated''.
In this paper, we propose an adaptive observer-based synchronization approach for a class of chaotic Lur'e systems with slope restricted nonlinearities and delayed outputs. The delay is assumed bounded and time varying and the information to be transmitted is assumed piece-wise constant. Based on the Lyapunov-Krasovskii approach, we show that for sufficiently small values of the time-delay upper bound, both synchronization and information reconstruction objectives are ensured under a condition of persistent excitation and after solving a convex optimization problem. The result is illustrated via a numerical example of a chaotic communication system subject to a transmission delay.
We propose a robust adaptive chaotic synchronization method based on unknown-input observers for master-slave syn- chronization of chaotic systems, with application to secured com- munication. The slave system is modelled by an unknown input observer in which, the unknown input is the transmitted informa- tion. As in the general observer-based synchronization paradigm, the information is recovered if the master and slave systems ro- bustly synchronize. In the context of unknown-input observers, this is tantamount to estimating the master's states and the unknown inputs. The set-up also considers the presence of perturbations in the chaotic transmitter dynamics and in the output equations (the transmitted signal). That is, the estimator (slave system) must syn- chronize albeit noisy measurements and reject the effect of pertur- bations on the transmitter dynamics. We provide necessary and sufficient conditions for synchronization to take place. To highlight our contribution, we also present some simulation results with the purpose of comparing the proposed method to classical adaptive observer-based synchronization (without disturbance rejection). It is shown that additive noise is perfectly canceled and the encoded message is well recovered despite the perturbations.
In most animal species, vision is mediated by compound eyes, which offer lower resolution than vertebrate single-lens eyes, but significantly larger fields of view with negligible distortion and spherical aberration, as well as high temporal resolution in a tiny package. Compound eyes are ideally suited for fast panoramic motion perception. Engineering a miniature artificial compound eye is challenging because it requires accurate alignment of photoreceptive and optical components on a curved surface. Here, we describe a unique design method for biomimetic compound eyes featuring a panoramic, undistorted field of view in a very thin package. The design consists of three planar layers of separately produced arrays, namely, a microlens array, a neuromorphic photodetector array, and a flexible printed circuit board that are stacked, cut, and curved to produce a mechanically flexible imager. Following this method, we have prototyped and characterized an artificial compound eye bearing a hemispherical field of view with embedded and programmable low-power signal processing, high temporal resolution, and local adaptation to illumination. The prototyped artificial compound eye possesses several characteristics similar to the eye of the fruit fly Drosophila and other arthropod species. This design method opens up additional vistas for a broad range of applications in which wide field motion detection is at a premium, such as collision-free navigation of terrestrial and aerospace vehicles, and for the experimental testing of insect vision theories.
On étudiera les compléments de l'adjectif dans un traité technique, les RES RVSTICAE de Varron. On se demandera si, sur le modèle tesniérien de la valence verbale, on peut concevoir aussi une valence de l'adjectif latin. Cette analyse dépendancielle sera confrontée à une analyse interdépendancielle et rectionnelle.
There is a new Bayesian, or probabilistic, paradigm in the psychology of reasoning, with new psychological accounts of the indicative conditional of natural language. In psychological experiments in this new paradigm, people judge that the probability of the indicative conditional, P(if A then C), is the conditional probability of C given A, P(C | A). In other experiments, participants respond with what has been called the 'de- fective' truth table: they judge that if A then C is true when A holds and C holds, is false when A holds and C does not, and is neither true nor false when A does not hold. We argue that these responses are not 'defective' in any negative sense, as many psychologists have implied. We point out that a number of normative researchers, including de Finetti, have proposed such a table for various coherent interpretations of the third value. We review the relevant general tables in the normative literature, in which there is a third value for A and C and the logically compound forms of the natural language conditional, negation, conjunction, disjunction, and the material conditional. We describe the results of an experiment on which of these tables best describes ordinary people's judgements when the third value is interpreted as indicating uncertainty.
Adding to the on-going debate regarding vegetation recolonisation (more particularly the timing) in Europe and climate change since the Lateglacial, this study investigates a long sediment core (LL081) from Lake Ledro (652ma.s.l., southern Alps, Italy). Environmental changes were reconstructed using multiproxy analysis (pollen-based vegetation and climate reconstruction, lake levels, magnetic susceptibility and X-ray fluorescence (XRF) measurements) recorded climate and land-use changes during the Lateglacial and early-middle Holocene. The well-dated and high-resolution pollen record of Lake Ledro is compared with vegetation records from the southern and northern Alps to trace the history of tree species distribution. An altitudedependent progressive time delay of the first continuous occurrence of Abies (fir) and of the Larix (larch) development has been observed since the Lateglacial in the southern Alps. This pattern suggests that the mid-altitude Lake Ledro area was not a refuge and that trees originated from lowlands or hilly areas (e.g. Euganean Hills) in northern Italy. Preboreal oscillations (ca. 11 000 cal BP), Boreal oscillations (ca. 10 200, 9300 cal BP) and the 8.2 kyr cold event suggest a centennial-scale climate forcing in the studied area. Picea (spruce) expansion occurred preferentially around 10 200 and 8200 cal BP in the south-eastern Alps, and therefore reflects the long-lasting cumulative effects of successive boreal and the 8.2 kyr cold event. The extension of Abies is contemporaneous with the 8.2 kyr event, but its development in the southern Alps benefits from the wettest interval 8200-7300 cal BP evidenced in high lake levels, flood activity and pollen-based climate reconstructions. Since ca. 7500 cal BP, a weak signal of pollen-based anthropogenic activities suggest weak human impact. The period between ca. 5700 and ca. 4100 cal BP is considered as a transition period to colder and wetter conditions (particularly during summers) that favoured a dense beech (Fagus) forest development which in return caused a distinctive yew (Taxus) decline.We conclude that climate was the dominant factor controlling vegetation changes and erosion processes during the early and middle Holocene (up to ca. 4100 cal BP).
Dans cette thèse, nous étudions le problème de la localisation de sources sismo-volcanique, à partir des données enregistrées par des r\'{e}seaux de capteurs composés de nouveaux sismomètres à trois composantes (3C). Nous nous concentrerons sur le volcan Ubinas, l'un des plus actifs au Pérou. Nous développons une nouvelle approche (MUSIC-3C) basée sur la méthode MUSIC permettant de retourner les 3 paramètres utiles (lenteur, azimut et incidence). Pour valider notre méthodologie, nous analysons des sources synthétiques propagées en tenant compte de la topographie du volcan Ubinas. Dans cette expérience, les données synthétiques ont été générées pour plusieurs sources situées à différentes profondeurs sous le cratère Ubinas. Nous utilisons l'algorithme MUSIC-3C pour les relocaliser. Nous traitons également des données réelles provenant d'une expérience de terrain menée sur le volcan Ubinas (Pérou) en 2009 par les équipes de recherche de l'IRD-France (Institut de Recherche pour le Développement), UCD l'Irlande (projet VOLUME) et l'Institut de Géophysique du Pérou (IGP). Nous utilisons l'algorithme MUSIC-3C pour localiser les évènements explosifs (type vulcanien), ce qui nous permet d'identifier et d'analyser les processus physiques de ces évènements. Dans la suite de cette analyse, nous avons trouvé deux sources pour chaque explosion situées à 300 m et 1100 m en dessous du fond du cratère actif. Basé sur les mécanismes éruptifs proposés pour d'autres volcans du même type, nous interprétons la position de ces sources ainsi que les limites du conduit éruptif impliqué dans le processus de fragmentation.
Série du Dogger au Néocomien, molasse miocène et dépôts quaternaires. Zone plissée et chevauchante, affectée par des abaissements d'axe. Convergence du drainage karstique vers la zone structuralement la plus basse, transversale par rapport aux plis. Étude d'une retenue collinaire
It is a shared belief that Thomas Schelling' model of segregation is only weakly affected by the underlying spatial structure, whatever its complexity. Such a conclusion is important from an urban planning perspective as it suggests that only a very restricted range of possible actions, if any, would be able to contribute limiting social segregation, unless individual preferences are significantly modified. Our own simulations show that, using appropriate graph-based spatial structures, one can reveal significant spatial effects and thus provide alternative planning insights. Cliques in networks indeed play a significant role, reinforcing segregation effects in Schelling's model. Introducing a small amount of noise in the model permits us to reveal more precisely this effect, without modifying the global behavior of the initial model. Furthermore, we show how a logistic model describes in a concise but precise way this global behavior.
Haudricourt's main legacies to the field of Chinese historical phonology are his systematic account of tonogenesis, and his reconstruction of final *-s and of labiovelars. The method that he proposed under the term of Panchronic Phonology holds special promise for the study of the languages of China in their universal context.
Purpose: This study examines perpetrators and their fans media participation for the purpose of investigating whether new media produce school shootings anew. Method: We first analyze the narrative structure of eight school shooters' 75 self-produced videos (1999 2011), then conduct thematic and content analysis of this material. Then, based upon a three-year ethnographic investigation of a subculture on YouTube (2007 2010), from which a sample of 81 users, 142 videos, and screenshots of natural conversation was taken, we analyze the style and ritual practices, fan attachment, and online regulation of the subculture. Findings: The mirroring of the school shooters' videos and their fans' media practices highlights a trait of contemporary society: a need for distinction and intrinsic individuality directly linked to a modern era in which autonomy and self-production have become well-praised norms, and media a support for individuation. Social implications: We observe some of the pitfalls of contemporary social injunctions and how the media interplay into this dynamic. This research also emphasizes the role of regulation in an online subculture: opposition encountered tends to contribute to the individualization of positions rather than the reproduction of violence.
Cet article étudie la robustesse aux bruits de type outlier dans le cadre de la super-résolution. On utilise l'équivalence entre reconstruction parcimonieuse et robustesse aux outliers pointée par Candès et Tao. Elle permet de déduire des bornes sur le nombre d'images acquises en fonction de la quantité d'outliers qui garantissent une reconstruction parfaite par minimisation L1.
This paper presents the design and the implementation of a fully monolithic coupled-oscillator array, operating at 6 GHz with close to zero coupling phase, in 0.25 μm BICMOS SiGe process. This array is made of four LC-NMOS differential VCOs coupled through a resistor. The single LC-NMOS VCO structure is designed and optimized in terms of phase noise with a graphical optimization approach while satisfying design constraints. At 2.5 V power supply voltage, and a power dissipation of only 125 mW, the coupled oscillators array features a simulated phase noise of -127.3 dBc/Hz at 1 MHz frequency offset from a 6 GHz carrier, giving a simulated phase progression that was continuously variable over the range -64° < Δphi <64 ° and -116° < Δphi < 116°. This constant phase progression can be established by slightly detuning the peripheral array elements, while maintaining mutual synchronization.
The distinctive features of the loss of stability of elastic solids which undergo phase transitions are investigated for the case of small deformations. The non-uniqueness of the solution of the boundary-value problem for the describing of the thermodynamic equilibrium of a two-phase body is caused by the non-linearity associated with the unknown interface. The solution can be chosen by comparing the potential energies of the body in the two-phase and single phase states and by analysing of the local stability of the two-phase states. A linearized boundary-value problem is formulated which describes infinitesimal small perturbations of an initial two-phase state which is in thermodynamic equilibrium. Analysis of the stability of the two-phase state reduces to an investigation of the bifurcation points and the behaviour of the small solutions of the system of integrodifferential equations in terms of functions describing the perturbations of the interface. The problem of the non-uniqueness and loss of stability of centrisymmetric equilibrium two-phase deformations is investigated as an example. A theorem concerning the number of centrisymmetric solutions is proved. The energy changes accompanying the formation and development of two-phase states and the stability of the solutions obtained are investigated. The concept of topological instability as a bifurcation is introduced, as a result of which the type of geometry of a solution of the boundary-value problem changes and surfaces of separation of the phases actually appear and disappear. Macrodiagrams of the deformational are constructed which demonstrate the effect of deformation softening in the path of a phase transition.
The phytohormone auxin is known to regulate several aspects of plant development and Aux/IAA transcription factors play a pivotal role in auxin signaling. To further extend our understanding of the multiple functions of Aux/IAAs, the present study describes the functional characterization of Sl-IAA27, a member of the tomato Aux/IAA gene family. Sl-IAA27 displays a distinct behavior compared to most Aux/IAA regarding the regulation of its expression by auxin and the Sl-IAA27 encoded protein harbors a unique motif of unknown function also present in Sl-IAA9 and remarkably conserved in monocot and dicot species. Tomato transgenic plants under-expressing the Sl-IAA27 gene revealed multiple phenotypes related to vegetative and reproductive growth. Silencing of Sl-IAA27 results in higher auxin sensitivity, altered root development and reduced chlorophyll content in leaves. Both ovule and pollen display dramatic loss of fertility in Sl-IAA27 down-regulated lines and the internal anatomy of the flower and the fruit are modified with enlarged placenta in smaller fruits. In line with the reduced chlorophyll content in Sl-IAA27 RNAi leaves, genes involved in chlorophyll synthesis display lower expression at the level of transcript accumulation. Even though Sl-IAA27 is closely related to Sl-IAA9 in terms of sequence homology and the encoded proteins share common structural features, the data indicate that the two genes regulate tomato fruit initiation and development in a distinct manner.
BACKGROUND: Case management of imported malaria within the context of malaria pre-elimination is increasingly considered to be relevant because of the risk of resurgence. The assessment of malaria importation would provide key data i) to select countries with propitious conditions for pre-elimination phase and ii) to predict its feasibility. Recently, a sero-prevalence study in Djibouti indicated low malaria prevalence, which is propitious for the implementation of pre-elimination, but data on the extent of malaria importation remain unknown. METHODS: Djiboutian plasmodial populations were analysed over an eleven-year period (1998, 1999, 2002 and 2009). The risk of malaria importation was indirectly assessed by using plasmodial population parameters. Based on 5 microsatellite markers, expected heterozygosity (H.e.), multiplicity of infection, pairwise Fst index, multiple correspondence analysis and individual genetic relationship were determined. The prevalence of single nucleotide polymorphisms associated with pyrimethamine resistance was also determined. RESULTS: Data indicated a significant decline in genetic diversity (0.51, 0.59, 0.51 and 0 in 1998, 1999, 2002 and 2009, respectively) over the study period, which is inconsistent with the level of malaria importation described in a previous study. This suggested that Djiboutian malaria situation may have benefited from the decline of malaria prevalence that occurred in neighbouring countries, in particular in Ethiopia. The high Fst indices derived from plasmodial populations from one study period to another (0.12 between 1999 and 2002, and 0.43 between 2002 and 2009) suggested a random sampling of parasites, probably imported from neighbouring countries, leading to oligo-clonal expansion of few different strains during each transmission season. Nevertheless, similar genotypes observed during the study period suggested recurrent migrations and imported malaria. CONCLUSION: In the present study, the extent of genetic diversity was used to assess the risk of malaria importation in the low malaria transmission setting of Djibouti. The molecular approach highlights i) the evolution of Djiboutian plasmodial population profiles that are consistent and compatible with Djiboutian pre-elimination goals and ii) the necessity to implement the monitoring of plasmodial populations and interventions at the regional scale in the Horn of Africa to ensure higher efficiency of malaria control and elimination.
The paper proposes an observability analysis and estimation schemes for specific growth rates and biomass concentrations of the anaerobic digestion process. A 3-stage model of 5 dynamic states is assumed, describing the hydrolysis, acidogenesis and methanogenesis of two different populations of microorganisms (acidogenic and methanogenic). The main result is that the specific growth rates of the two populations of bacteria can be stability estimated only from easily measured quantities -- the dilution rate and the flow rates of methane and carbon dioxide in the biogas. The estimation schemes thus obtained have quite interesting features one of which is their freeness of most yield coefficients often hard to identify. The analysis rests on the differential algebraic approach of observation problems. The results are currently being confronted to experimental data from a 100m3 pilot bioreactor fed with cattle dung. Realistic simulations are presented in this paper as illustrations of the estimator performance.
Majorization-minimization algorithms consist of iteratively minimizing a majorizing surrogate of an objective function. Because of its simplicity and its wide applicability, this principle has been very popular in statistics and in signal processing. In this paper, we intend to make this principle scalable. We introduce and study a stochastic majorization-minimization scheme, which is able to deal with large-scale or possibly infinite data sets. When applied to convex optimization problems under suitable assumptions, we show that it achieves an expected convergence rate of O(1/\sqrt{n}) after n iterations, and O(1/n) for strongly convex functions. Equally important, our scheme almost surely converges to stationary points for a large class of non-convex problems. We derive from our framework several efficient algorithms. First, we propose a new stochastic proximal gradient method, which experimentally matches state-of-the-art solvers for large-scale l1-logistic regression. Second, we develop an online DC programming algorithm for non-convex sparse estimation. Finally, we demonstrate the effectiveness of our technique for solving large-scale structured matrix factorization problems.
We consider the problem of obtaining a prognostic on the survival time adjusted on covariates in a high-dimensional setting. Towards this end, we construct an estimator of the conditional intensity function that does not rely on an underlying model. We estimate it by the best Cox proportional hazards model given two dictionaries of functions. The first dictionary is used to construct an approximation of the logarithm of the baseline hazard function and the second to approximate the relative risk. As we are in high-dimension, we consider the Lasso procedure to estimate the unknown parameters of the best Cox model approximating the conditional hazard rate function. We provide non-asymptotic oracle inequalities for the Lasso estimator of the conditional hazard risk function. Our results rely on an empirical Bernstein's inequality for martingales with jumps.
In this work, we develop a method of adaptive nonparametric estimation, based on "warped" kernels. The aim is to estimate a real-valued function $s$ from a sample of random couples $(X,Y)$. We deal with transformed data $(\Phi(X),Y)$, with $\Phi$ a one-to-one function, to build a collection of kernel estimators. The data-driven selection of the best bandwidth is done with a method inspired by Goldenshluger and Lepski~(2011). The method permits to handle various problems such as additive and multiplicative regression, conditional density estimation, hazard rate estimation based on randomly right censored data, and cumulative distribution function estimation from current-status data. The interest is threefold. First, the squared-bias/variance trade-off is automatically realized. Next, non-asymptotic risk bounds are derived. Last, the estimator is easily computed thanks to its simple expression: a short simulation study is presented.
À l'attention du déposant
Le dépôt doit être effectué en accord avec les co-auteurs et dans le respect de la politique des éditeurs
La mise en ligne est assujettie à une modération, la direction de HAL se réservant le droit de refuser les articles ne correspondant pas aux critères de l'archive (voir le guide du déposant )
Tout dépôt est définitif, aucun retrait ne sera effectué après la mise en ligne de l'article
Consulter le ManuHAL Les fichiers textes au format pdf ou les fichiers images composant votre dépôt sont maintenant envoyés au CINES dans un contexte d'archivage à long terme.
À l'attention des lecteurs
Dans un contexte de diffusion électronique, tout auteur conserve ses droits intellectuels, notamment le fait de devoir être correctement cité et reconnu comme l'auteur d'un document.
Déposer
La convention de partenariat en faveur des archives ouvertes et de la plateforme mutualisée HAL a été signée le 2 avril 2013 :
en savoir plus
Déposer
Documents avec texte intégral
Répartition par domaines
Contact
Actualités
À voir
