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A method of determining the winsorization threshold, with an application to domain estimation
No full textInternational audienceIn business surveys, it is not unusual to collect economic variables for which the distribution is highly skewed. In this context, winsorization is often used to treat the problem of influential values. This technique requires the determination of a constant that corresponds to the threshold above which large values are reduced. In this paper, we consider a method of determining the constant which involves minimizing the largest estimated conditional bias in the sample. In the context of domain estimation, we also propose a method of ensuring consistency between the domain-level winsorized estimates and the population-level winsorized estimate. The results of two simulation studies suggest that the proposed methods lead to winsorized estimators that have good bias and relative efficiency properties
Hypergraph conditions for the solvability of the ergodic equation for zero-sum games
No full textInternational audienceThe ergodic equation is a basic tool in the study of mean-payoff stochastic games. Its solvability entails that the mean payoff is independent of the initial state. Moreover, optimal stationary strategies are readily obtained from its solution. In this paper, we give a general sufficient condition for the solvability of the ergodic equation, for a game with finite state space but arbitrary action spaces. This condition involves a pair of directed hypergraphs depending only on the ``growth at infinity'' of the Shapley operator of the game. This refines a recent result of the authors which only applied to games with bounded payments, as well as earlier nonlinear fixed point results for order preserving maps, involving graph conditions
Performance evaluation of an emergency call center: tropical polynomial systems applied to timed Petri nets
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Génération de seconde harmonique à partir de surfaces crystallines : description ab initio
No full textMore than 50 years after the first experimental observation of second-harmonic generation, the theoretical description of second-harmonic generation is still under debate, whereas it is well understood from an experimental point of view. This is the gap that this thesis aims to fill.This work aims to improve the theoretical description and understanding of the generation of second-harmonic from the surfaces of crystalline semiconductors.When applying an external electric field to a dielectric material, electric dipoles are created at a microscopic level. These dipoles are responsible for the apparition, inside the material, of an induced field. The fluctuations of the electric field at a microscopic level, the density fluctuations or any kind of microscopic inhomogeneities must be taken into account when describing the optical properties of a system. These effects are often referred as “local-field effects”.These local-field effects have been widely studied in the past and in particular their effects on the optical properties of bulk materials are now well established. In the case of surfaces, the theoretical description and the numerical simulations are more intricate than for bulk materials. The abrupt change in the electronic density leads to a huge variation of the electric field at the interface with vacuum. As a result, strong effects of the local-field are expected, in particular in the direction perpendicular to the plane of the surface. The goal of this thesis is to quantify how important these effects are for the linear and second-order optical properties of surfaces.A macroscopic theory of second-harmonic generation from crystal surfaces has been developed in order to account for local-field effects. The latter are calculated from first-principles, in the framework of the Time-Dependent Density-Functional Theory (TDDFT). The primary interest is the description of non-linear optical responses of surfaces, but new theoretical tools for improving the description of local-field effects in the case of linear optics have also been developed.The numerical simulations have been focused on the Si(001) surface, and the macroscopic formalism developed during this thesis has been applied to three surface reconstructions, namely the clean Si(001)2x1, the monohydride Si(001)2x1:H and the dihydride Si(001)1x1:2H surfaces.Comparison with available experimental results is also reported.Plus de 50 ans après la première observation expérimentale de la génération de deuxième harmonique, la description théorique de la génération de deuxième harmonique est toujours sujette à débat, alors qu'elle est bien comprise d'un point de vue expérimental. C'est ce fossé que cette thèse vise à combler.Ce travail a pour but d'améliorer la description théorique ainsi que la compréhension de la génération de deuxième harmonique à la surface des cristaux semi-conducteurs.Lorsque l'on applique un champ électrique extérieur à un matériau diélectrique, des dipôles électriques se créent au niveau microscopique. Ces dipôles sont responsables de l'apparition, à l'intérieur du matériau, d'un champ induit.Les fluctuations du champ électrique à l'échelle microscopique, les fluctuations de la densité ou tout type d'inhomogénéités microscopiques doivent être pris en compte lorsque l'on décrit les propriétés optiques d'un système. Ces effets sont souvent appelés “effets des champs locaux”.Ces effets des champs locaux ont été largement étudiés par le passé et en particulier leurs effets sur les propriétés optiques des matériaux massifs est maintenant bien établi.Dans le cas des surfaces, la description théorique et les simulations numériques sont plus compliquées que pour les matériaux massifs. Le changement abrupt de la densité électronique conduit à une variation importante du champ électrique à l'interface avec le vide. Par conséquent, de forts effets dû au champ local sont attendus, en particulier dans la direction perpendiculaire au plan de la surface.Le but de cette thèse est de quantifier à quel point ces effets affectent les propriétés optiques linéaires et non-linéaires des surfaces.Une théorie macroscopique de la génération de deuxième harmonique à la surface des cristaux a été développée afin de tenir compte des effets dû aux champs locaux. Ces derniers sont calculés à partir des premiers principes, dans le cadre de la théorie de la fonctionnelle de la densité dépendante du temps (TDDFT). L'intérêt principal de cette thèse est la description de la réponse non-linéaire des surfaces, mais de nouveaux outils théoriques permettant une meilleure description des champs locaux et de leurs effets sur les propriétés optiques linéaires ont aussi été développé.Les simulations numériques se sont focalisées sur la surface Si(001), et le formalisme macroscopique développé durant cette thèse a été appliqué à trois reconstructions de surface, ici la surface propre Si(001)2x1, la surface monohydrique Si(001)2x1:H et la surface dihydrique Si(001)1x1:2H.Des comparaisons avec les résultats expérimentaux disponibles sont aussi présentées
On the Relative Usefulness of Fireballs
No full textInternational audienceIn CSL-LICS 2014, Accattoli and Dal Lago [1] showed that there is an implementation of the ordinary (i.e. strong, pure, call-by-name) λ-calculus into models like RAM machines which is polynomial in the number of β-steps, answering a long-standing question. The key ingredient was the use of a calculus with useful sharing, a new notion whose complexity was shown to be polynomial, but whose implementation was not explored. This paper, meant to be complementary, studies useful sharing in a call-by-value scenario and from a practical point of view. We introduce the Fireball Calculus, a natural extension of call-by-value to open terms, that is an intermediary step towards the strong case, and we present three results. First, we adapt useful sharing, refining the meta-theory. Then, we introduce the GLAMOUr, a simple abstract machine implementing the Fireball Calculus extended with useful sharing. Its key feature is that usefulness of a step is tested—surprisingly—in constant time. Third, we provide a further optimisation that leads to an implementation having only a linear overhead with respect to the number of β-steps
Transactions in the European Carbon Market: a Bubble of Compliance in a Whirlpool of Speculation
No full textURL des Documents de travail : http://ces.univ-paris1.fr/cesdp/cesdp2015.htmlDocuments de travail du Centre d'Economie de la Sorbonne 2015.74 - ISSN : 1955-611XThe European Union Emissions Trading Scheme (EU ETS) is supposed to help regulated installations to cover their CO2 emissions by trading in allowances. In practice, the EU ETS is mainly a financial market used for hedging and speculation. This financial feature is regarded as a solution (hedging and liquidity) to a problem (the price risk and volatility imposed on installations) which the market has actually created itself. This paper provides an estimation of the real underpinning of the scheme, i.e. the needs of installations for allowances transfers to achieve compliance in the two first exchange periods. This estimation, which was singularly lacking in the literature, shows that compliance transactions become more and more marginal as market activity grows and that they are drowned in a whirlpool of speculation. This challenges the role of the carbon price whose financial and self-referential evaluation can obviously not reveal installations' marginal abatement costs, the condition of cost-effectiveness expected from carbon trading.Le marché du carbone européen est créé en 2005 pour aider les installations assujetties à couvrir leurs émissions de CO2 à travers l'échange de quotas. En pratique, c'est essentiellement un marché financier dédié à l'échange de dérivés à des fins de couverture de risque et de spéculation. Cette dimension financière bien connue est présentée comme une solution (couverture de risque et liquidité) à un problème que le marché a lui-même créé (risque de prix et volatilité imposés par l'instrument, par opposition à un système de taxe). Ce papier établit une estimation du véritable sous-jacent du marché, i.e. des besoins de transferts de permis des installations à des fins de conformité. Cette estimation – singulièrement absente de la littérature – montre que les transactions à des fins de conformité sont de plus en plus marginales à mesure que l'activité sur le marché augmente, activité presque uniquement tirée par la spéculation. Se joue alors la capacité du prix du carbone à révéler les coûts marginaux des entreprises, principale condition d'efficacité attendue en théorie de ce type d'instrument
Cdc123, a Cell Cycle Regulator Needed for eIF2 Assembly, Is an ATP-Grasp Protein with Unique Features
No full textInternational audienceEukaryotic initiation factor 2 (eIF2), a heterotrimeric guanosine triphosphatase, has a central role in protein biosynthesis by supplying methionylated initiator tRNA to the ribosomal translation initiation complex and by serving as a target for translational control in response to stress. Recent work identified a novel step indispensable for eIF2 function: assembly of eIF2 from its three subunits by the cell proliferation protein Cdc123. We report the first crystal structure of a Cdc123 representative, that from Schizosaccharomyces pombe, both isolated and bound to domain III of Saccharomyces cerevisiae eIF2 gamma. The structures show that Cdc123 resembles enzymes of the ATP-grasp family. Indeed, Cdc123 binds ATP-Mg2+, and conserved residues contacting ATP-Mg2+ are essential for Cdc123 to support eIF2 assembly and cell viability. A docking of eIF2 alpha gamma onto Cdc123, combined with genetic and biochemical experiments, allows us to propose a model explaining how Cdc123 participates in the biogenesis of eIF2 through facilitating assembly of eIF2 gamma to eIF2 alpha
Selective and reduced numerical integrations for NURBS-based isogeometric analysis
No full textInternational audienceWe propose a new approach to construct selective and reduced integration rules for isogeometric analysis based on NURBS elements. The notion of an approximation space that approximates the target space is introduced. We explore the use of various approximation spaces associated with optimal patch-wise numerical quadratures that exactly integrate the polynomials in approximation spaces with the minimum number of quadrature points. Patch rules exploit the higher continuity of spline basis functions. The tendency of smooth spline functions to exhibit numerical locking in nearly-incompressible problems when using a full Gauss–Legendre quadrature is alleviated with selective or reduced integration. Stability and accuracy of the schemes are examined analyzing the discrete spectrum in a generalized eigenvalue problem. We propose a local algorithm, which is robust and computationally efficient, to compute element-by-element the quadrature points and weights in patch rules. The performance of the methods is assessed on several numerical examples in two-dimensional elasticity and Reissner–Mindlin shell structures
Retraction of large liquid strips
No full textInternational audienceWe study the behaviour of elongated puddles deposited on non-wetting substrates. Such liquid strips retract and adopt circular shapes after a few oscillations. Their thickness and horizontal surface area remain constant during this reorganization, so that the energy of the system is only lowered by minimizing the length of the contour (and the corresponding surface energy); despite the large scale of the experiments (several centimetres), motion is driven by surface tension. We focus on the retraction stage, and show that its velocity results from a balance between the capillary driving force and inertia, due to the frictionless motion on non-wetting substrates. As a consequence, the retraction velocity has a special Taylor-Culick structure, where the puddle width replaces the usual thickness
Source contributions to 2012 summertime aerosols in the Euro-Mediterranean region
No full textInternational audienceIn the Mediterranean area, aerosols may originate from anthropogenic or natural emissions (biogenic, mineral dust, fire and sea salt) before undergoing complex chemistry. In case of a huge pollution event, it is important to know whether European pollution limits are exceeded and, if so, whether the pollution is due to anthropogenic or natural sources. In this study, the relative contribution of emissions to surface PM10, surface PM2.5 and total aerosol optical depth (AOD) is quantified. For Europe and the Mediterranean regions and during the summer of 2012, the WRF and CHIMERE models are used to perform a sensitivity analysis on a 50 km resolution domain (from −10° W to 40° E and from 30° N to 55° N): one simulation with all sources (reference) and all others with one source removed. The reference simulation is compared to data from the AirBase network and two ChArMEx stations, and from the AERONET network and the MODIS satellite instrument, to quantify the ability of the model to reproduce the observations. It is shown that the correlation ranges from 0.19 to 0.57 for surface particulate matter and from 0.35 to 0.75 for AOD. For the summer of 2012, the model shows that the region is mainly influenced by aerosols due to mineral dust and anthropogenic emissions (62 and 19 %, respectively, of total surface PM10 and 17 and 52 % of total surface PM2.5). The western part of the Mediterranean is strongly influenced by mineral dust emissions (86 % for surface PM10 and 44 % for PM2.5), while anthropogenic emissions dominate in the northern Mediterranean basin (up to 75 % for PM2.5). Fire emissions are more sporadic but may represent 20 % of surface PM2.5, on average, during the period near local sources. Sea salt mainly contributes for coastal sites (up to 29 %) and biogenic emissions mainly in central Europe (up to 20 %)