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Generic uniqueness of the bias vector of mean payoff zero-sum games
No full textSee also arXiv:1411.1211International audienceZero-sum mean payoff games can be studied by means of a nonlinear spectral problem. When the state space is finite, the latter consists in finding an eigenpair (u,λ) solution of T(u)=λ1+u where T is the Shapley (dynamic programming) operator, λ is a scalar, 1 is the unit vector, and u is a n dimensional vector. The scalar λ yields the mean payoff per time unit, and the vector u, called the bias, allows one to determine optimal stationary strategies. The existence of the eigenpair (u,λ) is generally related to ergodicity conditions. A basic issue is to understand for which classes of games the bias vector is unique (up to an additive constant). In this paper, we consider perfect information zero-sum stochastic games with finite state and action spaces, thinking of the transition payments as variable parameters, transition probabilities being fixed. We identify structural conditions on the support of the transition probabilities which guarantee that the spectral problem is solvable for all values of the transition payments. Then, we show that the bias vector, thought of as a function of the transition payments, is generically unique (up to an additive constant). The proof uses techniques of max-plus (tropical) algebra and nonlinear Perron-Frobenius theory
Disorder-induced topological change of the superconducting gap structure in iron pnictides
No full textInternational audienceIn superconductors with unconventional pairing mechanisms, the energy gap in the excitationspectrum often has nodes, which allow quasiparticle excitations at low energies. In manycases, such as in d-wave cuprate superconductors, the position and topology of nodes areimposed by the symmetry, and thus the presence of gapless excitations is protected againstdisorder. Here we report on the observation of distinct changes in the gap structure of iron–pnictide superconductors with increasing impurity scattering. By the successive introductionof nonmagnetic point defects into BaFe2(As1-xPx)2 crystals via electron irradiation, we findfrom the low-temperature penetration depth measurements that the nodal state changes to anodeless state with fully gapped excitations. Moreover, under further irradiation the gappedstate evolves into another gapless state, providing bulk evidence of unconventionalsign-changing s-wave superconductivity. This demonstrates that the topology of the superconductinggap can be controlled by disorder, which is a strikingly unique feature of ironpnictides
Diffusion Matrices from Algebraic-Geometry Codes with Efficient SIMD Implementation
No full textInternational audienceThis paper investigates large linear mappings with very good diffusion and efficient software implementations, that can be used as part of a block cipher design. The mappings are derived from linear codes over a small field (typically F 2 4) with a high dimension (typically 16) and a high minimum distance. This results in diffusion matrices with equally high dimension and a large branch number. Because we aim for parameters for which no MDS code is known to exist, we propose to use more flexible algebraic-geometry codes. We present two simple yet efficient algorithms for the software implementation of matrix-vector multi-plication in this context, and derive conditions on the generator matrices of the codes to yield efficient encoders. We then specify an appropriate code and use its automorphisms as well as random sampling to find good such matrices. We provide concrete examples of parameters and implementations, and the corresponding assembly code. We also give performance figures in an example of application which show the interest of our ap-proach
Special issue on computational logic in honour of Roy Dyckhoff. Journal of Logic and Computation.
No full textInternational audienc
Parametricity and Proving Free Theorems for Functional-Logic Languages
No full textInternational audienceThe goal of this paper is to provide the required foundations forestablishing free theorems – statements about program equivalence,guaranteed by polymorphic types – for the functional-logic pro-gramming language Curry. For the sake of presentation we restrictourselves to a language fragment that we call CuMin, and that hasthe characteristic features of Curry (both functional and logic). Wepresent a new denotational semantics based on partially ordered setswithout limits. We then introduce an intermediate language calledSaLT that is essentially a lambda-calculus extended with an abstractset type, and again give a denotational semantics. We show that thestandard (logical relations) techniques can be applied to obtain ageneral parametricity theorem for SaLT and derive free theoremsfrom it. Via a translation from CuMin to SaLT that fits the respectivesemantics, we then derive free theorems for CuMin
Inégalités de Korn-Poincaré pour des fonctions avec un petit ensemble de discontinuité
No full text"Special functions with bounded deformation" and p-integrable strain arise naturally in the study of geometrically linear fracture models. They have a jump set of finite (n − 1)-dimensional measure and, away from the jump set, a symmetrized gradient e(u) in Lp , p ≥ 1. We show that if the measure of the jump set is sufficiently small with respect to the size of the domain, then the function u can be approximated by an affine function away from a small exceptional set, with an error which depends solely on e(u). We also derive a corresponding trace statement
Reconstruction des leptons tau et recherche de bosons de Higgs se désintégrant en paire de leptons tau dans l'expérience CMS auprès du LHC.
No full textThis thesis presents a search for Higgs bosons decaying into tau pairs in the context of the Standard Model (SM) and its minimal supersymmetric extension (MSSM) with the Compact Muon Solenoid (CMS) experiment, using the data collected during the first years of operation at the LHC. After introducing the theoretical context relevant for the SM and MSSM Higgs bosons searches, the corresponding phenomenological aspects are discussed. The discovery of a scalar boson by the ATLAS and CMS Collaborations in 2012 is then presented. The design and performance of the CMS experiment are described as well as the identification and measurements of physical objects needed for the analysis. The accent is put on the tau lepton reconstruction including in particular a novel tau isolation that uses the lifetime information. We optimized this tool in terms of tau identification efficiency and fake tau rejection, particularly suited for boosted taus. A new technique for rejecting the electrons faking taus is also presented: a discriminator based on a multivariate analysis which considerably reduces the contamination from electrons faking taus while preserving the efficiency of identification is exposed.The SM and MSSM Higgs boson searches in the di-tau final state are presented. The dataset corresponds to an integrated luminosity of 4.9 fb-1 at sqrt{s}=7 TeV and 19.7 fb-1 at sqrt{s}=8 TeV recorded by CMS respectively in 2011 and 2012. The focus is put on the most sensitive semi-leptonic decay channels: where is either an electron or muon and stands for hadronic tau decays. After combining all the decay channels in SM Higgs boson to di-tau search and in particular using the new anti-electron discriminator, an excess of observed events with respect to the background-only hypothesis is found. The statistical significance of this excess corresponds to 3.2 standard deviations at a mass of 125 GeV. The measured signal strength is compatible with the SM Higgs signal expectation. This result constitutes an evidence for a coupling between the scalar boson and leptons.Finally, a new strategy in the search for the MSSM Higgs bosons is presented in this thesis. It combines both the novel tau isolation technique and a new refined categorization based on the transverse momentum. With respect to the previous CMS public result (2013), the sensitivity of the analysis presented in this document is improved by more than 30%. This is equivalent to an increase of the total integrated luminosity by a factor 3 to 4. The interpretation of the model independent upper limits on the cross-section times branching ratio of the production process shows no significant excess over the Standard Model backgrounds.Cette thèse présente une recherche du boson de Higgs du Modèle Standard (MS) et de son extension supersymétrique minimale (MSSM) dans la voie de désintégration en paires de leptons tau avec l'expérience CMS pendant les premières années d'exploitation du LHC. Après une introduction du contexte théorique pertinent pour la recherche du boson de Higgs du MS et du MSSM, les aspects phénoménologiques sont exposés. La découverte en 2012 d'un boson scalaire par les collaborations ATLAS et CMS est ensuite présentée. La description du détecteur CMS est abordée et la reconstruction des objets nécessaires a l'analyse est décrite. Une attention particulière est portée à la reconstruction des leptons tau avec notamment un algorithme d'isolation original incluant des informations sur le temps de vie. Nous avons optimisé cet outil en termes d'efficacité d'identification et de réjection de bruit de fond. Une nouvelle technique visant à supprimer des électrons reconstruits a tord comme des taus est également présentée: le développement d'un discriminateur anti-électron, basé sur une analyse multivariée réduit considérablement cette contamination tout en préservant l'efficacité d'identification.La recherche du boson de Higgs du MS et MSSM dans ses désintégrations en paires de taus est exposée. Les données utilisées correspondent à une luminosité intégrée de 4.9 fb-1 avec une énergie dans le centre de masse sqrt{s}=7 TeV et 19.7 fb-1 avec sqrt{s}=8 TeV collectées par CMS en 2011 et 2012 respectivement. Une attention particulière est portée aux canaux de désintégration semi-leptoniques: où représente un électron ou un muon et une désintégration hadronique de tau. La combinaison de tous les canaux de désintégration du Higgs du MS en paire de taus avec en particulier l'utilisation du nouveau discriminateur anti-électron conduit à un excès d'événements par rapport aux bruits de fond attendus. L'interprétation statistique correspond à 3.2 déviations standard pour une masse de 125 GeV et la force du signal est compatible avec le boson de Higgs du Modèle Standard. Ce résultat constitue une indication directe du couplage du boson de Higgs aux leptons.Finalement, une stratégie originale de recherche de bosons de Higgs du MSSM est présentée. Elle combine d'une part la nouvelle technique d'isolation de tau et d'autre part une définition optimisée des catégories d'analyse fondées sur l'impulsion transverse des taus. La sensibilité de l'analyse est ainsi augmentée de plus de 30 % par rapport au dernier résultat public de CMS (2013) ce qui est équivalent à un accroissement de 3 à 4 fois la luminosité totale intégrée. Aucun excès d'événements n'est observé par rapport aux bruits de fonds prédits par le MS suite à l'interprétation modèle indépendante des limites supérieures sur la section efficace fois le rapport d'embranchement pour chacun des modes de production
Trend in Global Black Carbon Emissions from 1960 to 2007
No full textInternational audienceBlack carbon (BC) plays an important role in both climate change and health impact. Still, BC emissions as well as the historical trends are associated with high uncertainties in existing inventories. In the present study, global BC emissions from 1960 to 2007 were estimated for 64 sources, by using recompiled fuel consumption and emission factor data sets. Annual BC emissions had increased from 5.3 (3.4-8.5 as an interquartile range) to 9.1 (5.6-14.4) teragrams during this period. Our estimations are 11-16% higher than those in previous inventories. Over the period, we found that the BC emission intensity, defined as the amount of BC emitted per unit of energy production, had decreased for all the regions, especially China and India. Improvements in combustion technology and changes in fuel composition had led to an increase in energy use efficiency, and subsequently a decline of BC emission intensities in power plants, the residential sector, and transportation. On the other hand, the BC emission intensities had increased in the industrial and agricultural sectors, mainly due to an expansion of low-efficiency industry (coke and brick production) in developing countries and to an increasing usage of diesel in agriculture in developed countries
Substrate interaction dynamics and oxygen control in the active site of thymidylate synthase ThyX
No full textInternational audienceThymidylate synthase ThyX, required for DNA synthesis in many pathogenic bacteria, is considered a promising antimicrobial target. It binds FAD and three substrates, producing dTMP (2′-deoxythymidine-5′-monophosphate) from dUMP (2′-deoxyuridine-5′-monophosphate). However, ThyX proteins also act as NADPH oxidase by reacting directly with O2. In the present study we investigated the dynamic interplay between the substrates and their role in competing with this wasteful and potentially harmful oxidase reaction in catalytically efficient ThyX from Paramecium bursaria Chlorella virus-1. dUMP binding accelerates the O2-insensitive half-reaction between NADPH and FAD by over four orders of magnitude to ~30 s−1. Thus, although dUMP does not have a direct role in FAD reduction, any turnover with molecular O2 requires its presence. Inversely, NADPH accommodation accelerates dUMP binding ~3-fold and apparently precedes dUMP binding under physiological conditions. In the oxidative half-reaction, excess CH2H4folate (N5,N10-methylene-5,6,7,8-tetrahydrofolate) was found to re-oxidize FADH2 within 1 ms, thus very efficiently competing with FADH2 oxidation by O2 (1.5 s−1 under aerobic conditions). The resulting reaction scheme points out how the interplay between the fast reactions with the native substrates, although not rate-limiting for overall catalysis, avoids NADPH oxidase activity in aerobic micro-organisms, including many pathogens. These observations also explain why ThyX proteins are also present in aerobic micro-organism
