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QCD description of backward vector meson hard electroproduction
No full textInternational audienceWe consider backward vector meson exclusive electroproduction off nucleons in the framework of collinear QCD factorization. Nucleon to vector meson transition distribution amplitudes arise as building blocks for the corresponding factorized amplitudes. In the near-backward kinematics, the suggested factorization mechanism results in the dominance of the transverse cross section of vector meson production (σ T ≫ σ L) and in the characteristic 1/Q 8-scaling behavior of the cross section. We evaluate nucleon to vector meson TDAs in the cross-channel nucleon exchange model and present estimates of the differential cross section for backward ρ 0 , ω and φ meson production off protons. The resulting cross sections are shown to be measurable in the forthcoming JLab@12 GeV experiments
Search for supersymmetry using razor variables in events with b-tagged jets in pp collisions at sqrt(s)=8 TeV
No full textsee paper for full list of authorsInternational audienceAn inclusive search for supersymmetry in events with at least one bottom-quark jet is performed using proton-proton collision data collected by the CMS experiment in 2012 at a center-of-mass energy of 8 TeV. The data set size corresponds to an integrated luminosity of 19.3 inverse femtobarns. The two-dimensional event distribution of the razor variables R^2 and M[R] is studied in events with and without leptons. The data are found to be consistent with the expected background, which is modeled with an empirical function. Exclusion limits on supersymmetric particle masses at a 95% confidence level are derived in several simplified supersymmetric scenarios for several choices of the branching fractions. By combining the likelihoods of a search in events without leptons and a search that requires a single lepton (electron or muon), an improved bound on the top-squark mass is obtained. Assuming the lightest supersymmetric particle to be stable, weakly interacting, and to have a mass of 100 GeV, the branching-fraction-dependent (-independent) production of gluinos is excluded for gluino masses up to 1310 (1175) GeV. The corresponding limit for top-squark pair production is 730 (645) GeV
A global uniqueness result for acoustic tomography of moving fluid
No full textInternational audienceWe consider a model time-harmonic wave equation of acoustic tomography of moving fluid in an open bounded domain in dimension . We give global uniqueness theorems for related inverse boundary value problem at fixed frequency
Non-Markovian optimal stopping problems andconstrained BSDEs with jump
No full textWe consider a non-Markovian optimal stopping problem on finite horizon. We prove that the value process can be represented by means of a backward stochastic differential equation (BSDE), defined on an enlarged probability space, containing a stochastic integral having a one-jump point process as integrator and an (unknown) process with a sign constraint as integrand.This provides an alternative representation with respect to the classicalone given by a reflected BSDE. The connection between the two BSDEsis also clarified. Finally, we prove that the value of the optimalstopping problem is the same as the value of an auxiliaryoptimization problem where the intensity ofthe point process is controlled
The high-energy -ray emission of AP Librae
No full text15 pages, 6 figures - See paper for full list of authorsInternational audienceThe -ray spectrum of the low-frequency-peaked BL Lac (LBL) object AP Librae is studied, following the discovery of very-high-energy (VHE; ) -ray emission up to the TeV range by the H.E.S.S. experiment. This makes AP Librae one of the few VHE emitters of the LBL type. The measured spectrum yields a flux of above 130 GeV and a spectral index of . This study also makes use of \textit{Fermi}-LAT, observations in the high energy (HE, E100 MeV) range, providing the longest continuous light curve (5 years) ever published on this source. The source underwent a flaring event between MJD 56306-56376 in the HE range, with a flux increase of a factor 3.5 in the 14-day bin light curve and no significant variation in spectral shape with respect to the low-flux state. While the H.E.S.S., and (low state) \textit{Fermi}-LAT fluxes are in good agreement where they overlap, a spectral curvature between the steep VHE spectrum and the \textit{Fermi}-LAT, spectrum is observed. The maximum of the -ray emission in the spectral energy distribution is located below the GeV energy range
Structural Cryptanalysis of McEliece Schemes with Algebraic Geometry codes
No full textInternational audienceCode-based Cryptography together with lattice-based cryptography, multivariate cryptography and hash-based cryptography are the principal available techniques for Post-quantum cryptography. McEliece proposed the first cryptosystem based on the theory of error correcting codes in 1978. The principle of code-based cryptography is based on the following one-way trapdoor function: it is easy and fast to encode a message using linear transformation;but the general decoding problem was proven to be NP-complete in 1978 for the Hamming metric. Decoding is also believed to be hard for a quantum computer. The trapdoor information is that there exists families of codes that have efficient decoding algorithms. McEliece proposed to use binary Goppa codes. But several proposals based on other families of algebraic codes appeared in the literature. For instance, Generalized Reed-Solomon codes, subcodes of them and Binary Reed-Muller codes. All of these shemes are subject to polynomial or sub-exponential time attacks.Another attempt, suggested by Janwa and Moreno was to introduce Algebraic Geometry codes. This scheme was broken for codes on curves of genus g 2 by Faurer and Minder. However this attack has several drawbacks which makes it impossible to extend to higher genera. In this talk we present a general attack against this proposal based on squarecode considerations, that is the component wise product of codewords. The point is that evaluation codes do not behave like random codes with respect to the star product “the square of Algebraic Geometry codes has smaller dimension than that of the square of a random code of the same dimension”.The attack presented in this talk consist in pushing this argument forward in order to compute a filtration of the public code by a family of very particular subcodes. This filtration methods yields to an Error Correcting Pair of the public code in O(n4) operations in Fq where n denotes the code length. This Error-Correcting Pair allows to decrypt any encrypted message in O(n3) operations. This alternative attack has been implemented in Magma and broke for instance a [729; 404] 126–error correcting Hermitian code (with genus 36) over F81 (which had 182-bits security with respect to ISD attacks)in 21 minutes. Using an Intel r CoreTM 2 Duo 2.8 GHz
Photometric Compensation to Dynamic Surfaces in a Projector-Camera System
No full textInternational audienceIn this paper, a novel approach that allows color compensated projection on an arbitrary surface is presented. Assuming that the geometry of the surface is known, this method can be used in dynamic environments, where the surface color is not static. A simple calibration process is performed offline and only a single input image under reference illumination is sufficient for the estimation of the compensation. The system can recover the reflectance of the surface pixel-wise and provide an accurate photometric compensation to minimize the visibility of the projection surface. The color matching between the desired appearance of the projected image and the projection on the surface is performed in the device-independent color space CIE 1931 XYZ. The results of the evaluation confirm that this method provides a robust and accurate compensation even for surfaces with saturated colors and high spatial frequency patterns. This promising method can be the cornerstone of a real time projector-camera system for dynamic scenes
Solar spectrum measurements during 6 month: spectral mismatch induced on crystalline silicon and amorphous silicon photovoltaic cells
No full textInternational audienceCurrently predicted photovoltaic (PV) yield are made considering solar irradiation, ambient temperature, incidence angle and partially (or not) the solar spectrum. However, the solar spectrum is not always the same. It varies depending on the site location, atmospheric conditions, day of the year, time of the day... This may impact the conversion efficiency differently according to the PV technology. This paper presents measurements of the impact on the short-circuit current of the mismatch between the solar spectrum and the reference ASTM AM1.5G spectrum, for a specific site, throughout the year. A spectroradiometer is used. We investigate these losses every minute during 6 month for a site located at Gif-sur-Yvette and present the results that give an idea of the impact of the spectral mismatch on two different technologies (a-Si and c-Si) under continental sky. We also study the links of the spectral mismatch with the diffuse irradiance. We show in particular that the spectral mismatch has a wider impact for the a-Si and for both has a relevant impact concerning the average on 6 months: Isc(a-Si) is 1.17% higher than the rated one and Isc(c-Si) is 1.4% lower than the rated one (measurements are mainly led during overcast days
Ressource éolienne en France métropolitaine : méthodes d'évaluation du potentiel, variabilité et tendances
No full textFrance has one of the largest wind potentials in Europe, yet far from being fully exploited. The wind resource and energy yield assessment is a key step before building a wind farm, aiming at predicting the future electricity production. Any over-estimation in the assessment process puts in jeopardy the project's profitability. This has been the case in the recent years, when wind farm managers have noticed that they produced less than expected.The under-production problem leads to questioning both the validity of the assessment methods and the inter-annual wind variability. This thesis tackles these two issues. In a first part are investigated the errors linked to the assessment methods, especially in two steps: the vertical extrapolation of wind measurements and the statistical modelling of wind-speed data by a Weibull distribution. The second part investigates the inter-annual to decadal variability of wind speeds, in order to understand how this variability may have contributed to the under-production and so that it is better taken into account in the future.La France possède un gisement éolien parmi les plus importants d'Europe, et qui est encore loin d'être exploité à son maximum. L'évaluation du potentiel éolien d'un site est une étape clé en amont de la construction d'un parc éolien pour estimer la production électrique future et toute sur-estimation dans cette évaluation met en péril la rentabilité du parc. Or, cela a été le cas ces dernières années, les exploitants éoliens ont constaté qu'ils avaient produit moins que prévu.Cette question de la sous-production soulève deux problématiques sur lesquelles se penche ce travail de thèse: d'une part les incertitudes associées aux méthodes utilisées pour évaluer le potentiel éolien et d'autre part la variabilité interannuelle du vent. La première partie porte sur les erreurs des méthodes d'évaluation du potentiel, en particulier lors de l'extrapolation verticale des mesures de vent et lors de la modélisation statistique du vent par la distribution de Weibull. La deuxième partie porte sur la variabilité du vent aux échelles annuelles à décennales, afin de comprendre comment cette variabilité a pu contribuer à une sous-production, et de mieux l'appréhender à l'avenir