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Laminar-turbulent patterning in wall-bounded shear flows: a Galerkin model
No full textInternational audienceOn its way to turbulence, plane Couette flow–the flow between counter-translating parallel plates–displays a puzzling steady oblique laminar-turbulent pattern. We approach this problem via Galerkin modelling of the Navier–Stokes equations. The wall-normal dependence of the hydrodynamic field is treated by means of expansions on functional bases fitting the boundary conditions exactly. This yields a set of partial differential equations for spatiotemporal dynamics in the plane of the flow. Truncating this set beyond the lowest nontrivial order is numerically shown to produce the expected pattern, therefore improving over what was obtained at the cruder effective wall-normal resolution. Perspectives opened by this approach are discussed
Simultaneous measurement of forward-backward asymmetry and top polarization in dilepton final states from production at the Tevatron
No full text16 pages, 16 figures, see paper for full list of authorsInternational audienceWe present a simultaneous measurement of the forward-backward asymmetry and the top-quark polarization in production in dilepton final states using 9.7 fb of proton-antiproton collisions at TeV with the D0 detector. To reconstruct the distributions of kinematic observables we employ a matrix element technique that calculates the likelihood of the possible kinematic configurations. After accounting for the presence of background events and for calibration effects, we obtain a forward-backward asymmetry of and a top-quark polarization times spin analyzing power in the beam basis of , with a correlation of between the measurements. If we constrain the forward-backward asymmetry to its expected standard model value, we obtain a measurement of the top polarization of If we constrain the top polarization to its expected standard model value, we measure a forward-backward asymmetry of A combination with the D0 measurement in the lepton+jets final state yields an asymmetry of Within their respective uncertainties, all these results are consistent with the standard model expectations
Search for narrow high-mass resonances in proton-proton collisions at sqrt(s) = 8 TeV decaying to Z and Higgs bosons
No full textsee paper for full list of authorsInternational audienceThe first search for a narrow, high-mass resonance decaying into Z and Higgs (H) bosons is presented. The final state studied consists of a merged jet pair and a tau pair resulting from the decays of Z and H bosons, respectively. The analysis is based on a data sample of proton-proton collisions at a center-of-mass energy of 8 TeV, collected with the CMS experiment in 2012, and corresponding to an integrated luminosity of 19.7 inverse femtobarns. In the resonance mass range of interest, the Z and H bosons are produced with large momenta, which implies that the final products of the two quarks or the two tau leptons must be detected within a small angular interval. From a combination of all possible decay modes of the tau leptons, production cross sections in a range between 0.9 and 27.8 fb are excluded at 95% confidence level, depending on the resonance mass
FREE BOUNDARY MINIMAL SURFACES IN THE UNIT 3-BALL
No full textIn a recent paper A. Fraser and R. Schoen have proved the existence of free boundary minimal surfaces in which have genus and boundary components, for all . For large , we give an independent construction of and prove the existence of free boundary minimal surfaces in which have genus and boundary components. As tends to infinity, the sequence converges to a double copy of the unit horizontal (open) disk, uniformly on compacts of while the sequence converges to a double copy of the unit horizontal (open) punctured disk, uniformly on compacts of
Path-dependent equations and viscosity solutions in infinite dimension
No full textPath Dependent PDE's (PPDE's) are natural objects to study when one deals with non Markovian models. Recently, after the introduction (see [12]) of the so-called pathwise (or functional or Dupire) calculus, various papers have been devoted to study the well-posedness of such kind of equations, both from the point of view of regular solutions (see e.g. [18]) and viscosity solutions (see e.g. [13]), in the case of finite dimensional underlying space. In this paper, motivated by the study of models driven by path dependent stochastic PDE's, we give a first well-posedness result for viscosity solutions of PPDE's when the underlying space is an infinite dimensional Hilbert space. The proof requires a substantial modification of the approach followed in the finite dimensional case. We also observe that, differently from the finite dimensional case, our well-posedness result, even in the Markovian case, apply to equations which cannot be treated, up to now, with the known theory of viscosity solutions
A cost benefit analysis of fuel cell electric vehicles
No full textThis study develops a consistent framework to compare FCEV with gasoline ICE (ignition combustion engine) and applies this framework to the German market over the period 2015-2050. As such it provides for:- The formulation of a proper cost benefit analysis, including the definition of the abatement cost for the hydrogen technology;- The simulation of the results under various technological and cost assumptions;- The identification of the major conceptual issues to facilitate analytical developments.The sources used in the analysis are based on an update of previous industry studies. The main conclusion is that FCEV could be a socially beneficial alternative for decarbonizing part of the projected German car park at the horizon 2050. The corresponding abatement cost would fall inthe range of 50 €/t CO2 to 60 €/t CO2. This range is higher than the current estimate for the normative cost of carbon as expressed in Quinet (2009 and 2013), which is around 30€/t in 2015. Still the gap is not out of hand. We identify the market and cost conditions that would shorten the gap.The methodology used in this study could be expanded to integrate two pending issues noted in the literature for the successful deployment of FCEV:- Making the deployment for FCEV endogenous and depending on the public and private instruments that could induce the decreasing of costs and the acceptance of the FCEV technology by consumers.- Designing an appropriate institutional framework to promote cooperation for manufacturing FCEV, producing carbon free H2 and investing in the distribution of H2. The initial sunk costs necessary for investment cannot be recouped through pure market equilibrium behavior. This study already provides an order of magnitude to quantify these issues
Bayesian computation: a perspective on the current state, and sampling backwards and forwards
No full textThe past decades have seen enormous im-provements in computational inference based on sta-tistical models, with continual enhancement in a wide range of computational tools, in competition. In Bayesian inference, first and foremost, MCMC techniques con-tinue to evolve, moving from random walk proposals to Langevin drift, to Hamiltonian Monte Carlo, and so on, with both theoretical and algorithmic inputs opening wider access to practitioners. However, this impressive evolution in capacity is confronted by an even steeper increase in the complexity of the models and datasets to be addressed. The difficulties of modelling and then handling ever more complex datasets most likely call for a new type of tool for computational inference that dramatically reduce the dimension and size of the raw data while capturing its essential aspects. Approximate models and algorithms may thus be at the core of the next computational revolution
Beam test performance of the SKIROC2 ASIC
No full textInternational audienceBeam tests of the first layers of CALICE silicon tungsten ECAL technological prototype were performed in April and July 2012 using 1–6 GeV electron beam at DESY. This paper presents an analysis of the SKIROC2 readout ASIC performance under test beam conditions
Matrix completion by singular value thresholding: sharp bounds
No full textInternational audienceWe consider the matrix completion problem where the aim is to esti-mate a large data matrix for which only a relatively small random subset of its entries is observed. Quite popular approaches to matrix completion problem are iterative thresholding methods. In spite of their empirical success, the theoretical guarantees of such iterative thresholding methods are poorly understood. The goal of this paper is to provide strong theo-retical guarantees, similar to those obtained for nuclear-norm penalization methods and one step thresholding methods, for an iterative thresholding algorithm which is a modification of the softImpute algorithm. An im-portant consequence of our result is the exact minimax optimal rates of convergence for matrix completion problem which were known until know only up to a logarithmic factor
Stochastic Target Games and Dynamic Programming via Regularized Viscosity Solutions
No full textInternational audienceWe study a class of stochastic target games where one player tries to find a strategy such that the state process almost-surely reaches a given target, no matter which action is chosen by the opponent. Our main result is a geometric dynamic programming principle which allows us to characterize the value function as the viscosity solution of a non-linear partial differential equation. Because abstract mea-surable selection arguments cannot be used in this context, the main obstacle is the construction of measurable almost-optimal strategies. We propose a novel approach where smooth supersolutions are used to define almost-optimal strategies of Markovian type, similarly as in ver-ification arguments for classical solutions of Hamilton–Jacobi–Bellman equations. The smooth supersolutions are constructed by an exten-sion of Krylov's method of shaken coefficients. We apply our results to a problem of option pricing under model uncertainty with different interest rates for borrowing and lending