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Resultados filtrados por Publicador: Universidade Cornell

Enhanced Techniques for PDF Image Segmentation and Text Extraction

Sasirekha, D.; Chandra, E.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 01/10/2012 Português
Relevância na Pesquisa
26.408977%
Extracting text objects from the PDF images is a challenging problem. The text data present in the PDF images contain certain useful information for automatic annotation, indexing etc. However variations of the text due to differences in text style, font, size, orientation, alignment as well as complex structure make the problem of automatic text extraction extremely difficult and challenging job. This paper presents two techniques under block-based classification. After a brief introduction of the classification methods, two methods were enhanced and results were evaluated. The performance metrics for segmentation and time consumption are tested for both the models.; Comment: 5 pages, 5 figures

PDF Fits at HERA

Cooper-Sarkar, A M
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 09/12/2011 Português
Relevância na Pesquisa
26.408977%
The HERAPDF1.0 PDF set, which was an NLO QCD analysis based on H1 and ZEUS combined inclusive cross section data from HERA-I, has been updated to HERAPDF1.5 by including preliminary inclusive cross section data from HERA-II running. Studies have also been made by adding various other HERA data sets: combined charm data, combined low energy run data and H1 and ZEUS jet data. These data give information on the treatment of charm and the charm quark mass and on the value of $\alpha_s(M_Z)$. The PDF analysis has also been extended to NNLO. The PDFs give a good description of Tevatron and early LHC data.; Comment: On behalf of ZEUS and H1 collaborations, 6 pages, 6 figures. To appear in the Proceedings of the 2011 Europhysics Conference on High Energy Physics, HEP 2011, July 2011, Grenoble, France

Hessian PDF reweighting meets the Bayesian methods

Paukkunen, Hannu; Zurita, Pia
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 20/08/2014 Português
Relevância na Pesquisa
26.408977%
We discuss the Hessian PDF reweighting - a technique intended to estimate the effects that new measurements have on a set of PDFs. The method stems straightforwardly from considering new data in a usual $\chi^2$-fit and it naturally incorporates also non-zero values for the tolerance, $\Delta\chi^2>1$. In comparison to the contemporary Bayesian reweighting techniques, there is no need to generate large ensembles of PDF Monte-Carlo replicas, and the observables need to be evaluated only with the central and the error sets of the original PDFs. In spite of the apparently rather different methodologies, we find that the Hessian and the Bayesian techniques are actually equivalent if the $\Delta\chi^2$ criterion is properly included to the Bayesian likelihood function that is a simple exponential.; Comment: Transcription of the talk given in DIS2014 conference

Lagrangian Investigation of Auto-ignition in a Hydrogen Jet Flame in a Vitiated Co-flow: Animations of Particle Trajectories in Composition Space from PDF Model Calculations

Wang, Haifeng; Pope, Stephen B.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/09/2007 Português
Relevância na Pesquisa
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PDF model calculations have been performed of the Cabra lifted hydrogen flame in a vitiated co-flow. Particle trajectories are extracted from the Lagrangian particle method used to solve the modeled PDF equation. The particle trajectories in the mixture fraction-temperature plane reveal (at successive downstream locations): essentially inert mixing between the cold fuel jet and the hot co-flow; the auto-ignition of very lean particles; and, subsequent mixing and reaction, leading to near-equilibrium compositions. The purpose of this paper is to present animations of the particle trajectories obtained using different turbulent mixing models.; Comment: 5 pages, 3 figures. Video 1 (EMST) http://ecommons.library.cornell.edu/bitstream/1813/8237/2/LIFTED_H2_EMST_FUEL.mpg Video 2 (IEM) http://ecommons.library.cornell.edu/bitstream/1813/8237/4/LIFTED_H2_IEM_FUEL.mpg

Measuring the History of Cosmic Reionization using the 21-cm Difference PDF

Pan, Tony; Barkana, Rennan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 25/09/2012 Português
Relevância na Pesquisa
26.408977%
During cosmic reionization, the 21-cm brightness fluctuations were highly non-Gaussian, and complementary statistics can be extracted from the distribution of pixel brightness temperatures that are not derivable from the 21-cm power spectrum. One such statistic is the 21-cm difference PDF, the probability distribution function of the difference in the 21-cm brightness temperatures between two points, as a function of the distance between the points. Guided by 21-cm difference PDFs extracted from simulations, we perform a maximum likelihood analysis on mock observational data, and analyze the ability of present and future low-frequency radio array experiments to estimate the shape of the 21-cm difference PDF, and measure the history of cosmic reionization. We find that one-year data with an experiment such as the Murchison Wide-field Array should suffice for probing large scales during the mid-to-late stages of reionization, while a second-generation experiment should yield detailed measurements over a wide range of scales during most of the reionization era.; Comment: 11 pages, 17 figures. Submitted to MNRAS

Theoretical issues in PDF determination and associated uncertainties

The NNPDF Collaboration; Ball, Richard D.; Bertone, Valerio; Del Debbio, Luigi; Forte, Stefano; Guffanti, Alberto; Rojo, Juan; Ubiali, Maria
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
26.408977%
We study several sources of theoretical uncertainty in the determination of parton distributions (PDFs) which may affect current PDF sets used for precision physics at the Large Hadron Collider, and explain discrepancies between them. We consider in particular the use of fixed-flavor versus variable-flavor number renormalization schemes, higher twist corrections, and nuclear corrections. We perform our study in the framework of the NNPDF2.3 global PDF determination, by quantifying in each case the impact of different theoretical assumptions on the output PDFs. We also study in each case the implications for benchmark cross sections at the LHC. We find that the impact in a global fit of a fixed-flavor number scheme is substantial, the impact of higher twists is negligible, and the impact of nuclear corrections is moderate and circumscribed.; Comment: 18 pages, 13 figures. Final version, to be published in Phys. Lett. B. Tab. 2 added and Fig 13 updated. Several small improvements, including revised discussion of Ref.[24]

PDF uncertainties on the W boson mass measurement from the lepton transverse momentum distribution

Bozzi, Giuseppe; Citelli, Luca; Vicini, Alessandro
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
26.408977%
We study the charged current Drell-Yan process and we evaluate the proton parton densities uncertainties on the lepton transverse momentum distribution and their impact on the determination of the W-boson mass. We consider the global PDF sets CT10, MSTW2008CPdeut, NNPDF2.3, NNPDF3.0, MMHT2014, and apply the PDF4LHC recipe to combine the individual results, obtaining an uncertainty on MW that ranges between +-18 and +-24 MeV, depending on the final state, collider energy and kind. We discuss the dependence of the uncertainty on the acceptance cuts and the role of the individual parton densities in the final result. We remark that some PDF sets predict an uncertainty on MW of O(10 MeV); this encouraging result is spoiled, in the combined analysis of the different sets, by an important spread of the central values predicted by each group.; Comment: version accepted for publication on Phys.Rev.D, one figure and two references added

Multi-variate joint PDF for non-Gaussianities: exact formulation and generic approximations

Verde, Licia; Jimenez, Raul; Alvarez-Gaume, Luis; Heavens, Alan F.; Matarrese, Sabino
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
26.408977%
We provide an exact expression for the multi-variate joint probability distribution function of non-Gaussian fields primordially arising from local transformations of a Gaussian field. This kind of non-Gaussianity is generated in many models of inflation. We apply our expression to the non- Gaussianity estimation from Cosmic Microwave Background maps and the halo mass function where we obtain analytical expressions. We also provide analytic approximations and their range of validity. For the Cosmic Microwave Background we give a fast way to compute the PDF which is valid up to 7{\sigma} for fNL values (both true and sampled) not ruled out by current observations, which consists of expressing the PDF as a combination of bispectrum and trispectrum of the temperature maps. The resulting expression is valid for any kind of non-Gaussianity and is not limited to the local type. The above results may serve as the basis for a fully Bayesian analysis of the non-Gaussianity parameter.; Comment: Matches accepted verion to JCAP; conclusions unchaged, extra references added

Uncertainties on alpha_S in global PDF analyses and implications for predicted hadronic cross sections

Martin, A. D.; Stirling, W. J.; Thorne, R. S.; Watt, G.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
26.408977%
We determine the uncertainty on the strong coupling alpha_S due to the experimental errors on the data fitted in global analysis of hard-scattering data, within the standard framework of leading-twist fixed-order collinear factorisation in the MSbar scheme, finding that alpha_S(M_Z^2) = 0.1202^{+0.0012}_{-0.0015} at next-to-leading order (NLO) and alpha_S(M_Z^2) = 0.1171^{+0.0014}_{-0.0014} at next-to-next-to-leading order (NNLO). We do not address in detail the issue of the additional theory uncertainty on alpha_S(M_Z^2), but an estimate is +/-0.003 at NLO and at most +/-0.002 at NNLO. We investigate the interplay between uncertainties on alpha_S and uncertainties on parton distribution functions (PDFs). We show, for the first time, how both these sources of uncertainty can be accounted for simultaneously in calculations of cross sections, and we provide eigenvector PDF sets with different fixed alpha_S values to allow further studies by the general user. We illustrate the application of these PDF sets by calculating cross sections for W, Z, Higgs boson and inclusive jet production at the Tevatron and LHC.; Comment: 45 pages, 17 figures. Grids can be found at http://projects.hepforge.org/mstwpdf/ and in LHAPDF V5.7.1. v2: version to appear in EPJC

PDF uncertainties in WH production at Tevatron

Nadolsky, P. M.; Sullivan, Z.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
26.408977%
We apply a method proposed by members of CTEQ Collaboration to estimate the uncertainty in associated $W$-Higgs boson production at Run II of the Tevatron due to our imprecise knowledge of parton distribution functions. We find that the PDF uncertainties for the signal and background rates are of the order 3%. The PDF uncertainties for the important statistical quantities (significance of the Higgs boson discovery, accuracy of the measurement of the (WH) cross section) are smaller (1.5%) due to the strong correlation of the signal and background.; Comment: A typo in Eq. (4) corrected

PDF fit in the fixed-flavor-number scheme

Alekhin, S.; Bluemlein, J.; Moch, S.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 21/02/2012 Português
Relevância na Pesquisa
26.408977%
We discuss the heavy-quark contribution to deep inelastic scattering in the scheme with $n_f=3,4,5$ fixed flavors. Based on the recent ABM11 PDF analysis of world data for deep-inelastic scattering and fixed-target data for the Drell-Yan process with the running-mass definition for heavy quarks we show that fixed flavor number scheme is sufficient for describing the deep-inelastic-scattering data in the entire kinematic range. We compare with other PDF sets and comment on the implications for measuring the strong coupling constant $\alpha_s(M_Z)$.; Comment: 11 pages with 10 figures, to appear in the proceedings of the "Ringberg Workshop: New Trends in HERA Physics 2011", Ringberg Castle, Germany, 25-28 September, 2011