Página 4 dos resultados de 15310 itens digitais encontrados em 0.007 segundos
Resultados filtrados por Publicador: Universidade Cornell

Cosmological Implications of the PSCz PDF and its Moments

Plionis, Manolis; Basilakos, Spyros
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
248.29727%
We compare the {\em pdf} and its low-order moments (variance and skewness) of the smoothed PSCz galaxy density field and of the corresponding simulated PSCz look-alikes, generated from N-body simulations of 6 different DM models; four structure normalized with $\Gamma=0.25$ and $\sigma_{8}=0.55 \Omega_{\circ}^{-0.6}$, one COBE normalized and the old SCDM. The galaxy distributions are smoothed with a Gaussian window at three different smoothing scales $R_{sm}=5$, 10 and $15 \hm$. We find that the simulation PSCz look-alike {\em pdf}'s are sensitive only on the normalization of the power spectrum, probably due to shape similarity of the simulated galaxy power spectrum on the relevant scales. We find that the only models that are consistent, at a high significance level, with the observed PSCz {\em pdf} are models with a relatively low power spectrum normalization $(\sigma_{8}=0.83)$. From the phenomenologically derived $\sigma_{8}-moments$ relation, fitted from the simulation data, we find that the PSCz moments suggest $\sigma_{8} \simeq 0.7$.; Comment: final version, MNRAS Vol.327, L32

Comparison and combination of ZEUS and H1 PDF analyses

Cooper-Sarkar, A.; Gwenlan, C.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 30/08/2005 Português
Relevância na Pesquisa
248.29727%
The H1 and ZEUS published PDF analyses are compared, including a discussion of the different treatments of correlated systematic uncertainties. Differences in the data sets and the analyses are investigated by putting the H1 data set through both PDF analyses and by putting the ZEUS and H1 data sets through the same (ZEUS) analysis, separately. Finally the HERA averaged data set is put through the ZEUS PDF analysis and the result is compared to that obtained when putting the ZEUS and H1 data sets through this analysis together, using both the Offset and the Hessian methods of treating correlated systematic uncertainties.; Comment: To appear in Proceedings of the HERA-LHC workshop 2005

PDF Steganography based on Chinese Remainder Theorem

Ndoundam, Rene; Ekodeck, Stephane Gael Raymond
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 03/06/2015 Português
Relevância na Pesquisa
248.29727%
We propose different approaches of PDF files based steganography, essentially based on the Chinese Remainder Theorem. Here, after a cover PDF document has been released from unnecessary A0, a secret message is hidden in it using one of the proposed approaches, making it invisible to common PDF readers, and the file is then transmitted through a non-secure communication channel. Where each of our methods, ensure the condition that the number of inserted A0 is less than the number of characters of the secret message s.; Comment: 29pages, 5 figures

Predicting PDF tails in systems with logarithmic non-linearity

Anderson, Johan; Kim, Eun-jin
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
248.29727%
The probability density function (PDF) of flux $R$ is computed in systems with logarithmic non-linearity using a model non-linear dynamical equation. The PDF tails of the first moment flux are analytically predicted to be power law. These PDF tails are shown to be broader than a Gaussian distribution and are a manifestation of intermittency caused by short lived coherent structures (instantons).; Comment: 18 pages, 1 figure

Predicting PDF tails of flux in plasma sheath region

Anderson, Johan; Kim, Eun-jin
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
248.29727%
This letter provides the first prediction of the probability density function (PDF) of flux $R$ in plasma sheath sheath region in magnetic fusion devices which is characterized by dynamical equations with exponential non-linearities. By using a non-perturbative statistical theory (instantons), the PDF tails of first moment are shown to be modified Gumbel distribution which represents a frequency distribution of the extreme values of the ensemble. The non-Gaussian PDF tails that are enhanced over Gaussian predictions are the result of intermittency caused by short lived coherent structures (instantons).; Comment: 13 pages, 1 figure

Analysis of non-Gaussian CMB maps based on the N-pdf. Application to WMAP data

Vielva, P.; Sanz, J. L.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
248.29727%
We present a new method based on the N-point probability distribution (pdf) to study non-Gaussianity in cosmic microwave background (CMB) maps. Likelihood and Bayesian estimation are applied to a local non-linear perturbed model up to third order, characterized by a linear term which is described by a Gaussian N-pdf, and a second and third order terms which are proportional to the square and the cube of the linear one. We also explore a set of model selection techniques (the Akaike and the Bayesian Information Criteria, the minimum description length, the Bayesian Evidence and the Generalized Likelihood Ratio Test) and their application to decide whether a given data set is better described by the proposed local non-Gaussian model, rather than by the standard Gaussian temperature distribution. As an application, we consider the analysis of the WMAP 5-year data at a resolution of around 2 degrees. At this angular scale (the Sachs-Wolfe regime), the non-Gaussian description proposed in this work defaults (under certain conditions) to an approximative local form of the weak non-linear coupling inflationary model (e.g. Komatsu & Spergel 2001) previously addressed in the literature. For this particular case, we obtain an estimation for the non-linear coupling parameter of -94 < F_nl < 154 at 95% CL. Equally...

Galaxy bias determination through the N-pdf of the galaxy number density

Arnalte-Mur, Pablo; Vielva, Patricio; Martínez, Vicent J.; Sanz, José L.; Saar, Enn; Paredes, Silvestre
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 25/06/2015 Português
Relevância na Pesquisa
248.29727%
We present a full description of the N-probability density function of the galaxy number density fluctuations. This N-pdf is given in terms, on the one hand, of the cold dark matter correlations and, on the other hand, of the galaxy bias parameter. The method relies on the assumption commonly adopted that the dark matter density fluctuations follow a local non-linear transformation of the initial energy density perturbations. The N-pdf of the galaxy number density fluctuations allows for an optimal estimation of the bias parameter (e.g., via maximum-likelihood estimation, or Bayesian inference if there exists any \emph{a priori} information on the bias parameter). It also provides the proper framework to perform model selection between two competitive hypotheses (e.g., galaxy biasing versus a one-to-one relation between the galaxy number density and the dark matter perturbations). The bias estimation capabilities of the N-pdf are proved by SDSS-like simulations, showing that our estimator is unbiased. We apply our formalism to the 7th release of the SDSS main sample (for a volume-limited subset with absolute magnitudes $M_r \leq -20$). We obtain a maximum-likelihood bias estimate $\hat{b} = 1.500 \pm 0.036$, for galaxy number density fluctuations in cells of the size of $30h^{-1}$Mpc. Different model selection criteria show that galaxy biasing is clearly favoured.; Comment: Submitted to JCAP...

The 1-point PDF of the Initial Conditions of our Local Universe from the IRAS PSC redshift catalogue

Monaco, P.; Efstathiou, G.; Maddox, S. J.; Branchini, E.; Frenk, C. S.; McMahon, R. G.; Oliver, S. J.; Rowan-Robinson, M.; Saunders, W.; Sutherland, W. J.; Tadros, H.; White, S. D. M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 05/06/2000 Português
Relevância na Pesquisa
248.29727%
The algorithm ZTRACE of Monaco & Efstathiou (1999) is applied to the IRAS PSCz catalogue to reconstruct the initial conditions of our local Universe with a resolution down to ~5 Mpc/h. The 1-point PDF of the reconstructed initial conditions is consistent with the assumptions that (i) IRAS galaxies trace mass on scales of ~5 Mpc/h, and (ii) the statistics of primordial density fluctuations is Gaussian. We use simulated PSCz catalogues, constructed from N-body simulations with Gaussian initial conditions, to show that local non-linear bias can cause the recovered initial PDF (assuming no bias) to be non-Gaussian. However, for plausible bias models, the distortions of the recovered PDF would be difficult to detect using the volume finely sampled by the PSCz catalogue. So, for Gaussian initial conditions, a range of bias models remain compatible with our PSCz reconstruction results.; Comment: 13 pages, figures included (needs mn.sty), in press on MNRAS

Construction of the one-point PDF of the local aperture mass in weak lensing maps

Bernardeau, F.; Valageas, P.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
248.29727%
We present a general method for the reconstruction of the one-point Probability Distribution Function of the local aperture mass in weak lensing maps. Exact results, that neglect the lens-lens coupling and departure form the Born approximation, are derived for both the quasilinear regime at leading order and the strongly nonlinear regime assuming the tree hierarchical model is valid. We describe in details the projection effects on the properties of the PDF and the associated generating functions. In particular, we show how the generic features which are common to both the quasilinear and nonlinear regimes lead to two exponential tails for $P(\Map)$. We briefly investigate the dependence of the PDF with cosmology and with the shape of the angular filter. Our predictions are seen to agree reasonably well with the results of numerical simulations and should be able to serve as foundations for alternative methods to measure the cosmological parameters that take advantage of the full shape of the PDF.; Comment: 17 pages, final version published in A&A

PDF of Velocity Fluctuation in Turbulence by a Statistics based on Generalized Entropy

Arimitsu, Toshihico; Arimitsu, Naoko
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
248.29727%
An analytical formula for the probability density function (PDF) of the velocity fluctuation in fully-developed turbulence is derived, non-perturbatively, by assuming that its underlying statistics is the one based on the generalized measures of entropy, the R\'{e}nyi entropy or the Tsallis-Havrda-Charvat (THC) entropy. The parameters appeared in the PDF, including the index $q$ which appears in the measures of the R\'{e}nyi entropy or of the THC entropy are determined self-consistently with the help of the observed value $\mu$ of the intermittency exponent. The derived PDF explains quite well the experimentally observed density functions.; Comment: 10 pages, 2 figures

Implications of CTEQ PDF analysis for collider observables

Nadolsky, Pavel M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
248.29727%
In the context of a recent CTEQ6.6 global analysis, we review a new technique for studying correlated theoretical uncertainties in hadronic observables associated with imperfect knowledge of parton distribution functions (PDFs). The technique is based on the computation of correlations between the predicted values of physical observables in the Hessian matrix method. It can be used, for example, to link the dominant PDF uncertainty in a hadronic cross section to PDFs for individual parton flavors at well-defined $(x,\mu)$ values. As an illustration, we apply the PDF correlation analysis to study regularities in the PDF dependence of Z, W, and Higgs boson production cross sections at the Tevatron and LHC.; Comment: Contribution to the Proceedings of XVI International Workshop on Deep-Inelastic Scattering and Related Subjects (DIS 2008), London, UK, 7-11 April 2008; 4 pages

APFEL: A PDF Evolution Library with QED corrections

Bertone, Valerio; Carrazza, Stefano; Rojo, Juan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
248.29727%
Quantum electrodynamics and electroweak corrections are important ingredients for many theoretical predictions at the LHC. This paper documents APFEL, a new PDF evolution package that allows for the first time to perform DGLAP evolution up to NNLO in QCD and to LO in QED, in the variable-flavor-number scheme and with either pole or MSbar heavy quark masses. APFEL consistently accounts for the QED corrections to the evolution of quark and gluon PDFs and for the contribution from the photon PDF in the proton. The coupled QCD+QED equations are solved in x-space by means of higher order interpolation, followed by Runge-Kutta solution of the resulting discretized evolution equations. APFEL is based on an innovative and flexible methodology for the sequential solution of the QCD and QED evolution equations and their combination. In addition to PDF evolution, APFEL provides a module that computes Deep-Inelastic Scattering structure functions in the FONLL general-mass variable-flavor-number scheme up to O($\alpha_s^2$). All the functionalities of APFEL can be accessed via a Graphical User Interface, supplemented with a variety of plotting tools for PDFs, parton luminosities and structure functions. Written in Fortran 77, APFEL can also be used via the C/C++ and Python interfaces...

Top production at the LHC: the impact of PDF uncertainties and correlations

Guffanti, Alberto; Rojo, Juan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 27/08/2010 Português
Relevância na Pesquisa
248.29727%
In this contribution we discuss the impact of PDF uncertainties on t\bar{t} and t-channel single-top production at the LHC. We present predictions for total cross-sections computed at NLO accuracy with different PDF sets. For single- top production, we point out that the uncertainty arising from the choice of the bottom quark mass is one of the dominant theoretical uncertainties on the total cross-section. Finally, the possibility of using PDF induced correlations between top quark and electroweak vector boson production cross-sections to improve the accuracy of LHC measurements is investigated.; Comment: 8 pages, 5 figures. To appear in the Proceedings of the International Workshop on Top Quark Physics (top2010), Bruges, Belgium, May 31 - June 4, 2010