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Resultados filtrados por Publicador: Universidade Cornell

## PDF modeling of turbulent flows on unstructured grids

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 03/06/2010
Português

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In probability density function (PDF) methods of turbulent flows, the joint
PDF of several flow variables is computed by numerically integrating a system
of stochastic differential equations for Lagrangian particles. A mathematically
exact treatment of advection, viscous effects and arbitrarily complex chemical
reactions is possible; these processes are treated without closure assumptions.
A set of algorithms is proposed to provide an efficient solution of the PDF
transport equation modeling the joint PDF of turbulent velocity, frequency and
concentration of a passive scalar in geometrically complex configurations. An
unstructured Eulerian grid is employed to extract Eulerian statistics, to solve
for quantities represented at fixed locations of the domain and to track
particles. All three aspects regarding the grid make use of the finite element
method. Compared to hybrid methods, the current methodology is stand-alone,
therefore it is consistent both numerically and at the level of turbulence
closure without the use of consistency conditions. Several newly developed
algorithms are described that facilitate the numerical solution in complex flow
geometries, including a stabilized mean-pressure projection scheme, the
estimation of conditional and unconditional Eulerian statistics and their
derivatives from stochastic particle fields...

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## Detecting Table Region in PDF Documents Using Distant Supervision

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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#Computer Science - Computer Vision and Pattern Recognition#Computer Science - Information Retrieval

Superior to state-of-the-art approaches which compete in table recognition
with 67 annotated government reports in PDF format released by {\it ICDAR 2013
Table Competition}, this paper contributes a novel paradigm leveraging
large-scale unlabeled PDF documents to open-domain table detection. We
integrate the paradigm into our latest developed system ({\it PdfExtra}) to
detect the region of tables by means of 9,466 academic articles from the entire
repository of {\it ACL Anthology}, where almost all papers are archived by PDF
format without annotation for tables. The paradigm first designs heuristics to
automatically construct weakly labeled data. It then feeds diverse evidences,
such as layouts of documents and linguistic features, which are extracted by
{\it Apache PDFBox} and processed by {\it Stanford NLP} toolkit, into different
canonical classifiers. We finally use these classifiers, i.e. {\it Naive
Bayes}, {\it Logistic Regression} and {\it Support Vector Machine}, to
collaboratively vote on the region of tables. Experimental results show that
{\it PdfExtra} achieves a great leap forward, compared with the
state-of-the-art approach. Moreover, we discuss the factors of different
features, learning models and even domains of documents that may impact the
performance. Extensive evaluations demonstrate that our paradigm is compatible
enough to leverage various features and learning models for open-domain table
region detection within PDF files.

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## Heavy-quark mass dependence in global PDF analyses and 3- and 4-flavour parton distributions

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

Relevância na Pesquisa

26.590781%

We study the sensitivity of our recent MSTW 2008 NLO and NNLO PDF analyses to
the values of the charm- and bottom-quark masses, and we provide additional
public PDF sets for a wide range of these heavy-quark masses. We quantify the
impact of varying m_c and m_b on the cross sections for W, Z and Higgs
production at the Tevatron and the LHC. We generate 3- and 4-flavour versions
of the (5-flavour) MSTW 2008 PDFs by evolving the input PDFs and alpha_S
determined from fits in the 5-flavour scheme, including the eigenvector PDF
sets necessary for calculation of PDF uncertainties. As an example of their
use, we study the difference in the Z total cross sections at the Tevatron and
LHC in the 4- and 5-flavour schemes. Significant differences are found,
illustrating the need to resum large logarithms in Q^2/m_b^2 by using the
5-flavour scheme. The 4-flavour scheme is still necessary, however, if cuts are
imposed on associated (massive) b-quarks, as is the case for the experimental
measurement of Z b bbar production and similar processes.; Comment: 40 pages, 11 figures. Grids can be found at
http://projects.hepforge.org/mstwpdf/ and in LHAPDF V5.8.4. v2: version
published in EPJC

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## Measuring the History of Cosmic Reionization using the 21-cm PDF from Simulations

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

Relevância na Pesquisa

26.590781%

The 21-cm PDF (i.e., distribution of pixel brightness temperatures) is
expected to be highly non-Gaussian during reionization and to provide important
information on the distribution of density and ionization. We measure the 21-cm
PDF as a function of redshift in a large simulation of cosmic reionization and
propose a simple empirical fit. Guided by the simulated PDF, we then carry out
a maximum likelihood analysis of the ability of upcoming experiments to measure
the shape of the 21-cm PDF and derive from it the cosmic reionization history.
Under the strongest assumptions, we find that upcoming experiments can measure
the reionization history in the mid to late stages of reionization to 1-10%
accuracy. Under a more flexible approach that allows for four free parameters
at each redshift, a similar accuracy requires the lower noise levels of
second-generation 21-cm experiments.; Comment: 13 pages, 16 figures, submitted to MNRAS

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## Joint PDF modelling of turbulent flow and dispersion in an urban street canyon

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 23/03/2010
Português

Relevância na Pesquisa

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#Physics - Geophysics#Physics - Computational Physics#Physics - Fluid Dynamics#85A10, 76F25, 76F55, 76M35, 37N10

The joint probability density function (PDF) of turbulent velocity and
concentration of a passive scalar in an urban street canyon is computed using a
newly developed particle-in-cell Monte Carlo method. Compared to moment
closures, the PDF methodology provides the full one-point one-time PDF of the
underlying fields containing all higher moments and correlations. The
small-scale mixing of the scalar released from a concentrated source at the
street level is modelled by the interaction by exchange with the conditional
mean (IECM) model, with a micro-mixing time scale designed for geometrically
complex settings. The boundary layer along no-slip walls (building sides and
tops) is fully resolved using an elliptic relaxation technique, which captures
the high anisotropy and inhomogeneity of the Reynolds stress tensor in these
regions. A less computationally intensive technique based on wall functions to
represent boundary layers and its effect on the solution are also explored. The
calculated statistics are compared to experimental data and large-eddy
simulation. The present work can be considered as the first example of
computation of the full joint PDF of velocity and a transported passive scalar
in an urban setting. The methodology proves successful in providing high level
statistical information on the turbulence and pollutant concentration fields in
complex urban scenarios.; Comment: Accepted in Boundary-Layer Meteorology...

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## An SMLD joint PDF model for turbulent non-premixed combustion using the flamelet progress-variable approach

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 20/04/2015
Português

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This paper provides an improved flamelet/progress variable (FPV) model for
the simulation of turbulent combustion, employing the statistically most likely
distribution (SMLD) approach for the joint probability density function (PDF)
of the mixture fraction, Z, and of the progress parameter, {\Lambda} .
Steady-state FPV models are built presuming the func- tional shape of the joint
PDF of Z and {\Lambda} in order to evaluate Favre-averages of thermody- namic
quantities. The mixture fraction is widely assumed to behave as a passive
scalar with a mono-modal behaviour modelled by a \b{eta} -distribution.
Moreover, under the hypothesis that Z and {\Lambda} are statistically
independent, the joint PDF coincides with the product of the two marginal PDFs.
In this work we discuss these two constitutive hypotheses. The proposed model
evaluates the most probable joint distribution of Z and {\Lambda} , relaxing
some crucial as- sumption on their statistical behaviour. This provides a more
general model in the context of FPV approach and an effective tool to verify
the adequateness of widely used hypotheses. The model is validated versus
experimental data of well-known test cases, namely, the San- dia flames. The
results are also compared with those obtained by the standard FPV approach...

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## Feasibility of top quark measurements at LHCb and constraints on the large-$x$ gluon PDF

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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The forward LHCb acceptance opens interesting possibilities of studying
precision Standard Model hard processes in a kinematical region beyond the
reach of ATLAS and CMS. In this paper we perform a feasibility study for
cross-section measurements of top quark pairs with the LHCb detector, with an
analysis of signal and background rates for selected final states, and
determine the potential precision achievable at $\sqrt{s} =$ 7 and 14~TeV. We
then study the dependence of theoretical uncertainties on the pseudorapidity
distribution of top quarks produced in pair production at NLO, and observe that
a cross-section measurement at high pseudorapidity has enhanced sensitivity to
probe the high-$x$ gluon PDF as compared to measurements in the central-region.
Based on simulated pseudodata, the impact of a 14~TeV cross-section measurement
on the gluon PDF and charge asymmetry is quantified.; Comment: 25 pages, 14 figures, 8 tables. Extended PDF analysis to include
ABM11 5flv nlo. Added summary plots of LHCb cross-sections. Include shift of
gluon PDF central value for CT10, NNPDF sets assuming different pseudodata
values. Matches version to be published in JHEP

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## The impact of PDF uncertainties on the measurement of the W boson mass at the Tevatron and the LHC

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 11/04/2011
Português

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We study at a quantitative level the impact of the uncertainties on the value
of the W boson mass measured at hadron colliders due to: the proton parton
distribution functions (PDFs), the value of the strong coupling constant
alpha_S and the value of the charm mass used in the PDF determination. The
value of the W boson mass is extracted, by means of a template fit technique,
from the lepton-pair transverse mass distribution measured in the charged
current Drell-Yan process. We study the determination of M_W at the Tevatron
and at the LHC with 7 and 14 TeV of center-of-mass energy in a realistic
experimental setup. The analysis has been done at the Born level using the
event generator HORACE and at NLO-QCD using the event generators DYNNLO and
ResBos. We consider the three global PDF sets, CTEQ6.6, MSTW2008 and NNPDF2.1.
We estimate that the total PDF uncertainty on M_W is below 10 MeV both at the
Tevatron and at the LHC for all energies and final states. We conclude that PDF
uncertainties do not challenge a measurement of the W boson mass at the level
of 10 MeV accuracy.; Comment: 22 pages, 14 figures

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## Precoder Design for Multi-antenna Partial Decode-and-Forward (PDF) Cooperative Systems with Statistical CSIT and MMSE-SIC Receivers

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 28/02/2012
Português

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Cooperative communication is an important technology in next generation
wireless networks. Aside from conventional amplify-and-forward (AF) and
decode-and-forward (DF) protocols, the partial decode-and-forward (PDF)
protocol is an alternative relaying scheme that is especially promising for
scenarios in which the relay node cannot reliably decode the complete source
message. However, there are several important issues to be addressed regarding
the application of PDF protocols. In this paper, we propose a PDF protocol and
MIMO precoder designs at the source and relay nodes. The precoder designs are
adapted based on statistical channel state information for correlated MIMO
channels, and matched to practical minimum mean-square-error successive
interference cancelation (MMSE-SIC) receivers at the relay and destination
nodes. We show that under similar system settings, the proposed MIMO precoder
design with PDF protocol and MMSE-SIC receivers achieves substantial
performance enhancement compared with conventional baselines.

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## The impact of PDF and alphas uncertainties on Higgs Production in gluon fusion at hadron colliders

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 06/04/2010
Português

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We present a systematic study of uncertainties due to parton distributions
and the strong coupling on the gluon-fusion production cross section of the
Standard Model Higgs at the Tevatron and LHC colliders. We compare procedures
and results when three recent sets of PDFs are used, CTEQ6.6, MSTW08 and
NNPDF1.2, and we discuss specifically the way PDF and strong coupling
uncertainties are combined. We find that results obtained from different PDF
sets are in reasonable agreement if a common value of the strong coupling is
adopted. We show that the addition in quadrature of PDF and alphas
uncertainties provides an adequate approximation to the full result with exact
error propagation. We discuss a simple recipe to determine a conservative
PDF+alphas uncertainty from available global parton sets, and we use it to
estimate this uncertainty on the given process to be about 10% at the Tevatron
and 5% at the LHC for a light Higgs.; Comment: 29 pages, 13 figures

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