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## Stable spatial Langmuir solitons as a model of long-lived atmospheric plasma structures

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 02/07/2014
Português

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#Physics - Plasma Physics#Nonlinear Sciences - Pattern Formation and Solitons#Physics - Atmospheric and Oceanic Physics

I study stable spatial Langmuir solitons in plasma based on nonlinear radial
oscillations of charged particles. I discuss two situations when a Langmuir
soliton can be stable. In the former case the stability of solitons against the
collapse is due to electron-electron interactions which result in the nonlocal
terms in the nonlinear Schr\"{o}dinger equation. In the latter situation I
derive the new cubic-quintic nonlinear Schr\"{o}dinger equation with accounts
for the interaction of induced dipole moments of diatomic ions with a rapidly
oscillating electric field and show that the collapse of Langmuir waves can be
also arrested. In both cases I find the numerical solutions of the nonlinear
Schr\"{o}dinger equation and analyze their stability using the
Vakhitov-Kolokolov criterion. I discuss the application of my results for the
description of long-lived atmospheric plasma structures. I show that, using my
model, one can explain the existence of atmospheric plasmoids in the upper
ionosphere. It is also demonstrated that Langmuir solitons described by the
cubic-quintic nonlinear Schr\"{o}dinger equation can describe atmospheric
plasmoids at the initial stages of their evolution. Note that, besides the
modeling of atmospheric plasma structures...

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## Volatility in Financial Markets: Stochastic Models and Empirical Results

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 28/02/2002
Português

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We investigate the historical volatility of the 100 most capitalized stocks
traded in US equity markets. An empirical probability density function (pdf) of
volatility is obtained and compared with the theoretical predictions of a
lognormal model and of the Hull and White model. The lognormal model well
describes the pdf in the region of low values of volatility whereas the Hull
and White model better approximates the empirical pdf for large values of
volatility. Both models fails in describing the empirical pdf over a moderately
large volatility range.; Comment: 6 pages, 2 figures

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## A Redux on "When is the Top Quark a Parton?"

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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If a new heavy particle phi is produced in association with the top quark in
a hadron collider, the production cross section exhibits a collinear
singularity of the form log(m_phi/m_t), which can be resummed by introducing a
top quark parton distribution function (PDF). We reassess the necessity of such
resummation in the context of a high energy pp collider. We find that the
introduction of a top PDF typically has a small effect at sqrt(S) ~ 100 TeV due
to three factors: 1) alpha_s at the scale mu = m_phi is quite small when
log(m_phi/m_t) is large, 2) the Bjorken x << 1 for m_phi < ~10 TeV, and 3) the
kinematic region where log(m_phi/m_t) >> 1 is suppressed by phase space. We
show that the effect of a top PDF is generically smaller than that of a bottom
PDF in the associated production of b phi and consider the example of pp -> t
H+ at next-to-leading logarithm order.; Comment: 26 pages, 7 figures; minor changes, version accepted by PRD

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## Parton distributions based on a maximally consistent dataset

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 10/09/2014
Português

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The choice of data that enters a global QCD analysis can have a substantial
impact on the resulting parton distributions and their predictions for collider
observables. One of the main reasons for this has to do with the possible
presence of inconsistencies, either internal within an experiment or external
between different experiments. In order to assess the robustness of the global
fit, different definitions of a conservative PDF set, that is, a PDF set based
on a maximally consistent dataset, have been introduced. However, these
approaches are typically affected by theory biases in the selection of the
dataset. In this contribution, after a brief overview of recent NNPDF
developments, we propose a new, fully objective, definition of a conservative
PDF set, based on the Bayesian reweighting approach. Using the new NNPDF3.0
framework, we produce various conservative sets, which turn out to be mutually
in agreement within the respective PDF uncertainties, as well as with the
global fit. We explore some of their implications for LHC phenomenology,
finding also good consistency with the global fit result. These results provide
a non-trivial validation test of the new NNPDF3.0 fitting methodology, and
indicate that possible inconsistencies in the fitted dataset do not affect
substantially the global fit PDFs.; Comment: 6 pages...

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## Fast Computation of Solvation Free Energies with Molecular Density Functional Theory: Thermodynamic-Ensemble Partial Molar Volume Corrections

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 11/06/2014
Português

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Molecular Density Functional Theory (MDFT) offers an efficient implicit-
solvent method to estimate molecule solvation free-energies whereas conserving
a fully molecular representation of the solvent. Even within a second order ap-
proximation for the free-energy functional, the so-called homogeneous reference
uid approximation, we show that the hydration free-energies computed for a
dataset of 500 organic compounds are of similar quality as those obtained from
molecular dynamics free-energy perturbation simulations, with a computer cost
reduced by two to three orders of magnitude. This requires to introduce the
proper partial volume correction to transform the results from the grand
canoni- cal to the isobaric-isotherm ensemble that is pertinent to experiments.
We show that this correction can be extended to 3D-RISM calculations, giving a
sound theoretical justifcation to empirical partial molar volume corrections
that have been proposed recently.; Comment: Version with correct equation numbers is here:
http://compchemmpi.wikispaces.com/file/view/sergiievskyi_et_al.pdf/513575848/sergiievskyi_et_al.pdf
Supporting information available online at:
http://compchemmpi.wikispaces.com/file/view/SuppInf_sergiievskyi_et_al_07-04-2014.pdf/513576008/SuppInf_sergiievskyi_et_al_07-04-2014.pdf

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## Multiple Andreev Reflections in a Carbon Nanotube Quantum Dot

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 10/04/2003
Português

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We report resonant multiple Andreev relections in a multiwall carbon nanotube
quantum dot coupled to superconducting leads. The position and magnitude of the
subharmonic gap structure is found to depend strongly on the level positions of
the single-electron states which are adjusted with a gate electrode. We discuss
a theoretical model of the device and compare the calculated differential
conductance with the experimental data. (pdf including figures, see:
www.unibas.ch/phys-meso/Research/Papers/2003/MAR-MWNT.pdf); Comment: pdf including figures, see:
http://www.unibas.ch/phys-meso/Research/Papers/2003/MAR-MWNT.pdf

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## Cosmological Density Fluctuations on 100Mpc Scales and their ISW Effect

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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We measure the matter probability distribution function (PDF) via counts in
cells in a volume limited subsample of the Sloan Digital Sky Survey Luminous
Red Galaxy Catalog on scales from $30 h^{-1}$Mpc to $150 h^{-1}$Mpc and
estimate the linear Integrated Sachs--Wolfe effect produced by supervoids and
superclusters in the tail of the PDF. We characterize the PDF by the variance,
$S_3$, and $S_4$, and study in simulations the systematic effects due to finite
volume, survey shape and redshift distortion. We compare our measurement to the
prediction of $\Lambda$CDM with linear bias and find a good agreement. We use
the moments to approximate the tail of the PDF with analytic functions. A
simple Gaussian model for the superstructures appears to be consistent with the
claim by Granett et al. that density fluctuations on $100 h^{-1}$Mpc scales
produce hot and cold spots with $\Delta T \approx 10\mu K$ on the cosmic
microwave background.; Comment: 9 pages, 9 figures, 2 tables, Updates to match the article accepted
to ApJ

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## Parton Distribution Functions properties of the statistical model

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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We show that the parton distribution functions (PDF) described by the
statistical model have very interesting physical properties which help to
understand the structure of partons. The role of the quark helicity components
is emphasized as they represent the building blocks of the PDF. In the model
the sign of the polarized quarks PDF comes out in a quite natural way once the
thermodynamical potentials with a given helicity are known. Introducing the
concept of entropy we study the states madeof |2u + d >, |u +d +s > and $|2\bar
u +\bar d >$, for a fixed Q^2, the variation with x shows that the first state
has a dominant entropy due to the effect of u quark. We prove that the PDF
parameters obtained from experiments give in fact an optimal solution of an
entropy equation subject to constraints. We develop a new approach of the
polarized gluon density based on a neural model which explains its property, in
particular, a large positivity value and an agreement with the positvity
constraint. An extension of this neural approach is applied to quarks giving a
coherent description of the partons structure.; Comment: 22 pages, 19 figures, new results added

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## Weak Limit of the 3-State Quantum Walk on the Line

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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We revisit the one dimensional discrete time quantum walk with 3 states and
the Grover coin. We derive analytic expressions for observed the localization,
an long time approximation for the probability density function (PDF). We also
connect the time averaged approximation to the PDF found by Inui et. al. to a
spatial average of the walk. We show that this smooth approximation constitutes
a proper PDF that predicts moments of the real PDF accurately.; Comment: 8 pages, revtex, for related information see
http://www.physics.emory.edu/faculty/boettcher/ v2: minor changes, references
added

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## Fokker-Planck Kinetic description of small-scale fluid turbulence for classical incompressible fluids

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 30/06/2008
Português

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Extending the statistical approach proposed in a parallel paper \cite%
{Tessarotto2008-aa}, purpose of this work is to propose a stochastic inverse
kinetic theory for small-scale hydrodynamic turbulence based on the
introduction of a suitable \textit{local phase-space probability density
function} (pdf). In particular, we pose the problem of the construction of
Fokker-Planck kinetic models of hydrodynamic turbulence. The approach here
adopted is based on the so-called IKT approach (inverse kinetic theory),
developed by Ellero et al. (2004-2008) which permits an exact phase-space
description of incompressible fluids based on the adoption of a local pdf. We
intend to show that for prescribed models of stochasticity the present approach
permits to determine uniquely the time evolution of the stochastic fluid
fields. The stochastic-averaged local pdf is shown to obey a kinetic equation
which, although generally non-Markovian, locally in velocity-space can be
approximated by means of a suitable Fokker-planck kinetic equation. As a side
result, the same pdf is proven to have generally a non-Gaussian behavior.; Comment: Contributed paper at RGD26 (Kyoto, Japan, July 2008)

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## Global parton distributions with nuclear and finite-Q^2 corrections

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

Relevância na Pesquisa

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#High Energy Physics - Phenomenology#High Energy Physics - Experiment#Nuclear Experiment#Nuclear Theory

We present three new sets of next-to-leading order parton distribution
functions (PDFs) determined by global fits to a wide variety of data for hard
scattering processes. The analysis includes target mass and higher twist
corrections needed for the description of deep inelastic scattering data at
large x and low Q^2, and nuclear corrections for deuterium targets. The PDF
sets correspond to three different models for the nuclear effects, and provide
a more realistic uncertainty range for the d quark PDF, in particular, compared
with previous fits. We describe the PDF error sets for each choice of the
nuclear corrections, and provide a user interface for utilizing the
distributions.; Comment: 25 pages, 7 figures, 2 tables. Extended discussion of PDF
parametrizations and conventions

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## An analytical framework to describe the orientation of dark matter halos and galaxies within the large-scale structure

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 05/12/2009
Português

Relevância na Pesquisa

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We provide a set of general tools for studying the alignments of dark matter
halos and galaxies with respect to the large scale structure. The statistics of
the positioning of these objects is represented by a Probability Distribution
Function (PDF) of their Euler angles. The PDF corresponding to halos located in
the shells of the cosmic voids is inferred from previous results. This PDF is
used to show how to recover the outcomes found for the alignments of the axes
of these halos in simulations. We also explore the orientation of the angular
momentum of the halos, both with respect to the halo axes and with respect to
the large scale structure. We present an expression which describes well
numerical results for the alignment of the angular momentum of the halo with
respect to the halo axes for randomly chosen halos. We also propose a model
that relates the orientation of the angular momentum with the halos axes
accounting for the orientation of the halo axes with the large scale structure.
This model is shown to recover accurately the observed PDF of the halo angular
momentum with respect to the void radial direction. In addition, we give an
expression for determining the degradation of the angular momentum intrinsic
alignment when observational errors are accounted. This expression is also used
to determine the departure of the observed value of the alignment from the
initial expectation (as provided by the tidal torque theory) due to the
rotation of the angular momentum of the halo with respect to the initial
torque. For voids...

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## Temperature dependent fluctuations in the two-dimensional XY model

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 18/07/2005
Português

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We present a detailed investigation of the probability density function (PDF)
of order parameter fluctuations in the finite two-dimensional XY (2dXY) model.
In the low temperature critical phase of this model, the PDF approaches a
universal non-Gaussian limit distribution in the limit T-->0. Our analysis
resolves the question of temperature dependence of the PDF in this regime, for
which conflicting results have been reported. We show analytically that a weak
temperature dependence results from the inclusion of multiple loop graphs in a
previously-derived graphical expansion. This is confirmed by numerical
simulations on two controlled approximations to the 2dXY model: the Harmonic
and ``Harmonic XY'' models. The Harmonic model has no
Kosterlitz-Thouless-Berezinskii (KTB) transition and the PDF becomes
progressively less skewed with increasing temperature until it closely
approximates a Gaussian function above T ~ 4\pi. Near to that temperature we
find some evidence of a phase transition, although our observations appear to
exclude a thermodynamic singularity.; Comment: 15 pages, 5 figures and 1 table

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## Posterior Exploration based Sequential Monte Carlo for Global Optimization

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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We propose a global optimization algorithm based on the Sequential Monte
Carlo (SMC) sampling framework. In this framework, the objective function is
normalized to be a probabilistic density function (pdf), based on which a
sequence of annealed target pdfs is designed to asymptotically converge on the
set of global optima. A sequential importance sampling (SIS) procedure is
performed to simulate the resulting targets, and the maxima of the objective
function is assessed from the yielded samples. The disturbing issue lies in the
design of the importance sampling (IS) pdf, which crucially influences the IS
efficiency. We propose an approach to design the IS pdf online by embedding a
posterior exploration (PE) procedure into each iteration of the SMC framework.
The PE procedure can also explore the important regions of the parameter space
supported by the target pdf. A byproduct of the PE procedure is an adaptive
mechanism to design the annealing temperature schedule online. We compare the
performance of the proposed algorithm with those of several existing related
alternatives by applying them to over a dozen standard benchmark functions. The
result demonstrates the appealing properties of our algorithm.; Comment: 14 pages, 10 figures

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## Coins falling in water

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 08/12/2013
Português

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When a coin falls in water, its trajectory is one of four types determined by
its dimensionless moment of inertia $I^\ast$ and Reynolds number Re: (A)
steady; (B) fluttering; (C) chaotic; or (D) tumbling. The dynamics induced by
the interaction of the water with the surface of the coin, however, makes the
exact landing site difficult to predict a priori. Here, we describe a carefully
designed experiment in which a coin is dropped repeatedly in water, so that we
can determine the probability density functions (pdf) associated with the
landing positions for each of the four trajectory types, all of which are
radially symmetric about the center-drop line. In the case of the steady mode,
the pdf is approximately Gaussian distributed, with variances that are small,
indicating that the coin is most likely to land at the center, right below the
point it is dropped from. For the other falling modes, the center is one of the
least likely landing sites. Indeed, the pdf's of the fluttering, chaotic and
tumbling modes are characterized by a "dip" around the center. For the tumbling
mode, the pdf is a ring configuration about the center-line, with a ring width
that depends on the dimensionless parameters $I^\ast$ and Re and height from
which the coin is dropped. For the chaotic mode...

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## Direct pivotal predictive inference

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 19/10/2004
Português

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#Mathematics - Statistics Theory#Mathematics - Probability#Physics - Data Analysis, Statistics and Probability#62A01#62G99#62F99

Without assuming any pdf for some measured parameter, we derive a predictive
pdf for the outcome of a second measurement, given the outcome of the first
measurement and two common assumptions about the noise. These are that (1) it
is additive, and (2) it is of some known pdf. The argument is based on a
Bayesian analysis of the noise when no pdf is provided for the value of the
parameter. In this way we avoid assuming an ad-hoc prior. We clarify how this
method of direct predictive inference is distinct from fiducial prediction. We
specify the distinct flaw in the fiducial argument, and outline the importance
of this development in the foundations of probability and statistics.
Keywords: nonparametric predictive inference, direct pivotal argument,
pivotal argument, fiducial argument, fiducial prediction, Bayesian inference,
reference prior, reference class.; Comment: 7 pages

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## Statistical Mechanics of Double sinh-Gordon Kinks

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 02/08/1998
Português

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#Condensed Matter - Statistical Mechanics#High Energy Physics - Lattice#High Energy Physics - Phenomenology

We study the classical thermodynamics of the double sinh-Gordon (DSHG) theory
in 1+1 dimensions. This model theory has a double well potential, thus allowing
for the existence of kinks and antikinks. Though it is nonintegrable, the DSHG
model is remarkably amenable to analysis. Below we obtain exact single kink and
kink lattice solutions as well as the asymptotic kink-antikink interaction. In
the continuum limit, finding the classical partition function is equivalent to
solving for the ground state of a Schrodinger-like equation obtained via the
transfer integral method. For the DSHG model, this equation turns out to be
quasi-exactly solvable. We exploit this property to obtain exact energy
eigenvalues and wavefunctions for several temperatures both above and below the
symmetry breaking transition temperature. The availability of exact results
provides an excellent testing ground for large scale Langevin simulations. The
probability distribution function (PDF) calculated from Langevin dynamics is
found to be in striking agreement with the exact PDF obtained from the ground
state wavefunction. This validation points to the utility of a PDF-based
computation of thermodynamics utilizing Langevin methods. In addition to the
PDF, field-field and field fluctuation correlation functions were computed and
also found to be in excellent agreement with the exact results.; Comment: 10 pages...

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## Progress in the NNPDF global analysis

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 09/04/2013
Português

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We report on recent progress in the NNPDF framework of global PDF analysis.
The NNPDF2.3 set is the first and only available PDF set with includes LHC
data. A recent benchmark comparison of NNPDF2.3 and all other modern NNLO PDF
sets with LHC data was performed. We have also studied theoretical
uncertainties due to heavy quark renormalization schemes, higher twists and
deuterium corrections in PDFs. Finally, we report on the release of positive
definite PDF sets, based on the NNPDF2.3 analysis, specially suited for use in
Monte Carlo event generators.; Comment: 4 pages, 3 figures, to appear in the proceedings of Rencontres de
Moriond 2013, QCD and High Energy Interactions

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## Inverse cascade and intermittency of passive scalar in 1d smooth flow

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 12/06/1997
Português

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Random advection of Lagrangian tracer scalar field $\theta (t,x)$ by a
one-dimensional, spatially smooth and short-correlated in time velocity field
is considered. Scalar fluctuations are maintained by a source concentrated at
the integral scale $L$. The statistical properties of both scalar differences
and the dissipation field are analytically determined, exploiting the dynamical
formulation of the model. The Gaussianity known to be present at small scales
for incompressible velocity fields emerges here at large scales ($x\gg L$).
These scales are shown to be excited by an inverse cascade of $\theta ^{2}$ and
the probability distribution function (PDF) of the corresponding scalar
differences to approach the Gaussian form, as larger and larger scales are
considered. Small scales ($x\ll L$) statistics is shown to be strongly
non-Gaussian. Collapse of scaling exponents for scalar structure
functions\thinspace takes place: moments of order $p\ge 1$ scale all linearly,
independently of the order $p$. Smooth scaling $x^{p}$ is found for $-1

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## Schinzel's Problem: Imprimitive covers and the monodromy method

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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#Mathematics - Algebraic Geometry#Mathematics - Group Theory#141130, 20B15, 20C15, 30F10 (Primary) 12D05, 12E30, 12F10, 20E22
(Secondary)

Schinzel's original problem was to describe when an expression f(x)-g(y),
with f,g nonconstant and having complex coefficients, is reducible. We call
such an (f,g) a Schinzel pair if this happens nontrivially: f(x)-g(y) is newly
reducible. Fried accomplished this as a special case of a result in
"http://www.math.uci.edu/~mfried/paplist-ff/dav-red.pdf">dav-red.pdf, when f is
indecomposable. That work featured using primitive permutation representations.
Even after 42 years going beyond using primitivity is a challenge to the
monodromy method despite many intervening related papers (see
http://www.math.uci.edu/~mfried/paplist-ff/UMStory.pdf">UMStory.pdf. Here we
develop a formula for branch cycles that characterizes Schinzel pairs
satisfying a condition of Avanzi, Gusic and Zannier and relate it to this
ongoing story.; Comment: 15 pages, 1 figure, to Appear in Acta Arithmetica early 2012 for the
75th birthday volume for Andrzej Schinzel

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