1,666 research outputs found
The evolution of bits and bottlenecks in a scientific workflow trying to keep up with technology: Accelerating 4D image segmentation applied to nasa data
In 2016, a team of earth scientists directly engaged a team of computer scientists to identify cyberinfrastructure (CI) approaches that would speed up an earth science workflow. This paper describes the evolution of that workflow as the two teams bridged CI and an image segmentation algorithm to do large scale earth science research. The Pacific Research Platform (PRP) and The Cognitive Hardware and Software Ecosystem Community Infrastructure (CHASE-CI) resources were used to significantly decreased the earth science workflow's wall-clock time from 19.5 days to 53 minutes. The improvement in wall-clock time comes from the use of network appliances, improved image segmentation, deployment of a containerized workflow, and the increase in CI experience and training for the earth scientists. This paper presents a description of the evolving innovations used to improve the workflow, bottlenecks identified within each workflow version, and improvements made within each version of the workflow, over a three-year time period
Signature of Gravity Waves in Polarization of the Microwave Background
Using spin-weighted decomposition of polarization in the Cosmic Microwave
Background (CMB) we show that a particular combination of Stokes and
parameters vanishes for primordial fluctuations generated by scalar modes, but
does not for those generated by primordial gravity waves. Because of this
gravity wave detection is not limited by cosmic variance as in the case of
temperature fluctuations. We present the exact expressions for various
polarization power spectra, which are valid on any scale. Numerical evaluation
in inflation-based models shows that the expected signal is of the order of 0.5
, which could be directly tested in future CMB experiments.Comment: 4 pages, 1 figure, RevTeX, matches the accepted version (to appear in
Phys. Rev. Lett.); code available at
http://arcturus.mit.edu:80/~matiasz/CMBFAST/cmbfast.htm
The Doppler Peaks from Cosmic Texture
We compute the angular power spectrum of temperature anisotropies on the
microwave sky in the cosmic texture theory, with standard recombination
assumed. The spectrum shows `Doppler' peaks analogous to those in scenarios
based on primordial adiabatic fluctuations such as `standard CDM', but at quite
different angular scales. There appear to be excellent prospects for using this
as a discriminant between inflationary and cosmic defect theories.Comment: 14 pages, latex, 3 figures, compressed and uuencoded, replaced
version has minor typographical correction
CMB Anisotropy Induced by Cosmic Strings on Angular Scales
We have computed an estimate of the angular power spectrum of the Cosmic
Microwave Background (CMB) induced by cosmic strings on angular scales , using a numerical simulation of a cosmic string network; and decomposed
this pattern into scalar, vector, and tensor parts. We find no evidence for
strong acoustic oscillations in the scalar anisotropy but rather a broad peak.
The anisotropies from vector modes dominate except on very small angular scales
while the tensor anisotropies are sub-dominant on all angular scales. The
anisotropies generated after recombination are even more important than in
adiabatic models. We expect that these qualitative features are robust to the
varying of cosmological parameters, a study which has not yet been done.Comment: 4 pages, 2 figure
Non-Gaussian bubbles in the sky
We point out a possible generation mechanism of non-Gaussian bubbles in the
sky due to bubble nucleation in the early universe. We consider a curvaton
scenario for inflation and assume that the curvaton field phi, whose energy
density is subdominant during inflation but which is responsible for the
curvature perturbation of the universe, is coupled to another field sigma which
undergoes false vacuum decay through quantum tunneling. For this model, we
compute the skewness of the curvaton fluctuations due to its interaction with
sigma during tunneling, that is, on the background of an instanton solution
that describes false vacuum decay. We find that the resulting skewness of the
curvaton can become large in the spacetime region inside the bubble. We then
compute the corresponding skewness in the statistical distribution of the
cosmic microwave background (CMB) temperature fluctuations. We find a
non-vanishing skewness in a bubble-shaped region in the sky. It can be large
enough to be detected in the near future, and if detected it will bring us
invaluable information about the physics in the early universe.Comment: 6 pages, 6 figure
Comments on Exclusive Electroproduction of Transversely Polarized Vector Mesons
We discuss the electroproduction of light vector mesons from transversely
polarized photons. Here QCD factorization cannot be applied as shown explicitly
in a leading order calculation of corresponding Feynman diagrams. It is
emphasized that present infrared singular contributions cannot be regularized
through phenomenological meson distribution amplitudes with suppressed endpoint
configurations. We point out that infrared divergencies arise also from
integrals over skewed parton distributions of the nucleons.
In a phenomenological analysis of transverse vector meson production model
dependent regularizations have to be applied. If this procedure preserves the
analytic structure suggested by a leading order calculation of Feynman
diagrams, one obtains contributions from nucleon parton distributions and their
derivatives. In particular polarized gluons enter only through their
derivative
Analytic marginalization over CMB calibration and beam uncertainty
With the increased accuracy and angular scale coverage of the recent CMB
experiments it has become important to include calibration and beam
uncertainties when estimating cosmological parameters. This requires an
integration over possible values of the calibration and beam size, which can be
done numerically but increases computation times. We present a fast and simple
algorithm for marginalization over beam and calibration errors by analytical
integration. We also illustrate the effect of incorporating these uncertainties
by calculating the constraints on various cosmological and inflationary
parameters including the spectral index n_s and the physical baryon density
Omega_b h^2, using the latest CMB data. We find that parameter constraints are
significantly changed when calibration/beam uncertainties are taken into
account. Typically the best fit parameters are shifted and the errors bars are
increased by up to fifty per cent for e.g. n_s and Omega_b h^2, although as
expected there is no change for Omega_K, because it is constrained by the
positions of the peaks.Comment: Shortened to match version accepted by MNRA
Cosmic Shear Analysis with CFHTLS Deep data
We present the first cosmic shear measurements obtained from the T0001
release of the Canada-France-Hawaii Telescope Legacy Survey. The data set
covers three uncorrelated patches (D1, D3 and D4) of one square degree each
observed in u*, g', r', i' and z' bands, out to i'=25.5. The depth and the
multicolored observations done in deep fields enable several data quality
controls. The lensing signal is detected in both r' and i' bands and shows
similar amplitude and slope in both filters. B-modes are found to be
statistically zero at all scales. Using multi-color information, we derived a
photometric redshift for each galaxy and separate the sample into medium and
high-z galaxies. A stronger shear signal is detected from the high-z subsample
than from the low-z subsample, as expected from weak lensing tomography. While
further work is needed to model the effects of errors in the photometric
redshifts, this results suggests that it will be possible to obtain constraints
on the growth of dark matter fluctuations with lensing wide field surveys. The
various quality tests and analysis discussed in this work demonstrate that
MegaPrime/Megacam instrument produces excellent quality data. The combined Deep
and Wide surveys give sigma_8= 0.89 pm 0.06 assuming the Peacock & Dodds
non-linear scheme and sigma_8=0.86 pm 0.05 for the halo fitting model and
Omega_m=0.3. We assumed a Cold Dark Matter model with flat geometry.
Systematics, Hubble constant and redshift uncertainties have been marginalized
over. Using only data from the Deep survey, the 1 sigma upper bound for w_0,
the constant equation of state parameter is w_0 < -0.8.Comment: 14 pages, 16 figures, accepted A&
CMB Anisotropies: Total Angular Momentum Method
A total angular momentum representation simplifies the radiation transport
problem for temperature and polarization anisotropy in the CMB. Scattering
terms couple only the quadrupole moments of the distributions and each moment
corresponds directly to the observable angular pattern on the sky. We develop
and employ these techniques to study the general properties of anisotropy
generation from scalar, vector and tensor perturbations to the metric and the
matter, both in the cosmological fluids and from any seed perturbations (e.g.
defects) that may be present. The simpler, more transparent form and derivation
of the Boltzmann equations brings out the geometric and model-independent
aspects of temperature and polarization anisotropy formation. Large angle
scalar polarization provides a robust means to distinguish between isocurvature
and adiabatic models for structure formation in principle. Vector modes have
the unique property that the CMB polarization is dominated by magnetic type
parity at small angles (a factor of 6 in power compared with 0 for the scalars
and 8/13 for the tensors) and hence potentially distinguishable independent of
the model for the seed. The tensor modes produce a different sign from the
scalars and vectors for the temperature-polarization correlations at large
angles. We explore conditions under which one perturbation type may dominate
over the others including a detailed treatment of the photon-baryon fluid
before recombination.Comment: 32 pg., 10 figs., RevTeX, minor changes reflect published version,
minor typos corrected, also available at http://www.sns.ias.edu/~wh
Recovering the Inflationary Potential
A procedure is developed for the recovery of the inflationary potential over
the interval that affects astrophysical scales (\approx 1\Mpc - 10^4\Mpc).
The amplitudes of the scalar and tensor metric perturbations and their
power-spectrum indices, which can in principle be inferred from large-angle CBR
anisotropy experiments and other cosmological data, determine the value of the
inflationary potential and its first two derivatives. From these, the
inflationary potential can be reconstructed in a Taylor series and the
consistency of the inflationary hypothesis tested. A number of examples are
presented, and the effect of observational uncertainties is discussed.Comment: 13 pages LaTeX, 6 Figs. available on request, FNAL-Pub-93/182-
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