1,832 research outputs found
Reduced convergence and the local smoothness parameter: bridging two different descriptions of weak lensing amplification
Weak gravitational lensing due to the inhomogeneous matter distribution in
the universe is an important systematic uncertainty in the use of standard
candles in cosmology. There are two different descriptions of weak lensing
amplification, one uses a local smoothness parameter , the
other uses reduced convergence (where
is convergence). The description involves Dyer-Roeder distance
( corresponds to a smooth universe);
it is simple and convenient, and has been used by the community to illustrate
the effect of weak lensing on point sources such as type Ia supernovae. Wang
(1999) has shown that the description can be made realistic by
allowing to be a local variable, the local smoothness
parameter. The description has been used by Wang, Holz, & Munshi (2002)
to derive a universal probability distribution (UPDF) for weak lensing
amplification. In this paper, we bridge the two different descriptions of weak
lensing amplification by relating the reduced convergence and the local
smoothness parameter . We give the variance of
in terms of the matter power spectrum, thus providing a quantitative guidance
to the use of Dyer-Roeder distances in illustrating the effect of weak lensing.
The by-products of this work include a corrected definition of the reduced
convergence, and simple and accurate analytical expressions for
. Our results should be very useful in studying the weak
lensing of standard candles.Comment: Revised and expanded version. ApJ accepte
Predicting H{\alpha} emission line galaxy counts for future galaxy redshift surveys
Knowledge of the number density of H emitting galaxies is vital for
assessing the scientific impact of the Euclid and WFIRST missions. In this work
we present predictions from a galaxy formation model, Galacticus, for the
cumulative number counts of H-emitting galaxies. We couple Galacticus
to three different dust attenuation methods and examine the counts using each
method. A minimisation approach is used to compare the model
predictions to observed galaxy counts and calibrate the dust parameters. We
find that weak dust attenuation is required for the Galacticus counts to be
broadly consistent with the observations, though the optimum dust parameters
return large values for , suggesting that further calibration of
Galacticus is necessary. The model predictions are also consistent with
observed estimates for the optical depth and the H luminosity function.
Finally we present forecasts for the redshift distributions and number counts
for two Euclid-like and one WFIRST-like survey. For a Euclid-like survey with
redshift range and H blended
flux limit of we
predict a number density between 3900--4800 galaxies per square degree. For a
WFIRST-like survey with redshift range and blended
flux limit of we
predict a number density between 10400--15200 galaxies per square degree.Comment: 21 pages (including appendix), 12 figures, 6 tables. Accepted b
Illuminating the dark universe with a very high density galaxy redshift survey over a wide area
The nature of dark energy remains a profound mystery 20 years after the discovery of cosmic acceleration. A very high number density galaxy redshift survey over a wide area (HD GRS Wide) spanning the redshift range of 0.5<z<4 using the same tracer, carried out using massively parallel wide field multi-object slit spectroscopy from space, will provide definitive dark energy measurements with minimal observational systematics by design. The HD GRS Wide will illuminate the nature of dark energy, and lead to revolutionary advances in particle physics and cosmology. It will also trace the cosmic web of dark matter and provide key insight into large-scale structure in the Universe. The required observational facility can be established as part of the probe portfolio by NASA within the next decade
Faculty Recital: Horn and Clarinet Faculty Recital
State University University School of Music presents Horn and Clarinet Faculty Recital featuring Jason Eklund on horn, John Warren on clarinet, and Soohyun Yun on piano.https://digitalcommons.kennesaw.edu/musicprograms/1072/thumbnail.jp
The WFIRST Galaxy Survey Exposure Time Calculator
This document describes the exposure time calculator for the Wide-Field
Infrared Survey Telescope (WFIRST) high-latitude survey. The calculator works
in both imaging and spectroscopic modes. In addition to the standard ETC
functions (e.g. background and S/N determination), the calculator integrates
over the galaxy population and forecasts the density and redshift distribution
of galaxy shapes usable for weak lensing (in imaging mode) and the detected
emission lines (in spectroscopic mode). The source code is made available for
public use.Comment: 44 pages. The current C source code and version history can be found
at http://www.tapir.caltech.edu/~chirata/web/software/space-etc/ ; IPAC
maintains a web interface at
http://wfirst-web.ipac.caltech.edu/wfDepc/wfDepc.js
2014 Kennesaw State University Concert Band Invitational
Kennesaw State University School of Music presents 2014 Concert Band Invitational.https://digitalcommons.kennesaw.edu/musicprograms/1382/thumbnail.jp
Ferroelectric and octahedral tilt twin disorder and the lead-free piezoelectric, sodium potassium niobate system
Using electron diffraction, trends in the local structural behaviour of the KxNa1-xNbO3 (KNN x) 'solid solution' system are investigated and interpreted using an order/disorder based theoretical framework. At room temperature, electron diffraction shows a single plane of transverse polarised, diffuse intensity perpendicular to [0 1 0]p (p for parent sub-structure) across the entire phase diagram, indicative of ferroelectric disorder along the [0 1 0]p direction co-existing with long range ferroelectric order along the orthogonal [1 0 0]p and [0 0 1]p directions. An additional characteristic pattern of diffuse scattering is also observed, involving rods of diffuse intensity running along the [1 0 0]p (*) and [0 0 1]p (*) directions of the perovskite sub-structure and indicative of octahedral tilt disorder about the [1 0 0]p and [0 0 1]p axes co-existing with long range ordered octahedral tilting around the [0 1 0]p direction. A possible crystal chemical explanation for the existence of this latter octahedral tilt disorder is explored through bond valence sum calculations. The possible influence of both types of disorder on the previously refined, room temperature space group/s and average crystal structure/s is examined
Distributed Estimation for Principal Component Analysis: an Enlarged Eigenspace Analysis
The growing size of modern data sets brings many challenges to the existing
statistical estimation approaches, which calls for new distributed
methodologies. This paper studies distributed estimation for a fundamental
statistical machine learning problem, principal component analysis (PCA).
Despite the massive literature on top eigenvector estimation, much less is
presented for the top--dim () eigenspace estimation, especially in a
distributed manner. We propose a novel multi-round algorithm for constructing
top--dim eigenspace for distributed data. Our algorithm takes advantage of
shift-and-invert preconditioning and convex optimization. Our estimator is
communication-efficient and achieves a fast convergence rate. In contrast to
the existing divide-and-conquer algorithm, our approach has no restriction on
the number of machines. Theoretically, the traditional Davis-Kahan theorem
requires the explicit eigengap assumption to estimate the top--dim
eigenspace. To abandon this eigengap assumption, we consider a new route in our
analysis: instead of exactly identifying the top--dim eigenspace, we show
that our estimator is able to cover the targeted top--dim population
eigenspace. Our distributed algorithm can be applied to a wide range of
statistical problems based on PCA, such as principal component regression and
single index model. Finally, We provide simulation studies to demonstrate the
performance of the proposed distributed estimator
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