100 research outputs found
Using Simulation to Estimate Vehicle Emissions in Response to Urban Sprawl within Geauga County, Ohio
Author Institution: Division of Mathematics & Natural Sciences, Penn State University--Altoona CollegeUrban sprawl often leads to rapid expansion and haphazard developments of low density residential land uses that are spatially disjoined. Populations occupying these new developments are expected to contribute to increased traffic volumes and vehicle emissions through increased home-work journeys. Computer simulation is one of few feasible approaches to model projected trends of local communities to understand how they evolve and better plan their future courses. The VERTUS model was developed as a planning tool to estimate vehicle emissions in response to urban sprawl. The model is specific towards estimating
vehicle emissions at the local and highway levels during the home-work journey. The model was applied to Geauga County, Ohio to estimate how an increase in housing over a 20-year period from 2000-2020 will influence vehicle emissions generated. Results indicate that emissions are currently highest in the western part of the county where the greatest number of households is located. This geographic distribution remains when emissions are estimated for growth in housing. While additional housing translates to more vehicle emissions, this research found that differences exist among the countyâs individual municipalities in terms of emissions generated. In several instances, municipalities with a smaller growth in housing generate a greater amount of emissions than a municipality with a larger growth in housing. These differences result from variations in the commuting characteristics of each municipalityâs residents and provide insight into how household travel patterns relate to vehicle emissions
An Investigation of Subscriber Attitudes Toward The Clark County Courier
Although the editor of a weekly newspaper can use the size of his subscription list and the letters to the editor to determine how area residents feel about his newspaper, the amount of information acquired and the accuracy of such information are limited. Another determinant which the editor could use is feedback the employees of the newspaper receive from the subscribers and the other residents of the community. It was through this feedback that some dissatisfaction with the Clark County Courier was noticed. The author of this paper began working for The Clark County Courier as advertising manager in June, 1970. The previous advertising manager stated that certain people in the surrounding communities believed that The Clark County Courier was not doing a very good job as a weekly county newspaper. As one of the newspaper\u27s representatives to the surrounding communities, the author noticed that many residents in these communities did seem dissatisfied with the newspaperâs performance concerning their area. Most complaints dealt with the adequacy and accuracy of news coverage of the several communities and with the newspaperâs representatives concerning political parties. Advertisers also complained about mistakes in their advertisements. (See more in text
Baryon Oscillations and Consistency Tests for Photometrically-Determined Redshifts of Very Faint Galaxies
Weak lensing surveys that can potentially place strong constraints on dark
energy parameters can only do so if the source redshift means and error
distributions are very well known. We investigate prospects for controlling
errors in these quantities by exploiting their influence on the power spectra
of the galaxies. Although, from the galaxy power spectra alone, sufficiently
precise and simultaneous determination of redshift biases and variances is not
possible, a strong consistency test is. Given the redshift error rms, galaxy
power spectra can be used to determine the mean redshift of a group of galaxies
to subpercent accuracy. Although galaxy power spectra cannot be used to
determine the redshift error rms, they can be used to determine this rms
divided by the Hubble parameter, a quantity that may be even more valuable for
interpretation of cosmic shear data than the rms itself. We also show that
galaxy power spectra, due to the baryonic acoustic oscillations, can
potentially lead to constraints on dark energy that are competitive with those
due to the cosmic shear power spectra from the same survey.Comment: 8 pages, 6 figures, submitted to Ap
Improved forecasts for the baryon acoustic oscillations and cosmological distance scale
We present the cosmological distance errors achievable using the baryon
acoustic oscillations as a standard ruler. We begin from a Fisher matrix
formalism that is upgraded from Seo & Eisenstein (2003). We isolate the
information from the baryonic peaks by excluding distance information from
other less robust sources. Meanwhile we accommodate the Lagrangian displacement
distribution into the Fisher matrix calculation to reflect the gradual loss of
information in scale and in time due to nonlinear growth, nonlinear bias, and
nonlinear redshift distortions. We then show that we can contract the
multi-dimensional Fisher matrix calculations into a 2-dimensional or even
1-dimensional formalism with physically motivated approximations. We present
the resulting fitting formula for the cosmological distance errors from galaxy
redshift surveys as a function of survey parameters and nonlinearity, which
saves us going through the 12-dimensional Fisher matrix calculations. Finally,
we show excellent agreement between the distance error estimates from the
revised Fisher matrix and the precision on the distance scale recovered from
N-body simulations.Comment: Submitted to ApJ, 21 pages, LaTe
Dark energy and curvature from a future baryonic acoustic oscillation survey using the Lyman-alpha forest
We explore the requirements for a Lyman-alpha forest (LyaF) survey designed
to measure the angular diameter distance and Hubble parameter at 2~<z~<4 using
the standard ruler provided by baryonic acoustic oscillations (BAO). The goal
would be to obtain a high enough density of sources to probe the
three-dimensional density field on the scale of the BAO feature. A
percent-level measurement in this redshift range can almost double the Dark
Energy Task Force Figure of Merit, relative to the case with only a similar
precision measurement at z~1, if the Universe is not assumed to be flat. This
improvement is greater than the one obtained by doubling the size of the z~1
survey, with Planck and a weak SDSS-like z=0.3 BAO measurement assumed in each
case. Galaxy BAO surveys at z~1 may be able to make an effective LyaF
measurement simultaneously at minimal added cost, because the required number
density of quasars is relatively small. We discuss the constraining power as a
function of area, magnitude limit (density of quasars), resolution, and
signal-to-noise of the spectra. For example, a survey covering 2000 sq. deg.
and achieving S/N=1.8 per Ang. at g=23 (~40 quasars per sq. deg.) with an
R~>250 spectrograph is sufficient to measure both the radial and transverse
oscillation scales to 1.4% from the LyaF (or better, if fainter magnitudes and
possibly Lyman-break galaxies can be used). At fixed integration time and in
the sky-noise-dominated limit, a wider, noisier survey is generally more
efficient; the only fundamental upper limit on noise being the need to identify
a quasar and find a redshift. Because the LyaF is much closer to linear and
generally better understood than galaxies, systematic errors are even less
likely to be a problem.Comment: 18 pages including 6 figures, submitted to PR
Lensing Corrections to Features in the Angular Two-Point Correlation Function and Power Spectrum
It is well known that magnification bias, the modulation of galaxy or quasar
source counts by gravitational lensing, can change the observed angular
correlation function. We investigate magnification-induced changes to the shape
of the observed correlation function w(\theta) and the angular power spectrum
C_{\ell}, paying special attention to the matter-radiation equality peak and
the baryon wiggles. Lensing mixes the correlation function of the source
galaxies with the matter correlation at the lower redshifts of the lenses.
Since the lenses probe structure nearer to the observer, the angular scale
dependence of the lensing terms is different from that of the sources, thus the
observed correlation function is distorted. We quantify how the lensing
corrections depend on the width of the selection function, the galaxy bias b,
and the number count slope s. The correction increases with redshift and larger
corrections are present for sources with steep number count slopes and/or broad
redshift distributions. The most drastic changes to C_{\ell} occur for
measurements at z >~1.5 and \ell <~ 100. For the source distributions we
consider, magnification bias can shift the matter-radiation equality scale by
1-6% at z ~ 1.5 and by z ~ 3.5 the shift can be as large as 30%. The baryon
bump in \theta^2w(\theta) is shifted by <~ 1% and the width is typically
increased by ~10%. Shifts of >~ 0.5% and broadening of >~ 20% occur only for
very broad selection functions and/or galaxies with (5s-2)/b>~2. However, near
the baryon bump the magnification correction is not constant but a gently
varying function which depends on the source population. Depending on how the
w(\theta) data is fitted, this correction may need to be accounted for when
using the baryon acoustic scale for precision cosmology.Comment: v2: 8 pages, 5 figures, text and figures condensed, references adde
Optimizing future imaging survey of galaxies to confront dark energy and modified gravity models
We consider the extent to which future imaging surveys of galaxies can
distinguish between dark energy and modified gravity models for the origin of
the cosmic acceleration. Dynamical dark energy models may have similar
expansion rates as models of modified gravity, yet predict different growth of
structure histories. We parameterize the cosmic expansion by the two
parameters, and , and the linear growth rate of density fluctuations
by Linder's , independently. Dark energy models generically predict
, while the DGP model . To determine
if future imaging surveys can constrain within 20 percent (or
), we perform the Fisher matrix analysis for a weak lensing
survey such as the on-going Hyper Suprime-Cam (HSC) project. Under the
condition that the total observation time is fixed, we compute the Figure of
Merit (FoM) as a function of the exposure time \texp. We find that the
tomography technique effectively improves the FoM, which has a broad peak
around \texp\simeq {\rm several}\sim 10 minutes; a shallow and wide survey is
preferred to constrain the parameter. While
cannot be achieved by the HSC weak-lensing survey alone, one can improve the
constraints by combining with a follow-up spectroscopic survey like WFMOS
and/or future CMB observations.Comment: 18 pages, typos correcte
Explicit computation of shear three-point correlation functions: the one-halo model case
We present a method for calculating explicit expressions of the shear
three-point function for various cosmological models. The method is applied
here to the one-halo model in case of power law density profiles for which
results are detailed. The three-point functions are found to reproduce to a
large extent patterns in the shear correlations obtained in numerical
simulations and may serve as a guideline to implement optimized methods for
detecting the shear three-point function. In principle, the general method
presented here can also be applied for other models of matter correlation.Comment: 8 pages, 6 figures, submitted to A
3D Spherical Analysis of Baryon Acoustic Oscillations
Baryon Acoustic Oscillations (BAOs) are oscillatory features in the galaxy
power spectrum and are a standard rod to measure the cosmological expansion.
These have been studied in Cartesian space (Fourier or real space) or in
Spherical Harmonic (SH) space in thin shells. Future wide-field surveys will
cover both wide and deep regions of the sky and thus require a simultaneous
treatment of the spherical sky and of an extended radial coverage. The
Spherical Fourier-Bessel (SFB) decomposition is a natural basis for the
analysis of fields in this geometry and facilitates the combination of BAO
surveys with other cosmological probes readily described in this basis. We
present here a new way to analyse BAOs by studying the BAO wiggles from the SFB
power spectrum. In SFB space, the power spectrum generally has both a radial
(k) and tangential (l) dependence and so do the BAOs. In the deep survey limit
and ignoring evolution, the SFB power spectrum becomes radial and reduces to
the Cartesian Fourier power spectrum. In the limit of a thin shell, all the
information is contained in the tangential modes described by the 2D SH power
spectrum. We find that the radialisation of the SFB power spectrum is still a
good approximation even when considering an evolving and biased galaxy field
with a finite selection function. This effect can be observed by all-sky
surveys with depths comparable to current surveys. We find that the BAOs
radialise more rapidly than the full SFB power spectrum. Our results suggest
the first peak of the BAOs in SFB space becomes radial out to l ~ 10 for
all-sky surveys with the same depth as SDSS or 2dF, and out to l ~ 70 for an
all-sky stage IV survey. Subsequent BAO peaks also become radial, but for
shallow surveys these may be in the non-linear regime. For modes that have
become radial, measurements at different l's are useful in practice to reduce
measurement errors.Comment: 6 pages + Appendix. Astro-ph abstract is abridged. Updated with
comments from anonymous referee. Corrected axes of Figure 2. Extended
discussion of radialisation. Accepted for publication in Astronomy &
Astrophysic
Dark Energy Constraints from the CTIO Lensing Survey
We perform a cosmological parameter analysis of the 75 square degree CTIO
lensing survey in conjunction with CMB and Type Ia supernovae data. For Lambda
CDM cosmologies, we find that the amplitude of the power spectrum at low
redshift is given by sigma_8 = 0.81 (+0.15,-0.10, 95% c.l.), where the error
bar includes both statistical and systematic errors. The total of all
systematic errors is smaller than the statistical errors, but they do make up a
significant fraction of the error budget. We find that weak lensing improves
the constraints on dark energy as well. The (constant) dark energy equation of
state parameter, w, is measured to be -0.89 (+0.16,-0.21, 95% c.l.).
Marginalizing over a constant slightly changes the estimate of sigma_8 to
0.79 (+0.17, -0.14, 95% c.l.). We also investigate variable w cosmologies, but
find that the constraints weaken considerably; the next generation surveys are
needed to obtain meaningful constraints on the possible time evolution of dark
energy.Comment: 10 pages, 4 figures, v3 matches version accepted by ApJ. Significant
changes in section 4.2.3. Otherwise, mostly minor change
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