4,973 research outputs found
New Hybrid Protected Lands Layer for Vermont Conservation Design Analysis (February 2019)
This shapefile (.shp) is a hybrid of the March 2017 Edition of the Vermont Center for Geographic Information\u27s (VCGI) Vermont Protected Lands Database (VPLD), the Vermont Land Trust\u27s February 2019 Protected Lands database, and The Nature Conservancy\u27s Secured Areas (SA 2018+) database. The VLT and SA 2018+ datasets were used as the scaffolding for the hybrid protected lands layer, with some VCGI VPLD polygons retained if they contained unique contributions. These datasets were combined by C.D. Loeb because each input dataset was missing some protected lands polygons in the state of Vermont. Additionally, the VCGI VPLD dataset contained many overlapping polygons, making it unusable for the area calculations of interest to our study on the overlap between formally protected lands and Vermont Conservation Design landscape-level targets (see publication reference).
This hybrid protected lands layer creates a more complete snapshot of Vermont’s protected lands for our study’s purposes than any other known, publicly available dataset as of February 2019, and also corrects for all improperly overlapping polygons. However, we know that this hybrid product still does not capture all of Vermont\u27s protected lands. Specifically, some Upper Valley Land Trust-protected parcels are missing from this hybrid protected lands layer, and there are probably other protected parcels that could not be captured by the input datasets. Thus, our hybrid product will likely underrepresent actual protections.
This layer was created to intersect with Vermont Conservation Design targets for input into the software Tableau. Its purpose was to perform cross tabulations to compare Vermont Conservation Design targets with protected lands in Vermont to-date, and to calculate acreages of protected lands that are also design targets by primary protecting agency. All parcel attributes and delineations in the hybrid output are only as good as the parent datasets. In areas where parcels were digitized differently between parent datasets, “slivers” may have been generated by merging them. Our study objectives originally included an analysis of the GAP Status of protected lands in Vermont (reflected in this layer\u27s metadata); however, some serious errors were detected in parent datasets with regards to GAP Status, so GAP Status was discarded as an analysis object. Please note author-identified GAP Status issues if using this dataset.
Please see the shapefile\u27s metadata for detailed creation steps. The user implies knowledge of the limitations of this dataset. This dataset should not be used to ascertain boundaries or legal acreages for any parcels.
Note: This version of the hybrid protected lands layer does not have county boundaries embedded in it nor waterbodies excluded from it, since it was created to capture all formally protected lands in the state of Vermont to the best of the authors’ abilities. Prior to use in our analysis, this layer was modified to exclude waterbodies and to introduce county boundaries. To obtain the same hybrid protected lands layer with county boundaries embedded in it and waterbodies excluded from it, please contact C. D. Loeb at [email protected]
Reionization of Hydrogen and Helium by Early Stars and Quasars
We compute the reionization histories of hydrogen and helium due to the
ionizing radiation fields produced by stars and quasars. For the quasars we use
a model based on halo-merger rates that reproduces all known properties of the
quasar luminosity function at high redshifts. The less constrained properties
of the ionizing radiation produced by stars are modeled with two free
parameters: (i) a transition redshift, z_tran, above which the stellar
population is dominated by massive, zero-metallicity stars and below which it
is dominated by a Scalo mass function; (ii) the product of the escape fraction
of stellar ionizing photons from their host galaxies and the star-formation
efficiency, f_esc f_*. We constrain the allowed range of these free parameters
at high redshifts based on the lack of the HI Gunn-Peterson trough at z<6 and
the upper limit on the total intergalactic optical depth for electron
scattering, tau_es<0.18, from recent cosmic microwave background (CMB)
experiments. We find that quasars ionize helium by a redshift z~4, but cannot
reionize hydrogen by themselves before z~6. A major fraction of the allowed
combinations of f_esc f_* and z_tran lead to an early peak in the ionized
fraction due to metal-free stars at high redshifts. This sometimes results in
two reionization epochs, namely an early HII or HeIII overlap phase followed by
recombination and a second overlap phase. Even if early overlap is not
achieved, the peak in the visibility function for scattering of the CMB often
coincides with the early ionization phase rather than with the actual
reionization epoch. Consequently, tau_es does not correspond directly to the
reionization redshift. We generically find values of tau_es>7%, that should be
detectable by the MAP satellite.Comment: 33 pages, 10 figures, Accepted for publication in Ap
The Impact of Cell Phones and BAC Laws on Motor Vehicle Fatality Rates
This paper develops a set of models for the determinants of automobile fatalities with particular attention devoted to the effects of increased cell phone usage. Cell phones have been associated with both life-taking and life-saving properties. However, prior statistical evaluations of the effects of cell phones have led to fragile results. We develop in this paper econometric models using time series data, allowing for polynomial structures of the regressors. The models are evaluated with a set of specification error tests providing reliable estimates of the effects of the various policy and driving related variables evaluated. The statistical results indicate the effect of cell phones is non-monotonic depending on the volume of phones in use, first having a net life-taking effect, then a net life-saving effect, followed finally with a net life-taking effect as the volume of phone use increases.Motor Vehicle Fatalities, Cell Phones, BAC Laws
Prestige and piety in the Iranian synagogue
Journal ArticleAmong Iranian Jews, long deprived of meaningful political power and afraid to conspicuously display material wealth, relative prestige became more valued that authority of opulence. The synagogue provides the traditional public forum where meaningful interaction among its members reinforces rand differences. Through a network of concerns centering upon the apportioning of ritual honors, the synagogue provides mechanisms fro limited social mobility. This paper examines the processes of selecting the recipients of these honors, the strategies of participation and their manipulation by the potential social climber
A Model Connecting Galaxy Masses, Star Formation Rates, and Dust Temperatures Across Cosmic Time
We investigate the evolution of dust content in galaxies from redshifts z=0
to z=9.5. Using empirically motivated prescriptions, we model galactic-scale
properties -- including halo mass, stellar mass, star formation rate, gas mass,
and metallicity -- to make predictions for the galactic evolution of dust mass
and dust temperature in main sequence galaxies. Our simple analytic model,
which predicts that galaxies in the early Universe had greater quantities of
dust than their low-redshift counterparts, does a good job at reproducing
observed trends between galaxy dust and stellar mass out to z~6. We find that
for fixed galaxy stellar mass, the dust temperature increases from z=0 to z=6.
Our model forecasts a population of low-mass, high-redshift galaxies with
interstellar dust as hot as, or hotter than, their more massive counterparts;
but this prediction needs to be constrained by observations. Finally, we make
predictions for observing 1.1-mm flux density arising from interstellar dust
emission with the Atacama Large Millimeter Array.Comment: Accepted for publication in Ap
A Dynamical Method for Measuring Masses of Stars with Transiting Planets
As a planet transits the face of a star, it accelerates along the
line-of-sight. The changing delay in the propagation of photons produces an
apparent deceleration of the planet across the sky throughout the transit. This
persistent transverse deceleration breaks the time-reversal symmetry in the
transit lightcurve of a spherical planet in a circular orbit around a perfectly
symmetric star. For `hot Jupiter' systems, ingress advances at a higher rate
than egress by a fraction of 10^{-4}-10^{-3}. Forthcoming space telescopes such
as Kepler or COROT will reach the sensitivity required to detect this
asymmetry. The scaling of the fractional asymmetry with stellar mass M and
planetary orbital radius R as M/R^2 is different from the scaling of the
orbital period as (M/R^3)^{-1/2}. Therefore, this effect constitutes a new
method for a purely dynamical determination of the mass of the star, which is
currently inferred indirectly with theoretical uncertainties based on spectral
modeling. Radial velocity data for the reflex motion of the star can then be
used to determine the planet's mass. Although orbital eccentricity could
introduce a larger asymmetry than the light propagation delay, the eccentricity
is expected to decay by tidal dissipation to negligible values for a close-in
planet with no perturbing third body. Future detection of the eclipse of a
planet's emission by its star could be used to measure the light propagation
delay across the orbital diameter, 46.7(R/7x10^{11}cm) seconds, and also
determine the stellar mass from the orbital period.Comment: 4 pages, 2 figures, submitted to ApJ
Scattered Lyman-alpha Radiation Around Sources Before Cosmological Reionization
The spectra of the first galaxies and quasars in the Universe should be
strongly absorbed shortward of their rest-frame Lyman-alpha wavelength by
neutral hydrogen (HI) in the intervening intergalactic medium. However, the
Lyman-alpha line photons emitted by these sources are not eliminated but rather
scatter until they redshift out of resonance and escape due to the Hubble
expansion of the surrounding intergalactic HI. We calculate the resulting
brightness distribution and the spectral shape of the diffuse Lyman-alpha line
emission around high redshift sources, before the intergalactic medium was
reionized. Typically, the Lyman-alpha photons emitted by a source at z=10
scatter over a characteristic angular radius of order 15 arcseconds around the
source and compose a line which is broadened and redshifted by about a thousand
km/s relative to the source. The scattered photons are highly polarized.
Detection of the diffuse Lyman-alpha halos around high redshift sources would
provide a unique tool for probing the neutral intergalactic medium before the
epoch of reionization. On sufficiently large scales where the Hubble flow is
smooth and the gas is neutral, the Lyman-alpha brightness distribution can be
used to determine the cosmological mass densities of baryons and matter.Comment: 21 pages, 5 Postscript figures, accepted by ApJ; figures 1--3
corrected; new section added on the detectability of Lyman alpha halos;
conclusions update
Measuring the Direction and Angular Velocity of a Black Hole Accretion Disk via Lagged Interferometric Covariance
We show that interferometry can be applied to study irregular, rapidly
rotating structures, as are expected in the turbulent accretion flow near a
black hole. Specifically, we analyze the lagged covariance between
interferometric baselines of similar lengths but slightly different
orientations. For a flow viewed close to face-on, we demonstrate that the peak
in the lagged covariance indicates the direction and angular velocity of the
emission pattern from the flow. Even for moderately inclined flows, the
covariance robustly estimates the flow direction, although the estimated
angular velocity can be significantly biased. Importantly, measuring the
direction of the flow as clockwise or counterclockwise on the sky breaks a
degeneracy in accretion disk inclinations when analyzing time-averaged images
alone. We explore the potential efficacy of our technique using
three-dimensional, general relativistic magnetohydrodynamic (GRMHD)
simulations, and we highlight several baseline pairs for the Event Horizon
Telescope (EHT) that are well-suited to this application. These results
indicate that the EHT may be capable of estimating the direction and angular
velocity of the emitting material near Sagittarius A*, and they suggest that a
rotating flow may even be utilized to improve imaging capabilities.Comment: 8 Pages, 4 Figures, accepted for publication in Ap
Redshifted 21cm Signatures Around the Highest Redshift Quasars
The Ly-alpha absorption spectrum of the highest redshift quasars indicates
that they are surrounded by giant HII regions, a few Mpc in size. The neutral
gas around these HII regions should emit 21cm radiation in excess of the Cosmic
Microwave Background, and enable future radio telescopes to measure the
transverse extent of these HII regions. At early times, the HII regions expand
with a relativistic speed. Consequently, their measured sizes along the
line-of-sight (via Ly-alpha absorption) and transverse to it (via 21 cm
emission) should have different observed values due to relativistic time-delay.
We show that the combined measurement of these sizes would directly constrain
the neutral fraction of the surrounding intergalactic medium (IGM) as well as
the quasar lifetime. Based on current number counts of luminous quasars at z>6,
an instrument like LOFAR should detect >2 redshifted 21cm shells per field
(with a radius of 11 degrees) around active quasars as bright as those already
discovered by SDSS, and >200 relic shells of inactive quasars per field. We
show that Ly-alpha photons from the quasar are unable to heat the IGM or to
couple the spin and kinetic temperatures of atomic hydrogen beyond the edge of
the HII region. The detection of the IGM in 21cm emission around high redshift
quasars would therefore gauge the presence of a cosmic Ly-alpha background
during the reionization epoch.Comment: 11 pages, 6 figures. Submitted to Ap
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