5,820 research outputs found
List Price Information in Residential Appraisal and Underwriting
This article examines the usefulness of listing prices as leading indicators of house values and as predictors of the direction of housing markets. With Multiple Listing Service data from a large metropolitan area, we create two price indexes, using first listing price and then selling price as the dependent variable in the hedonic regressions. The market is then geographically and categorically segmented, and Granger causality tests are performed to analyze the leading aspect of list prices in the list price-sales price relationship. We find that different segments of the market perform quite differently over the time period of our study, suggesting that for data-based appraisal purposes care is needed in determining the manner and level of aggregation. We also find, however, that market list prices continue to convey important information about subsequent selling prices in most market segments.
Theory of Weak Hypernuclear Decay
The weak nonmesonic decay of Lambda-hypernuclei is studied in the context of
a one-meson-exchange model. Predictions are made for the decay rate, p/n
stimulation ratio and the asymmetry in polarized hypernuclear decay.Comment: Standard 41 page Latex fil
Survival in Common Snapping Turtles, Chelydra serpentina (Testudines: Chelydridae), in western Nebraska
Annual estimates of survival for Common Snapping Turtles (Chelydra serpentina) in western Nebraska USA were generated from mark-recapture data from nesting females encountered in 2005–2017. Our population models suggested no annual variation in either adult annual survival (0.947 ± 0.017 SE) or annual capture probability (0.294 ± 0.027 SE). However, there was a tendency toward higher survival in larger females. High annual survival (e.g. \u3e 90%) characterises populations of Chelydra from Ontario to Texas
Population Size and Sex Ratio of Snapping Turtles on the Crescent Lake National Wildlife Refuge
Mark and recapture studies of Common Snapping Turtles (Chelydra serpentina) on the Crescent Lake National Wildlife Refuge in the Sandhills of western Nebraska revealed a sex ratio strongly biased toward males by a factor of two, an average density of 2.32 adults and subadults per hectare, and a standing crop biomass of 19.35 kg/ha. Sex ratios were most biased (7.5:1.0) in July–August. Density and biomass were comparable to values from previously studied lakes, and were inversely related to wetland size across all studies of snapping turtles
A high resolution mid-infrared survey of water emission from protoplanetary disks
We present the largest survey of spectrally resolved mid-infrared water
emission to date, with spectra for 11 disks obtained with the Michelle and
TEXES spectrographs on Gemini North. Water emission is detected in 6 of 8 disks
around classical T Tauri stars. Water emission is not detected in the
transitional disks SR 24 N and SR 24 S, in spite of SR 24 S having
pre-transitional disk properties like DoAr 44, which does show water emission
(Salyk et al. 2015). With R~100,000, the TEXES water spectra have the highest
spectral resolution possible at this time, and allow for detailed lineshape
analysis. We find that the mid-IR water emission lines are similar to the
"narrow component" in CO rovibrational emission (Banzatti & Pontoppidan 2015),
consistent with disk radii of a few AU. The emission lines are either single
peaked, or consistent with a double peak. Single-peaked emission lines cannot
be produced with a Keplerian disk model, and may suggest that water
participates in the disk winds proposed to explain single-peaked CO emission
lines (Bast et al. 2011, Pontoppidan et al. 2011). Double-peaked emission lines
can be used to determine the radius at which the line emission luminosity drops
off. For HL Tau, the lower limit on this measured dropoff radius is consistent
with the 13 AU dark ring (ALMA partnership et al. 2015). We also report
variable line/continuum ratios from the disks around DR Tau and RW Aur, which
we attribute to continuum changes and line flux changes, respectively. The
reduction in RW Aur line flux corresponds with an observed dimming at visible
wavelengths (Rodriguez et al. 2013).Comment: To appear in the Astrophysical Journa
Fully-Coupled Simulation of Cosmic Reionization. I: Numerical Methods and Tests
We describe an extension of the Enzo code to enable fully-coupled radiation
hydrodynamical simulation of inhomogeneous reionization in large cosmological volumes with thousands to millions of point sources. We
solve all dynamical, radiative transfer, thermal, and ionization processes
self-consistently on the same mesh, as opposed to a postprocessing approach
which coarse-grains the radiative transfer. We do, however, employ a simple
subgrid model for star formation which we calibrate to observations. Radiation
transport is done in the grey flux-limited diffusion (FLD) approximation, which
is solved by implicit time integration split off from the gas energy and
ionization equations, which are solved separately. This results in a faster and
more robust scheme for cosmological applications compared to the earlier
method. The FLD equation is solved using the hypre optimally scalable geometric
multigrid solver from LLNL. By treating the ionizing radiation as a grid field
as opposed to rays, our method is scalable with respect to the number of
ionizing sources, limited only by the parallel scaling properties of the
radiation solver. We test the speed and accuracy of our approach on a number of
standard verification and validation tests. We show by direct comparison with
Enzo's adaptive ray tracing method Moray that the well-known inability of FLD
to cast a shadow behind opaque clouds has a minor effect on the evolution of
ionized volume and mass fractions in a reionization simulation validation test.
We illustrate an application of our method to the problem of inhomogeneous
reionization in a 80 Mpc comoving box resolved with Eulerian grid
cells and dark matter particles.Comment: 32 pages, 23 figures. ApJ Supp accepted. New title and substantial
revisions re. v
The TRENDS High-Contrast Imaging Survey. V. Discovery of an Old and Cold Benchmark T-dwarf Orbiting the Nearby G-star HD 19467
The nearby Sun-like star HD 19467 shows a subtle radial velocity (RV)
acceleration of -1.37+/-0.09 m/s/yr over an 16.9 year time baseline (an RV
trend), hinting at the existence of a distant orbiting companion. We have
obtained high-contrast adaptive optics images of the star using NIRC2 at Keck
Observatory and report the direct detection of the body that causes the
acceleration. The companion, HD 19467 B, is dK=12.57+/-0.09 mag fainter than
its parent star (contrast ratio of 9.4e-6), has blue colors J-K_s=-0.36+/-0.14
(J-H=-0.29+/-0.15), and is separated by 1.653+/-0.004" (51.1+/-1.0 AU).
Follow-up astrometric measurements obtained over an 1.1 year time baseline
demonstrate physical association through common parallactic and proper motion.
We calculate a firm lower-limit of m>51.9^{+3.6}_{-4.3}Mjup for the companion
mass from orbital dynamics using a combination of Doppler observations and
imaging. We estimate a model-dependent mass of m=56.7^{+4.6}_{-7.2}Mjup from a
gyrochronological age of 4.3^{+1.0}_{-1.2} Gyr. Isochronal analysis suggests a
much older age of Gyr, which corresponds to a mass of
m=67.4^{+0.9}_{-1.5}Mjup. HD 19467 B's measured colors and absolute magnitude
are consistent with a late T-dwarf [~T5-T7]. We may infer a low metallicity of
[Fe/H]=-0.15+/-0.04 for the companion from its G3V parent star. HD 19467 B is
the first directly imaged benchmark T-dwarf found orbiting a Sun-like star with
a measured RV acceleration.Comment: Updated to reflect ApJ versio
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