9,768 research outputs found
MONTAGE: AGB nucleosynthesis with full s-process calculations
We present MONTAGE, a post-processing nucleosynthesis code that combines a
traditional network for isotopes lighter than calcium with a rapid algorithm
for calculating the s-process nucleosynthesis of the heavier isotopes. The
separation of those parts of the network where only neutron-capture and
beta-decay reactions are significant provides a substantial advantage in
computational efficiency. We present the yields for a complete set of s-process
isotopes for a 3 Mo, Z = 0.02 stellar model, as a demonstration of the utility
of the approach. Future work will include a large grid of models suitable for
use in calculations of Galactic chemical evolution.Comment: 9 pages, 4 figures. Accepted by PAS
Towards Rapid Parameter Estimation on Gravitational Waves from Compact Binaries using Interpolated Waveforms
Accurate parameter estimation of gravitational waves from coalescing compact
binary sources is a key requirement for gravitational-wave astronomy.
Evaluating the posterior probability density function of the binary's
parameters (component masses, sky location, distance, etc.) requires computing
millions of waveforms. The computational expense of parameter estimation is
dominated by waveform generation and scales linearly with the waveform
computational cost. Previous work showed that gravitational waveforms from
non-spinning compact binary sources are amenable to a truncated singular value
decomposition, which allows them to be reconstructed via interpolation at fixed
computational cost. However, the accuracy requirement for parameter estimation
is typically higher than for searches, so it is crucial to ascertain that
interpolation does not lead to significant errors. Here we provide a proof of
principle to show that interpolated waveforms can be used to recover posterior
probability density functions with negligible loss in accuracy with respect to
non-interpolated waveforms. This technique has the potential to significantly
increase the efficiency of parameter estimation.Comment: 7 pages, 2 figure
Propellant material compatibility program and results
The effects of long-term (up to 10 years) contact of inert materials with earth-storable propellants were studied for the purpose of designing chemical propulsion system components that can be used for current as well as future planetary spacecraft. The primary experimental work, and results to date are reported. Investigations include the following propellants: hydrazine, hydrazine-hydrazine nitrate blends, monomethyl-hydrazine, and nitrogen tetroxide. Materials include: aluminum alloys, corrosion-resistant steels, and titanium alloys. More than 700 test specimen capsules were placed in long-term storage testing at 43 C in the special material compatibility facility. Material ratings relative to the 10-year requirement have been assigned
Radio Sources in the 2dF Galaxy Redshift Survey. I. Radio Source Populations
We present the first results from a study of the radio continuum properties
of galaxies in the 2dF Galaxy Redshift Survey, based on thirty 2dF fields
covering a total area of about 100 square degrees. About 1.5% of galaxies with
b(J) < 19.4 mag are detected as radio continuum sources in the NRAO VLA Sky
Survey (NVSS). Of these, roughly 40% are star-forming galaxies and 60% are
active galaxies (mostly low-power radio galaxies and a few Seyferts). The
combination of 2dFGRS and NVSS will eventually yield a homogeneous set of
around 4000 radio-galaxy spectra, which will be a powerful tool for studying
the distriibution and evolution of both AGN and starburst galaxies out to
redshift z=0.3.Comment: 14 pages, 7 figures, accepted for publication in PAS
Epistomatal Wax Injury to Red Spruce Needles (Picea rubens Sarg.) Grown in Elevated Levels of Ozone and Acidified Rain
Red spruce seedlings (Picea rubens Sarg.) were exposed to charcoal-filtered air, at 0.07 ppm or 0.15 ppm ozone (O3), alone or in combination with pH 4.2 or pH 3.0 acidified rain, and examined with scanning electron microscopy (SEM) to determine if epistomatal wax fine structure was affected. Acidified rain in combination with 0.15 ppm O3 produced changes in wax tubule morphology. Changes were moderate at pH 4.2 and severe at pH 3.0. Needles collected from Whiteface Mountain, New York, displayed injured epistomatal wax structure similar to that observed on needles exposed in the laboratory to 0.15 ppm O3 plus pH 3.0 acidified rain
Clues on the evolution of the Carina dwarf spheroidal galaxy from the color distribution of its red giant stars
The thin red giant branch (RGB) of the Carina dwarf spheroidal galaxy appears
at first sight quite puzzling and seemingly in contrast with the presence of
several distinct bursts of star formation. In this Letter, we provide a
measurement of the color spread of red giant stars in Carina based on new BVI
wide-field observations, and model the width of the RGB by means of synthetic
color-magnitude diagrams. The measured color spread, Sigma{V-I}=0.021 +/-
0.005, is quite naturally accounted for by the star-formation history of the
galaxy. The thin RGB appears to be essentially related to the limited age range
of its dominant stellar populations, with no need for a metallicity dispersion
at a given age. This result is relatively robust with respect to changes in the
assumed age-metallicity relation, as long as the mean metallicity over the
galaxy lifetime matches the observed value ([Fe/H] = -1.91 +/- 0.12 after
correction for the age effects). This analysis of photometric data also sets
some constraints on the chemical evolution of Carina by indicating that the
chemical abundance of the interstellar medium in Carina remained low throughout
each episode of star formation even though these episodes occurred over many
Gyr.Comment: 4 pages, 3 figures, accepted for publication in the Astrophysical
Journal Letter
Techniques for measuring atmospheric aerosols at the High Resolution Fly's Eye experiment
We describe several techniques developed by the High Resolution Fly's Eye
experiment for measuring aerosol vertical optical depth, aerosol horizontal
attenuation length, and aerosol phase function. The techniques are based on
measurements of side-scattered light generated by a steerable ultraviolet laser
and collected by an optical detector designed to measure fluorescence light
from cosmic-ray air showers. We also present a technique to cross-check the
aerosol optical depth measurement using air showers observed in stereo. These
methods can be used by future air fluorescence experiments.Comment: Accepted for publication in Astroparticle Physics Journal 16 pages, 9
figure
The use of water bowls in the dairy barn
1. Dairy cows, watered by means of water bowls, drank approximately 18 percent more water and yielded 3.5 percent more milk and 10.7 percent more butterfat than cows that were watered twice per day at an outside tank.
2. Cows watered with water bowls drank an average of about 10 times in each 24 hours. Approximately two-thirds of the water was consumed in the daytime, that is between 5 a. m. and 5 p. m., and the other one-third at night.
3. Cows watered at the outside tank frequently drank but once per day. This occurred about 30 percent of the times the cows were offered water. This refusal to drink more than once per day was distributed among all of the cows, although certain cows showed a greater disposition to drink but once per day than did others. The inclination to drink but once per day was not consistently correlated with the quantity of milk yielded.
4. One unusual observation was that when the cows were watered with water bowls, they usually yielded not only more milk but milk containing a higher percentage of butterfat. A mathematical treatment of the data shows that the probability is only about 4 in 100 that a result as large and consistent could have come by chance alone.
5. The temperature of the water apparently did not influence the water consumption as greatly as did atmospheric temperature. The relative consumption of water increased as temperature rose
The M81 Group Dwarf Irregular Galaxy DDO 165. I. High Velocity Neutral Gas in a Post-Starburst System
We present new multi-configuration VLA HI spectral line observations of the
M81 group dIrr post-starburst galaxy DDO 165. The HI morphology is complex,
with multiple column density peaks surrounding a large region of very low HI
surface density that is offset from the center of the stellar distribution. The
bulk of the neutral gas is associated with the southern section of the galaxy;
a secondary peak in the north contains ~15% of the total HI mass. These
components appear to be kinematically distinct, suggesting that either tidal
processes or large-scale blowout have recently shaped the ISM of DDO 165. Using
spatially-resolved position-velocity maps, we find multiple localized
high-velocity gas features. Cross-correlating with radius-velocity analyses, we
identify eight shell/hole structures in the ISM with a range of sizes (~400-900
pc) and expansion velocities (~7-11 km/s). These structures are compared with
narrow- and broad-band imaging from KPNO and HST. Using the latter data, recent
works have shown that DDO 165's previous "burst" phase was extended temporally
(>1 Gyr). We thus interpret the high-velocity gas features, HI holes, and
kinematically distinct components of the galaxy in the context of the immediate
effects of "feedback" from recent star formation. In addition to creating HI
holes and shells, extended star formation events are capable of creating
localized high velocity motion of the surrounding interstellar material. A
companion paper connects the energetics from the HI and HST data.Comment: The Astrophysical Journal, in press. Full-resolution version
available on request from the first autho
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