654 research outputs found
Pressures and Preferences Affecting Willingness to Apply Beef Manure on Crops in the Colorado High Plains
Little is known about producers' willingness to use manure. Past studies have focused on substitutability for fertilizers. We surveyed crop producers in a cattle-dense region of the Colorado Plains about whether and why they apply manure, focusing on how pressures (like owning cattle) or preferences (pro and con) affect their adoption. Using logistic regression, findings show that pressure and preference (PS/PF) significantly affect adoption. A producer with high PS/PF was 10 times more likely to use manure than one with low PS/PF. Policy and decision makers can use such findings to inform education and policy aimed at increasing the land application of manure.cattle, economic benefits, economic costs, management, manure application, Crop Production/Industries,
Economic performance of exotic dairy cattle under smallholder conditions in the marginal zones of Kenya using three analytical approaches
Smallholder exotic dairy cattle have been adopted in the dry marginal zones of Kenya from the high potential areas over the last two decades contrary to the opinion of experts. The objective of this study therefore was to evaluate the economic performance of this dairy establishment in the marginal zones. Three approaches were used for the evaluation: the stochastic cost frontier to determine inefficiencies and the causative institutional and socio-economic factors; cost-factor demand systems; and the supply response analyses to determine the elasticity estimates of policy variables. The results from these approaches are supplementary and seem to support the need for government interventions in institutional and socio-economic factors that have a high public good component in order to expand dairy establishment in the marginal zones.Marginal zones, stochastic frontier, systems analysis, institutional and socio-economic factors, Institutional and Behavioral Economics,
When two become one: an apparent QSO pair turns out to be a single quasar
We report on our serendipitous discovery that the objects Q 01323-4037 and Q
0132-4037, listed in the V\'eron-Cetty & V\'eron catalog (2006) as two
different quasars, are actually a quasar and a star. We briefly discuss the
origin of the misidentification, and provide a refined measurement of the
quasar redshift.Comment: 3 pages, 2 figures; accepted for publication in A&
The Grism Lens-Amplified Survey from Space (GLASS). XII. Spatially Resolved Galaxy Star Formation Histories and True Evolutionary Paths at z > 1
Modern data empower observers to describe galaxies as the spatially and
biographically complex objects they are. We illustrate this through case
studies of four, systems based on deep, spatially resolved, 17-band
+ G102 + G141 Hubble Space Telescope grism spectrophotometry. Using full
spectrum rest-UV/-optical continuum fitting, we characterize these galaxies'
observed kpc-scale structures and star formation rates (SFRs) and
reconstruct their history over the age of the universe. The sample's
diversity---passive to vigorously starforming; stellar masses to ---enables us to draw spatio-temporal inferences
relevant to key areas of parameter space (Milky Way- to super-Andromeda-mass
progenitors). Specifically, we find signs that bulge mass-fractions () and
SF history shapes/spatial uniformity are linked, such that higher s
correlate with "inside-out growth" and central specific SFRs that peaked above
the global average for all starforming galaxies at that epoch. Conversely, the
system with the lowest had a flat, spatially uniform SFH with normal peak
activity. Both findings are consistent with models positing a feedback-driven
connection between bulge formation and the switch from rising to falling SFRs
("quenching"). While sample size forces this conclusion to remain tentative,
this work provides a proof-of-concept for future efforts to refine or refute
it: JWST, WFIRST, and the 30-m class telescopes will routinely produce data
amenable to this and more sophisticated analyses. These samples---spanning
representative mass, redshift, SFR, and environmental regimes---will be ripe
for converting into thousands of sub-galactic-scale empirical windows on what
individual systems actually looked like in the past, ushering in a new dialog
between observation and theory.Comment: 18 pp, 15 figs, 3 tables (main text); 5 pp, 5 figs, 1 table
(appendix); Submitted to AAS Journals 1 October 201
Stellar Rotation in Young Clusters. I. Evolution of Projected Rotational Velocity Distributions
Open clusters offer us the means to study stellar properties in samples with
well-defined ages and initial chemical composition. Here we present a survey of
projected rotational velocities for a large sample of mainly B-type stars in
young clusters to study the time evolution of the rotational properties of
massive stars. The survey is based upon moderate resolution spectra made with
the WIYN 3.5 m and CTIO 4 m telescopes and Hydra multi-object spectrographs,
and the target stars are members of 19 young open clusters with an age range of
approximately 6 to 73 Myr. We made fits of the observed lines He I 4026, 4387,
4471 and Mg II 4481 using model theoretical profiles to find projected
rotational velocities for a total of 496 OB stars. We find that there are fewer
slow rotators among the cluster B-type stars relative to nearby B stars in the
field. We present evidence consistent with the idea that the more massive B
stars (M > 9 solar masses) spin down during their main sequence phase. However,
we also find that the rotational velocity distribution appears to show an
increase in the numbers of rapid rotators among clusters with ages of 10 Myr
and higher. These rapid rotators appear to be distributed between the zero age
and terminal age main sequence locations in the Hertzsprung-Russell diagram,
and thus only a minority of them can be explained as the result of a spin up at
the terminal age main sequence due to core contraction. We suggest instead that
some of these rapid rotators may have been spun up through mass transfer in
close binary systems.Comment: 33 pages, 11 figures, accepted by Ap
Through the looking GLASS: HST spectroscopy of faint galaxies lensed by the Frontier Fields cluster MACS0717.5+3745
The Grism Lens-Amplified Survey from Space (GLASS) is a Hubble Space
Telescope (HST) Large Program, which will obtain 140 orbits of grism
spectroscopy of the core and infall regions of 10 galaxy clusters, selected to
be among the very best cosmic telescopes. Extensive HST imaging is available
from many sources including the CLASH and Frontier Fields programs. We
introduce the survey by analyzing spectra of faint multiply-imaged galaxies and
galaxy candidates obtained from the first seven orbits out of
fourteen targeting the core of the Frontier Fields cluster MACS0717.5+3745.
Using the G102 and G141 grisms to cover the wavelength range 0.8-1.7m, we
confirm 4 strongly lensed systems by detecting emission lines in each of the
images. For the 9 galaxy candidates clear from contamination, we do
not detect any emission lines down to a seven-orbit 1 noise level of
510erg scm. Taking lensing magnification
into account, our flux sensitivity reaches 0.2-510erg
scm. These limits over an uninterrupted wavelength range rule out
the possibility that the high- galaxy candidates are instead strong line
emitters at lower redshift. These results show that by means of careful
modeling of the background - and with the assistance of lensing magnification -
interesting flux limits can be reached for large numbers of objects, avoiding
pre-selection and the wavelength restrictions inherent to ground-based
multi-slit spectroscopy. These observations confirm the power of slitless HST
spectroscopy even in fields as crowded as a cluster core.Comment: Accepted by ApJ letters, 8 pages, 4 figures, GLASS website at
http://glass.physics.ucsb.ed
Stellar Rotation in Young Clusters. II. Evolution of Stellar Rotation and Surface Helium Abundance
We derive the effective temperatures and gravities of 461 OB stars in 19
young clusters by fitting the H-gamma profile in their spectra. We use
synthetic model profiles for rotating stars to develop a method to estimate the
polar gravity for these stars, which we argue is a useful indicator of their
evolutionary status. We combine these results with projected rotational
velocity measurements obtained in a previous paper on these same open clusters.
We find that the more massive B-stars experience a spin down as predicted by
the theories for the evolution of rotating stars. Furthermore, we find that the
members of binary stars also experience a marked spin down with advanced
evolutionary state due to tidal interactions. We also derive non-LTE-corrected
helium abundances for most of the sample by fitting the He I 4026, 4387, 4471
lines. A large number of helium peculiar stars are found among cooler stars
with Teff < 23000 K. The analysis of the high mass stars (8.5 solar masses < M
< 16 solar masses) shows that the helium enrichment process progresses through
the main sequence (MS) phase and is greater among the faster rotators. This
discovery supports the theoretical claim that rotationally induced internal
mixing is the main cause of surface chemical anomalies that appear during the
MS phase. The lower mass stars appear to have slower rotation rates among the
low gravity objects, and they have a large proportion of helium peculiar stars.
We suggest that both properties are due to their youth. The low gravity stars
are probably pre-main sequence objects that will spin up as they contract.
These young objects very likely host a remnant magnetic field from their natal
cloud, and these strong fields sculpt out surface regions with unusual chemical
abundances.Comment: 50 pages 18 figures, accepted by Ap
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