4,061 research outputs found
Slaves for Sale: Abolitionist Art and the American Slave Trade
Visual Representations of Slavery
Maurie McInnis, an art professor at the University of Virginia has written a rare book. In the first instance she has thrown fresh light on slavery and abolition, two much-studied topics. Secondly, she has produced a book that deserves considerable atte...
A deep, wide-field search for substellar members in NGC 2264
We report the first results of our ongoing campaign to discover the first
brown dwarfs (BD) in NGC 2264, a young (3 Myr), populous star forming region
for which our optical studies have revealed a very high density of potential
candidates - 236 in 1 deg - from the substellar limit down to at least
20 M for zero reddening. Candidate BD were first selected
using wide field () band imaging with CFH12K, by reference to current
theoretical isochrones. Subsequently, 79 (33%) of the sample were found
to have near-infrared 2MASS photometry ( 0.3 mag. or better),
yielding dereddened magnitudes and allowing further investigation by comparison
with the location of NextGen and DUSTY isochrones in colour-colour and
colour-magnitude diagrams involving various combinations of ,, and
. We discuss the status and potential substellarity of a number of
relatively unreddened (A 5) likely low-mass members in our
sample, but in spite of the depth of our observations in , we are as yet
unable to unambiguously identify substellar candidates using only 2MASS data.
Nevertheless, there are excellent arguments for considering two faint (observed
18.4 and 21.2) objects as cluster candidates with masses
respectively at or rather below the hydrogen burning limit. More current
candidates could be proven to be cluster members with masses around 0.1
M {\it via} gravity-sensitive spectroscopy, and deeper near-infrared
imaging will surely reveal a hitherto unknown population of young brown dwarfs
in this region, accessible to the next generation of deep near-infrared
surveys.Comment: 10 pages, 12 figures, accepted by A&
An Evaluation of Tennessee Soybean Growers’ Views on a New Generation Cooperative to Produce Biodiesel
Substituting petroleum diesel with biodiesel could decrease air emissions, reduce reliance on foreign oil, and help expand markets for U.S. farmers. Soybean producers can potentially capture this value-added by forward integrating the processing of soybeans into biodiesel via a New Generation Cooperative (NGC). Using probit analysis, this study examines factors influencing soybean producers’ willingness to participate in an NGC to produce biodiesel. Tobit analysis is used to examine the factors influencing the number of shares the soybean producer would be willing to purchase. Survey results indicate that over 70% of the soybean producers in the study group are interested in investing in an NGC to produce biodiesel. Among those producers willing to participate, the average number of shares they would purchase was just under 3,460.biodiesel, New Generation Cooperative, probit analysis, soybean producers, tobit analysis, Marketing, Research Methods/ Statistical Methods,
CONSUMER PREFERENCES FOR ELECTRICITY FROM BIOENERGY AND OTHER RENEWABLES
This study ascertains residential electricity consumers' support and willingness to pay for electricity from renewable sources. Then, willingness to pay for specified renewable energy sources (solar, wind, landfill wastes, bioenergy from fast growing crops, and bioenergy from forest products wastes). Effects of demographics and environmental behaviors are estimated.Institutional and Behavioral Economics,
Dust and Gas in the disc of HL Tauri: Surface density, dust settling, and dust-to-gas ratio
The recent ALMA observations of the disc surrounding HL Tau reveal a very
complex dust spatial distribution. We present a radiative transfer model
accounting for the observed gaps and bright rings as well as radial changes of
the emissivity index. We find that the dust density is depleted by at least a
factor 10 in the main gaps compared to the surrounding rings. Ring masses range
from 10-100 M in dust, and, we find that each of the deepest gaps is
consistent with the removal of up to 40 M of dust. If this material
has accumulated into rocky bodies, these would be close to the point of runaway
gas accretion. Our model indicates that the outermost ring is depleted in
millimetre grains compared to the central rings. This suggests faster grain
growth in the central regions and/or radial migration of the larger grains. The
morphology of the gaps observed by ALMA - well separated and showing a high
degree of contrast with the bright rings over all azimuths - indicates that the
millimetre dust disc is geometrically thin (scale height 1 au at 100
au) and that a large amount of settling of large grains has already occurred.
Assuming a standard dust settling model, we find that the observations are
consistent with a turbulent viscosity coefficient of a few . We
estimate the gas/dust ratio in this thin layer to be of the order of 5 if the
initial ratio is 100. The HCO and CO emission is consistent with gas in
Keplerian motion around a 1.7 star at radii from au.Comment: 12 pages, 8 figures, published in ApJ, same version as before but
with slightly extended discussion on temperature and masses to account for
literature published since initial submissio
Farmer Willingness to Supply Poultry Litter for Energy Conversion and to Invest in an Energy Conversion Cooperative
Conversion of poultry litter to energy can serve as a renewable energy source and provide an alternative to land application in areas where poultry production is intensive. Economies of size may limit a farmer’s ability to economically use on-farm conversion. Capital costs can be spread across several poultry farmers to convert poultry litter to energy in a centralized facility. This research determined influences on the amount of litter poultry producers will to sell to a centralized conversion facility, on their willingness to invest in a conversion cooperative, and on the prices for litter required to divert litter from current uses.poultry litter, supply, renewable energy, Agribusiness, Agricultural Finance, Farm Management, Financial Economics, Resource /Energy Economics and Policy, Q12, Q13,
Microlensing of Circumstellar Disks
We investigate the microlensing effects on a source star surrounded by a
circumstellar disk, as a function of wavelength. The microlensing light curve
of the system encodes the geometry and surface brightness profile of the disk.
In the mid- and far-infrared, the emission of the system is dominated by the
thermal emission from the cold dusty disk. For a system located at the Galactic
center, we find typical magnifications to be of order 10-20% or higher,
depending on the disk surface brightness profile, and the event lasts over one
year. At around 20 microns, where the emission for the star and the disk are
comparable, the difference in the emission areas results in a chromatic
microlensing event. Finally, in the near-infrared and visible, where the
emission of the star dominates, the fraction of star light directly reflected
by the disk slightly modifies the light curve of the system which is no longer
that of a point source. In each case, the corresponding light curve can be used
to probe some of the disk properties. A fraction of 0.1% to 1% optical
microlensing events are expected to be associated with circumstellar disk
systems. We show that the lensing signal of the disk can be detected with
sparse follow-up observations of the next generation space telescopes. While
direct imaging studies of circumstellar disks are limited to the solar
neighborhood, this microlensing technique can probe very distant disk systems
living in various environments and has the potential to reveal a larger
diversity of circumstellar disks.Comment: 9 pages, 7 figures. Accepted for publication in Ap
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