3,451 research outputs found
Corporate Giving Gets Smarter: ConAgra Foods Foundation Fights Childhood Hunger
· This article discusses how a better “map” can develop strategic focus and alignment, increasing the potential for results.
· Program development and evaluation are best done hand in hand.
· In complex systems, co-construction has huge yield. It promotes accuracy, comprehensiveness, and utility.
· Grantmakers can provide more than funding; they can identify and use new tools, processes, and resources with multiple stakeholders for effectiveness.
· Alignment and integration are powerful principles inside and outside organizations as well as across sectors in pursuit of social change
Coplanar Circumbinary Debris Disks
We present resolved Herschel images of circumbinary debris disks in the alpha
CrB (HD139006) and beta Tri (HD13161) systems. We find that both disks are
consistent with being aligned with the binary orbital planes. Though secular
perturbations from the binary can align the disk, in both cases the alignment
time at the distances at which the disk is resolved is greater than the stellar
age, so we conclude that the coplanarity was primordial. Neither disk can be
modelled as a narrow ring, requiring extended radial distributions. To satisfy
both the Herschel and mid-IR images of the alpha CrB disk, we construct a model
that extends from 1-300AU, whose radial profile is broadly consistent with a
picture where planetesimal collisions are excited by secular perturbations from
the binary. However, this model is also consistent with stirring by other
mechanisms, such as the formation of Pluto-sized objects. The beta Tri disk
model extends from 50-400AU. A model with depleted (rather than empty) inner
regions also reproduces the observations and is consistent with binary and
other stirring mechanisms. As part of the modelling process, we find that the
Herschel PACS beam varies by as much as 10% at 70um and a few % at 100um. The
70um variation can therefore hinder image interpretation, particularly for
poorly resolved objects. The number of systems in which circumbinary debris
disk orientations have been compared with the binary plane is now four. More
systems are needed, but a picture in which disks around very close binaries
(alpha CrB, beta Tri, and HD 98800, with periods of a few weeks to a year) are
aligned, and disks around wider binaries (99 Her, with a 50 yr period) are
misaligned, may be emerging. This picture is qualitatively consistent with the
expectation that the protoplanetary disks from which the debris emerged are
more likely to be aligned if their binaries have shorter periods.Comment: accepted to MNRA
Post-main sequence evolution of A star debris discs
While the population of main sequence debris discs is well constrained,
little is known about debris discs around evolved stars. This paper provides a
theoretical framework considering the effects of stellar evolution on debris
discs, particularly the production and loss of dust within them. Here we repeat
a steady state model fit to disc evolution statistics for main sequence A
stars, this time using realistic grain optical properties, then evolve that
population to consider its detectability at later epochs. Our model predicts
that debris discs around giant stars are harder to detect than on the main
sequence because radiation pressure is more effective at removing small dust
around higher luminosity stars. Just 12% of first ascent giants within 100pc
are predicted to have discs detectable with Herschel at 160um. However this is
subject to the uncertain effect of sublimation on the disc, which we propose
can thus be constrained with such observations. Our model also finds that the
rapid decline in stellar luminosity results in only very young white dwarfs
having luminous discs. As such systems are on average at larger distances they
are hard to detect, but we predict that the stellar parameters most likely to
yield a disc detection are a white dwarf at 200pc with cooling age of 0.1Myr,
in line with observations of the Helix Nebula. Our model does not predict
close-in (<0.01AU) dust, as observed for some white dwarfs, however we find
that stellar wind drag leaves significant mass (~10^{-2}Msolar), in bodies up
to ~10m in diameter, inside the disc at the end of the AGB phase which may
replenish these discs
Field Trials with Zinc on Corn
Zinc deficiency in corn has been found in isolated instances in Kentucky during the past few years. Usually the deficiency is found in fields having a high pH or in high-phosphate soils with somewhat lower pH values. At present zinc deficiency in Kentucky soils does not appear widespread enough to justify recommending its application except where known deficiencies exist
Reconciling Semiclassical and Bohmian Mechanics: III. Scattering states for continuous potentials
In a previous paper [J. Chem. Phys. 121 4501 (2004)] a unique bipolar
decomposition, Psi = Psi1 + Psi2 was presented for stationary bound states Psi
of the one-dimensional Schroedinger equation, such that the components Psi1 and
Psi2 approach their semiclassical WKB analogs in the large action limit. The
corresponding bipolar quantum trajectories, as defined in the usual Bohmian
mechanical formulation, are classical-like and well-behaved, even when Psi has
many nodes, or is wildly oscillatory. A modification for discontinuous
potential stationary stattering states was presented in a second paper [J.
Chem. Phys. 124 034115 (2006)], whose generalization for continuous potentials
is given here. The result is an exact quantum scattering methodology using
classical trajectories. For additional convenience in handling the tunneling
case, a constant velocity trajectory version is also developed.Comment: 16 pages and 14 figure
Debris Disks: Probing Planet Formation
Debris disks are the dust disks found around ~20% of nearby main sequence
stars in far-IR surveys. They can be considered as descendants of
protoplanetary disks or components of planetary systems, providing valuable
information on circumstellar disk evolution and the outcome of planet
formation. The debris disk population can be explained by the steady
collisional erosion of planetesimal belts; population models constrain where
(10-100au) and in what quantity (>1Mearth) planetesimals (>10km in size)
typically form in protoplanetary disks. Gas is now seen long into the debris
disk phase. Some of this is secondary implying planetesimals have a Solar
System comet-like composition, but some systems may retain primordial gas.
Ongoing planet formation processes are invoked for some debris disks, such as
the continued growth of dwarf planets in an unstirred disk, or the growth of
terrestrial planets through giant impacts. Planets imprint structure on debris
disks in many ways; images of gaps, clumps, warps, eccentricities and other
disk asymmetries, are readily explained by planets at >>5au. Hot dust in the
region planets are commonly found (<5au) is seen for a growing number of stars.
This dust usually originates in an outer belt (e.g., from exocomets), although
an asteroid belt or recent collision is sometimes inferred.Comment: Invited review, accepted for publication in the 'Handbook of
Exoplanets', eds. H.J. Deeg and J.A. Belmonte, Springer (2018
The Carnegie Supernova Project: The Low-Redshift Survey
Supernovae are essential to understanding the chemical evolution of the
Universe. Type Ia supernovae also provide the most powerful observational tool
currently available for studying the expansion history of the Universe and the
nature of dark energy. Our basic knowledge of supernovae comes from the study
of their photometric and spectroscopic properties. However, the presently
available data sets of optical and near-infrared light curves of supernovae are
rather small and/or heterogeneous, and employ photometric systems that are
poorly characterized. Similarly, there are relatively few supernovae whose
spectral evolution has been well sampled, both in wavelength and phase, with
precise spectrophotometric observations. The low-redshift portion of the
Carnegie Supernova Project (CSP) seeks to remedy this situation by providing
photometry and spectrophotometry of a large sample of supernovae taken on
telescope/filter/detector systems that are well understood and well
characterized. During a five-year program which began in September 2004, we
expect to obtain high-precision u'g'r'i'BVYJHKs light curves and optical
spectrophotometry for about 250 supernovae of all types. In this paper we
provide a detailed description of the CSP survey observing and data reduction
methodology. In addition, we present preliminary photometry and spectra
obtained for a few representative supernovae during the first observing
campaign.Comment: 45 pages, 13 figures, 3 tables, accepted by PAS
Extrasolar Kuiper Belts
Extrasolar debris disks are the dust disks found around nearby main sequence
stars arising from the break-up of asteroids and comets orbiting the stars.
Far-IR surveys (e.g., with Herschel) showed that ~20% of stars host detectable
dust levels. While dust temperatures suggest a location at 10s of au comparable
with our Kuiper belt, orders of magnitude more dust is required implying a
planetesimal population more comparable with the primordial Kuiper belt. High
resolution imaging (e.g., with ALMA) has mapped the nearest and brightest
disks, providing evidence for structures shaped by an underlying planetary
system. Some of these are analogous to structures in our own Kuiper belt (e.g.,
the hot and cold classical, resonant, scattered disk and cometary populations),
while others have no Solar System counterpart. CO gas is seen in some debris
disks, and inferred to originate in the destruction of planetesimals with a
similar volatile-rich composition to Solar System comets. This chapter reviews
our understanding of extrasolar Kuiper belts and of how our own Kuiper belt
compares with those of neighbouring stars.Comment: Chapter to be published in the book "The Trans-Neptunian Solar
System" (D. Prialnik, M.A. Barucci and L. Young, eds.). 25 pages, 8 figure
The Carnegie Supernova Project: Analysis of the First Sample of Low-Redshift Type-Ia Supernovae
We present the analysis of the first set of low-redshift Type Ia supernovae
(SNe Ia) by the Carnegie Supernova Project. Well-sampled, high-precision
optical (ugriBV) and near-infrared (NIR; YJHKs) light curves obtained in a
well-understood photometric system are used to provide light-curve parameters,
and ugriBVYJH template light curves. The intrinsic colors at maximum light are
calibrated to compute optical--NIR color excesses for the full sample, thus
allowing the properties of the reddening law in the host galaxies to be
studied. A low value of Rv~1.7, is derived when using the entire sample of SNe.
However, when the two highly reddened SNe in the sample are excluded, a value
Galactic standard of Rv~3.2 is obtained. The colors of these two events are
well matched by a reddening model due to circumstellar dust. The peak
luminosities are calibrated using a two-parameter linear fit to the decline
rates and the colors, or alternatively, the color excesses. In both cases,
dispersions in absolute magnitude of 0.12--0.16 mag are obtained, depending on
the filter-color combination. In contrast to the results obtained from color
excesses, these fits give Rv~1--2, even when the two highly reddened SNe are
excluded. This discrepancy suggests that, beyond the "normal" interstellar
reddening produced in the host galaxies, there is an intrinsic dispersion in
the colors of SNe Ia which is correlated with luminosity but independent of the
decline rate. Finally, a Hubble diagram is produced by combining the results of
the fits for each filter. The resulting scatter of 0.12 mag appears to be
limited by peculiar velocities as evidenced by the strong correlation between
the distance-modulus residuals among the different filters. The implication is
that the actual precision of SN Ia distances is 3--4%.Comment: 76 pages, 20 figures, accepted for publication in A
A peculiar class of debris disks from Herschel/DUNES - A steep fall off in the far infrared
Aims. We present photometric data of debris disks around HIP 103389 (HD
199260), HIP 107350 (HN Peg, HD206860), and HIP 114948 (HD 219482), obtained in
the context of our Herschel Open Time Key Program DUNES (DUst around NEarby
Stars). Methods. We used Herschel/PACS to detect the thermal emission of the
three debris disks with a 3 sigma sensitivity of a few mJy at 100 um and 160
um. In addition, we obtained Herschel/PACS photometric data at 70 um for HIP
103389. Two different approaches are applied to reduce the Herschel data to
investigate the impact of data reduction on the photometry. We fit analytical
models to the available spectral energy distribution (SED) data. Results. The
SEDs of the three disks potentially exhibit an unusually steep decrease at
wavelengths > 70 um. We investigate the significance of the peculiar shape of
these SEDs and the impact on models of the disks provided it is real. Our
modeling reveals that such a steep decrease of the SEDs in the long wavelength
regime is inconsistent with a power-law exponent of the grain size distribution
-3.5 expected from a standard equilibrium collisional cascade. In contrast, a
very distinct range of grain sizes is implied to dominate the thermal emission
of such disks. However, we demonstrate that the understanding of the data of
faint sources obtained with Herschel is still incomplete and that the
significance of our results depends on the version of the data reduction
pipeline used. Conclusions. A new mechanism to produce the dust in the
presented debris disks, deviations from the conditions required for a standard
equilibrium collisional cascade (grain size exponent of -3.5), and/or
significantly different dust properties would be necessary to explain the
potentially steep SED shape of the three debris disks presented. (abridged)Comment: 14 pages, 4 figures, accepted by A&
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