378 research outputs found
Optimizing exoplanet atmosphere retrieval using unsupervised machine-learning classification
One of the principal bottlenecks to atmosphere characterisation in the era of
all-sky surveys is the availability of fast, autonomous and robust atmospheric
retrieval methods. We present a new approach using unsupervised machine
learning to generate informed priors for retrieval of exoplanetary atmosphere
parameters from transmission spectra. We use principal component analysis (PCA)
to efficiently compress the information content of a library of transmission
spectra forward models generated using the PLATON package. We then apply a
-means clustering algorithm in PCA space to segregate the library into
discrete classes. We show that our classifier is almost always able to
instantaneously place a previously unseen spectrum into the correct class, for
low-to-moderate spectral resolutions, , in the range and noise
levels up to ~per~cent of the peak-to-trough spectrum amplitude. The
distribution of physical parameters for all members of the class therefore
provides an informed prior for standard retrieval methods such as nested
sampling. We benchmark our informed-prior approach against a standard
uniform-prior nested sampler, finding that our approach is up to a factor two
faster, with negligible reduction in accuracy. We demonstrate the application
of this method to existing and near-future observatories, and show that it is
suitable for real-world application. Our general approach is not specific to
transmission spectroscopy and should be more widely applicable to cases that
involve repetitive fitting of trusted high-dimensional models to large data
catalogues, including beyond exoplanetary science.Comment: Accepted for publication in MNRA
Proposal for Austere Light Attack Aircraft â Project Aardvark
The WickedAir senior design team at the University of Alabama in Huntsville is developing the preliminary design of an aircraft for the AIAA Undergraduate Team Aircraft Design Competition. The RFP calls for an affordable light attack aircraft capable of executing missions currently only feasible with attack helicopters. The aircraft must be able to operate from short austere fields and accommodate a crew of two. Additional design goals include enhanced survivability and the ability for deploying a variety of weapons including an integrated gun for ground targets. The aircraft must accomplish an attack mission with a full weapons load and a long-range ferry mission with a 60% weapons load. Through evaluation of existing attack aircraft and helicopters and initial trade studies, the team has produced a conceptual design for the ZA-13 âAardvarkâ. The 12,000 lbf Aardvark has twin turboprop engines mounted on a 6.9 aspect ratio swept wing. Two sponsons offer weapons attachment points similar to those of a helicopter. This design offers low speed performance, a high payload capacity, and a short takeoff length. Specific consideration was given to the effects of foreign object debris and particulate matter pollution with regards to the lifespan and vulnerability of the aircraft in various austere environments. This paper summarizes the detailed design, cost analysis, and mission capabilities behind the current aircraft
Revisiting the Transit Timing and Atmosphere Characterization of the Neptune-mass Planet HAT-P-26 b
We present the transit timing variation (TTV) and planetary atmosphere
analysis of the Neptune-mass planet HAT-P-26~b. We present a new set of 13
transit light curves from optical ground-based observations and combine them
with light curves from the Wide Field Camera 3 (WFC3) on the Hubble Space
Telescope (HST), Transiting Exoplanet Survey Satellite (TESS), and previously
published ground-based data. We refine the planetary parameters of HAT-P-26 b
and undertake a TTV analysis using 33 transits obtained over seven years. The
TTV analysis shows an amplitude signal of 1.98 0.05 minutes, which could
result from the presence of an additional planet at the 1:2
mean-motion resonance orbit. Using a combination of transit depths spanning
optical to near-infrared wavelengths, we find that the atmosphere of HAT-P-26 b
contains % of HO with a derived temperature of
K.Comment: 34 pages, accepted by A
The Seventh Data Release of the Sloan Digital Sky Survey
This paper describes the Seventh Data Release of the Sloan Digital Sky Survey
(SDSS), marking the completion of the original goals of the SDSS and the end of
the phase known as SDSS-II. It includes 11663 deg^2 of imaging data, with most
of the roughly 2000 deg^2 increment over the previous data release lying in
regions of low Galactic latitude. The catalog contains five-band photometry for
357 million distinct objects. The survey also includes repeat photometry over
250 deg^2 along the Celestial Equator in the Southern Galactic Cap. A
coaddition of these data goes roughly two magnitudes fainter than the main
survey. The spectroscopy is now complete over a contiguous area of 7500 deg^2
in the Northern Galactic Cap, closing the gap that was present in previous data
releases. There are over 1.6 million spectra in total, including 930,000
galaxies, 120,000 quasars, and 460,000 stars. The data release includes
improved stellar photometry at low Galactic latitude. The astrometry has all
been recalibrated with the second version of the USNO CCD Astrograph Catalog
(UCAC-2), reducing the rms statistical errors at the bright end to 45
milli-arcseconds per coordinate. A systematic error in bright galaxy photometr
is less severe than previously reported for the majority of galaxies. Finally,
we describe a series of improvements to the spectroscopic reductions, including
better flat-fielding and improved wavelength calibration at the blue end,
better processing of objects with extremely strong narrow emission lines, and
an improved determination of stellar metallicities. (Abridged)Comment: 20 pages, 10 embedded figures. Accepted to ApJS after minor
correction
The Fifth Data Release of the Sloan Digital Sky Survey
This paper describes the Fifth Data Release (DR5) of the Sloan Digital Sky
Survey (SDSS). DR5 includes all survey quality data taken through June 2005 and
represents the completion of the SDSS-I project (whose successor, SDSS-II will
continue through mid-2008). It includes five-band photometric data for 217
million objects selected over 8000 square degrees, and 1,048,960 spectra of
galaxies, quasars, and stars selected from 5713 square degrees of that imaging
data. These numbers represent a roughly 20% increment over those of the Fourth
Data Release; all the data from previous data releases are included in the
present release. In addition to "standard" SDSS observations, DR5 includes
repeat scans of the southern equatorial stripe, imaging scans across M31 and
the core of the Perseus cluster of galaxies, and the first spectroscopic data
from SEGUE, a survey to explore the kinematics and chemical evolution of the
Galaxy. The catalog database incorporates several new features, including
photometric redshifts of galaxies, tables of matched objects in overlap regions
of the imaging survey, and tools that allow precise computations of survey
geometry for statistical investigations.Comment: ApJ Supp, in press, October 2007. This paper describes DR5. The SDSS
Sixth Data Release (DR6) is now public, available from http://www.sdss.or
Sloan Digital Sky Survey Imaging of Low Galactic Latitude Fields: Technical Summary and Data Release
The Sloan Digital Sky Survey (SDSS) mosaic camera and telescope have obtained
five-band optical-wavelength imaging near the Galactic plane outside of the
nominal survey boundaries. These additional data were obtained during
commissioning and subsequent testing of the SDSS observing system, and they
provide unique wide-area imaging data in regions of high obscuration and star
formation, including numerous young stellar objects, Herbig-Haro objects and
young star clusters. Because these data are outside the Survey regions in the
Galactic caps, they are not part of the standard SDSS data releases. This paper
presents imaging data for 832 square degrees of sky (including repeats), in the
star-forming regions of Orion, Taurus, and Cygnus. About 470 square degrees are
now released to the public, with the remainder to follow at the time of SDSS
Data Release 4. The public data in Orion include the star-forming region NGC
2068/NGC 2071/HH24 and a large part of Barnard's loop.Comment: 31 pages, 9 figures (3 missing to save space), accepted by AJ, in
press, see http://photo.astro.princeton.edu/oriondatarelease for data and
paper with all figure
Paying for Performance: The Education Impacts of a Community College Scholarship Program for Low-Income Adults
We evaluate the effect of performance-based incentive programs on educational outcomes for
community college students from a random assignment experiment at three campuses. Incentive
payments over two semesters were tied to meeting two conditionsÂżenrolling at least half time
and maintaining a ÂżCÂż or better grade point average. Eligibility increased the likelihood of
enrolling in the second semester after random assignment and total number of credits earned.
Over two years, program group students completed nearly 40 percent more credits. We find little
evidence that program eligibility changed types of courses taken but some evidence of increased
academic performance and effort
Hundreds of variants clustered in genomic loci and biological pathways affect human height
Most common human traits and diseases have a polygenic pattern of inheritance: DNA sequence variants at many genetic loci influence the phenotype. Genome-wide association (GWA) studies have identified more than 600 variants associated with human traits, but these typically explain small fractions of phenotypic variation, raising questions about the use of further studies. Here, using 183,727 individuals, we show that hundreds of genetic variants, in at least 180 loci, influence adult height, a highly heritable and classic polygenic trait. The large number of loci reveals patterns with important implications for genetic studies of common human diseases and traits. First, the 180 loci are not random, but instead are enriched for genes that are connected in biological pathways (P = 0.016) and that underlie skeletal growth defects (Pâ<â0.001). Second, the likely causal gene is often located near the most strongly associated variant: in 13 of 21 loci containing a known skeletal growth gene, that gene was closest to the associated variant. Third, at least 19 loci have multiple independently associated variants, suggesting that allelic heterogeneity is a frequent feature of polygenic traits, that comprehensive explorations of already-discovered loci should discover additional variants and that an appreciable fraction of associated loci may have been identified. Fourth, associated variants are enriched for likely functional effects on genes, being over-represented among variants that alter amino-acid structure of proteins and expression levels of nearby genes. Our data explain approximately 10% of the phenotypic variation in height, and we estimate that unidentified common variants of similar effect sizes would increase this figure to approximately 16% of phenotypic variation (approximately 20% of heritable variation). Although additional approaches are needed to dissect the genetic architecture of polygenic human traits fully, our findings indicate that GWA studies can identify large numbers of loci that implicate biologically relevant genes and pathways.
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Quantitative Trait Loci Associated with the Tocochromanol (Vitamin E) Pathway in Barley
The Genome-Wide Association Studies approach was used to detect Quantitative Trait Loci associated with tocochromanol concentrations using a panel of 1,466 barley accessions. All major tocochromanol types- α-, ÎČ-, ÎŽ-, Îł-tocopherol and tocotrienol- were assayed. We found 13 single nucleotide polymorphisms associated with the concentration of one or more of these tocochromanol forms in barley, seven of which were within 2 cM of sequences homologous to cloned genes associated with tocochromanol production in barley and/or other plants. These associations confirmed a prior report based on bi-parental QTL mapping. This knowledge will aid future efforts to better understand the role of tocochromanols in barley, with specific reference to abiotic stress resistance. It will also be useful in developing barley varieties with higher tocochromanol concentrations, although at current recommended daily consumption amounts, barley would not be an effective sole source of vitamin E. However, it could be an important contributor in the context of whole grains in a balanced diet
Global and local concerns: What attitudes and beliefs motivate farmers to mitigate and adapt to climate change?
In response to agriculture\u27s vulnerability and contribution to climate change, many governments are developing initiatives that promote the adoption of mitigation and adaptation practices among farmers. Since most climate policies affecting agriculture rely on voluntary efforts by individual farmers, success requires a sound understanding of the factors that motivate farmers to change practices. Recent evidence suggests that past experience with the effects of climate change and the psychological distance associated with people\u27s concern for global and local impacts can influence environmental behavior. Here we surveyed farmers in a representative rural county in California\u27s Central Valley to examine how their intention to adopt mitigation and adaptation practices is influenced by previous climate experiences and their global and local concerns about climate change. Perceived changes in water availability had significant effects on farmers\u27 intention to adopt mitigation and adaptation strategies, which were mediated through global and local concerns respectively. This suggests that mitigation is largely motivated by psychologically distant concerns and beliefs about climate change, while adaptation is driven by psychologically proximate concerns for local impacts. This match between attitudes and behaviors according to the psychological distance at which they are cognitively construed indicates that policy and outreach initiatives may benefit by framing climate impacts and behavioral goals concordantly; either in a global context for mitigation or a local context for adaptation
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