548 research outputs found
In-situ Observation of AlN Formation from Ni-Al Solution Using an Electromagnetic Levitation Technique
Aluminum nitride is a promising substrate material for AlGaN-based UV-LED. In order to develop a robust growth processing route for AlN single crystals, fundamental studies of solution growth experiments using Ni-Al alloy melts as a new solution system were performed. Al can be stably kept in solution the Ni-Al liquid even at high temperature; in addition, the driving force of the AlN formation reaction from solution can be controlled by solution composition and temperature. To investigate AlN crystal growth behavior we developed an in situ observation system using an electromagnetic levitation technique. AlN formation behavior, including nucleation and growth, was quantitatively analyzed by an image processing pipeline. The nucleation rate of AlN decreased with increasing growth temperature and decreasing aluminum composition. In addition, hexagonal c-axis oriented AlN crystal successfully grew on the levitated Ni-40 mol%Al droplet reacted at low driving force (1960 K), on the other hand, AlN crystal with dendritic morphology appeared on the sample with higher driving force (Ni-50 mol%Al, 1960 K). Thus, the nucleation rate and crystal morphology were dominated by the driving force of the AlN formation reaction
The Holy Grail: A road map for unlocking the climate record stored within Mars' polar layered deposits
In its polar layered deposits (PLD), Mars possesses a record of its recent climate, analogous to terrestrial ice sheets containing climate records on Earth. Each PLD is greater than 2 km thick and contains thousands of layers, each containing information on the climatic and atmospheric state during its deposition, creating a climate archive. With detailed measurements of layer composition, it may be possible to extract age, accumulation rates, atmospheric conditions, and surface activity at the time of deposition, among other important parameters; gaining the information would allow us to “read” the climate record. Because Mars has fewer complicating factors than Earth (e.g. oceans, biology, and human-modified climate), the planet offers a unique opportunity to study the history of a terrestrial planet’s climate, which in turn can teach us about our own planet and the thousands of terrestrial exoplanets waiting to be discovered.
During a two-part workshop, the Keck Institute for Space Studies (KISS) hosted 38 Mars scientists and engineers who focused on determining the measurements needed to extract the climate record contained in the PLD. The group converged on four fundamental questions that must be answered with the goal of interpreting the climate record and finding its history based on the climate drivers.
The group then proposed numerous measurements in order to answer these questions and detailed a sequence of missions and architecture to complete the measurements. In all, several missions are required, including an orbiter that can characterize the present climate and volatile reservoirs; a static reconnaissance lander capable of characterizing near surface atmospheric processes, annual accumulation, surface properties, and layer formation mechanism in the upper 50 cm of the PLD; a network of SmallSat landers focused on meteorology for ground truth of the low-altitude orbiter data; and finally, a second landed platform to access ~500 m of layers to measure layer variability through time. This mission architecture, with two landers, would meet the science goals and is designed to save costs compared to a single very capable landed mission. The rationale for this plan is presented below.
In this paper we discuss numerous aspects, including our motivation, background of polar science, the climate science that drives polar layer formation, modeling of the atmosphere and climate to create hypotheses for what the layers mean, and terrestrial analogs to climatological studies. Finally, we present a list of measurements and missions required to answer the four major questions and read the climate record.
1. What are present and past fluxes of volatiles, dust, and other materials into and out of the polar regions?
2. How do orbital forcing and exchange with other reservoirs affect those fluxes?
3. What chemical and physical processes form and modify layers?
4. What is the timespan, completeness, and temporal resolution of the climate history recorded in the PLD
HPV Genotypes in High Grade Cervical Lesions and Invasive Cervical Carcinoma as Detected by Two Commercial DNA Assays, North Carolina, 2001–2006
HPV typing using formalin fixed paraffin embedded (FFPE) cervical tissue is used to evaluate HPV vaccine impact, but DNA yield and quality in FFPE specimens can negatively affect test results. This study aimed to evaluate 2 commercial assays for HPV detection and typing using FFPE cervical specimens.Four large North Carolina pathology laboratories provided FFPE specimens from 299 women ages18 and older diagnosed with cervical disease from 2001 to 2006. For each woman, one diagnostic block was selected and unstained serial sections were prepared for DNA typing. Extracts from samples with residual lesion were used to detect and type HPV using parallel and serial testing algorithms with the Linear Array and LiPA HPV genotyping assays.LA and LiPA concordance was 0.61 for detecting any high-risk (HR) and 0.20 for detecting any low-risk (LR) types, with significant differences in marginal proportions for HPV16, 51, 52, and any HR types. Discordant results were most often LiPA-positive, LA-negative. The parallel algorithm yielded the highest prevalence of any HPV type (95.7%). HR type prevalence was similar using parallel (93.1%) and serial (92.1%) approaches. HPV16, 33, and 52 prevalence was slightly lower using the serial algorithm, but the median number of HR types per woman (1) did not differ by algorithm. Using the serial algorithm, HPV DNA was detected in >85% of invasive and >95% of pre-invasive lesions. The most common type was HPV16, followed by 52, 18, 31, 33, and 35; HPV16/18 was detected in 56.5% of specimens. Multiple HPV types were more common in lower grade lesions.We developed an efficient algorithm for testing and reporting results of two commercial assays for HPV detection and typing in FFPE specimens, and describe HPV type distribution in pre-invasive and invasive cervical lesions in a state-based sample prior to HPV vaccine introduction
Conservation risk of Batrachochytrium salamandrivorans to endemic lungless salamanders
The emerging fungal pathogen, Batrachochytrium salamandrivorans (Bsal ), is a significant conservation threat to salamander biodiversity in Europe, although its potential to affect North American species is poorly understood. We tested the susceptibility of two genera (Eurycea and Pseudotriton ) and three populations of lungless salamanders (Plethodontidae ) to Bsal . All species became infected with Bsal and two (Pseudotriton ruber and Eurycea wilderae ) developed chytridiomycosis. We also documented that susceptibility of E. wilderae differed among populations. Regardless of susceptibility, all species reduced feeding when exposed to Bsal at the highest zoospore dose, and P. ruber and one population of E. wilderae used cover objects less. Our results indicate that Bsal invasion in eastern North America could have significant negative impacts on endemic lungless salamander populations. Future conservation efforts should include surveillance for Bsal in the wild and in captivity, and championing legislation that requires and subsidizes pathogen‐free trade of amphibians
Conservation risk of Batrachochytrium salamandrivorans to endemic lungless salamanders
The emerging fungal pathogen, Batrachochytrium salamandrivorans (Bsal), is a significant conservation threat to salamander biodiversity in Europe, although its potential to affect North American species is poorly understood. We tested the susceptibility of two genera (Eurycea and Pseudotriton) and three populations of lungless salamanders (Plethodontidae) to Bsal. All species became infected with Bsal and two (Pseudotriton ruber and Eurycea wilderae) developed chytridiomycosis. We also documented that susceptibility of E. wilderae differed among populations. Regardless of susceptibility, all species reduced feeding when exposed to Bsal at the highest zoospore dose, and P. ruber and one population of E. wilderae used cover objects less. Our results indicate that Bsal invasion in eastern North America could have significant negative impacts on endemic lungless salamander populations. Future conservation efforts should include surveillance for Bsal in the wild and in captivity, and championing legislation that requires and subsidizes pathogen-free trade of amphibians
Variation in histone configurations correlates with gene expression across nine inbred strains of mice.
The diversity outbred (DO) mice and their inbred founders are widely used models of human disease. However, although the genetic diversity of these mice has been well documented, their epigenetic diversity has not. Epigenetic modifications, such as histone modifications and DNA methylation, are important regulators of gene expression, and as such are a critical mechanistic link between genotype and phenotype. Therefore, creating a map of epigenetic modifications in the DO mice and their founders is an important step toward understanding mechanisms of gene regulation and the link to disease in this widely used resource. To this end, we performed a strain survey of epigenetic modifications in hepatocytes of the DO founders. We surveyed four histone modifications (H3K4me1, H3K4me3, H3K27me3, and H3K27ac), and DNA methylation. We used ChromHMM to identify 14 chromatin states, each of which represented a distinct combination of the four histone modifications. We found that the epigenetic landscape was highly variable across the DO founders and was associated with variation in gene expression across strains. We found that epigenetic state imputed into a population of DO mice recapitulated the association with gene expression seen in the founders suggesting that both histone modifications and DNA methylation are highly heritable mechanisms of gene expression regulation. We illustrate how DO gene expression can be aligned with inbred epigenetic states to identify putative cis-regulatory regions. Finally, we provide a data resource that documents strain-specific variation in chromatin state and DNA methylation in hepatocytes across nine widely used strains of laboratory mice
Kepler-16: A Transiting Circumbinary Planet
We report the detection of a planet whose orbit surrounds a pair of low-mass
stars. Data from the Kepler spacecraft reveal transits of the planet across
both stars, in addition to the mutual eclipses of the stars, giving precise
constraints on the absolute dimensions of all three bodies. The planet is
comparable to Saturn in mass and size, and is on a nearly circular 229-day
orbit around its two parent stars. The eclipsing stars are 20% and 69% as
massive as the sun, and have an eccentric 41-day orbit. The motions of all
three bodies are confined to within 0.5 degree of a single plane, suggesting
that the planet formed within a circumbinary disk.Comment: Science, in press; for supplemental material see
http://www.sciencemag.org/content/suppl/2011/09/14/333.6049.1602.DC1/1210923.Doyle.SOM.pd
The HST/ACS Coma Cluster Survey. II. Data Description and Source Catalogs
The Coma cluster was the target of a HST-ACS Treasury program designed for
deep imaging in the F475W and F814W passbands. Although our survey was
interrupted by the ACS instrument failure in 2007, the partially completed
survey still covers ~50% of the core high-density region in Coma. Observations
were performed for 25 fields that extend over a wide range of cluster-centric
radii (~1.75 Mpc) with a total coverage area of 274 arcmin^2. The majority of
the fields are located near the core region of Coma (19/25 pointings) with six
additional fields in the south-west region of the cluster. In this paper we
present reprocessed images and SExtractor source catalogs for our survey
fields, including a detailed description of the methodology used for object
detection and photometry, the subtraction of bright galaxies to measure faint
underlying objects, and the use of simulations to assess the photometric
accuracy and completeness of our catalogs. We also use simulations to perform
aperture corrections for the SExtractor Kron magnitudes based only on the
measured source flux and half-light radius. We have performed photometry for
~73,000 unique objects; one-half of our detections are brighter than the
10-sigma point-source detection limit at F814W=25.8 mag (AB). The slight
majority of objects (60%) are unresolved or only marginally resolved by ACS. We
estimate that Coma members are 5-10% of all source detections, which consist of
a large population of unresolved objects (primarily GCs but also UCDs) and a
wide variety of extended galaxies from a cD galaxy to dwarf LSB galaxies. The
red sequence of Coma member galaxies has a constant slope and dispersion across
9 magnitudes (-21<M_F814W<-13). The initial data release for the HST-ACS Coma
Treasury program was made available to the public in 2008 August. The images
and catalogs described in this study relate to our second data release.Comment: Accepted for publication in ApJS. A high-resolution version is
available at http://archdev.stsci.edu/pub/hlsp/coma/release2/PaperII.pd
Planetary Candidates Observed by Kepler, III: Analysis of the First 16 Months of Data
New transiting planet candidates are identified in sixteen months (May 2009 -
September 2010) of data from the Kepler spacecraft. Nearly five thousand
periodic transit-like signals are vetted against astrophysical and instrumental
false positives yielding 1,091 viable new planet candidates, bringing the total
count up to over 2,300. Improved vetting metrics are employed, contributing to
higher catalog reliability. Most notable is the noise-weighted robust averaging
of multi-quarter photo-center offsets derived from difference image analysis
which identifies likely background eclipsing binaries. Twenty-two months of
photometry are used for the purpose of characterizing each of the new
candidates. Ephemerides (transit epoch, T_0, and orbital period, P) are
tabulated as well as the products of light curve modeling: reduced radius
(Rp/R*), reduced semi-major axis (d/R*), and impact parameter (b). The largest
fractional increases are seen for the smallest planet candidates (197% for
candidates smaller than 2Re compared to 52% for candidates larger than 2Re) and
those at longer orbital periods (123% for candidates outside of 50-day orbits
versus 85% for candidates inside of 50-day orbits). The gains are larger than
expected from increasing the observing window from thirteen months (Quarter 1--
Quarter 5) to sixteen months (Quarter 1 -- Quarter 6). This demonstrates the
benefit of continued development of pipeline analysis software. The fraction of
all host stars with multiple candidates has grown from 17% to 20%, and the
paucity of short-period giant planets in multiple systems is still evident. The
progression toward smaller planets at longer orbital periods with each new
catalog release suggests that Earth-size planets in the Habitable Zone are
forthcoming if, indeed, such planets are abundant.Comment: Submitted to ApJS. Machine-readable tables are available at
http://kepler.nasa.gov, http://archive.stsci.edu/kepler/results.html, and the
NASA Exoplanet Archiv
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