13,509 research outputs found
Quantile regression for mixed models with an application to examine blood pressure trends in China
Cardiometabolic diseases have substantially increased in China in the past 20
years and blood pressure is a primary modifiable risk factor. Using data from
the China Health and Nutrition Survey, we examine blood pressure trends in
China from 1991 to 2009, with a concentration on age cohorts and urbanicity.
Very large values of blood pressure are of interest, so we model the
conditional quantile functions of systolic and diastolic blood pressure. This
allows the covariate effects in the middle of the distribution to vary from
those in the upper tail, the focal point of our analysis. We join the
distributions of systolic and diastolic blood pressure using a copula, which
permits the relationships between the covariates and the two responses to share
information and enables probabilistic statements about systolic and diastolic
blood pressure jointly. Our copula maintains the marginal distributions of the
group quantile effects while accounting for within-subject dependence, enabling
inference at the population and subject levels. Our population-level regression
effects change across quantile level, year and blood pressure type, providing a
rich environment for inference. To our knowledge, this is the first quantile
function model to explicitly model within-subject autocorrelation and is the
first quantile function approach that simultaneously models multivariate
conditional response. We find that the association between high blood pressure
and living in an urban area has evolved from positive to negative, with the
strongest changes occurring in the upper tail. The increase in urbanization
over the last twenty years coupled with the transition from the positive
association between urbanization and blood pressure in earlier years to a more
uniform association with urbanization suggests increasing blood pressure over
time throughout China, even in less urbanized areas. Our methods are available
in the R package BSquare.Comment: Published at http://dx.doi.org/10.1214/15-AOAS841 in the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Using a Grid-Enabled Wireless Sensor Network for Flood Management
Flooding is becoming an increasing problem. As a result there is a need to deploy more sophisticated sensor networks to detect and react to flooding. This paper outlines a demonstration that illustrates our proposed solution to this problem involving embedded wireless hardware, component based middleware and overlay networks
The Dust-to-Gas Ratio in the Small Magellanic Cloud Tail
The Tail region of the Small Magellanic Cloud (SMC) was imaged using the MIPS
instrument on the Spitzer Space Telescope as part of the SAGE-SMC Spitzer
Legacy. Diffuse infrared emission from dust was detected in all the MIPS bands.
The Tail gas-to-dust ratio was measured to be 1200 +/- 350 using the MIPS
observations combined with existing IRAS and HI observations. This gas-to-dust
ratio is higher than the expected 500-800 from the known Tail metallicity
indicating possible destruction of dust grains. Two cluster regions in the Tail
were resolved into multiple sources in the MIPS observations and local
gas-to-dust ratios were measured to be ~440 and ~250 suggests dust formation
and/or significant amounts of ionized gas in these regions. These results
support the interpretation that the SMC Tail is a tidal tail recently stripped
from the SMC that includes gas, dust, and young stars.Comment: 6 pages, 3 figures, ApJ Letters, in press, (version with full
resolution figures at
http://www.stsci.edu/~kgordon/papers/PS_files/sage-smc_taildust_v1.62.pdf
The trypanosome alternative oxidase:a potential drug target?
New drugs against Trypanosoma brucei, the causative agent of Human African Trypanosomiasis, are urgently needed to replace the highly toxic and largely ineffective therapies currently used. The trypanosome alternative oxidase (TAO) is an essential and unique mitochondrial protein in these parasites and is absent from mammalian mitochondria, making it an attractive drug target. The structure and function of the protein are now well characterized, with several inhibitors reported in the literature which show potential as clinical drug candidates. In this review we provide an update on the functional activity and structural aspects of TAO. We then discuss TAO inhibitors reported to date, problems encountered with in vivo testing of these compounds, and discuss the future of TAO as a therapeutic target.PostprintPeer reviewe
Flame Retardant Effect of Aerogel and Nanosilica on Engineered Polymers
Aerogels are typically manufactured vIa high temperature and pressure-critical-point drying of a colloidal metal oxide gel filled with solvents. Aerogel materials derived from silica materials represent a structural morphology (amorphous, open-celled nanofoams) rather than a particular chemical constituency. Aerogel is not like conventional foams in that it is a porous material with extreme microporosity and composed of individual features only a few nanometers in length with a highly porous dendriticlike structure. This unique substance has unusual properties such as low thermal conductivity, refractive index and sound suppression; in addition to its exceptional ability to capture fast moving dust. The highly porous nature of the aerogel's structure provides large amounts of surface area per unit weight. For instance, a silica aerogel material with a density of 100 kilograms per cubic meters can have surface areas of around 800 to 1500 square meters per gram depending on the precursors and process utilized to produce it. To take advantage of the unique properties of silica aerogels, especially the ultra light weight and low thermal conductivity, their composites with various engineering polymers were prepared and their flammability was investigated by Cone Calorimetry. The flammability of various polystyrene/silica aerogel nanocomposites were measured. The combination of these nanocomposites with a NASA patented flame retardant SINK were also studied. The results were compared with the base polymer to show the differences between composites with different forms of silica
New HErschel Multi-wavelength Extragalactic Survey of Edge-on Spirals (NHEMESES)
Edge-on spiral galaxies offer a unique perspective on the vertical structure
of spiral disks, both stars and the iconic dark dustlanes. The thickness of
these dustlanes can now be resolved for the first time with Herschel in
far-infrared and sub-mm emission. We present NHEMESES, an ongoing project that
targets 12 edge-on spiral galaxies with the PACS and SPIRE instruments on
Herschel. These vertically resolved observations of edge-on spirals will impact
on several current topics.
First and foremost, these Herschel observations will settle whether or not
there is a phase change in the vertical structure of the ISM with disk mass.
Previously, a dramatic change in dustlane morphology was observed as in massive
disks the dust collapses into a thin lane. If this is the case, the vertical
balance between turbulence and gravity dictates the ISM structure and
consequently star-formation and related phenomena (spiral arms, bars etc.). We
specifically target lower mass nearby edge-ons to complement existing Herschel
observations of high-mass edge-on spirals (the HEROES project).
Secondly, the combined data-set, together with existing Spitzer observations,
will drive a new generation of spiral disk Spectral Energy Distribution models.
These model how dust reprocesses starlight to thermal emission but the dust
geometry remains the critical unknown.
And thirdly, the observations will provide an accurate and unbiased census of
the cold dusty structures occasionally seen extending out of the plane of the
disk, when backlit by the stellar disk. To illustrate the NHEMESES project, we
present early results on NGC 4244 and NGC 891, two well studies examples of a
low and high-mass edge-on spiral.Comment: 3 pages, 4 figures, to appear in the proceedings of IAU 284, "The
Spectral Energy Distribution of Galaxies", (SED2011), 5-9 September 2011,
Preston, UK, editors, R.J. Tuffs & C.C.Popescu (v2 updated metadata
Gaps in the cloud cover? Comparing extinction measures in spiral disks
Dust in galaxies can be mapped by either the FIR/sub-mm emission, the optical
or infrared reddening of starlight, or the extinction of a known background
source. We compare two dust extinction measurements for a set of fifteen
sections in thirteen nearby galaxies, to determine the scale of the dusty ISM
responsible for disk opacity: one using stellar reddening and the other a known
background source. In our earlier papers, we presented extinction measurements
of 29 galaxies, based on calibrated counts of distant background objects
identified though foreground disks in HST/WFPC2 images. For the 13 galaxies
that overlap with the Spitzer Infrared Nearby Galaxies Survey (SINGS), we now
compare these results with those obtained from an I-L color map. Our goal is to
determine whether or not a detected distant galaxy indicates a gap in the dusty
ISM, and hence to better understand the nature and geometry of the disk
extinction.
We find that distant galaxies are predominantly in low-extinction sections
marked by the color maps, indicating that their number depends both on the
cloud cover of {\it Spitzer}-resolved dust structures --mostly the spiral
arms--and a diffuse, unresolved underlying disk. We note that our infrared
color map (E[I-L]) underestimates the overall dust presence in these disks
severely, because it implicitly assumes the presence of a dust screen in front
of the stellar distribution.Comment: 22 pages, 2 figures, 3 tables, accepted for publication in A
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