1,629 research outputs found
Predictive models for nanotoxicology: current challenges and future opportunities.
Characterizing the risks posed by nanomaterials is extraordinarily complex because these materials can have a wide range of sizes, shapes, chemical compositions and surface modifications, all of which may affect toxicity. There is an urgent need for a testing strategy that can rapidly and efficiently provide a screening approach for evaluating the potential hazard of nanomaterials and inform the prioritization of additional toxicological testing where necessary. Predictive toxicity models could form an integral component of such an approach by predicting which nanomaterials, as a result of their physico-chemical characteristics, have potentially hazardous properties. Strategies for directing research towards predictive models and the ancillary benefits of such research are presented here
Socioeconomic and Racial Disparities in Cancer Risk from Air Toxics in Maryland
We linked risk estimates from the U.S. Environmental Protection Agency’s National Air Toxics Assessment (NATA) to racial and socioeconomic characteristics of census tracts in Maryland (2000 Census) to evaluate disparities in estimated cancer risk from exposure to air toxics by emission source category. In Maryland, the average estimated cancer risk across census tracts was highest from on-road sources (50% of total risk from nonbackground sources), followed by nonroad (25%), area (23%), and major sources (< 1%). Census tracts in the highest quartile defined by the fraction of African-American residents were three times more likely to be high risk (> 90th percentile of risk) than those in the lowest quartile (95% confidence interval, 2.0–5.0). Conversely, risk decreased as the proportion of whites increased (p < 0.001). Census tracts in the lowest quartile of socioeconomic position, as measured by various indicators, were 10–100 times more likely to be high risk than those in the highest quartile. We observed substantial risk disparities for on-road, area, and nonroad sources by socioeconomic measure and on-road and area sources by race. There was considerably less evidence of risk disparities from major source emissions. We found a statistically significant interaction between race and income, suggesting a stronger relationship between race and risk at lower incomes. This research demonstrates the utility of NATA for assessing regional environmental justice, identifies an environmental justice concern in Maryland, and suggests that on-road sources may be appropriate targets for policies intended to reduce the disproportionate environmental health burden among economically disadvantaged and minority populations
Proton-coupled dynamics in lactose permease
Lactose permease of Escherichia coli (LacY) catalyzes symport of a
galactopyranoside and an H+ via an alternating access mechanism. The
transition from an inward- to an outward-facing conformation of LacY involves
sugar-release followed by deprotonation. Because the transition depends
intimately upon the dynamics of LacY in a bilayer environment, molecular
dynamics (MD) simulations may be the only means of following the accompanying
structural changes in atomic detail. Here, we describe MD simulations of wild-
type apo LacY in phosphatidylethanolamine (POPE) lipids that features two
protonation states of the critical Glu325. While the protonated system
displays configurational stability, deprotonation of Glu325 causes significant
structural rearrangements that bring into proximity side chains important for
H+ translocation and sugar binding and closes the internal cavity. Moreover,
protonated LacY in phosphatidylcholine (DMPC) lipids shows that the observed
dynamics are lipid-dependent. Together, the simulations describe early
dynamics of the inward-to-outward transition of LacY that agree well with
experimental data
Chandra X-Ray Observatory Observations of the Globular Cluster M71
We observed the nearby, low-density globular cluster M71 (NGC 6838) with the
Chandra X-ray Observatory to study its faint X-ray populations. Five X-ray
sources were found inside the cluster core radius, including the known
eclipsing binary millisecond pulsar (MSP) PSR J1953+1846A. The X-ray light
curve of the source coincident with this MSP shows marginal evidence for
periodicity at the binary period of 4.2 h. Its hard X-ray spectrum and
luminosity resemble those of other eclipsing binary MSPs in 47 Tuc, suggesting
a similar shock origin of the X-ray emission. A further 24 X-ray sources were
found within the half-mass radius, reaching to a limiting luminosity of 1.5
10^30 erg/s (0.3-8 keV). From a radial distribution analysis, we find that
18+/-6 of these 29 sources are associated with M71, somewhat more than
predicted, and that 11+/-6 are background sources, both galactic and
extragalactic. M71 appears to have more X-ray sources between L_X=10^30--10^31
erg/s than expected by extrapolating from other studied clusters using either
mass or collision frequency. We explore the spectra and variability of these
sources, and describe the results of ground-based optical counterpart searches.Comment: 36 pages including 7 figures and 8 tables, accepted by The
Astrophysical Journa
Comparison of three video laryngoscopy devices to direct laryngoscopy for intubating obese patients: a randomized controlled trial
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The Century Survey Galactic Halo Project III: A Complete 4300 deg^2 Survey of Blue Horizontal Branch Stars in the Metal-Weak Thick Disk and Inner Halo
We present a complete spectroscopic survey of 2414 2MASS-selected blue
horizontal branch (BHB) candidates selected over 4300 deg^2 of the sky. We
identify 655 BHB stars in this non-kinematically selected sample. We calculate
the luminosity function of field BHB stars and find evidence for very few hot
BHB stars in the field. The BHB stars located at a distance from the Galactic
plane |Z|<4 kpc trace what is clearly a metal-weak thick disk population, with
a mean metallicity of [Fe/H]= -1.7, a rotation velocity gradient of
dv_{rot}/d|Z|= -28+-3.4 km/s in the region |Z|<6 kpc, and a density scale
height of h_Z= 1.26+-0.1 kpc. The BHB stars located at 5<|Z|<9 kpc are a
predominantly inner-halo population, with a mean metallicity of [Fe/H]= -2.0
and a mean Galactic rotation of -4+-31 km/s. We infer the density of halo and
thick disk BHB stars is 104+-37 kpc^-3 near the Sun, and the relative
normalization of halo to thick-disk BHB stars is 4+-1% near the Sun.Comment: 12 pages in emulateapj format, accepted for publication in February
A
Gravity modes as a way to distinguish between hydrogen- and helium-burning red giant stars
Red giants are evolved stars that have exhausted the supply of hydrogen in
their cores and instead burn hydrogen in a surrounding shell. Once a red giant
is sufficiently evolved, the helium in the core also undergoes fusion.
Outstanding issues in our understanding of red giants include uncertainties in
the amount of mass lost at the surface before helium ignition and the amount of
internal mixing from rotation and other processes. Progress is hampered by our
inability to distinguish between red giants burning helium in the core and
those still only burning hydrogen in a shell. Asteroseismology offers a way
forward, being a powerful tool for probing the internal structures of stars
using their natural oscillation frequencies. Here we report observations of
gravity-mode period spacings in red giants that permit a distinction between
evolutionary stages to be made. We use high-precision photometry obtained with
the Kepler spacecraft over more than a year to measure oscillations in several
hundred red giants. We find many stars whose dipole modes show sequences with
approximately regular period spacings. These stars fall into two clear groups,
allowing us to distinguish unambiguously between hydrogen-shell-burning stars
(period spacing mostly about 50 seconds) and those that are also burning helium
(period spacing about 100 to 300 seconds).Comment: to appear as a Letter to Natur
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