3,294 research outputs found
X-Ray Absorption from the Milky Way Halo and the Local Group
Million degree gas is present at near-zero redshift and is due either to a
gaseous Galactic Halo or a more diffuse but very massive Local Group medium. We
can discriminate between these models because the column densities should
depend on location in the sky, either relative to the Galaxy bulge or to the
M31-Milky Way axis. To search for these signatures, we measured the OVII Kalpha
absorption line strength toward 25 bright AGNs, plus LMC X-3, using XMM-Newton
RGS archival data. The data are in conflict with a purely Local Group model,
but support the Galactic Halo model. The strongest correlation is between the
OVII equivalent widths and the ROSAT background emission measurement in the R45
band (0.4-1 keV), for which OVII emission makes the largest single
contribution. This suggests that much of the OVII emission and absorption are
cospatial, from which the radius of a uniform halo appears to lie the range
15-110 kpc. The present data do not constrain the type of halo gas model and an
equally good fit is obtained in a model where the gas density decreases as a
power-law, such as r^(-3/2). For a uniform halo with a radius of 20 kpc, the
electron density would be 9E-4 cm^(-3), and the gas mass is 4E8 Msolar. The
redshift of the four highest S/N OVII measurements is consistent with a Milky
Way origin rather than a Local Group origin.Comment: 32 pages (14 figures); ApJ, in pres
Identifying ILI Cases from Chief Complaints: Comparing the Accuracy of Keyword and Support Vector Machine Methods
We compared the accuracy of two methods of identifying ILI cases from chief complaints. We found that a support vector machine method was more accurate than a keyword method
A Two Hour Quasi-Period in an Ultra-luminous X-Ray source in NGC628
Quasi-periodic oscillations and X-ray spectroscopy are powerful probes of
black hole masses and accretion disks, and here we apply these diagnostics to
an ultraluminous X-ray source (ULX) in the spiral galaxy NGC628 (M74). This
object was observed four times over two years with the Chandra X-ray
Observatory and XMM-Newton, with three long observations showing dramatic
variability, distinguished by a series of outbursts with a quasi-period (QPO)
of 4,000-7,000 seconds. This is unique behavior among both ULXs and Galactic
X-ray binaries due to the combination of its burst-like peaks and deep troughs,
its long quasi-periods, its high variation amplitudes of %, and its
substantial variability between observations. The X-ray spectra is fitted by an
absorbed accretion disk plus a power-law component, suggesting the ULX was in a
spectral state analogous to the Low Hard state or the Very High state of
Galactic black hole X-ray binaries. A black hole mass of -- is estimated from the -- scaling relation found in the
Galactic X-ray binaries and active galactic nuclei.Comment: 12 pages, 3 figures. accepted for publication in ApJ Lette
Maternal immune activation during pregnancy in rats impairs working memory capacity of the offspring
Peer Reviewe
On the Lack of a Soft X-Ray Excess from Clusters of Galaxies
A soft X-ray excess has been claimed to exist in and around a number of
galaxy clusters and this emission has been attributed to the warm-hot
intergalactic medium that may constitute most of the baryons in the local
universe. We have re-examined a study of the XMM-Newton observations on this
topic by Kaastra et al. (2003) and find that the X-ray excess (or deficit)
depends upon Galactic latitude and appears to be most closely related to the
surface brightness of the 1/4 keV emission, which is largely due to emission
from the Local hot bubble and the halo of the Milky Way. We suggest that the
presence of the soft X-ray excess is due to incorrect subtraction of the soft
X-ray background. An analysis is performed where we choose a 1/4 keV background
that is similar to the background near the cluster (and for similar HI column).
We find that the soft X-ray excess largely disappears using our background
subtraction and conclude that these soft X-ray excesses are not associated with
the target clusters. We also show that the detections of "redshifted" O VII
lines claimed by Kaastra et al. (2003) are correlated with solar system charge
exchange emission suggesting that they are not extragalactic either.Comment: 8 pages, 6 figures, accepted for publication in Ap
An EAGLEâs View of Ex-situ Galaxy Growth
Modern observational and analytic techniques now enable the direct measurement of star formation histories and the inference of galaxy assembly histories. However, current theoretical predictions of assembly are not ideally suited for direct comparison with such observational data. We therefore extend the work of prior examinations of the contribution of ex-situ stars to the stellar mass budget of simulated galaxies. Our predictions are specifically tailored for direct testing with a new generation of observational techniques by calculating ex-situ fractions as functions of galaxy mass and morphological type, for a range of surface brightnesses. These enable comparison with results from large FoV IFU spectrographs, and increasingly accurate spectral fitting, providing a look-up method for the estimated accreted fraction. We furthermore provide predictions of ex-situ mass fractions as functions of galaxy mass, galactocentric radius and environment. Using z = 0 snapshots from the 100cMpc3 and 25cMpc3 EAGLE simulations we corroborate the findings of prior studies, finding that ex-situ fraction increases with stellar mass for central and satellite galaxies in a stellar mass range of 2Ă 107 - 1.9Ă 1012 Mâ. For those galaxies of mass M*>5Ă 108Mâ, we find that the total ex-situ mass fraction is greater for more extended galaxies at fixed mass. When categorising satellite galaxies by their parent group/cluster halo mass we find that the ex-situ fraction decreases with increasing parent halo mass at fixed galaxy mass. This apparently counter-intuitive result may be due to high passing velocities within large cluster halos inhibiting efficient accretion onto individual galaxies
A Transparent Conductive Adhesive Laminate Electrode for High-Efficiency Organic-Inorganic Lead Halide Perovskite Solar Cells
A self-adhesive laminate solar-cell electrode is presented based on a metal grid embedded in a polymer film (xây conduction) and set in contact with the active layer using a pressure-sensitive adhesive containing a very low quantity (1.8%) of organic conductor, which self-organizes to provide z conduction to the grid. This ITO-free material performs in an identical fashion to evaporated gold in high-efficiency perovskite solar cells
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Effects of two contrasting canopy manipulations on growth and water use of London plane (Platanus x acerifolia) trees
Aims: Two contrasting canopy manipulations were compared to unpruned controls on London plane trees, to determine the effects on canopy regrowth, soil and leaf water relations.
Methods: âCanopy reductionâ, was achieved by removing the outer 30 % length of all major branches and âcanopy thinningâ, by removing 30 % of lateral branches arising from major branches.
Results: Total canopy leaf areas recovered within two and three years of pruning for the canopy-thinned and reduced trees respectively. Canopy reduction increased mean leaf size, nitrogen concentration, canopy leaf area density and conserved soil moisture for up to 3 years, whereas canopy thinning had no effects. Another experiment compared more severe canopy reduction to unpruned trees. This produced a similar growth response to the previous experiment, but soil moisture was conserved nearer to the trunk. Analysis of 13C and 18O signals along with leaf water relations and soil moisture data suggested that lower boundary layer conductance within the canopy-reduced trees restricted tree water use, whereas for the canopy-thinned trees the opposite occurred.
Conclusions: Only canopy reduction conserved soil moisture and this was due to a combination of reduced total canopy leaf area and structural changes in canopy architecture
Trends in adult cardiovascular disease risk factors and their socio-economic patterning in the Scottish population 1995â2008: cross-sectional surveys
<p>Objectives To examine secular and socio-economic changes in cardiovascular disease risk factor prevalences in the Scottish population. This could contribute to a better understanding of why the decline in coronary heart disease mortality in Scotland has recently stalled along with a widening of socio-economic inequalities.</p>
<p>Design Four Scottish Health Surveys 1995, 1998, 2003 and 2008 (6190, 6656, 5497 and 4202 respondents, respectively, aged 25â64â
years) were used to examine gender-stratified, age-standardised prevalences of smoking, alcohol consumption, physical activity, fruit and vegetable consumption, discretionary salt use and self-reported diabetes or hypertension. Prevalences were determined according to education and social class. Inequalities were assessed using the slope index of inequality, and time trends were determined using linear regression.</p>
<p>Results There were moderate secular declines in the prevalence of smoking, excess alcohol consumption and physical inactivity. Smoking prevalence declined between 1995 and 2008 from 33.4% (95% CI 31.8% to 35.0%) to 29.9% (27.9% to 31.8%) for men and from 36.1% (34.5% to 37.8%) to 27.4% (25.5% to 29.3%) for women. Adverse trends in prevalence were noted for self-reported diabetes and hypertension. Over the four surveys, the diabetes prevalence increased from 1.9% (1.4% to 2.4%) to 3.6% (2.8% to 4.4%) for men and from 1.7% (1.2% to 2.1%) to 3.0% (2.3% to 3.7%) for women. Socio-economic inequalities were evident for almost all risk factors, irrespective of the measure used. These social gradients appeared to be maintained over the four surveys. An exception was self-reported diabetes where, although inequalities were small, the gradient increased over time. Alcohol consumption was unique in consistently showing an inverse gradient, especially for women.</p>
<p>Conclusions There has been only a moderate decline in behavioural cardiovascular risk factor prevalences since 1995, with increases in self-reported diabetes and hypertension. Adverse socio-economic gradients have remained unchanged. These findings could help explain the recent stagnation in coronary heart disease mortalities and persistence of related inequalities.</p>
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