1,667 research outputs found
Water Quality at the Inlet to the St. Lawrence River, 1977 to 1983
Daily nutrients analyses and weekly major ions and trace metals analyses have been performed since 1977 on water samples collected in the south channel of the St. Lawrence River at Wolfe Island. This report presents the results of the first seven years of this program.
Data analyses showed that pH and total phosphorus were underestimated. Calcium carbonate precipitation is suspected to occur almost every year in August or September. Most of the major ions have decreased, especially chloride and sodium. All trace metal data were below the objectives of the International Joint Commission in 90% of the cases or more.
The Wolfe Island station was found to be a good tool for following the general trend of the main water quality parameters. More attention, however, should be focused on the problems of shipping delays and containers
Tyloses Structure
A tylosis is an outgrowth from vertical or ray parenchyma cells through bordered pits into the lumen of a xylem vessel element. This study reports additional information on the ontogeny of tyloses, formation of the developing tylosis wall, and chemical composition of the tylosis wall. The development and structure of tyloses in several species of oak (Quercus) were studied with the transmitting and scanning electron microscopes. The tylosis wall was layered with a complement of wall layers found in xylem elements. Cellulose and lignin were constituents of the tylosis wall
Clostridium difficile infection among veterans health administration patients
OBJECTIVETo report on the prevalence and incidence of Clostridium difficile infection (CDI) from 2009 to 2013 among Veterans Healthcare Administration patientsDESIGNA retrospective descriptive analysis of data extracted from a large electronic medical record (EMR) databaseSETTINGData were acquired from VHA healthcare records from 2009 to 2013 that included outpatient clinical visits, long-term care, and hospitalized care as well as pharmacy and laboratory information.RESULTSIn 2009, there were 10,207 CDI episodes, and in 2013, there were 12,143 CDI episodes, an increase of 19.0%. The overall CDI rate increased by 8.4% from 193 episodes per 100,000 patient years in 2009 to 209 episodes per 100,000 patient years in 2013. Of the CDI episodes identified in 2009, 58% were identified during a hospitalization, and 42% were identified in an outpatient setting. In 2013, 44% of the CDI episodes were identified in an outpatient setting.CONCLUSIONThis is one of the largest studies that has utilized timely EMR data to describe the current CDI epidemiology at the VHA. Despite an aging population with greater burden of comorbidity than the general US population, our data show that VHA CDI rates stabilized between 2011 and 2013 following increases likely attributable to the introduction of the more sensitive nucleic acid amplification tests (NAATs). The findings in this report will help establish an accurate benchmark against which both current and future VA CDI prevention initiatives can be measured.Infect. Control Hosp. Epidemiol. 2015;36(9):1038–1045</jats:sec
Characterisation of spatial network-like patterns from junctions' geometry
We propose a new method for quantitative characterization of spatial
network-like patterns with loops, such as surface fracture patterns, leaf vein
networks and patterns of urban streets. Such patterns are not well
characterized by purely topological estimators: also patterns that both look
different and result from different morphogenetic processes can have similar
topology. A local geometric cue -the angles formed by the different branches at
junctions- can complement topological information and allow to quantify the
large scale spatial coherence of the pattern. For patterns that grow over time,
such as fracture lines on the surface of ceramics, the rank assigned by our
method to each individual segment of the pattern approximates the order of
appearance of that segment. We apply the method to various network-like
patterns and we find a continuous but sharp dichotomy between two classes of
spatial networks: hierarchical and homogeneous. The first class results from a
sequential growth process and presents large scale organization, the latter
presents local, but not global organization.Comment: version 2, 14 page
Spatial and temporal characterization of a Bessel beam produced using a conical mirror
We experimentally analyze a Bessel beam produced with a conical mirror,
paying particular attention to its superluminal and diffraction-free
properties. We spatially characterized the beam in the radial and on-axis
dimensions, and verified that the central peak does not spread over a
propagation distance of 73 cm. In addition, we measured the superluminal phase
and group velocities of the beam in free space. Both spatial and temporal
measurements show good agreement with the theoretical predictions.Comment: 5 pages, 6 figure
Interactive effects of low molecular weight carbon compounds on N2O emissions
Low molecular weight carbon (C) compounds in hotspots such as the rhizosphere can greatly affect nitrate reduction processes. Towards a better prediction of N2O emission from denitrification, we are still lacking understanding of responses to the supply of complex C compound mixtures such as rhizodeposits versus the often examined response to individually amended C compounds. In a laboratory study, we applied three C compounds, glucose, citric acid and glutamic acid, individually or as a three-compound mixture to 14NH415NO3 amended soil at 80% water-filled pore space. For the individual C compound treatments, the substrateswere enriched in 13C-C. The mixture was enriched in 13C-C either in all constituent compounds or in one of the compounds only, resulting in four different treatments. This set-up enabled quantification of the utilization of each compound for heterotrophic respiration when applied individually and in combination, and for this to be related to the dynamics of 15N-NO3- reduction to 15N-N2O. The total 15N-N2O emission from the compound mixture over 10 days was similar to the total emission predicted from the average of the individual compound treatments This could suggest potential predictability of denitrification responses to complex mixtures of C based on knowledge of its constituents. However, immediate and simultaneous peaks of 15N-N2O and 13C-CO2 fluxes from the compound mixture contrasted with observed delays in 15N-N2O and 13C-CO2 fluxes when the compounds had been applied individually. Moreover, relative contributions of the C compounds to 13C-CO2 respiration from the compound mixture were different from the predicted contributions based on their individual application. While contributions of glutamic acid-C and citric acid-C to respiration in mixture during peak 15N-N2O emission were increased, glucose utilization in the mixture treatment was significantly lower. These findings give a glimpse of the challenges we are facing when trying to predict nitrate reduction occurring in the rhizosphere where interactions between C compounds and the soil matrix, as well as within the wider heterotrophic community, determine process rates. Given that most of our understanding of the role of C in regulating nitrate reduction, is informed from single compound studies, we require more evidence on the effects and innate interactions of compound mixtures to be able to predict responses to C sources
An XMM-Newton Observation of the Local Bubble Using a Shadowing Filament in the Southern Galactic Hemisphere
We present an analysis of the X-ray spectrum of the Local Bubble, obtained by
simultaneously analyzing spectra from two XMM-Newton pointings on and off an
absorbing filament in the Southern galactic hemisphere (b ~ -45 deg). We use
the difference in the Galactic column density in these two directions to deduce
the contributions of the unabsorbed foreground emission due to the Local
Bubble, and the absorbed emission from the Galactic halo and the extragalactic
background. We find the Local Bubble emission is consistent with emission from
a plasma in collisional ionization equilibrium with a temperature and an emission measure of 0.018 cm^{-6} pc. Our
measured temperature is in good agreement with values obtained from ROSAT
All-Sky Survey data, but is lower than that measured by other recent XMM-Newton
observations of the Local Bubble, which find
(although for some of these observations it is possible that the foreground
emission is contaminated by non-Local Bubble emission from Loop I). The higher
temperature observed towards other directions is inconsistent with our data,
when combined with a FUSE measurement of the Galactic halo O VI intensity. This
therefore suggests that the Local Bubble is thermally anisotropic.
Our data are unable to rule out a non-equilibrium model in which the plasma
is underionized. However, an overionized recombining plasma model, while
observationally acceptable for certain densities and temperatures, generally
gives an implausibly young age for the Local Bubble (\la 6 \times 10^5 yr).Comment: Accepted for publication in the Astrophysical Journal. 16 pages, 9
figure
X-ray Spectroscopy of the Virgo Cluster out to the Virial Radius
We present results from the analysis of a mosaic of thirteen XMM-Newton
pointings covering the Virgo Cluster from its center northwards out to a radius
r~1.2 Mpc (~4.5 degrees), reaching the virial radius and beyond. This is the
first time that the properties of a modestly sized (M_vir~1.4e14 M_sun, kT~2.3
keV), dynamically young cluster have been studied out to the virial radius. The
density profile of the cluster can be described by a surprisingly shallow
power-law with index 1.21+/-0.12. In the radial range of 0.3r_vir<r<r_vir, the
best fit temperature drops by roughly 60 per cent. Within a radius r<450 kpc,
the entropy profile has an approximate power-law form with index 1.1, as
expected for gravitationally collapsed gas in hydrostatic equilibrium. Beyond
r~450 kpc, however, the temperature and metallicity drop abruptly, and the
entropy profile becomes flatter, staying consistently below the expected value
by a factor of 2-2.5. The most likely explanation for the unusually shallow
density profile and the flattening of entropy at large radius is clumping in
the ICM. Our data provide direct observational evidence that the ICM is
enriched by metals all the way to r_200 to at least Z=0.1 Solar.Comment: Accepted for publication in MNRA
Diffuse Thermal X-Ray Emission in the Core of the Young Massive Cluster Westerlund 1
We present an analysis of the diffuse hard X-ray emission in the core of the
young massive Galactic cluster Westerlund 1 based on a 48 ks XMM-Newton
observation. Chandra results for the diffuse X-ray emission have indicated a
soft thermal component together with a hard component that could be either
thermal or non-thermal. We seek to resolve this ambiguity regarding the hard
component exploiting the higher sensitivity of XMM-Newton to diffuse emission.
Our new X-ray spectra from the central (2' radius) diffuse emission are found
to exhibit He-like Fe 6.7 keV line emission, demonstrating that the hard
emission in the cluster core is predominantly thermal in origin. Potential
sources of this hard component are reviewed, namely an unresolved Pre-Main
Sequence population, a thermalized cluster wind and Supernova Remnants
interacting with stellar winds. We find that the thermalized cluster wind
likely contributes the majority of the hard emission with some contribution
from the Pre-Main Sequence population. It is unlikely that Supernova Remnants
are contributing significantly to the Wd1 diffuse emission at the current
epoch
Cold fronts and multi-temperature structures in the core of Abell 2052
The physics of the coolest phases in the hot Intra-Cluster Medium (ICM) of
clusters of galaxies is yet to be fully unveiled. X-ray cavities blown by the
central Active Galactic Nucleus (AGN) contain enough energy to heat the
surrounding gas and stop cooling, but locally blobs or filaments of gas appear
to be able to cool to low temperatures of 10^4 K. In X-rays, however, gas with
temperatures lower than 0.5 keV is not observed. Using a deep XMM-Newton
observation of the cluster of galaxies Abell 2052, we derive 2D maps of the
temperature, entropy, and iron abundance in the core region. About 130 kpc
South-West of the central galaxy, we discover a discontinuity in the surface
brightness of the hot gas which is consistent with a cold front. Interestingly,
the iron abundance jumps from ~0.75 to ~0.5 across the front. In a smaller
region to the North-West of the central galaxy we find a relatively high
contribution of cool 0.5 keV gas, but no X-ray emitting gas is detected below
that temperature. However, the region appears to be associated with much cooler
H-alpha filaments in the optical waveband. The elliptical shape of the cold
front in the SW of the cluster suggests that the front is caused by sloshing of
the hot gas in the clusters gravitational potential. This effect is probably an
important mechanism to transport metals from the core region to the outer parts
of the cluster. The smooth temperature profile across the sharp jump in the
metalicity indicates the presence of heat conduction and the lack of mixing
across the discontinuity. The cool blob of gas NW of the central galaxy was
probably pushed away from the core and squeezed by the adjacent bubble, where
it can cool efficiently and relatively undisturbed by the AGN. Shock induced
mixing between the two phases may cause the 0.5 keV gas to cool non-radiatively
and explain our non-detection of gas below 0.5 keV.Comment: 11 pages, 9 figures, A&A, in pres
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