771 research outputs found
Comparing Population Density Estimation Techniques for Columbia Black-tailed Deer (Odocoileus Hemionus Columbianus): Fecal Standing Crop and Distance Sampling Methods
I estimated deer density and population size on Blakely Island, WA, using the fecal standing crop (FSC) method described by Martin et al. (2011). I compared the FSC method with a well established and broadly applicable estimation method, distance sampling. Additionally, architecture of a commonly browsed shrub, Ocean Spray (Holodiscus discolor), was measured as an indicator of browsing pressure. Fecal standing crop was estimated by counting pellet groups along 26, 100 x 2m line transects. Deer density was estimated using these data and the equation derived by Martin et al. (2011). Distance sampling consisted of recording perpendicular distance from transect line to deer, along 16 saw-toothed transects placed across Blakely Island. An average architecture value (ratio of plant diameter at 1 and 2m) of 0.223 indicated a high browsing pressure on the island, suggesting high deer density. Deer density based on FSC method was 1.72 (95% CI: 1.21 â 2.23) deer ha-1, whereas the concurrent deer density based on distance sampling was 0.23 (95% CI: 0.138 â 0.375) deer ha-1. Previous studies on Blakely using the latter method have shown deer density at â0.3 deer ha-1. As the FSC density estimation was much greater than that of distance sampling, and because it did not compare to other high-density island populations of deer, I concluded that this newer technique may not be comparable to well established methods. Further experimentation is necessary to parse out the possible confounding factors associated with the FSC technique
NGC 2992 in an X-ray high state observed by XMM: Response of the Relativistic Fe K Line to the Continuum
We present the analysis of an XMM observation of the Seyfert galaxy NGC 2992.
The source was found in its highest level of X-ray activity yet detected, a
factor higher in 2--10 keV flux than the historical minimum. NGC
2992 is known to exhibit X-ray flaring activity on timescales of days to weeks,
and the XMM data provide at least factor of better spectral resolution
in the Fe K band than any previously measured flaring X-ray state. We find that
there is a broad feature in the \sim 5-7 keV band which could be interpreted as
a relativistic Fe K emission line. Its flux appears to have increased
in tandem with the 2--10 keV continuum when compared to a previous Suzaku
observation when the continuum was a factor of lower than that during
the XMM observation. The XMM data are consistent with the general picture that
increased X-ray activity and corresponding changes in the Fe K line
emission occur in the innermost regions of the putative accretion disk. This
behavior contrasts with the behavior of other AGN in which the Fe K
line does not respond to variability in the X-ray.Comment: 30 pages, 6 figures, Accepted to Ap
The Distribution and Cosmic Density of Relativistic Iron Lines in Active Galactic Nuclei
X-ray observations of several active galactic nuclei show prominent iron
K-shell fluorescence lines that are sculpted due to special and general
relativistic effects. These observations are important because they probe the
space-time geometry close to distant black holes. However, the intrinsic
distribution of Fe line strengths in the cosmos has never been determined. This
uncertainty has contributed to the controversy surrounding the relativistic
interpretation of the emission feature. Now, by making use of the latest
multi-wavelength data, we show theoretical predictions of the cosmic density of
relativistic Fe lines as a function of their equivalent width and line flux. We
are able to show unequivocally that the most common relativistic iron lines in
the universe will be produced by neutral iron fluorescence in Seyfert galaxies
and have equivalent widths < 100 eV. Thus, the handful of very intense lines
that have been discovered are just the bright end of a distribution of line
strengths. In addition to validating the current observations, the predicted
distributions can be used for planning future surveys of relativistic Fe lines.
Finally, the predicted sky density of equivalent widths indicate that the X-ray
source in AGNs can not, on average, lie on the axis of the black hole.Comment: 12 pages, 3 figures, accepted by ApJ Letter
Classification of Liver Trauma
The classification of liver injuries is important for clinical practice, clinical research and quality assurance activities. The Organ Injury Scaling (OIS) Committee of the American Association for the Surgery of
Trauma proposed the OIS for liver trauma in 1989. The purpose ofthe present study was to apply this scale
to a cohort ofliver trauma patients managed at a single Canadian trauma centre from January 1987 to June
1992.170 study patients were identified and reviewed. The mean age was 30, with 69% male and a mean ISS
of 33.90% had a blunt mechanism ofinjury. The 170 patients were categorized into the 60IS grades ofliver
injury. The number of units of blood transfused, the magnitude of the operative treatment required, the
liver-related complications and the liver-related mortality correlated well with the OIS grade. The OIS
grade was unable to predict the need for laparotomy or the length of stay in hospital. We conclude that the
OIS is a useful, practical and important tool for the categorization of liver injuries, and it may prove to be
the universally accepted classification scheme in liver trauma
A Correlation Between the Ionization State of the Inner Accretion Disk and the Eddington Ratio of Active Galactic Nuclei
X-ray reflection features observed from the innermost regions of accretion
disks in Active Galactic Nuclei (AGNs) allow important tests of accretion
theory. In recent years it has been possible to use the Fe K line and
reflection continuum to parametrize the ionization state of the irradiated
inner accretion disk. Here, we collect 10 measurements of xi, the disk
ionization parameter, from 8 AGNs with strong evidence for reflection from the
inner accretion disk and good black hole mass estimates. We find strong
statistical evidence (98.56% confidence) for a nearly linear correlation
between xi and the AGN Eddington ratio. Moreover, such a correlation is
predicted by a simple application of alpha-disk accretion theory, albeit with a
stronger dependence on the Eddington ratio. The theory shows that there will be
intrinsic scatter to any correlation as a result of different black hole spins
and radii of reflection. There are several possibilities to soften the
predicted dependence on the Eddington ratio to allow a closer agreement with
the observed correlation, but the current data does not allow for an unique
explanation. The correlation can be used to estimate that MCG-6-30-15 should
have a highly ionized inner accretion disk, which would imply a black hole spin
of ~0.8. Additional measurements of xi from a larger sample of AGNs are needed
to confirm the existence of this correlation, and will allow investigation of
the accretion disk/corona interaction in the inner regions of accretion disks.Comment: 21 pages, 2 figures, accepted by Ap
Revealing the X-ray Variability of AGN with Principal Component Analysis
We analyse a sample of 26 active galactic nuclei with deep XMM-Newton
observations, using principal component analysis (PCA) to find model
independent spectra of the different variable components. In total, we identify
at least 12 qualitatively different patterns of spectral variability, involving
several different mechanisms, including five sources which show evidence of
variable relativistic reflection (MCG-6-30-15, NGC 4051, 1H 0707-495, NGC 3516
and Mrk 766) and three which show evidence of varying partial covering neutral
absorption (NGC 4395, NGC 1365, and NGC 4151). In over half of the sources
studied, the variability is dominated by changes in a power law continuum, both
in terms of changes in flux and power law index, which could be produced by
propagating fluctuations within the corona. Simulations are used to find unique
predictions for different physical models, and we then attempt to qualitatively
match the results from the simulations to the behaviour observed in the real
data. We are able to explain a large proportion of the variability in these
sources using simple models of spectral variability, but more complex models
may be needed for the remainder. We have begun the process of building up a
library of different principal components, so that spectral variability in AGN
can quickly be matched to physical processes. We show that PCA can be an
extremely powerful tool for distinguishing different patterns of variability in
AGN, and that it can be used effectively on the large amounts of high-quality
archival data available from the current generation of X-ray telescopes.Comment: 25 pages, 27 figures, accepted to MNRAS. Analysis code available on
request to lead author. Edit: Rogue table remove
On the Prospect of Constraining Black-Hole Spin Through X-ray Spectroscopy of Hotspots
Future X-ray instrumentation is expected to allow us to significantly improve
the constraints derivedfrom the Fe K lines in AGN, such as the black-hole
angular momentum (spin) and the inclination angle of the putative accretion
disk. We consider the possibility that measurements of the persistent,
time-averaged Fe K line emission from the disk could be supplemented by the
observation of a localized flare, or "hotspot", orbiting close to the black
hole. Although observationally challenging, such measurements would recover
some of the information loss that is inherent to the radially-integrated line
profiles. We present calculations for this scenario to assess the extent to
which, in principle, black-hole spin may be measured. We quantify the
feasibility of this approach using realistic assumptions about likely
measurement uncertainties.Comment: 7 pages, 7 figures. Accepted for publication in Ap
A Hard Look at NGC 5347: Revealing a Nearby Compton-thick AGN
Current measurements show that the observed fraction of Compton-thick (CT) active galactic nuclei (AGN) is smaller than the expected values needed to explain the cosmic X-ray background. Prior fits to the X-ray spectrum of the nearby Seyfert-2 galaxy NGC 5347 (z = 0.00792, D = 35.5 Mpc ) have alternately suggested a CT and Compton-thin source. Combining archival data from Suzaku, Chandra, andâmost importantlyânew data from NuSTAR, ... See full text for complete abstrac
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