448 research outputs found
B3 0003+387: AGN Marked Large-Scale Structure at z=1.47?
We present evidence for a significant overdensity of red galaxies, as much as
a factor of 14 over comparable field samples, in the field of the z=1.47 radio
galaxy B3 0003+387. The colors and luminosities of the brightest red galaxies
are consistent with their being at z>0.8. The radio galaxy and one of the red
galaxies are separated by 5" and show some evidence of a possible interaction.
However, the red galaxies do not show any strong clustering around the radio
galaxy nor around any of the brighter red galaxies. The data suggest that we
are looking at a wall or sheet of galaxies, possibly associated with the radio
galaxy at z=1.47. Spectroscopic redshifts of these red galaxies will be
necessary to confirm this large-scale structure.Comment: 19 pages, 7 figures, LaTeX2e/AASTeX v5.0.2. The full photometric
catalog is included as a separate deluxetable file. To appear in the
Astronomical Journal (~Nov 00
Exploring the views of students on the use of Facebook in university teaching and learning
Facebook use among students is almost ubiquitous; however, its use for formal academic purposes remains contested. Through an online survey monitoring student use of module Facebook pages and focus groups, this study explores studentsâ current academic uses of Facebook and their
views on using Facebook within university modules. Students reported using Facebook for academic purposes, notably peerâpeer communication around group work and assessment â a use not always conceptualised by students as learning. Focus groups revealed that students are not ready or equipped for the collaborative style of learning envisaged by the tutor and see Facebook as their personal domain, within which they
will discuss academic topics where they see a strong relevance and purpose, notably in connection with assessment. Students use Facebook for their own mutually deïŹned purposes and a change in student mind- and skill-sets is required to appropriate the collaborative learning beneïŹts of Facebook in formal educational contexts
The Deficit of Distant Galaxy Clusters in the RIXOS X-ray Survey
Clusters of galaxies are the largest gravitationally bound systems and
therefore provide an important way of studying the formation and evolution of
the large scale structure of the Universe. Cluster evolution can be inferred
from observations of the X-ray emission of the gas in distant clusters, but
interpreting these data is not straightforward. In a simplified view, clusters
grow from perturbations in the matter distribution: their intracluster gas is
compressed and shock-heated by the gravitational collapse. The resulting
X-ray emission is determined by the hydrostatic equilibrium of the gas in the
changing gravitational potential. However, if processes such as radiative
cooling or pre-collapse heating of the gas are important, then the X-ray
evolution will be strongly influenced by the thermal history of the gas. Here
we present the first results from a faint flux-limited sample of X-ray selected
clusters compiled as part of the ROSAT International X-ray and Optical Survey
(RIXOS). Very few distant clusters have been identified. Most importantly,
their redshift distribution appears to be inconsistent with simple models based
on the evolution of the gravitational potential. Our results suggest that
radiative cooling or non-gravitational heating of the intracluster gas must
play an important role in the evolution of clusters.Comment: uuencoded compressed postscript. The preprint is also available at
http://www.ast.cam.ac.uk/preprint/PrePrint.htm
A comparison between magnetic resonance angiography at 3 teslas (time-of-flight and contrast-enhanced) and flat-panel digital subtraction angiography in the assessment of embolized brain aneurysms
PURPOSE: To compare the time-of-flight and contrast-enhanced- magnetic resonance angiography techniques in a 3 Tesla magnetic resonance unit with digital subtraction angiography with the latest flat-panel technology and 3D reconstruction in the evaluation of embolized cerebral aneurysms. INTRODUCTION: Many embolized aneurysms are subject to a recurrence of intra-aneurismal filling. Traditionally, imaging surveillance of coiled aneurysms has consisted of repeated digital subtraction angiography. However, this method has a small but significant risk of neurological complications, and many authors have advocated the use of noninvasive imaging methods for the surveillance of embolized aneurysms. METHODS: Forty-three aneurysms in 30 patients were studied consecutively between November 2009 and May 2010. Two interventional neuroradiologists rated the time-of-flight-magnetic resonance angiography, the contrast-enhanced-magnetic resonance angiography, and finally the digital subtraction angiography, first independently and then in consensus. The status of aneurysm occlusion was assessed according to the Raymond scale, which indicates the level of recanalization according to degrees: Class 1: excluded aneurysm; Class 2: persistence of a residual neck; Class 3: persistence of a residual aneurysm. The agreement among the analyses was assessed by applying the Kappa statistic. RESULTS: Inter-observer agreement was excellent for both methods (K = 0.93; 95 % CI: 0.84-1). Inter-technical agreement was almost perfect between time-of-flight-magnetic resonance angiography and digital subtraction angiography (K = 0.98; 95 % CI: 0.93-1) and between time-of-flight-magnetic resonance angiography and contrast-enhanced-magnetic resonance angiography (K = 0.98; 95% CI: 0.93-1). Disagreement occurred in only one case (2.3%), which was classified as Class I by time-of-flight-magnetic resonance angiography and Class II by digital subtraction angiography. The agreement between contrast-enhanced-magnetic resonance angiography and digital subtraction angiography was perfect (K = 1; 95% CI: 1-1). In three patients, in-stent stenosis was identified by magnetic resonance angiography but not confirmed by digital subtraction angiography. CONCLUSION: Digital subtraction angiography and both 3T magnetic resonance angiography techniques have excellent reproducibility for the assessment of aneurysms embolized exclusively with coils. In those cases also treated with stent remodeling, digital subtraction angiography may still be necessary to confirm eventual parent artery stenosis, as identified by magnetic resonance angiography
Morphological Evolution of Galaxies
We simulate the growth of large-scale structure in the universe using a
N-body code. By combining these simulations with a Monte-Carlo method, we
generate galaxy distributions at present that reproduces the observed
morphology-density relation, with most ellipticals concentrated in the densest
regions. By "tying" each galaxy to its nearest particle, we trace the
trajectory of that galaxy back in time. This enables us to reconstruct the
distribution of galaxies at high redshift, and the trajectory of each galaxy
from its formation epoch to the present. Our goal is to determine whether the
morphological type of galaxies is primarily determined by the initial
conditions in which these galaxies form, or by evolutionary processes occurring
later. We compare the environment in which galaxies are at the epoch of galaxy
formation (z=3) and at the present. Making the null hypothesis that
morphological types do not evolve, we compare the galaxies that form in low
density environments but end up later in high density environments to the ones
that form also in low density environment but remain in low density
environment. The first group contains a larger proportion of E and S0 galaxies
than the second group. We assume that the galaxy formation process cannot
distinguish a low density environment that will always remain low density from
one that will eventually become high density. Hence, these results force us to
discard the null hypothesis of no morphological evolution. Our study suggests
that 75% of the E and S0 galaxies observed at present formed as such, while the
remaining 25% formed as spirals, and underwent morphological evolution. We
conclude that most galaxies did not undergo morphological evolution, but a
non-negligible fraction did.Comment: 29 pages (AAS latex) + 7 figures (postscript) combined in one gzip-ed
tar file. Submitted to The Astrophysical Journal (Dec 1996
The X-ray properties of optically-selected z>0.6 clusters in the ESO Distant Cluster Survey
We present XMM-Newton observations of three optically-selected z > 0.6
clusters from the ESO Distant Cluster Survey (EDisCS), comprising the first
results of a planned X-ray survey of the full EDisCS high-redshift sample. The
EDisCS clusters were identified in the Las Campanas Distant Cluster Survey as
surface brightness fluctuations in the optical sky and their masses and galaxy
populations are well described by extensive photometric and spectroscopic
observations. We detect two of the three clusters in the X-ray and place a firm
upper limit on diffuse emission in the third cluster field. We are able to
constrain the X-ray luminosity and temperature of the detected clusters and
estimate their masses. We find the X-ray properties of the detected EDisCS
clusters are similar to those of X-ray-selected clusters of comparable mass and
-- unlike other high-redshift, optically-selected clusters -- are consistent
with the T - sigma and L_x - sigma relations determined from X-ray selected
clusters at low redshift. The X-ray determined mass estimates are generally
consistent with those derived from weak lensing and spectroscopic analyses.
These preliminary results suggest that the novel method of optical selection
used to construct the EDisCS catalog may, like selection by X-ray luminosity,
be well-suited for identification of relaxed, high-redshift clusters whose
intracluster medium is in place and stable by z ~ 0.8.Comment: MNRAS accepted. 21 pages text, 20 figures, 10 pages tabular data.
Version with full resolution figures available at
http://www.roe.ac.uk/~cocj/ediscs_fullres.htm
The Color-Magnitude Effect in Early-Type Cluster Galaxies
We present the analysis of the color-magnitude relation (CMR) for a sample of
57 X-ray detected Abell clusters within the redshift interval 0.02 <= z <=
0.18. We use the B-R vs R color-magnitude plane to establish that the CMR is
present in all our low-redshift clusters and can be parameterized by a single
straight line.We find that the CMRs for this large cluster sample of different
richness and cluster types are consistent with having universal properties. The
k-corrected color of the individual CMRs in the sample at a fixed absolute
magnitude have a small intrinsic dispersion of ~0.05 mag. The slope of the CMR
is consistent with being the same for all clusters, with the variations
entirely accountable by filter band shifting effects. We determine the mean of
the dispersion of the 57 CMRs to be 0.074 mag, with a small rms scatter of
0.026 mag. However, a modest amount of the dispersion arises from photometric
measurement errors and possible background cluster superpositions; and the
derived mean dispersion is an upper limit. Models which explain the CMR in
terms of metallicity and passive evolution can naturally reproduce the observed
behavior of the CMR in this paper. The observed properties of the CMR are
consistent with models in which the last episode of significant star formation
in cluster early-type galaxies occurred significantly more than ~3 Gyr ago, and
that the core set of early-type galaxies in clusters were formed more than 7
Gyr ago. (abridged)Comment: Accepted ApJ, 17 pages, 4 figures (high-res fig 1 available in ApJ
version
Prevalence of Disorders Recorded in Dogs Attending Primary-Care Veterinary Practices in England
Purebred dog health is thought to be compromised by an increasing occurence of inherited diseases but inadequate prevalence data on common disorders have hampered efforts to prioritise health reforms. Analysis of primary veterinary practice clinical data has been proposed for reliable estimation of disorder prevalence in dogs. Electronic patient record (EPR) data were collected on 148,741 dogs attending 93 clinics across central and south-eastern England. Analysis in detail of a random sample of EPRs relating to 3,884 dogs from 89 clinics identified the most frequently recorded disorders as otitis externa (prevalence 10.2%, 95% CI: 9.1-11.3), periodontal disease (9.3%, 95% CI: 8.3-10.3) and anal sac impaction (7.1%, 95% CI: 6.1-8.1). Using syndromic classification, the most prevalent body location affected was the head-and-neck (32.8%, 95% CI: 30.7-34.9), the most prevalent organ system affected was the integument (36.3%, 95% CI: 33.9-38.6) and the most prevalent pathophysiologic process diagnosed was inflammation (32.1%, 95% CI: 29.8-34.3). Among the twenty most-frequently recorded disorders, purebred dogs had a significantly higher prevalence compared with crossbreds for three: otitis externa (Pâ=â0.001), obesity (Pâ=â0.006) and skin mass lesion (Pâ=â0.033), and popular breeds differed significantly from each other in their prevalence for five: periodontal disease (Pâ=â0.002), overgrown nails (Pâ=â0.004), degenerative joint disease (Pâ=â0.005), obesity (Pâ=â0.001) and lipoma (Pâ=â0.003). These results fill a crucial data gap in disorder prevalence information and assist with disorder prioritisation. The results suggest that, for maximal impact, breeding reforms should target commonly-diagnosed complex disorders that are amenable to genetic improvement and should place special focus on at-risk breeds. Future studies evaluating disorder severity and duration will augment the usefulness of the disorder prevalence information reported herein
Plasma concentration of Propionibacterium acnes antibodies and prostate cancer risk: results from an Australian population-based caseâcontrol study
Background:Recent studies in prostatic tissue suggest that Propionibacterium acnes (P. acnes), a bacterium associated with acne that normally lives on the skin, is the most prevalent bacterium in the prostate and in men with benign prostatic hyperplasia. Its prevalence is higher in samples from patients subsequently diagnosed with prostate cancer. The aim of our study was to test whether circulating levels of P. acnes antibodies are associated with prostate cancer risk and tumour characteristics using plasma samples from a population-based case-control study.Methods:We measured plasma concentration of P. acnes antibodies for 809 cases and 584 controls using a recently developed ELISA assay. We compared antibody titres between cases and controls using unconditional logistic regression adjusted for batch and variables associated with the study design (i.e., age, year of selection and centre). The primary analysis included P. acnes titres in the model as a dichotomous variable using the median value for controls as the cut-off value.Results:P. acnes antibody titres for both cases and controls ranged from 1: 16 (i.e., low concentration) to 1: 65 536 (i.e., high concentration; median value1: 1024). The odds ratio for prostate cancer associated with titres at or above the median value was 0.73 (95% CI 0.58-0.91, P0.005). The association appeared to be particularly strong for advanced prostate cancer (AJCC Stage grouping III-IV) for which the odds ratio was 0.59 (95% CI 0.43-0.81, P0.001) but there was insufficient evidence that the association differed by tumour stage (p heterogeneity0.07).Conclusion: These results need to be confirmed in prospective studies but they are consistent with the hypothesis that P. acnes has a role in prostate cancer. © 2010 Cancer Research UK All rights reserved
The Gemini Deep Deep Survey. VII. The Redshift Evolution of the Mass-Metallicity Relation
We have investigated the mass-metallicity (M-Z) relation using galaxies at
0.4<z<1.0 from the Gemini Deep Deep Survey and Canada-France Redshift Survey.
Deep K and z' band photometry allowed us to measure stellar masses for 69
galaxies. From a subsample of 56 galaxies, for which metallicity of the
interstellar medium is also measured, we identified a strong correlation
between mass and metallicity, for the first time in the distant Universe. This
was possible because of the larger base line spanned by the sample in terms of
metallicity (a factor of 7) and mass (a factor of 400) than in previous works.
This correlation is much stronger and tighter than the luminosity-metallicity,
confirming that stellar mass is a more meaningful physical parameter than
luminosity. We find clear evidence for temporal evolution in the M-Z relation
in the sense that at a given mass, a galaxy at z=0.7 tends to have lower
metallicity than a local galaxy of similar mass. We use the z=0.1 SDSS M-Z
relation, and a small sample of z=2.3 Lyman break galaxies with known mass and
metallicity, to propose an empirical redshift-dependent M-Z relation, according
to which the stellar mass and metallicity in small galaxies evolve for a longer
time than in massive galaxies. This relation predicts that the generally metal
poor damped Lyman-alpha galaxies have stellar masses of the order of 10^8.8
M_sun (with a dispersion of 0.7 dex) all the way from z=0.2 to z=4. The
observed redshift evolution of the M-Z relation can be reproduced remarkably
well by a simple closed-box model where the key assumption is an e-folding time
for star formation which is higher or, in other words, a period of star
formation that lasts longer in less massive galaxies than in more massive
galaxies. Such a picture supports the downsizing scenario for galaxy formation.Comment: ApJ in pres
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