1,556 research outputs found
Substructure within the SSA22 protocluster at
We present the results of a densely sampled spectroscopic survey of the SSA22
protocluster at . Our sample with Keck/LRIS spectroscopy
includes 106 Ly Emitters (LAEs) and 40 Lyman Break Galaxies (LBGs) at
. These galaxies are contained within the region in
which the protocluster was discovered, which also hosts the maximum galaxy
overdensity in the SSA22 region. The redshift histogram of our spectroscopic
sample reveals two distinct peaks, at (blue, 43 galaxies) and
(red, 103 galaxies). Furthermore, objects in the blue and red peaks
are segregated on the sky, with galaxies in the blue peak concentrating towards
the western half of the field. These results suggest that the blue and red
redshift peaks represent two distinct structures in physical space. Although
the double-peaked redshift histogram is traced in the same manner by LBGs and
LAEs, and brighter and fainter galaxies, we find that nine out of 10 X-ray AGNs
in SSA22, and all seven spectroscopically-confirmed giant Ly "blobs,"
reside in the red peak. We combine our dataset with sparsely sampled
spectroscopy from the literature over a significantly wider area, finding
preliminary evidence that the double-peaked structure in redshift space extends
beyond the region of our dense spectroscopic sampling. In order to fully
characterize the three-dimensional structure, dynamics, and evolution of
large-scale structure in the SSA22 overdensity, we require the measurement of
large samples of LAE and LBG redshifts over a significantly wider area, as well
as detailed comparisons with cosmological simulations of massive cluster
formation.Comment: 6 pages, 4 figures, Accepted to ApJ Letter
Effective education for children with autistic spectrum disorder:Perceptions of parents and professionals
Effects of network topology on the OpenAnswer’s Bayesian model of peer assessment
The paper investigates if and how the topology of the peer assessment network can affect the performance of the Bayesian model adopted in Ope
nAnswer. Performance is evaluated in terms of the comparison of predicted grades with actual teacher’s grades. The global network is built by interconnecting smaller subnetworks, one for each student, where intra subnetwork nodes represent student's characteristics, and peer assessment assignments make up inter subnetwork connections and determine evidence propagation. A possible subset of teacher graded answers is dynamically determined by suitable selec
tion and stop rules. The research questions addressed are: RQ1) “does the topology (diameter) of the network negatively influence the precision of predicted
grades?”̀ in the affirmative case, RQ2) “are we able to reduce the negative effects of high diameter networks through an appropriate choice of the subset of
students to be corrected by the teacher?” We show that RQ1) OpenAnswer is less effective on higher diameter topologies, RQ2) this can be avoided if the subset of corrected students is chosen considering the network topology
Understanding large-scale structure in the SSA22 protocluster region using cosmological simulations
We investigate the nature and evolution of large-scale structure within the
SSA22 protocluster region at using cosmological simulations. A
redshift histogram constructed from current spectroscopic observations of the
SSA22 protocluster reveals two separate peaks at (blue) and (red). Based on these data, we report updated overdensity and mass
calculations for the SSA22 protocluster. We find ,
for the blue and red peaks, respectively, and
for the entire region. These overdensities
correspond to masses of , , and
for the red, blue, and
total peaks, respectively. We use the Small MultiDark Planck (SMDPL) simulation
to identify comparably massive protoclusters, and uncover the
underlying structure and ultimate fate of the SSA22 protocluster. For this
analysis, we construct mock redshift histograms for each simulated
protocluster, quantitatively comparing them with the observed SSA22 data. We
find that the observed double-peaked structure in the SSA22 redshift histogram
corresponds not to a single coalescing cluster, but rather the proximity of a
protocluster and at least one cluster progenitor. Such associations in the SMDPL simulation are
easily understood within the framework of hierarchical clustering of dark
matter halos. We finally find that the opportunity to observe such a phenomenon
is incredibly rare, with an occurrence rate of 7.4h^3 \mbox{ Gpc}^{-3}.Comment: 13 pages, 8 figures, Accepted to Ap
Fit for Registration: A mixed methods study integrating data and theory to illuminate mentor decision making in the assessment of student competence in care settings.
Recommended from our members
The effects of landscape modifications on the long-term persistence of animal populations
Background: The effects of landscape modifications on the long-term persistence of wild animal populations is of crucial
importance to wildlife managers and conservation biologists, but obtaining experimental evidence using real landscapes is
usually impossible. To circumvent this problem we used individual-based models (IBMs) of interacting animals in
experimental modifications of a real Danish landscape. The models incorporate as much as possible of the behaviour and
ecology of four species with contrasting life-history characteristics: skylark (Alauda arvensis), vole (Microtus agrestis), a
ground beetle (Bembidion lampros) and a linyphiid spider (Erigone atra). This allows us to quantify the population
implications of experimental modifications of landscape configuration and composition.
Methodology/Principal Findings: Starting with a real agricultural landscape, we progressively reduced landscape
complexity by (i) homogenizing habitat patch shapes, (ii) randomizing the locations of the patches, and (iii) randomizing the
size of the patches. The first two steps increased landscape fragmentation. We assessed the effects of these manipulations
on the long-term persistence of animal populations by measuring equilibrium population sizes and time to recovery after
disturbance. Patch rearrangement and the presence of corridors had a large effect on the population dynamics of species
whose local success depends on the surrounding terrain. Landscape modifications that reduced population sizes increased
recovery times in the short-dispersing species, making small populations vulnerable to increasing disturbance. The species
that were most strongly affected by large disturbances fluctuated little in population sizes in years when no perturbations
took place.
Significance: Traditional approaches to the management and conservation of populations use either classical methods of
population analysis, which fail to adequately account for the spatial configurations of landscapes, or landscape ecology,
which accounts for landscape structure but has difficulty predicting the dynamics of populations living in them. Here we
show how realistic and replicable individual-based models can bridge the gap between non-spatial population theory and
non-dynamic landscape ecology. A major strength of the approach is its ability to identify population vulnerabilities not
detected by standard population viability analyses
Cloud condensation nucleus (CCN) behavior of organic aerosol particles generated by atomization of water and methanol solutions
Cloud condensation nucleus (CCN) experiments were carried out for malonic acid, succinic acid, oxalacetic acid, DL-malic acid, glutaric acid, DL-glutamic acid monohydrate, and adipic acid, using both water and methanol as atomization solvents, at three operating supersaturations (0.11%, 0.21%, and 0.32%) in the Caltech three-column CCN instrument (CCNC3). Predictions of CCN behavior for five of these compounds were made using the Aerosol Diameter Dependent Equilibrium Model (ADDEM). The experiments presented here expose important considerations associated with the laboratory measurement of the CCN behavior of organic compounds. Choice of atomization solvent results in significant differences in CCN activation for some of the compounds studied, which could result from residual solvent, particle morphology differences, and chemical reactions between the particle and gas phases. Also, significant changes in aerosol size distribution occurred after classification in a differential mobility analyzer (DMA) for malonic acid and glutaric acid. Filter analysis of adipic acid atomized from methanol solution indicates that gas-particle phase reactions may have taken place after atomization and before the methanol was removed from the sample gas stream. Careful consideration of these experimental issues is necessary for successful design and interpretation of laboratory CCN measurements
Herd-level risk factors associated with the presence of Phage type 21/28 E. coli O157 on Scottish cattle farms
<p>Background: E. coli O157 is a bacterial pathogen that is shed by cattle and can cause severe disease in humans. Phage type (PT) 21/28 is a subtype of E. coli O157 that is found across Scotland and is associated with particularly severe human morbidity.</p>
<p>Methods: A cross-sectional survey of Scottish cattle farms was conducted in the period Feb 2002-Feb 2004 to determine the prevalence of E. coli O157 in cattle herds. Data from 88 farms on which E. coli O157 was present were analysed using generalised linear mixed models to identify risk factors for the presence of PT 21/28 specifically.</p>
<p>Results: The analysis identified private water supply, and northerly farm location as risk factors for PT 21/28 presence. There was a significant association between the presence of PT 21/28 and an increased number of E. coli O157 positive pat samples from a farm, and PT 21/28 was significantly associated with larger E. coli O157 counts than non-PT 21/28 E. coli O157.</p>
<p>Conclusion: PT 21/28 has significant risk factors that distinguish it from other phage types of E. coli O157. This finding has implications for the control of E. coli O157 as a whole and suggests that control could be tailored to target the locally dominant PT.</p>
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