2,876 research outputs found
Identifying Key Software Development Practices in the English-Speaking Caribbean Using the Nominal Group Technique
This paper explains how a simplified process improvement framework was developed with practices from the capability maturity model integration (CMMI) model using the nominal group technique (NGT). The NGT was used to generate consensus on key software process improvement practices that are likely to lead to the improvement of the quality of information systems (IS) in the English-speaking Caribbean (ESC). We present the approach taken, the results derived, and the benefits of using this approach. NGT sessions, involving 30 IS professionals were conducted in four ESC territories to reduce and finalize a list of key software development practices that would be more suitable for ESC nations to focus on
Ocular sequelae of congenital toxoplasmosis in Brazil compared with Europe
Toxoplasmic retinochoroiditis appears to be more severe in Brazil, where it is a leading cause of blindness, than in Europe, but direct comparisons are lacking. Evidence is accumulating that more virulent genotypes of Toxoplasma gondii predominate in South America
The Galaxy Population of Cluster RXJ0848+4453 at z=1.27
We present a study of the galaxy population in the cluster RXJ0848+4453 at
z=1.27, using deep HST NICMOS and WFPC2 images. We morphologically classify all
galaxies to K_s=20.6 that are covered by the HST imaging, and determine
photometric redshifts using deep ground based BRIzJK_s photometry. Of 22 likely
cluster members with morphological classifications, eleven (50%) are classified
as early-type galaxies, nine (41%) as spiral galaxies, and two (9%) as
``merger/peculiar''. At HST resolution the second brightest cluster galaxy is
resolved into a spectacular merger between three red galaxies of similar
luminosity, separated from each other by ~6 kpc, with an integrated magnitude
K=17.6 (~3 L* at z=1.27). The two most luminous early-type galaxies also show
evidence for recent or ongoing interactions. Mergers and interactions between
galaxies are possible because RXJ0848+4453 is not yet relaxed. The fraction of
early-type galaxies in our sample is similar to that in clusters at 0.5<z<1,
and consistent with a gradual decrease of the number of early-type galaxies in
clusters from z=0 to z=1.3. We find evidence that the color-magnitude relation
of the early-type galaxies is less steep than in the nearby Coma cluster. This
may indicate that the brightest early-type galaxies have young stellar
populations at z=1.27, but is also consistent with predictions of single age
``monolithic'' models with a galactic wind. The scatter in the color-magnitude
relation is ~0.04 in rest frame U-V, similar to that in clusters at 0<z<1.
Taken together, these results show that luminous early-type galaxies exist in
clusters at z~1.3, but that their number density may be smaller than in the
local Universe. Additional observations are needed to determine whether the
brightest early-type galaxies harbor young stellar populations.Comment: Accepted for publication in The Astrophysical Journal Letter
The Nascent Red Sequence at z~2
We present new constraints on the evolution of the early-type galaxy
color-magnitude relation (CMR) based on deep near-infrared imaging of a galaxy
protocluster at z=2.16 obtained using NICMOS on-board the Hubble Space
Telescope. This field contains a spectroscopically confirmed space-overdensity
of Lyman-alpha and H-alpha emitting galaxies which surrounds the powerful radio
galaxy MRC 1138-262. Using these NICMOS data we identify a significant
surface-overdensity (= 6.2x) of red J-H galaxies in the color-magnitude diagram
(when compared with deep NICMOS imaging from the HDF-N and UDF). The
optical-NIR colors of these prospective red-sequence galaxies indicate the
presence of on-going dust-obscured star-formation or recently formed (<~ 1.5
Gyr)stellar populations in a majority of the red galaxies. We measure the slope
and intrinsic scatter of the CMR for three different red galaxy samples
selected by a wide color cut, and using photometric redshifts both with and
without restrictions on rest-frame optical morphology. In all three cases both
the rest-frame slope and intrinsic color scatter are considerably higher
than corresponding values for lower redshift galaxy clusters. These results
suggest that while some relatively quiescent galaxies do exist in this
protocluster both the majority of the galaxy population and hence the
color-magnitude relation are still in the process of forming, as expected.Comment: 8 pages, 7 figures, accepted for publication in ApJ (to appear June
1, 2008, v679n2
Scaling Relations and Overabundance of Massive Clusters at z>~1 from Weak-Lensing Studies with HST
We present weak gravitational lensing analysis of 22 high-redshift (z >~1)
clusters based on Hubble Space Telescope images. Most clusters in our sample
provide significant lensing signals and are well detected in their
reconstructed two-dimensional mass maps. Combining the current results and our
previous weak-lensing studies of five other high-z clusters, we compare
gravitational lensing masses of these clusters with other observables. We
revisit the question whether the presence of the most massive clusters in our
sample is in tension with the current LambdaCDM structure formation paradigm.
We find that the lensing masses are tightly correlated with the gas
temperatures and establish, for the first time, the lensing mass-temperature
relation at z >~ 1. For the power law slope of the M-TX relation (M propto
T^{\alpha}), we obtain \alpha=1.54 +/- 0.23. This is consistent with the
theoretical self-similar prediction \alpha=3/2 and with the results previously
reported in the literature for much lower redshift samples. However, our
normalization is lower than the previous results by 20-30%, indicating that the
normalization in the M-TX relation might evolve. After correcting for Eddington
bias and updating the discovery area with a more conservative choice, we find
that the existence of the most massive clusters in our sample still provides a
tension with the current Lambda CDM model. The combined probability of finding
the four most massive clusters in this sample after marginalization over
current cosmological parameters is less than 1%.Comment: ApJ in press. See http://www.supernova.lbl.gov for additional
information pertaining to the HST Cluster SN Surve
P02.90. Equivalence of doctor interactions between Activator Methods and sham chiropractic protocols during an expertise-based randomized clinical trial
Protoclusters associated with z > 2 radio galaxies. I. Characteristics of high redshift protoclusters
[Abridged] We present the results of a large program conducted with the Very
Large Telescope and Keck telescope to search for forming clusters of galaxies
near powerful radio galaxies at 2.0 < z < 5.2. We obtained narrow- and
broad-band images of nine radio galaxies and their surroundings. The imaging
was used to select candidate Lyman alpha emitting galaxies in ~3x3 Mpc^2 areas
near the radio galaxies. A total of 337 candidate emitters were found with a
rest-frame Lyman alpha equivalent width of EW_0 > 15 A and Sigma = EW_0/Delta
EW_0 > 3. Follow-up spectroscopy confirmed 168 Lyman alpha emitters near eight
radio galaxies. The success rate of our selection procedure is 91%. At least
six of our eight fields are overdense in Lyman alpha emitters by a factor 3-5.
Also, the emitters show significant clustering in velocity space. In the
overdense fields, the width of the velocity distributions of the emitters is a
factor 2-5 smaller than the width of the narrow-band filters. Taken together,
we conclude that we have discovered six forming clusters of galaxies
(protoclusters). We estimate that roughly 75% of powerful (L_2.7GHz > 10^33
erg/s/Hz/sr) high redshift radio galaxies reside in a protocluster, with a
sizes of at least 1.75 Mpc. We estimate that the protoclusters have masses in
the range 2-9 x 10^14 Msun and they are likely to be progenitors of present-day
(massive) clusters of galaxies. For the first time, we have been able to
estimate the velocity dispersion of cluster progenitors from z~5 to ~2. The
velocity dispersion of the emitters increases with cosmic time, in agreement
with the dark matter velocity dispersion in numerical simulations of forming
massive clusters.Comment: 30 pages, 20 figures. Published in A&A. The article with high
resolution figures is available at
http://www.ast.cam.ac.uk/~venemans/research/datapaper/index.htm
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