42 research outputs found
Investigations of solutions of Einstein's field equations close to lambda-Taub-NUT
We present investigations of a class of solutions of Einstein's field
equations close to the family of lambda-Taub-NUT spacetimes. The studies are
done using a numerical code introduced by the author elsewhere. One of the main
technical complication is due to the S3-topology of the Cauchy surfaces.
Complementing these numerical results with heuristic arguments, we are able to
yield some first insights into the strong cosmic censorship issue and the
conjectures by Belinskii, Khalatnikov, and Lifschitz in this class of
spacetimes. In particular, the current investigations suggest that strong
cosmic censorship holds in this class. We further identify open issues in our
current approach and point to future research projects.Comment: 24 pages, 12 figures, uses psfrag and hyperref; replaced with
published version, only minor corrections of typos and reference
New Quasars Detected via Variability in the QUEST1 Survey
By observing the high galactic latitude equatorial sky in drift scan mode
with the QUEST (QUasar Equatorial Survey Team) Phase 1 camera, multi-bandpass
photometry on a large strip of sky, resolved over a large range of time scales
(from hourly to biennially) has been collected. A robust method of ensemble
photometry revealed those objects within the scan region that fluctuate in
brightness at a statistically significant level. Subsequent spectroscopic
observations of a subset of those varying objects easily discriminated the
quasars from stars. For a 13-month time scale, 38% of the previously known
quasars within the scan region were seen to vary in brightness and subsequent
spectroscopic observation revealed that approximately 7% of all variable
objects in the scan region are quasars. Increasing the time baseline to 26
months increased the percentage of previously known quasars which vary to 61%
and confirmed via spectroscopy that 7% of the variable objects in the region
are quasars. This reinforces previously published trends and encourages
additional and ongoing synoptic searches for new quasars and their subsequent
analysis. During two spectroscopic observing campaigns, a total of 30 quasars
were confirmed, 11 of which are new discoveries and 19 of which were determined
to be previously known. Using the previously cataloged quasars as a benchmark,
we have found it possible to better optimize future variability surveys. This
paper reports on the subset of variable objects which were spectroscopically
confirmed as quasars.Comment: 22 pages, 3 figures, 4 tables. ApJ, submitted revised version: 19
pages, 4 figures, 2 tables, added clarifications, fixed typos, accepted by
ApJ 24 Jan 200
The PAU Survey: a new constraint on galaxy formation models using the observed colour redshift relation
We use the GALFORM semi-analytical galaxy formation model implemented in the Planck Millennium N-body simulation to build a mock galaxy catalogue on an observer’s past lightcone. The mass resolution of this N-body simulation is almost an order of magnitude better than in previous simulations used for this purpose, allowing us to probe fainter galaxies and hence build a more complete mock catalogue at low redshifts. The high time cadence of the simulation outputs allows us to make improved calculations of galaxy properties and positions in the mock. We test the predictions of the mock against the Physics of the Accelerating Universe Survey, a narrow-band imaging survey with highly accurate and precise photometric redshifts, which probes the galaxy population over a lookback time of 8 billion years. We compare the model against the observed number counts, redshift distribution, and evolution of the observed colours and find good agreement; these statistics avoid the need for model-dependent processing of the observations. The model produces red and blue populations that have similar median colours to the observations. However, the bimodality of galaxy colours in the model is stronger than in the observations. This bimodality is reduced on including a simple model for errors in the GALFORM photometry. We examine how the model predictions for the observed galaxy colours change when perturbing key model parameters. This exercise shows that the median colours and relative abundance of red and blue galaxies provide constraints on the strength of the feedback driven by supernovae used in the model
The PAU Survey: a new constraint on galaxy formation models using the observed colour redshift relation
We use the GALFORM semi-analytical galaxy formation model implemented in the
Planck Millennium N-body simulation to build a mock galaxy catalogue on an
observer's past lightcone. The mass resolution of this N-body simulation is
almost an order of magnitude better than in previous simulations used for this
purpose, allowing us to probe fainter galaxies and hence build a more complete
mock catalogue at low redshifts. The high time cadence of the simulation
outputs allows us to make improved calculations of galaxy properties and
positions in the mock. We test the predictions of the mock against the Physics
of the Accelerating Universe Survey, a narrow band imaging survey with highly
accurate and precise photometric redshifts, which probes the galaxy population
over a lookback time of 8 billion years. We compare the model against the
observed number counts, redshift distribution and evolution of the observed
colours and find good agreement; these statistics avoid the need for
model-dependent processing of the observations. The model produces red and blue
populations that have similar median colours to the observations. However, the
bimodality of galaxy colours in the model is stronger than in the observations.
This bimodality is reduced on including a simple model for errors in the
GALFORM photometry. We examine how the model predictions for the observed
galaxy colours change when perturbing key model parameters. This exercise shows
that the median colours and relative abundance of red and blue galaxies provide
constraints on the strength of the feedback driven by supernovae used in the
model
The Evolution of Early-type Red Galaxies with the GEMS Survey: Luminosity-size and Stellar Mass-size Relations Since z=1
We combine HST/ACS imaging from the GEMS survey with redshifts and rest-frame
quantities from COMBO-17 to study the evolution of morphologically early-type
galaxies with red colors since z=1. We use a new large sample of 728 galaxies
with centrally-concentrated radial profiles (Sersic n>2.5) and rest-frame U-V
colors on the red sequence. By appropriate comparison with the local relations
from SDSS, we find that the luminosity-size (L-R) and stellar mass-size (M-R)
relations evolve in a manner that is consistent with the passive aging of
ancient stars. By itself, this result is consistent with a completely passive
evolution of the red early-type galaxy population. If instead, as demonstrated
by a number of recent surveys, the early-type galaxy population builds up in
mass by a factor of 2 since z=1, our results imply that new additions to the
early-type galaxy population follow similar L-R and M-R correlations, compared
to the older subset of early-type galaxies. Adding early-type galaxies to the
red sequence through disk fading appears to be consistent with the data.
Through comparison with models, the role of dissipationless merging is limited
to <1 major merger on average since z=1 for the most massive galaxies.
Predictions from models of gas-rich mergers are not yet mature enough to allow
a detailed comparison to our observations. We find tentative evidence that the
amount of luminosity evolution depends on galaxy stellar mass, such that the
least massive galaxies show stronger luminosity evolution compared to more
massive early types. This could reflect a different origin of low-mass
early-type galaxies and/or younger stellar populations; the present data is
insufficient to discriminate between these possibilities. (abridged)Comment: Submitted to ApJ, 23 pages, Latex using emulateapj5.sty and
onecolfloat.sty (included), 10 figures, version with full resolution figures
at http://www.astro.umass.edu/~dmac/Papers/ETevol.hires.p
SPACE: the spectroscopic all-sky cosmic explorer
We describe the scientific motivations, the mission concept and the instrumentation of SPACE, a class-M mission proposed for concept study at the first call of the ESA Cosmic-Vision 2015–2025 planning cycle. SPACE aims to produce the largest three-dimensional evolutionary map of the Universe over the past 10 billion years by taking near-IR spectra and measuring redshifts for more than half a billion galaxies at 0 < z < 2 down to AB ∼ 23 over 3π sr of the sky. In addition, SPACE will also target a smaller sky field, performing a deep spectroscopic survey of millions of galaxies to AB ∼ 26 and at 2 < z < 10+. These goals are unreachable with ground-based observations due to the ≈500 times higher sky background (see e.g. Aldering, LBNL report number LBNL-51157, 2001). To achieve the main science objectives, SPACE will use a 1.5 m diameter Ritchey- Chretien telescope equipped with a set of arrays of Digital Micro-mirror Devices covering a total field of view of 0.4 deg2, and will perform large-multiplexing multi-object spectroscopy (e.g. ≈6000 targets per pointing) at a spectral resolution of R∼400 as well as diffraction-limited imaging with continuous coverage from 0.8 to 1.8 μm. Owing to the depth, redshift range, volume coverage and quality of its spectra, SPACE will reveal with unique sensitivity most of the fundamental cosmological signatures, including the power spectrum of density fluctuations and its turnover. SPACE will also place high accuracy constraints on the dark energy equation of state parameter and its evolution by measuring the baryonic acoustic oscillations imprinted when matter and radiation decoupled, the distanceluminosity relation of cosmological supernovae, the evolution of the cosmic expansion rate, the growth rate of cosmic large-scale structure, and high-z galaxy clusters. The datasets from the SPACE mission will represent a long lasting legacy for the whole astronomical community whose data will be mined for many years to come
The Herschel-SPIRE Legacy Survey (HSLS): the scientific goals of a shallow and wide submillimeter imaging survey with SPIRE
A large sub-mm survey with Herschel will enable many exciting science opportunities, especially in an era of wide-field optical and radio surveys and high resolution cosmic microwave background experiments. The Herschel-SPIRE Legacy Survey (HSLS), will lead to imaging data over 4000 sq. degrees at 250, 350, and 500 micron. Major Goals of HSLS are: (a) produce a catalog of 2.5 to 3 million galaxies down to 26, 27 and 33 mJy (50% completeness; 5 sigma confusion noise) at 250, 350 and 500 micron, respectively, in the southern hemisphere (3000 sq. degrees) and in an equatorial strip (1000 sq. degrees), areas which have extensive multi-wavelength coverage and are easily accessible from ALMA. Two thirds of the of the sources are expected to be at z > 1, one third at z > 2 and about a 1000 at z > 5. (b) Remove point source confusion in secondary anisotropy studies with Planck and ground-based CMB data. (c) Find at least 1200 strongly lensed bright sub-mm sources leading to a 2% test of general relativity. (d) Identify 200 proto-cluster regions at z of 2 and perform an unbiased study of the environmental dependence of star formation. (e) Perform an unbiased survey for star formation and dust at high Galactic latitude and make a census of debris disks and dust around AGB stars and white dwarfs
Development of the SIOPE DIPG network, registry and imaging repository : a collaborative effort to optimize research into a rare and lethal disease
Diffuse intrinsic pontine glioma (DIPG) is a rare and deadly childhood malignancy. After 40 years of mostly single-center, often non-randomized trials with variable patient inclusions, there has been no improvement in survival. It is therefore time for international collaboration in DIPG research, to provide new hope for children, parents and medical professionals fighting DIPG. In a first step towards collaboration, in 2011, a network of biologists and clinicians working in the field of DIPG was established within the European Society for Paediatric Oncology (SIOPE) Brain Tumour Group: the SIOPE DIPG Network. By bringing together biomedical professionals and parents as patient representatives, several collaborative DIPG-related projects have been realized. With help from experts in the fields of information technology, and legal advisors, an international, web-based comprehensive database was developed, The SIOPE DIPG Registry and Imaging Repository, to centrally collect data of DIPG patients. As for April 2016, clinical data as well as MR-scans of 694 patients have been entered into the SIOPE DIPG Registry/Imaging Repository. The median progression free survival is 6.0 months (95% Confidence Interval (CI) 5.6-6.4 months) and the median overall survival is 11.0 months (95% CI 10.5-11.5 months). At two and five years post-diagnosis, 10 and 2% of patients are alive, respectively. The establishment of the SIOPE DIPG Network and SIOPE DIPG Registry means a paradigm shift towards collaborative research into DIPG. This is seen as an essential first step towards understanding the disease, improving care and (ultimately) cure for children with DIPG.Peer reviewe
Root Canal Anatomy of Maxillary and Mandibular Teeth
It is a common knowledge that a comprehensive understanding of the complexity of the internal anatomy of teeth is imperative to ensure successful root canal treatment. The significance of canal anatomy has been emphasized by studies demonstrating that variations in canal geometry before cleaning, shaping, and obturation procedures had a greater effect on the outcome than the techniques themselves. In recent years, significant technological advances for imaging teeth, such as CBCT and micro-CT, respectively, have been introduced. Their noninvasive nature allows to perform in vivo anatomical studies using large populations to address the influence of several variables such as ethnicity, aging, gender, and others, on the root canal anatomy, as well as to evaluate, quantitatively and/or qualitatively, specific and fine anatomical features of a tooth group. The purpose of this chapter is to summarize the morphological aspects of the root canal anatomy published in the literature of all groups of teeth and illustrate with three-dimensional images acquired from micro-CT technology.info:eu-repo/semantics/publishedVersio