1,431 research outputs found
BAL and non-BAL quasars: Continuum, emission, and absorption properties establish a common parent sample
Using a sample of 144,000 quasars from the Sloan Digital Sky Survey
data release 14 we investigate the outflow properties, evident both in
absorption and emission, of high-ionization Broad Absorption Line (BAL) and
non-BAL quasars with redshifts 1.6 3.5 and luminosities 45.3
48.2 erg s. Key to the investigation is a
continuum and emission-line reconstruction scheme, based on mean-field
independent component analysis, that allows the kinematic properties of the
CIV1550 emission line to be compared directly for both non-BAL and BAL
quasars. CIV-emission blueshift and equivalent-width (EW) measurements are thus
available for both populations. Comparisons of the emission-line and BAL-trough
properties reveal strong systematic correlations between the emission and
absorption properties. The dependence of quantitative outflow indicators on
physical properties such as quasar luminosity and luminosity relative to
Eddington-luminosity are also shown to be essentially identical for the BAL and
non-BAL populations. There is an absence of BALs in quasars with the hardest
spectral energy distributions (SEDs), revealed by the presence of strong
HeII1640 emission, large CIV1550-emission EW and no
measurable blueshift. In the remainder of the CIV-emission blueshift versus EW
space, BAL and non-BAL quasars are present at all locations; for every
BAL-quasar it is possible to identify non-BAL quasars with the same
emission-line outflow properties and SED-hardness. The co-location of BAL and
non-BAL quasars as a function of emission-line outflow and physical properties
is the key result of our investigation, demonstrating that (high-ionization)
BALs and non-BALs represent different views of the same underlying quasar
population
Characterizing Quasar C iv Emission-line Measurements from Time-resolved Spectroscopy
We use multi-epoch quasar spectroscopy to determine how accurately
single-epoch spectroscopy can locate quasars in emission-line parameter space
in order to inform investigations where time-resolved spectroscopy is not
available. We explore the improvements in emission-line characterization that
result from using non-parametric information from many lines as opposed to a
small number of parameters for a single line, utilizing reconstructions based
on an independent component analysis applied to the data from the Sloan Digital
Sky Survey Reverberation Mapping project. We find that most of the quasars are
well described by just two components, while more components signal a quasar
likely to yield a successful reverberation mapping analysis. In single-epoch
spectroscopy the apparent variability of equivalent width is exaggerated
because it is dependent on the continuum. Multi-epoch spectroscopy reveals that
single-epoch results do not significantly change where quasars are located in
CIV parameter space and do not have a significant impact on investigations of
the global Baldwin Effect. Quasars with emission line properties indicative of
higher are less variable, consistent with models with enhanced
accretion disk density. Narrow absorption features at the systemic redshift may
be indicative of orientation (including radio-quiet quasars) and may appear in
as much as 20% of the quasar sample. Future work applying these techniques to
lower luminosity quasars will be important for understanding the nature of
accretion disk winds
A Candidate Sub-Parsec Supermassive Binary Black Hole System
We identify SDSS J153636.22+044127.0, a QSO discovered in the Sloan Digital
Sky Survey, as a promising candidate for a binary black hole system. This QSO
has two broad-line emission systems separated by 3500 km/sec. The redder system
at z=0.3889 also has a typical set of narrow forbidden lines. The bluer system
(z=0.3727) shows only broad Balmer lines and UV Fe II emission, making it
highly unusual in its lack of narrow lines. A third system, which includes only
unresolved absorption lines, is seen at a redshift, z=0.3878, intermediate
between the two emission-line systems. While the observational signatures of
binary nuclear black holes remain unclear, J1536+0441 is unique among all QSOs
known in having two broad-line regions, indicative of two separate black holes
presently accreting gas. The interpretation of this as a bound binary system of
two black holes having masses of 10^8.9 and 10^7.3 solar masses, yields a
separation of ~ 0.1 parsec and an orbital period of ~100 years. The separation
implies that the two black holes are orbiting within a single narrow-line
region, consistent with the characteristics of the spectrum. This object was
identified as an extreme outlier of a Karhunen-Loeve Transform of 17,500 z <
0.7 QSO spectra from the SDSS. The probability of the spectrum resulting from a
chance superposition of two QSOs with similar redshifts is estimated at
2X10^-7, leading to the expectation of 0.003 such objects in the sample
studied; however, even in this case, the spectrum of the lower redshift QSO
remains highly unusual.Comment: 8 pages, 2 figures, Nature in pres
Dementia and risk of visual impairment in Chinese older adults
We had previously identified visual impairment increasing risk of incident dementia. While a bi-directional vision-cognition association has subsequently been proposed, no study has specifically examined the longitudinal association between dementia and incidence of clinically defined visual impairment. In this territory-wide community cohort study of 10,806 visually unimpaired older adults, we examined their visual acuity annually for 6 years and tested if dementia at baseline was independently associated with higher risk of incident visual impairment (LogMAR ≥ 0.50 in the better eye despite best correction, which is equivalent to moderate visual impairment according to the World Health Organization definition). By the end of Year 6, a total of 3151 (29.2%) participants developed visual impairment. However, we did not find baseline dementia associating with higher risk of incident visual impairment, after controlling for baseline visual acuity, cataract, glaucoma, diabetes, hypertension, hypercholesterolemia, heart diseases, stroke, Parkinson's disease, depression, hearing and physical impairments, physical, intellectual and social activities, diet, smoking, age, sex, educational level, and socioeconomic status. Among different covariables, baseline visual acuity appears to be more important than dementia in contributing to the development of visual impairment. Our present findings highlight the need for re-evaluating whether dementia is indeed a risk factor for visual impairment
Control of triceps surae stimulation based on shank orientation using a uniaxial gyroscope during gait
This article presents a stimulation control method using a uniaxial gyroscope measuring angular velocity of the shank in the sagittal plane, to control functional electrical stimulation of the triceps surae to improve push-off of stroke subjects during gait. The algorithm is triggered during each swing phase of gait when the angular velocity of the shank is relatively high. Subsequently, the start of the stance phase is detected by a change of sign of the gyroscope signal at approximately the same time as heel strike. Stimulation is triggered when the shank angle reaches a preset value since the beginning of stance. The change of angle is determined by integrating angular velocity from the moment of change of sign. The results show that the real-time reliability of stimulation control was at least 95% for four of the five stroke subjects tested, two of which were 100% reliable. For the remaining subject, the reliability was increased from 50% found during the experiment, to 99% during offline processing. Our conclusion is that a uniaxial gyroscope on the shank is a simple, more reliable alternative to the heel switch for the purpose of restoring push-off of stroke subjects during gait
Neutrophils in cancer: neutral no more
Neutrophils are indispensable antagonists of microbial infection and facilitators of wound healing. In the cancer setting, a newfound appreciation for neutrophils has come into view. The traditionally held belief that neutrophils are inert bystanders is being challenged by the recent literature. Emerging evidence indicates that tumours manipulate neutrophils, sometimes early in their differentiation process, to create diverse phenotypic and functional polarization states able to alter tumour behaviour. In this Review, we discuss the involvement of neutrophils in cancer initiation and progression, and their potential as clinical biomarkers and therapeutic targets
Ireland: Submerged Prehistoric Sites and Landscapes
Evidence of Ireland's drowned landscapes and settlements presently comprises 50 sites spread across the entire island. These comprise mainly intertidal find spots or small collections of flint artefacts. A handful of fully subtidal sites are known, generally from nearshore regions and consisting, with one exception, of isolated single finds. Evidence of organic remains is also sparse, with the exception of Mesolithic and Neolithic wooden fish traps buried in estuarine sediments under Dublin. The relatively small number of sites is probably due to lack of research as much as taphonomic issues, and thus the current evidence hints at the potential archaeological record which may be found underwater. Such evidence could contribute to knowledge of the coastal adaptations and seafaring abilities of Ireland's earliest inhabitants. Nonetheless, taphonomic considerations, specifically relating to Ireland's history of glaciation, sea-level change and also modern oceanographic conditions likely limit the preservation of submerged landscapes and their associated archaeology. Realistically, the Irish shelf is likely characterised by pockets of preservation, which makes detection and study of submerged landscapes difficult but not impossible. A range of potential routes of investigation are identifiable, including site-scale archaeological survey, landscape-scale seabed mapping, archival research and community engagement
De novo mutations in ARID1B associated with both syndromic and non-syndromic short stature
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