359 research outputs found
Nitrogen Production in Starburst Galaxies Detected by GALEX
We investigate the production of nitrogen in star-forming galaxies with ultraviolet (UV) radiation detected by the Galaxy Evolution Explorer Satellite (GALEX). We use a sample of 8745 GALEX emission-line galaxies matched to the Sloan Digital Sky Survey (SDSS) spectroscopic sample. We derive both gas-phase oxygen and nitrogen abundances for the sample and apply stellar population synthesis models to derive stellar masses and star formation histories of the galaxies. We compare oxygen abundances derived using three different diagnostics. We derive the specific star formation rates of the galaxies by modeling the seven-band GALEX+SDSS photometry. We find that galaxies that have log (SFR/M_*) ≳ − 10.0 typically have values of log (N/O) ~ 0.05 dex less than galaxies with log (SFR/M_*) ≾ − 10.0 and similar oxygen abundances
UV Star Formation Rates in the Local Universe
We measure star formation rates of ~50,000 optically-selected galaxies in the
local universe (z~0.1), spanning a range from gas-rich dwarfs to massive
ellipticals. We obtain dust-corrected SFRs by fitting the GALEX (UV) and SDSS
(optical) photometry to a library of population synthesis models that include
dust attenuation. For star-forming galaxies, our UV-based SFRs compare
remarkably well with those derived from SDSS H alpha. Deviations from perfect
agreement between these two methods are due to differences in the dust
attenuation estimates. In contrast to H alpha, UV provides reliable SFRs for
galaxies with weak or no H alpha emission, and where H alpha is contaminated
with an emission from an AGN. We use full-SED SFRs to calibrate a simple
prescription that uses GALEX UV magnitudes to produce good SFRs for normal
star-forming galaxies. The specific SFR is considered as a function of stellar
mass for (1) star-forming galaxies with no AGN, (2) those hosting an AGN, and
for (3) galaxies without H alpha emission. We find that the three have distinct
star formation histories, with AGN lying intermediate between the star-forming
and the quiescent galaxies. Normal star forming galaxies (without an AGN) lie
on a relatively narrow linear sequence. Remarkably, galaxies hosting a strong
AGN appear to represent the massive continuation of this sequence. Weak AGN,
while also massive, have lower SFR, sometimes extending to the realm of
quiescent galaxies. We propose an evolutionary sequence for massive galaxies
that smoothly connects normal star-forming galaxies to quiescent (red sequence)
galaxies via strong and weak AGN. We confirm that some galaxies with no H alpha
emission show signs of SF in the UV. We derive a UV-based cosmic SFR density at
z=0.1 with smaller total error than previous measurements (abridged).Comment: Accepted for publication in ApJ (Special GALEX Supplement issue - Dec
2007). v2: Typo in Eq. 2 correcte
Furin cleavage of SARS-CoV-2 Spike promotes but is not essential for infection and cell-cell fusion.
Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2) infects cells by binding to the host cell receptor ACE2 and undergoing virus-host membrane fusion. Fusion is triggered by the protease TMPRSS2, which processes the viral Spike (S) protein to reveal the fusion peptide. SARS-CoV-2 has evolved a multibasic site at the S1-S2 boundary, which is thought to be cleaved by furin in order to prime S protein for TMPRSS2 processing. Here we show that CRISPR-Cas9 knockout of furin reduces, but does not prevent, the production of infectious SARS-CoV-2 virus. Comparing S processing in furin knockout cells to multibasic site mutants reveals that while loss of furin substantially reduces S1-S2 cleavage it does not prevent it. SARS-CoV-2 S protein also mediates cell-cell fusion, potentially allowing virus to spread virion-independently. We show that loss of furin in either donor or acceptor cells reduces, but does not prevent, TMPRSS2-dependent cell-cell fusion, unlike mutation of the multibasic site that completely prevents syncytia formation. Our results show that while furin promotes both SARS-CoV-2 infectivity and cell-cell spread it is not essential, suggesting furin inhibitors may reduce but not abolish viral spread
Vestibular Perception following Acute Unilateral Vestibular Lesions.
Little is known about the vestibulo-perceptual (VP) system, particularly after a unilateral vestibular lesion. We investigated vestibulo-ocular (VO) and VP function in 25 patients with vestibular neuritis (VN) acutely (2 days after onset) and after compensation (recovery phase, 10 weeks). Since the effect of VN on reflex and perceptual function may differ at threshold and supra-threshold acceleration levels, we used two stimulus intensities, acceleration steps of 0.5°/s(2) and velocity steps of 90°/s (acceleration 180°/s(2)). We hypothesised that the vestibular lesion or the compensatory processes could dissociate VO and VP function, particularly if the acute vertiginous sensation interferes with the perceptual tasks. Both in acute and recovery phases, VO and VP thresholds increased, particularly during ipsilesional rotations. In signal detection theory this indicates that signals from the healthy and affected side are still fused, but result in asymmetric thresholds due to a lesion-induced bias. The normal pattern whereby VP thresholds are higher than VO thresholds was preserved, indicating that any 'perceptual noise' added by the vertigo does not disrupt the cognitive decision-making processes inherent to the perceptual task. Overall, the parallel findings in VO and VP thresholds imply little or no additional cortical processing and suggest that vestibular thresholds essentially reflect the sensitivity of the fused peripheral receptors. In contrast, a significant VO-VP dissociation for supra-threshold stimuli was found. Acutely, time constants and duration of the VO and VP responses were reduced - asymmetrically for VO, as expected, but surprisingly symmetrical for perception. At recovery, VP responses normalised but VO responses remained shortened and asymmetric. Thus, unlike threshold data, supra-threshold responses show considerable VO-VP dissociation indicative of additional, higher-order processing of vestibular signals. We provide evidence of perceptual processes (ultimately cortical) participating in vestibular compensation, suppressing asymmetry acutely in unilateral vestibular lesions
A large sample of low surface brightness disc galaxies from the SDSS- II. Metallicities in surface brightness bins
We study the spectroscopic properties of a large sample of Low Surface
Brightness galaxies (LSBGs) (with B-band central surface brightness mu0(B)>22
mag arcsec^(-2)) selected from the Sloan Digital Sky Survey Data Release 4
(SDSS-DR4) main galaxy sample. A large sample of disk-dominated High Surface
Brightness galaxies (HSBGs, with mu0(B)<22 mag arcsec^(-2)) are also selected
for comparison simultaneously. To study them in more details, these sample
galaxies are further divided into four subgroups according to mu0(B) (in units
of mag arcsec^(-2)): vLSBGs (24.5-22.75),iLSBGs (22.75-22.0), iHSBGs
(22.0-21.25), and vHSBGs (<21.25). The diagnostic diagram from spectral
emission-line ratios shows that the AGN fractions of all the four subgroups are
small (<9%). The 21,032 star-forming galaxies with good quality spectroscopic
observations are further selected for studying their dust extinction,
strong-line ratios, metallicities and stellar mass-metallicities relations. The
vLSBGs have lower extinction values and have less metal-rich and massive
galaxies than the other subgroups. The oxygen abundances of our LSBGs are not
as low as those of the HII regions in LSBGs studied in literature, which could
be because our samples are more luminous, and because of the different
metallicity calibrations used. We find a correlation between 12+log(O/H) and
mu0(B) for vLSBGs, iLSBGs and iHSBGs but show that this could be a result of
correlation between mu0(B) and stellar mass and the well-known mass-metallicity
relation. This large sample shows that LSBGs span a wide range in metallicity
and stellar mass, and they lie nearly on the stellar mass vs. metallicity and
N/O vs. O/H relations of normal galaxies. This suggests that LSBGs and HSBGs
have not had dramatically different star formation and chemical enrichment
histories.Comment: 14 pages, 11 figures, accepted for publication in MNRA
The UV-Optical Color Dependence of Galaxy Clustering in the Local Universe
We measure the UV-optical color dependence of galaxy clustering in the local
universe. Using the clean separation of the red and blue sequences made
possible by the NUV - r color-magnitude diagram, we segregate the galaxies into
red, blue and intermediate "green" classes. We explore the clustering as a
function of this segregation by removing the dependence on luminosity and by
excluding edge-on galaxies as a means of a non-model dependent veto of highly
extincted galaxies. We find that \xi (r_p, \pi) for both red and green galaxies
shows strong redshift space distortion on small scales -- the "finger-of-God"
effect, with green galaxies having a lower amplitude than is seen for the red
sequence, and the blue sequence showing almost no distortion. On large scales,
\xi (r_p, \pi) for all three samples show the effect of large-scale streaming
from coherent infall. On scales 1 Mpc/h < r_p < 10 Mpc/h, the projected
auto-correlation function w_p(r_p) for red and green galaxies fits a power-law
with slope \gamma ~ 1.93 and amplitude r_0 ~ 7.5 and 5.3, compared with \gamma
~ 1.75 and r_0 ~ 3.9 Mpc/h for blue sequence galaxies. Compared to the
clustering of a fiducial L* galaxy, the red, green, and blue have a relative
bias of 1.5, 1.1, and 0.9 respectively. The w_p(r_p) for blue galaxies display
an increase in convexity at ~ 1 Mpc/h, with an excess of large scale
clustering. Our results suggest that the majority of blue galaxies are likely
central galaxies in less massive halos, while red and green galaxies have
larger satellite fractions, and preferentially reside in virialized structures.
If blue sequence galaxies migrate to the red sequence via processes like
mergers or quenching that take them through the green valley, such a
transformation may be accompanied by a change in environment in addition to any
change in luminosity and color.Comment: accepted by MNRA
Evaluating the Implementation and Feasibility of a WebBased Tool to Support Timely Identification and Care for the Frail Population in Primary Healthcare Settings
Background: Understanding and addressing the needs of frail persons is an emerging health priority for Nova Scotia
and internationally. Primary healthcare (PHC) providers regularly encounter frail persons in their daily clinical work.
However, routine identification and measurement of frailty is not standard practice and, in general, there is a lack
of awareness about how to identify and respond to frailty. A web-based tool called the Frailty Portal was developed
to aid in identifying, screening, and providing care for frail patients in PHC settings. In this study, we will assess
the implementation feasibility and impact of the Frailty Portal to: (1) support increased awareness of frailty among
providers and patients, (2) identify the degree of frailty within individual patients, and (3) develop and deliver actions
to respond to frailtyl in community PHC practice.
Methods: This study will be approached using a convergent mixed method design where quantitative and qualitative
data are collected concurrently, in this case, over a 9-month period, analyzed separately, and then merged to summarize,
interpret and produce a more comprehensive understanding of the initiative’s feasibility and scalability. Methods will
be informed by the ‘Implementing the Frailty Portal in Community Primary Care Practice’ logic model and questions
will be guided by domains and constructs from an implementation science framework, the Consolidated Framework
for Implementation Research (CFIR).
Discussion: The ‘Frailty Portal’ aims to improve access to, and coordination of, primary care services for persons
experiencing frailty. It also aims to increase primary care providers’ ability to care for patients in the context of their
frailty. Our goal is to help optimize care in the community by helping community providers gain the knowledge they
may lack about frailty both in general and in their practice, support improved identification of frailty with the use of
screening tools, offer evidence based severity-specific care goals and connect providers with local available community
supports
An Integrated TCGA Pan-Cancer Clinical Data Resource to Drive High-Quality Survival Outcome Analytics
For a decade, The Cancer Genome Atlas (TCGA) program collected clinicopathologic annotation data along with multi-platform molecular profiles of more than 11,000 human tumors across 33 different cancer types. TCGA clinical data contain key features representing the democratized nature of the data collection process. To ensure proper use of this large clinical dataset associated with genomic features, we developed a standardized dataset named the TCGA Pan-Cancer Clinical Data Resource (TCGA-CDR), which includes four major clinical outcome endpoints. In addition to detailing major challenges and statistical limitations encountered during the effort of integrating the acquired clinical data, we present a summary that includes endpoint usage recommendations for each cancer type. These TCGA-CDR findings appear to be consistent with cancer genomics studies independent of the TCGA effort and provide opportunities for investigating cancer biology using clinical correlates at an unprecedented scale. Analysis of clinicopathologic annotations for over 11,000 cancer patients in the TCGA program leads to the generation of TCGA Clinical Data Resource, which provides recommendations of clinical outcome endpoint usage for 33 cancer types
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