2,449 research outputs found
Low mortality of people living with diabetes mellitus diagnosed with COVID-19 and managed at a field hospital in Western Cape Province, South Africa
Background. The novel coronavirus disease 2019 (COVID-19) was declared an international pandemic by the World Health Organization in March 2020. Throughout the pandemic, the association between diabetes mellitus (DM) and more severe COVID-19 has been well described internationally, with limited data, however, on South Africa (SA). The role of field hospitals in the management of patients with COVID-19 in SA has not yet been described. Objectives. To describe the mortality and morbidity of people living with DM (PLWD) and comorbid COVID-19, as well as to shed light on the role of intermediate facilities in managing DM and COVID-19 during the pandemic. Methods. This is a single-centre cross-sectional descriptive study that included all patients with confirmed COVID-19 and pre-existing or newly diagnosed DM (of any type) admitted to the Cape Town International Convention Centre (CTICC) Intermediate Care Bed Facility from June 2020 to August 2020. This study presents the profile of patients admitted to the CTICC, and reports on the clinical outcome of PLWD diagnosed with COVID-19, and additionally determines some associations between risk factors and death or escalation of care in this setting. Results. There were 1 447 admissions at the CTICC, with a total of 674 (46.6%) patients who had confirmed DM, of whom 125 (19%) were newly diagnosed diabetics and 550 (81%) had pre-existing DM. Included in this group were 57 referrals from the telemedicine platform – a platform that identified high-risk diabetic patients with COVID-19 in the community, and linked them directly to hospital inpatient care. Of the 674 PLWD admitted, 593 were discharged alive, 45 were escalated to tertiary hospital requiring advanced care and 36 died. PLWD who died were older, had more comorbidities (specifically chronic obstructive pulmonary disease, congestive cardiac failure and chronic kidney disease) and were more likely to be on insulin.Conclusions. In a resource-limited environment, interdisciplinary and interfacility collaboration ensured that complicated patients with DM and COVID-19 were successfully managed in a field hospital setting. Telemedicine offered a unique opportunity to identify high-risk patients in the community and link them to in-hospital monitoring and care. Future studies should explore ways to optimise this collaboration, as well as to explore possibilities for early identification and management of high-risk patients
Lyman Alpha Emitters in the Hierarchically Clustering Galaxy Formation
We present a new theoretical model for the luminosity functions (LFs) of
Lyman alpha (Lya) emitting galaxies in the framework of hierarchical galaxy
formation. We extend a semi-analytic model of galaxy formation that reproduces
a number of observations for local and high-z galaxies, without changing the
original model parameters but introducing a physically-motivated modelling to
describe the escape fraction of Lya photons from host galaxies (f_esc). Though
a previous study using a hierarchical clustering model simply assumed a
constant and universal value of f_esc, we incorporate two new effects on f_esc:
extinction by interstellar dust and galaxy-scale outflow induced as a star
formation feedback. It is found that the new model nicely reproduces all the
observed Lya LFs of the Lya emitters (LAEs) at different redshifts in z ~ 3-6.
Especially, the rather surprisingly small evolution of the observed LAE Lya LFs
compared with the dark halo mass function is naturally reproduced. Our model
predicts that galaxies with strong outflows and f_esc ~ 1 are dominant in the
observed LFs. This is also consistent with available observations, while the
simple universal f_esc model requires f_esc << 1 not to overproduce the
brightest LAEs. On the other hand, we found that our model significantly
overpredicts LAEs at z > 6, and absorption of Lya photons by neutral hydrogen
in intergalactic medium (IGM) is a reasonable interpretation for the
discrepancy. This indicates that the IGM neutral fraction x_HI rapidly evolves
from x_HI << 1 at z < 6 to a value of order unity at z ~ 6-7, which is broadly
consistent with other observational constraints on the reionization history.Comment: 14 pages, 7 figures, 1 table; accepted to ApJ; the html abstract is
replaced to match the accepted version, the .ps and .pdf files are strictly
identical between the 2nd and the 3rd version
A comparison of the galaxy populations in the Coma and distant clusters: the evolution of k+a galaxies and the role of the intracluster medium
The spectroscopic properties of galaxies in the Coma cluster are compared
with those of galaxies in rich clusters at , to investigate the
evolution of the star formation history in clusters. Luminous galaxies with
and post-starburst/post-starforming (k+a) spectra which
constitute a significant fraction of galaxies in distant cluster samples are
absent in Coma, where spectacular cases of k+a spectra are found instead at
and represent a significant proportion of the cluster dwarf galaxy
population. A simple inspection of their positions on the sky indicates that
this type of galaxy does not show a preferential location within the cluster,
but the bluest and strongest-lined group of k+a's lies in projection towards
the central 1.4 Mpc of Coma and have radial velocities significantly higher
than the cluster mean. We find a striking correlation between the positions of
these young and strong post-starburst galaxies and substructure in the hot
intracluster medium (ICM) identified from {\it XMM-Newton} data, with these
galaxies lying close to the edges of two infalling substructures. This result
strongly suggests that the interaction with the dense ICM could be responsible
for the quenching of the star formation (thus creating the k+a spectrum), and
possibly, for any previous starburst. The evolution with redshift of the
luminosity distribution of k+a galaxies can be explained by a ``downsizing
effect'', with the maximum luminosity/mass of actively star-forming galaxies
infalling onto clusters decreasing at lower redshift. We discuss the possible
physical origin of this downsizing effect and the implications of our results
for current scenarios of environmental effects on the star formation in
galaxies.Comment: 21 pages, 7 figures, to appear in ApJ, version after referee's
change
The Large, Oxygen-Rich Halos of Star-Forming Galaxies Are A Major Reservoir of Galactic Metals
The circumgalactic medium (CGM) is fed by galaxy outflows and accretion of
intergalactic gas, but its mass, heavy element enrichment, and relation to
galaxy properties are poorly constrained by observations. In a survey of the
outskirts of 42 galaxies with the Cosmic Origins Spectrograph onboard the
Hubble Space Telescope, we detected ubiquitous, large (150 kiloparsec) halos of
ionized oxygen surrounding star-forming galaxies, but we find much less ionized
oxygen around galaxies with little or no star formation. This ionized CGM
contains a substantial mass of heavy elements and gas, perhaps far exceeding
the reservoirs of gas in the galaxies themselves. It is a basic component of
nearly all star-forming galaxies that is removed or transformed during the
quenching of star formation and the transition to passive evolution.Comment: This paper is part of a set of three papers on circumgalactic gas
observed with the Cosmic Origins Spectrograph on HST, to be published in
Science, together with related papers by Tripp et al. and Lehner & Howk, in
the November 18, 2011 edition. This version has not undergone final
copyediting. Please see Science online for the final printed versio
Non-Abelian Dark Sectors and Their Collider Signatures
Motivated by the recent proliferation of observed astrophysical anomalies,
Arkani-Hamed et al. have proposed a model in which dark matter is charged under
a non-abelian "dark" gauge symmetry that is broken at ~ 1 GeV. In this paper,
we present a survey of concrete models realizing such a scenario, followed by a
largely model-independent study of collider phenomenology relevant to the
Tevatron and the LHC. We address some model building issues that are easily
surmounted to accommodate the astrophysics. While SUSY is not necessary, we
argue that it is theoretically well-motivated because the GeV scale is
automatically generated. Specifically, we propose a novel mechanism by which
mixed D-terms in the dark sector induce either SUSY breaking or a super-Higgs
mechanism precisely at a GeV. Furthermore, we elaborate on the original
proposal of Arkani-Hamed et al. in which the dark matter acts as a messenger of
gauge mediation to the dark sector. In our collider analysis we present
cross-sections for dominant production channels and lifetime estimates for
primary decay modes. We find that dark gauge bosons can be produced at the
Tevatron and the LHC, either through a process analogous to prompt photon
production or through a rare Z decay channel. Dark gauge bosons will decay back
to the SM via "lepton jets" which typically contain >2 and as many as 8
leptons, significantly improving their discovery potential. Since SUSY decays
from the MSSM will eventually cascade down to these lepton jets, the discovery
potential for direct electroweak-ino production may also be improved.
Exploiting the unique kinematics, we find that it is possible to reconstruct
the mass of the MSSM LSP. We also present decay channels with displaced
vertices and multiple leptons with partially correlated impact parameters.Comment: 44 pages, 25 figures, version published in JHE
Golden gaskets: variations on the Sierpi\'nski sieve
We consider the iterated function systems (IFSs) that consist of three
general similitudes in the plane with centres at three non-collinear points,
and with a common contraction factor \la\in(0,1).
As is well known, for \la=1/2 the invariant set, \S_\la, is a fractal
called the Sierpi\'nski sieve, and for \la<1/2 it is also a fractal. Our goal
is to study \S_\la for this IFS for 1/2<\la<2/3, i.e., when there are
"overlaps" in \S_\la as well as "holes". In this introductory paper we show
that despite the overlaps (i.e., the Open Set Condition breaking down
completely), the attractor can still be a totally self-similar fractal,
although this happens only for a very special family of algebraic \la's
(so-called "multinacci numbers"). We evaluate \dim_H(\S_\la) for these
special values by showing that \S_\la is essentially the attractor for an
infinite IFS which does satisfy the Open Set Condition. We also show that the
set of points in the attractor with a unique ``address'' is self-similar, and
compute its dimension.
For ``non-multinacci'' values of \la we show that if \la is close to 2/3,
then \S_\la has a nonempty interior and that if \la<1/\sqrt{3} then \S_\la$
has zero Lebesgue measure. Finally we discuss higher-dimensional analogues of
the model in question.Comment: 27 pages, 10 figure
Search for Small Trans-Neptunian Objects by the TAOS Project
The Taiwan-America Occultation Survey (TAOS) aims to determine the number of
small icy bodies in the outer reach of the Solar System by means of stellar
occultation. An array of 4 robotic small (D=0.5 m), wide-field (f/1.9)
telescopes have been installed at Lulin Observatory in Taiwan to simultaneously
monitor some thousand of stars for such rare occultation events. Because a
typical occultation event by a TNO a few km across will last for only a
fraction of a second, fast photometry is necessary. A special CCD readout
scheme has been devised to allow for stellar photometry taken a few times per
second. Effective analysis pipelines have been developed to process stellar
light curves and to correlate any possible flux changes among all telescopes. A
few billion photometric measurements have been collected since the routine
survey began in early 2005. Our preliminary result of a very low detection rate
suggests a deficit of small TNOs down to a few km size, consistent with the
extrapolation of some recent studies of larger (30--100 km) TNOs.Comment: 4 pages, 3 figures, IAU Symposium 23
The Taiwanese-American Occultation Survey Project Stellar Variability. II. Detection of 15 Variable Stars
The Taiwanese-American Occultation Survey (TAOS) project has collected more than a billion photometric measurements since 2005 January. These sky survey data—covering timescales from a fraction of a second to a few hundred days—are a useful source to study stellar variability. A total of 167 star fields, mostly along the ecliptic plane, have been selected for photometric monitoring with the TAOS telescopes. This paper presents our initial analysis of a search for periodic variable stars from the time-series TAOS data on one particular TAOS field, No. 151 (R.A. = 17^(h)30^(m)6^(s).7, decl. = 27°17'30", J2000), which had been observed over 47 epochs in 2005. A total of 81 candidate variables are identified in the 3 deg^2 field, with magnitudes in the range 8 < R < 16. On the basis of the periodicity and shape of the light curves, 29 variables, 15 of which were previously unknown, are classified as RR Lyrae, Cepheid, δ Scuti, SX Phonencis, semi-regular, and eclipsing binaries
Large-scale structure in the Lyman-alpha forest II: analysis of a group of ten QSOs
The spatial distribution of Ly-alpha forest absorption systems towards ten
QSOs has been analysed to search for large-scale structure over the redshift
range 2.2 < z < 3.4. The QSOs form a closely spaced group on the sky and are
concentrated within a 1 deg^2 field. We have employed a technique based on the
first and second moments of the transmission probability density function which
is capable of identifying and assessing the significance of regions of over- or
underdense Ly-alpha absorption. We find evidence for large-scale structure in
the distribution of Ly-alpha forest absorption at the > 99 per cent confidence
level. In individual spectra we find overdense Ly-alpha absorption on scales of
up to 1200 km s^-1. There is also strong evidence for correlated absorption
across line of sight pairs separated by < 3 h^-1 proper Mpc (q_0 = 0.5). For
larger separations the cross-correlation signal becomes progressively less
significant.Comment: 15 pages, LaTeX, 6 Postscript figures, accepted for publication in
MNRA
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