3,650 research outputs found
An exploratory model study of sediment transport sources and deposits in the Bohai Sea, Yellow Sea, and East China Sea
A regional ocean circulation model (ROMS) is used to simulate the Chinese land-derived sediment transport in the Bohai Sea, Yellow Sea, and East China Sea (BYECS). The model includes the effect of currents, tides, and waves on the sediment transport and is used to study the pathway and dynamic mechanisms of the fine-grain sediment transport from the Huanghe River (Yellow River), the Old Huanghe Delta, and the Changjiang River (Yangtze River) in the BYECS. The seasonal variability of the sediment transport in the BYECS and the sources of the Yellow Sea Trough mud patch, the mud patch southwest of Cheju Island, the mud patch offshore from the Zhejiang and Fujian provinces and the Okinawa Trough mud patch are discussed. The results show that the Huanghe River sediment can be transported to the Yellow Sea Trough, but little makes it to the outer shelf while the Old Huanghe Delta sediment is mainly transported to the Yellow Sea Trough. Most of the sediment from the Changjiang River mouth is carried to the mud patch off the coast of the Zhejiang and Fujian provinces but with part of this sediment also transported to the Yellow Sea Trough. The model shows that it is difficult to transport land-derived sediment to the Okinawa Trough mud patch under normal conditions. The model also has difficulty accounting for the deposition of sediment in the region to the southwest of Cheju Island and offshore from the Zhejiang and Fujian provinces, an issue requiring further study
Factors associated with patient, and diagnostic delays in Chinese TB patients: a systematic review and meta-analysis
BACKGROUND: Delay in seeking care is a major impediment to effective management of tuberculosis (TB) in China. To elucidate factors that underpin patient and diagnostic delays in TB management, we conducted a systematic review and meta-analysis of factors that are associated with delays in TB care-seeking and diagnosis in the country. METHODS: This review was prepared following standard procedures of the Cochrane Collaboration and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement and checklist. Relevant studies published up to November 2012 were identified from three major international and Chinese literature databases: Medline/PubMed, EMBASE and CNKI (China National Knowledge Infrastructure). RESULTS: We included 29 studies involving 38,947 patients from 17 provinces in China. Qualitative analysis showed that key individual level determinants of delays included socio-demographic and economic factors, mostly poverty, rural residence, lack of health insurance, lower educational attainment, stigma and poor knowledge of TB. Health facility determinants included limited availability of resources to perform prompt diagnosis, lack of qualified health workers and geographical barriers. Quantitative meta-analysis indicated that living in rural areas was a risk factor for patient delays (pooled odds ratio (OR) (95% confidence interval (CI)): 1.79 (1.62, 1.98)) and diagnostic delays (pooled OR (95% CI): 1.40 (1.23, 1.59)). Female patients had higher risk of patient delay (pooled OR (95% CI): 1.94 (1.13, 3.33)). Low educational attainment (primary school and below) was also a risk factor for patient delay (pooled OR (95% CI): 2.14 (1.03, 4.47)). The practice of seeking care first from Traditional Chinese Medicine (TMC) providers was also identified as a risk factor for diagnostic delay (pooled OR (95% CI): 5.75 (3.03, 10.94)). CONCLUSION: Patient and diagnostic delays in TB care are mediated by individual and health facility factors. Population-based interventions that seek to reduce TB stigma and raise awareness about the benefits of early diagnosis and prompt treatment are needed. Policies that remove patients’ financial barriers in access to TB care, and integration of the informal care sector into TB control in urban and rural settings are central factors in TB control
A Giant Protocluster of Galaxies at Redshift 5.7
Galaxy clusters trace the largest structures of the Universe and provide
ideal laboratories for studying galaxy evolution and cosmology. Clusters with
extended X-ray emission have been discovered at redshifts up to z ~ 2.5.
Meanwhile, there has been growing interest in hunting for protoclusters, the
progenitors of clusters, at higher redshifts. It is, however, very challenging
to find the largest protoclusters at early times when they start to assemble.
Here we report a giant protocluster of galaxies at redshift z = 5.7, when the
Universe was only one billion years old. This protocluster occupies a volume of
about 35x35x35 cubic co-moving megaparsecs. It is embedded in an even larger
overdense region with at least 41 spectroscopically confirmed, luminous
Lyman-alpha emitting galaxies (Lyman-alpha Emitters, or LAEs), including
several previously reported LAEs. Its LAE density is 6.6 times the average
density at z ~ 5.7. It is the only one of its kind in an LAE survey in four
square degrees on the sky. Such a large structure is also rarely seen in
current cosmological simulations. This protocluster will collapse into a galaxy
cluster with a mass of (3.6+/-0.9) x 10^{15} solar masses, comparable to those
of the most massive clusters or protoclusters known to date.Comment: Published in Nature Astronomy on Oct 15, 2018 (DOI:
10.1038/s41550-018-0587-9
Preprocessing Among the Infalling Galaxy Population of EDisCS Clusters
We present results from a low-resolution spectroscopic survey for 21 galaxy
clusters at selected from the ESO Distant Cluster Survey. We
measured spectra using the low-dispersion prism in IMACS on the Magellan Baade
telescope and calculate redshifts with an accuracy of . We
find 1763 galaxies that are brighter than in the large-scale cluster
environs. We identify the galaxies expected to be accreted by the clusters as
they evolve to using spherical infall models and find that
to of the cluster population lies outside the virial radius
at . For analogous clusters at , we calculate that the ratio
of galaxies that have fallen into the clusters since to those that
were already in the core at that redshift is typically between and
. This wide range of ratios is due to intrinsic scatter and is not a
function of velocity dispersion, so a variety of infall histories is to be
expected for clusters with current velocity dispersions of km s. Within the infall regions of clusters, we find a larger red fraction of galaxies than in the field and
greater clustering among red galaxies than blue. We interpret these findings as
evidence of "preprocessing", where galaxies in denser local environments have
their star formation rates affected prior to their aggregation into massive
clusters, although the possibility of backsplash galaxies complicates the
interpretation.Comment: Accepted for publication in Ap
Dwarf galaxies show little ISM evolution from to : a spectroscopic study of metallicity, star formation, and electron density
We present gas-phase metallicity measurements for 583 emission line galaxies
at , including 388 dwarf galaxies with , and explore the dependence of the metallicity on the stellar mass and
star formation properties of the galaxies. Metallicities are determined through
the measurement of emission lines in very deep (7 hr exposure)
Keck/DEIMOS spectra taken primarily from the HALO7D survey. We measure
metallicity with three strong-line calibrations (O3H, R23, and O3O2) for
the overall sample, as well as with the faint [Ne III]3869 and [O
III]4363 emission lines for 112 and 17 galaxies where robust
detections were possible. We construct mass-metallicity relations (MZR) for
each calibration method, finding MZRs consistent with other strong-line results
at comparable redshift, as well as with galaxies. We quantify the
intrinsic scatter in the MZR as a function of mass, finding it increases with
lower stellar mass. We also measure a weak but significant correlation between
increased MZR scatter and higher specific star formation rate. We find a weak
influence of SFR in the fundamental metallicity relation as well, with an SFR
coefficient of . Finally, we use the flux ratios of the [O
II]3727,3729 doublet to calculate gas electron density in
1000 galaxies with as a function of
redshift. We measure low electron densities ( cm) for
galaxies, again consistent with conditions, but measure higher
densities ( cm) at . These results all suggest that
there is little evolution in star-forming interstellar medium conditions from
to , confirmed with a more complete sample of low-mass galaxies
than has previously been available in this redshift range.Comment: 22 pages, 10 figures, accepted to Ap
A Magellan M2FS Spectroscopic Survey of Galaxies at 5.5<z<6.8: Program Overview and a Sample of the Brightest Lyman-alpha Emitters
We present a spectroscopic survey of high-redshift, luminous galaxies over
four square degrees on the sky, aiming to build a large and homogeneous sample
of Ly emitters (LAEs) at and 6.5, and Lyman-break
galaxies (LBGs) at . The fields that we choose to observe are
well-studied, such as SXDS and COSMOS. They have deep optical imaging data in a
series of broad and narrow bands, allowing efficient selection of galaxy
candidates. Spectroscopic observations are being carried out using the
multi-object spectrograph M2FS on the Magellan Clay telescope. M2FS is
efficient to identify high-redshift galaxies, owing to its 256 optical fibers
deployed over a circular field-of-view 30 arcmin in diameter. We have observed
square degrees. When the program is completed, we expect to identify
more than 400 bright LAEs at and 6.5, and a substantial number of
LBGs at . This unique sample will be used to study a variety of galaxy
properties and to search for large protoclusters. Furthermore, the statistical
properties of these galaxies will be used to probe cosmic reionization. We
describe the motivation, program design, target selection, and M2FS
observations. We also outline our science goals, and present a sample of the
brightest LAEs at and 6.5. This sample contains 32 LAEs with
Ly luminosities higher than 10 erg s. A few of them reach
erg s, comparable to the two most luminous LAEs
known at , `CR7' and `COLA1'. These LAEs provide ideal targets to study
extreme galaxies in the distant universe.Comment: 18 pages, 11 figures, Accepted for publication in The Astrophysical
Journa
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