946 research outputs found
Getting to the Finish Line: College Enrollment and Graduation
Presents data from a longitudinal study of the Boston public school system's class of 2000 -- how many had enrolled in college, had graduated, and remained enrolled as of 2007, by gender, race/ethnicity, and types of college and high school attended
Discovery of a Giant Stellar Tidal Stream Around the Disk Galaxy NGC 4013
We report the discovery of a giant, loop-like stellar structure around the
edge-on spiral galaxy NGC 4013. This arcing feature extends 6 arcmin (~26 kpc
in projected distance) northeast from the center and 3 arcmin (~=12 kpc) from
the disk plane; likely related features are also apparent on the southwest side
of the disk, extending to 4 arcmin (~17 kpc). The detection of this low
surface-brightness muR= 27.0+0.3-0.2 mag/sqarcsec) structure is independently
confirmed in three separate datasets from three different telescopes.
Although its true three dimensional geometry is unknown, the sky- projected
morphology of this structure displays a match with the theoretical predictions
for the edge-on, projected view of a stellar tidal streams of a dwarf satellite
moving in a low inclined (~25deg), nearly circular orbit. Using the recent
model of the Monoceros tidal stream in the Milky Way by Penarrubia et al. as
template, we find that the progenitor system may have been a galaxy with an
initial mass 6*10^8 Msun, of which current position and final fate is unknown.
According to this simulation, the tidal stream may be approximately ~2.8 Gyr of
age.
Our results demonstrate that NGC 4013, previously considered a prototypical
isolated disk galaxy in spite of having one of the most prominent HI warps
detected thus far, may have in fact suffered a recent minor merger. This
discovery highlights that undisturbed disks at high surface brightness levels
in the optical but warped in HI maps may in fact reveal complex signatures of
recent accretion events in deep photometric surveys.Comment: Comments: LaTeX, ApJ preprint style, 21 pages, 6 figures (reduced
quality), ApJ accepted. A high resolution version of the paper in addition to
a full version of the colour image of NGC 4013 can be found at
http://www.cosmotography.com/images/iac/ngc4013.html . Replaced to match
accepted version after revisions following referee's repor
Gaia-IGRINS synergy: Orbits of Newly Identified Milky Way Star Clusters
The recent exquisite Gaia astrometric, photometric, and radial velocity (RV)
measurements resulted in a substantial advancement for the determination of the
orbits for old star clusters, including the oldest Milky Way globular clusters
(MW GCs). The main goal of this paper is to use the Gaia DR3 and the VVVX
measurements to obtain the orbits for nearly a dozen new Galactic GC candidates
that have been poorly studied or previously unexplored. We use the Gaia DR3 and
VVVX databases to identify bonafide members of the Galactic GC candidates:
VVV-CL160, Patchick122, Patchick125, Patchick126, Kronberger99, Kronberger119,
Kronberger143, ESO92-18, ESO93-08, Gaia2, and Ferrero54. The relevant mean
cluster physical parameters are derived (distances, Galactic coordinates,
proper motions, RVs). We measure accurate mean RVs for the GCs VVV-CL160 and
Patchick126, using observations acquired at the Gemini-South telescope with the
IGRINS high-resolution spectrograph. Orbits for each cluster are then computed
using the GravPot16 model, assuming typical Galactic bar pattern speeds. We
reconstruct the orbits for these clusters for the first time. These include
star clusters with retrograde and prograde orbital motions, both in the
Galactic bulge and disk. Orbital properties, such as the mean time-variations
of perigalactic and apogalactic distances, eccentricities, vertical excursions
from the Galactic plane, and Z-components of the angular momentum are obtained
for our sample. Our main conclusion is that, based on the orbital parameters,
Patchick125 and Patchick126 are genuine MW bulge/halo GCs; Ferrero54, Gaia2 and
Patchick122 are MW disk GCs. The orbits of Kronberger99, Kronberger119,
Kronberger143, ESO92-18, and ESO93-08 are more consistent with old MW disk open
clusters. VVV-CL160 falls very close to the Galactic centre, but reaches larger
distances beyond the Sun, thus its origin is still unclear.Comment: 21 pages, 8 figures. Accepted for publication in A&
Climate change, climatic variation and extreme biological responses
Extreme climatic events could be major drivers of biodiversity change, but it is unclear whether extreme biological changes are (i) individualistic (species- or group-specific), (ii) commonly associated with unusual climatic events and/or (iii) important determinants of long-term population trends. Using population time series for 238 widespread species (207 Lepidoptera and 31 birds) in England since 1968, we found that population 'crashes' (outliers in terms of species' year-to-year population changes) were 46% more frequent than population 'explosions'. (i) Every year, at least three species experienced extreme changes in population size, and in 41 of the 44 years considered, some species experienced population crashes while others simultaneously experienced population explosions. This suggests that, even within the same broad taxonomic groups, species are exhibiting individualistic dynamics, most probably driven by their responses to different, short-term events associated with climatic variability. (ii) Six out of 44 years showed a significant excess of species experiencing extreme population changes (5 years for Lepidoptera, 1 for birds). These 'consensus years' were associated with climatically extreme years, consistent with a link between extreme population responses and climatic variability, although not all climatically extreme years generated excess numbers of extreme population responses. (iii) Links between extreme population changes and long-term population trends were absent in Lepidoptera and modest (but significant) in birds. We conclude that extreme biological responses are individualistic, in the sense that the extreme population changes of most species are taking place in different years, and that long-term trends of widespread species have not, to date, been dominated by these extreme changes.This article is part of the themed issue 'Behavioural, ecological and evolutionary responses to extreme climatic events'
Inhibition of exosome biogenesis affects cell motility in heterogeneous sub-populations of paediatric-type diffuse high-grade gliomas
Background: Paediatric-type diffuse High-Grade Gliomas (PDHGG) are highly heterogeneous tumours which include distinct cell sub-populations co-existing within the same tumour mass. We have previously shown that primary patient-derived and optical barcoded single-cell-derived clones function as interconnected networks. Here, we investigated the role of exosomes as a route for inter-clonal communication mediating PDHGG migration and invasion.
Results: A comprehensive characterisation of seven optical barcoded single-cell-derived clones obtained from two patient-derived cell lines was performed. These analyses highlighted extensive intra-tumour heterogeneity in terms of genetic and transcriptional profiles between clones as well as marked phenotypic differences including distinctive motility patterns. Live single-cell tracking analysis of 3D migration and invasion assays showed that the single-cell-derived clones display a higher speed and longer travelled distance when in co-culture compared to mono-culture conditions. To determine the role of exosomes in PDHGG inter-clonal cross-talks, we isolated exosomes released by different clones and characterised them in terms of marker expression, size and concentration. We demonstrated that exosomes are actively internalized by the cells and that the inhibition of their biogenesis, using the phospholipase inhibitor GW4689, significantly reduced the cell motility in mono-culture and more prominently when the cells from the clones were in co-culture. Analysis of the exosomal miRNAs, performed with a miRNome PCR panel, identified clone-specific miRNAs and a set of miRNA target genes involved in the regulation of cell motility/invasion/migration. These genes were found differentially expressed in co-culture versus mono-culture conditions and their expression levels were significantly modulated upon inhibition of exosome biogenesis.
Conclusions: In conclusion, our study highlights for the first time a key role for exosomes in the inter-clonal communication in PDHGG and suggests that interfering with the exosome biogenesis pathway may be a valuable strategy to inhibit cell motility and dissemination for these specific diseases
Pediatric hospital discharge interventions to reduce subsequent utilization: A systematic review
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106901/1/jhm2134.pd
Phylogenetic Relationships in Pterodroma Petrels Are Obscured by Recent Secondary Contact and Hybridization
The classification of petrels (Pterodroma spp.) from Round
Island, near Mauritius in the Indian Ocean, has confounded researchers since
their discovery in 1948. In this study we investigate the relationships between
Round Island petrels and their closest relatives using evidence from
mitochondrial DNA sequence data and ectoparasites. Far from providing clear
delimitation of species boundaries, our results reveal that hybridization among
species on Round Island has led to genetic leakage between populations from
different ocean basins. The most common species on the island,
Pterodroma arminjoniana, appears to be hybridizing with two
rarer species (P. heraldica and P. neglecta),
subverting the reproductive isolation of all three and allowing gene flow.
P. heraldica and P. neglecta breed
sympatrically in the Pacific Ocean, where P. arminjoniana is
absent, but no record of hybridization between these two exists and they remain
phenotypically distinct. The breakdown of species boundaries in Round Island
petrels followed environmental change (deforestation and changes in species
composition due to hunting) within their overlapping ranges. Such multi-species
interactions have implications not only for conservation, but also for our
understanding of the processes of evolutionary diversification and
speciation
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