158 research outputs found
Correction: Large cortical bone pores in the tibia are associated with proximal femur strength
[This corrects the article DOI: 10.1371/journal.pone.0215405.
Two Populations of Molecular Clouds in the Antennae Galaxies
Super star clusters --- extremely massive clusters found predominately in
starburst environments --- are essential building blocks in the formation of
galaxies and thought to dominate star formation in the high-redshift universe.
However, the transformation from molecular gas into these ultra-compact star
clusters is not well understood. To study this process, we used the
Submillimeter Array and the Plateau de Bure Interferometer to obtain high
angular resolution (~1.5" or 160 pc) images of the Antennae overlap region in
CO(2--1) to search for the molecular progenitors of the super star clusters. We
resolve the molecular gas distribution into a large number of clouds, extending
the differential cloud mass function down to a 5\sigma completeness limit of
3.8x10^5 M_sun. We identify a distinct break in the mass function around log
M_mol/M_sun ~ 6.5, which separates the molecular clouds into two distinct
populations. The smaller, less massive clouds reside in more quiescent areas in
the region, while the larger, more massive clouds cluster around regions of
intense star formation. A broken power-law fit to the mass function yields
slopes of \alpha = -1.39+/-0.10 and \alpha = -1.44+/-0.14 for the low- and
high-mass cloud population, well-matched to the mass function found for super
star clusters in the Antennae galaxies. We find large velocity gradients and
velocity dispersions at the locations of intense star formation, suggestive of
compressive shocks. It is likely that these environmental factors contribute to
the formation of the observed massive molecular clouds and super star clusters
in the Antennae galaxies.Comment: 20 pages, 13 figures, accepted by Ap
Does police size matter?:A review of the evidence regarding restructuring police organisations
Restructuring and merging public sector organisations is often seen as a way to enhance efficiency and efficacy. There is ongoing debate about the impact of police force sizes, structures and mergers as police organisations attempt to adapt to reductions in their budgets and changes in patterns of criminality. The article reviews the evidence regarding key aspects of police reform: finding mixed evidence regarding the links between size and performance, while noting risks that mergers may impair local policing. The article discusses the impact of mergers on protective services, governance and accountability, while also discussing potential risks and opportunities associated with the merger process itself. The review finds significant gaps in the available evidence, and significant opportunities to expand the evidence base on this topic. Given current gaps in the evidence regarding size, efficacy and efficiency, it is important to give due consideration to symbolic and rhetorical aspects of mergers
Long-term functional outcome of distal radius fractures is associated with early post-fracture bone stiffness of the fracture region:An HR-pQCT exploratory study
\u3cp\u3eIdentifying determinants of long-term functional outcome after a distal radius fracture is challenging. Previously, we reported on the association between early HR-pQCT measurements and clinical outcome 12 weeks after a conservatively treated distal radius fracture. We extended the follow-up and assessed functional outcome after two years in relation to early HR-pQCT derived bone parameters. HR-pQCT scans of the fracture region were performed in 15 postmenopausal women with a distal radius fracture at 1-2 (baseline), 3-4 weeks and 26 months post-fracture. Additionally, the contralateral distal radius was scanned at baseline. Bone density, micro-architecture parameters and bone stiffness using micro-finite element analysis (μFEA) were evaluated. During all visits, wrist pain and function were assessed using the patient-rated wrist evaluation questionnaire (PRWE), quantifying functional outcome with a score between 0 and 100. Two-year PRWE was associated with torsional and bending stiffness 3-4 weeks post-fracture (R2: 0.49, p = 0.006 and R2: 0.54, p = 0.003, respectively). In contrast, early micro-architecture parameters of the fracture region or contralateral bone parameters did not show any association with long-term outcome. This exploratory study indicates that HR-pQCT with μFEA performed within four weeks after a distal radius fracture captures biomechanical fracture characteristics that are associated with long-term functional outcome and therefore could be a valuable early outcome measure in clinical trials and clinical practice.\u3c/p\u3
Grain growth signatures in the protoplanetary discs of Chamaeleon and Lupus
We present ATCA results of a 3 and 7 mm continuum survey of 20 T Tauri stars
in the Chamaeleon and Lupus star forming regions. This survey aims to identify
protoplanetary discs with signs of grain growth. We detected 90% of the sources
at 3 and 7 mm, and determined the spectral slopes, dust opacity indices and
dust disc masses. We also present temporal monitoring results of a small
sub-set of sources at 7, 15 mm and 3+6 cm to investigate grain growth to cm
sizes and constrain emission mechanisms in these sources. Additionally, we
investigated the potential correlation between grain growth signatures in the
infrared (10 \mu m silicate feature) and millimetre (1-3 mm spectral slope,
{\alpha}). Eleven sources at 3 and 7 mm have dominant thermal dust emission up
to 7 mm, with 7 of these having a 1-3 mm dust opacity index less than unity,
suggesting grain growth up to at least mm sizes. The Chamaeleon sources
observed at 15 mm and beyond show the presence of excess emission from an
ionised wind and/or chromo- spheric emission. Long-timescale monitoring at 7 mm
indicated that cm-sized pebbles are present in at least four sources.
Short-timescale monitoring at 15 mm suggests the excess emission is from
thermal free-free emission. Finally, a weak correlation was found between the
strength of the 10 \mum feature and {\alpha}, suggesting simultaneous dust
evolution of the inner and outer parts of the disc. This survey shows that
grain growth up to cm-sized pebbles and the presence of excess emission at 15
mm and beyond are common in these systems, and that temporal monitoring is
required to disentangle these emission mechanisms.Comment: 31 pages, 13 figures, 11 tables, accepted for publication in MNRA
A Simple Model for the Relationship Between Star Formation and Surface Density
We investigate the relationship between the star formation rate per unit area
and the surface density of the ISM (the local Kennicutt-Schmitt law) using a
simplified model of the ISM and a simple estimate of the star formation rate
based on the mass of gas in bound clumps, the local dynamical timescales of the
clumps, and an efficiency parameter of around 5 per cent. Despite the
simplicity of the approach, we are able to reproduce the observed linear
relation between star formation rate and surface density of dense (molecular)
gas. We use a simple model for the dependence of H_2 fraction on total surface
density to argue why neither total surface density nor the HI surface density
are good local indicators of star formation rate. We also investigate the
dependence of the star formation rate on the depth of the spiral potential. Our
model indicates that the mean star formation rate does not depend significantly
on the strength of the spiral potential, but that a stronger spiral potential,
for a given mean surface density, does result in more of the star formation
occurring close to the spiral arms. This agrees with the observation that grand
design galaxies do not appear to show a larger degree of star formation
compared to their flocculent counterparts.Comment: 11 pages, 11 figures, accepted by MNRA
The Interstellar Environment of our Galaxy
We review the current knowledge and understanding of the interstellar medium
of our galaxy. We first present each of the three basic constituents - ordinary
matter, cosmic rays, and magnetic fields - of the interstellar medium, laying
emphasis on their physical and chemical properties inferred from a broad range
of observations. We then position the different interstellar constituents, both
with respect to each other and with respect to stars, within the general
galactic ecosystem.Comment: 39 pages, 12 figures (including 3 figures in 2 parts
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