1,465 research outputs found
Stellar Encounters with Massive Star-Disk Systems
The dense, clustered environment in which massive stars form can lead to
interactions with neighboring stars. It has been hypothesized that collisions
and mergers may contribute to the growth of the most massive stars. In this
paper we extend the study of star-disk interactions to explore encounters
between a massive protostar and a less massive cluster sibling using the
publicly available SPH code GADGET-2. Collisions do not occur in the parameter
space studied, but the end state of many encounters is an eccentric binary with
a semi-major axis ~ 100 AU. Disk material is sometimes captured by the
impactor. Most encounters result in disruption and destruction of the initial
disk, and periodic torquing of the remnant disk. We consider the effect of the
changing orientation of the disk on an accretion driven jet, and the evolution
of the systems in the presence of on-going accretion from the parent core.Comment: 11 pages, 10 figures, accepted to Ap
Stability of Affine G-varieties and Irreducibility in Reductive Groups
Let be a reductive affine algebraic group, and let be an affine
algebraic -variety. We establish a (poly)stability criterion for points
in terms of intrinsically defined closed subgroups of , and
relate it with the numerical criterion of Mumford, and with Richardson and
Bate-Martin-R\"ohrle criteria, in the case . Our criterion builds on a
close analogue of a theorem of Mundet and Schmitt on polystability and allows
the generalization to the algebraic group setting of results of Johnson-Millson
and Sikora about complex representation varieties of finitely presented groups.
By well established results, it also provides a restatement of the non-abelian
Hodge theorem in terms of stability notions.Comment: 29 pages. To appear in Int. J. Math. Note: this version 4 is
identical with version 2 (version 3 is empty
A longitudinal, observational study examining the relationships of patient satisfaction with services and mental well-being to their clinical course in young people with Type 1 diabetes mellitus during transition from child to adult health services
AIM: We hypothesized that participant well-being and satisfaction with services would be positively associated with a satisfactory clinical course during transition from child to adult health care.
METHODS: Some 150 young people with Type 1 diabetes mellitus from five diabetes units in England were recruited to a longitudinal study of transition. Each young person was visited at home four times by a research assistant; each visit was 1 year apart. Satisfaction with services (Mind the Gap; MTG) and mental well-being (Warwick-Edinburgh Mental Well-being Scale; WEMWBS) were captured. Change in HbA1c , episodes of ketoacidosis, clinic and retinal screening attendance were used to assess clinical course. In total, 108 of 150 (72%) young people had sufficient data for analysis at visit 4.
RESULTS: Mean age at entry was 16 years. By visit 4, 81.5% had left paediatric healthcare services. Median HbA1c increased significantly (P = 0.01) from 69 mmol/mol (8.5%) at baseline to 75 mmol/mol (9.0%) at visit 4. WEMWBS scores were comparable with those in the general population at baseline and were stable over the study period. MTG scores were also stable. By visit 4, some 32 individuals had a 'satisfactory' and 76 a 'suboptimal' clinical course. There were no significant differences in average WEMWBS and MTG scores between the clinical course groups (P = 0.96, 0.52 respectively); nor was there a significant difference in transfer status between the clinical course groups.
CONCLUSIONS: The well-being of young people with diabetes and their satisfaction with transition services are not closely related to their clinical course. Investigating whether innovative psycho-educational interventions can improve the clinical course is a research priority
Substellar companions and isolated planetary mass objects from protostellar disc fragmentation
Self-gravitating protostellar discs are unstable to fragmentation if the gas
can cool on a time scale that is short compared to the orbital period. We use a
combination of hydrodynamic simulations and N-body orbit integrations to study
the long term evolution of a fragmenting disc with an initial mass ratio to the
star of M_disc/M_star = 0.1. For a disc which is initially unstable across a
range of radii, a combination of collapse and subsequent accretion yields
substellar objects with a spectrum of masses extending (for a Solar mass star)
up to ~0.01 M_sun. Subsequent gravitational evolution ejects most of the lower
mass objects within a few million years, leaving a small number of very massive
planets or brown dwarfs in eccentric orbits at moderately small radii. Based on
these results, systems such as HD 168443 -- in which the companions are close
to or beyond the deuterium burning limit -- appear to be the best candidates to
have formed via gravitational instability. If massive substellar companions
originate from disc fragmentation, while lower-mass planetary companions
originate from core accretion, the metallicity distribution of stars which host
massive substellar companions at radii of ~1 au should differ from that of
stars with lower mass planetary companions.Comment: 5 pages, accepted for publication in MNRA
Return to school after acquired brain injury in the UK â the educators' perspectives
Childhood acquired brain injury (ABI) is associated with poorer life outcomes. Increasing numbers of children and young people are surviving severe brain injury and returning to mainstream schools with multiple impairments. It is widely acknowledged that for these children, their school becomes by default their rehabilitation centre. International studies of this transition and a recent UK government report criticize educators' inconsistent implementation of support strategies, lack of educator training and poor communication between clinicians, educators, child and family. The educators' perspectives of the return-to-school are, however, not well represented in the literature. This study therefore explored the experiences of educators in the UK (NÂ =Â 10) who had recently facilitated a return-to-school of a child with ABI aged 8â12 (NÂ =Â 5) using semi-structured interviews analysed by data-driven thematic analysis. The findings highlight common experiences: a continuum of intensive problem-solving with heavy reliance on the Special Educational Needs Coordinator; educators valuing collaboration with clinical specialists in context over general âtrainingâ; uncertainty over the validity of implementing support strategies from prior teaching experience; uncertainty about how to support the child's emotional needs; and frustration with UK statutory processes for Special Educational Needs and Disabilities. Recommendations are made for changes to practice and future research
Effects of stop-start features on residual stresses in a multipass austenitic stainless steel weld
The large-scale disk fraction of brown dwarfs in the Taurus cloud as measured with Spitzer
Aims. The brown dwarf (BD) formation process has not yet been completely
understood. To shed more light on the differences and similarities between star
and BD formation processes, we study and compare the disk fraction among both
kinds of objects over a large angular region in the Taurus cloud. In addition,
we examine the spatial distribution of stars and BD relative to the underlying
molecular gas Methods. In this paper, we present new and updated photometry
data from the Infrared Array Camera (IRAC) aboard the Spitzer Space Telescope
on 43 BDs in the Taurus cloud, and recalculate of the BD disk fraction in this
region. We also useed recently available CO mm data to study the spatial
distribution of stars and BDs relative to the cloud's molecular gas. Results.
We find that the disk fraction among BDs in the Taurus cloud is 41 \pm 12%, a
value statistically consistent with the one among TTS (58 \pm 9%). We find that
BDs in transition from a state where they have a disk to a diskless state are
rare, and we study one isolated example of a transitional disk with an inner
radius of \approx 0.1 AU (CFHT BD Tau 12, found via its relatively small mid-IR
excess compared to most members of Taurus that have disks. We find that BDs are
statistically found in regions of similar molecular gas surface density to
those associated with stars. Furthermore, we find that the gas column density
distribution is almost identical for stellar and substellar objects with and
without disks.Comment: 8 page, 6 figures, Accepted in Astronomy & Astrophysics
First report of generalized face processing difficulties in möbius sequence.
Reverse simulation models of facial expression recognition suggest that we recognize the emotions of others by running implicit motor programmes responsible for the production of that expression. Previous work has tested this theory by examining facial expression recognition in participants with Möbius sequence, a condition characterized by congenital bilateral facial paralysis. However, a mixed pattern of findings has emerged, and it has not yet been tested whether these individuals can imagine facial expressions, a process also hypothesized to be underpinned by proprioceptive feedback from the face. We investigated this issue by examining expression recognition and imagery in six participants with Möbius sequence, and also carried out tests assessing facial identity and object recognition, as well as basic visual processing. While five of the six participants presented with expression recognition impairments, only one was impaired at the imagery of facial expressions. Further, five participants presented with other difficulties in the recognition of facial identity or objects, or in lower-level visual processing. We discuss the implications of our findings for the reverse simulation model, and suggest that facial identity recognition impairments may be more severe in the condition than has previously been noted
Modeling high-energy light curves of the PSR B1259-63/LS 2883 binary based on 3-D SPH simulations
Temporal changes of X-ray to very-high-energy gamma-ray emissions from the
pulsar-Be star binary PSR B1259-63/LS 2883 are studied based on 3-D SPH
simulations of pulsar wind interaction with Be-disk and wind. We focus on the
periastron passage of the binary and calculate the variation of the synchrotron
and inverse-Compton emissions using the simulated shock geometry and pressure
distribution of the pulsar wind. The characteristic double-peaked X-ray light
curve from observations is reproduced by our simulation under a dense Be disk
condition (base density ~10^{-9} g cm^{-3}). We interpret the pre- and
post-periastron peaks as being due to a significant increase in the conversion
efficiency from pulsar spin down power to the shock-accelerated particle energy
at orbital phases when the pulsar crosses the disk before periastron passage,
and when the pulsar wind creates a cavity in the disk gas after periastron
passage, respectively. On the contrary, in the model TeV light curve, which
also shows a double peak feature, the first peak appears around the periastron
phase. The possible effects of cooling processes on the TeV light curve are
briefly discussed.Comment: 32 pages, 6 figues. Accepted for publication in Ap
- âŠ