780 research outputs found
Asymmetric Ejecta of Cool Supergiants and Hypergiants in the Massive Cluster Westerlund 1
We report new 5.5âGHz radio observations of the massive star cluster Westerlund 1, taken by the Australia Telescope Compact Array, detecting nine of the ten yellow hypergiants (YHGs) and red supergiants (RSGs) within the cluster. Eight of nine sources are spatially resolved. The nebulae associated with the YHGs Wd1-4a, -12a and -265 demonstrate a cometary morphology - the first time this phenomenon has been observed for such stars. This structure is also echoed in the ejecta of the RSGs Wd1-20 and -26; in each case the cometary tails are directed away from the cluster core. The nebular emission around the RSG Wd1-237 is less collimated than these systems but once again appears more prominent in the hemisphere facing the cluster. Considered as a whole, the nebular morphologies provide compelling evidence for sculpting via a physical agent associated with Westerlund 1, such as a cluster wind
A CNL for Contract-Oriented Diagrams
We present a first step towards a framework for defining and manipulating
normative documents or contracts described as Contract-Oriented (C-O) Diagrams.
These diagrams provide a visual representation for such texts, giving the
possibility to express a signatory's obligations, permissions and prohibitions,
with or without timing constraints, as well as the penalties resulting from the
non-fulfilment of a contract. This work presents a CNL for verbalising C-O
Diagrams, a web-based tool allowing editing in this CNL, and another for
visualising and manipulating the diagrams interactively. We then show how these
proof-of-concept tools can be used by applying them to a small example
Deep MERLIN 5GHz Radio Imaging of Supernova Remnants in the M82 Starburst
The results of an extremely deep, 8-day long observation of the central kpc
of the nearby starburst galaxy M82 using MERLIN (Multi-Element Radio Linked
Interferometer Network) at 5 GHz are presented. The 17E-06 Jy/beam, rms noise
level in the naturally weighted image make it the most sensitive high
resolution radio image of M82 made to date. Over 50 discrete sources are
detected, the majority of which are supernova remnants, but with 13 identified
as HII regions. Sizes, flux densities and radio brightnesses are given for all
of the detected sources, which are all well resolved with a majority showing
shell or partial shell structures. Those sources within the sample which are
supernova remnants have diameters ranging from 0.3 to 6.7 pc, with a mean size
of 2.9 pc.
From a comparison with previous MERLIN 5 GHz observations made in July 1992,
which gives a 9.75 year timeline, it has been possible to measure the expansion
velocities of ten of the more compact sources, eight of which have not been
measured before. These derived expansion velocities range between 2200 and
10500 km/s.Comment: 34 pages, 10 figures. Accepted by MNRA
Thermodynamics of an attractive 2D Fermi gas
Thermodynamic properties of matter are conveniently expressed as functional
relations between variables known as equations of state. Here we experimentally
determine the compressibility, density and pressure equations of state for an
attractive 2D Fermi gas in the normal phase as a function of temperature and
interaction strength. In 2D, interacting gases exhibit qualitatively different
features to those found in 3D. This is evident in the normalized density
equation of state, which peaks at intermediate densities corresponding to the
crossover from classical to quantum behaviour.Comment: Contains minor revision
ALMA observations of the supergiant B[e] star Wd1-9
Mass-loss in massive stars plays a critical role in their evolution, although the precise mechanism(s) responsible â radiatively driven winds, impulsive ejection and/or binary interaction â remain uncertain. In this Letter, we present Atacama Large Millimetre/Submillimeter Array line and continuum observations of the supergiant B[e] star Wd1-9, a massive post-main-sequence object located within the starburst cluster Westerlund 1 (Wd1). We find it to be one of the brightest stellar point sources in the sky at millimetre wavelengths, with (serendipitously identified) emission in the H41α radio recombination line. We attribute these properties to a low velocity (âŒ100 km s-1 ) ionized wind, with an extreme mass-loss rate âł6.4 Ă 105(d/5âkpc)1.5 MÈŻyr-1. External to this is an extended aspherical ejection nebula indicative of a prior phase of significant mass-loss. Taken together, the millimetre properties of Wd1-9 show a remarkable similarity to those of the highly luminous stellar source MWC349A. We conclude that these objects are interacting binaries evolving away from the main sequence and undergoing rapid case-A mass transfer. As such they â and by extension the wider class of supergiant B[e] stars â may provide a unique window into the physics of a process that shapes the life-cycle of âŒ70 per cent of massive stars found in binary systems
Rapport amministrattiv tal-Kunsill ta' l-Akkademja tal-Malti għas-snin 1974-75
L-awtur jagħmel dan ir-rapport amministrattiv tal-Akkademja tal-Malti mis-sena 1974 sas-sena 1975.peer-reviewe
Post-tonsillectomy bleeding in Malta
Patients presenting with post-tonsillectomy haemorrhage
are frequently readmitted to hospital, usually for observation,
but surgical intervention may sometimes be necessary. A 10
year retrospective analysis of 3553 patients who underwent
tonsillectomy with or without adenoidectomy at the Mater Dei
hospital was carried out. Clinical notes were used to determine
the post-tonsillectomy haemorrhage rate and its relationship to
the use of antibiotics.peer-reviewe
Volatile aldehydes in libraries and archives
Volatile aldehydes are produced during degradation of paper-based materials. This may result in their accumulation in archival and library repositories. However, no systematic study has been performed so far. In the frame of this study, passive sampling was carried out at ten locations in four libraries and archives. Despite the very variable sampling locations, no major differences were found, although air-filtered repositories were found to have lower concentrations while a non-ventilated newspaper repository exhibited the highest concentrations of volatile aldehydes (formaldehyde, acetaldehyde, furfural and hexanal). Five employees in one institution were also provided with personal passive samplers to investigate employeesâ exposure to volatile aldehydes. All values were lower than the presently valid exposure limits.
The concentration of volatile aldehydes, acetic acid, and volatile organic compounds (VOCs) in general was also compared with that of outdoor-generated pollutants. It was evident that inside the repository and particularly inside archival boxes, the concentration of VOCs and acetic acid was much higher than the concentration of outdoor-generated pollutants, which are otherwise more routinely studied in connection with heritage materials. This indicates that further work on the pro-degradative effect of VOCs on heritage materials is necessary and that monitoring of VOCs in heritage institutions should become more widespread
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