268 research outputs found
Preliminary Investigation into Modeling The Damage to Carbon Fibre Composites Due to the Thermo-electric Effects of a Lightning Strikes
The impact of a lightning strike causes a short high electrical current burst through Carbon Fibre Composites (CFC). Due to the electrical properties of CFC the large current leads to a rapid heating of the surrounding impact area which degrades and damages the CFC. It is therefore necessary to study in detail the thermal response and possible degradation processes caused to CFC. The degradation takes place in two ways, firstly via direct mechanical fracture due to the thermal expansion of the CFC and secondly via thermo-chemical processes (phase change and pyrolysis) at high temperatures. The main objective of this work is to construct a numerical model of the major physical processes involved, and to understand the correlation between the damage mechanisms and the damage witnessed in modern CFC. For this work we are only considering the thermo-chemical degradation of CFC. Bespoke numerical models have been constructed to predict the extent of the damage caused by the two thermo-chemical processes separately (e.g. a model for phase change and a model for pyrolysis). The numerical model predictions have then been verified experimental by decoupling of the damage mechanisms, e.g. the real Joule heating from a lightning strike is replaced by a high power laser beam acting on composite surface. This was done to simplify the physical processes which occur when a sample is damaged. The experimentally damaged samples were then investigated using X-ray tomography to determine the physical extent of the damage. The experimental results are then compared with the numerical predictions by considering the physical extent of the polymer removal. The extent of polymer removal predicted by the numerical model, solving for pyrolysis, gave a reasonable agreement with the damage seen in the experimental sample. Furthermore the numerical model predicts that the damage caused by polymer phase change has a minimal contribution to the overall extent of the damage
Measured Sensitivity of the First Mark II Phased Array Feed on an ASKAP Antenna
This paper presents the measured sensitivity of CSIRO's first Mk. II phased
array feed (PAF) on an ASKAP antenna. The Mk. II achieves a minimum
system-temperature-over-efficiency of 78 K at 1.23 GHz
and is 95 K or better from 835 MHz to 1.8 GHz. This PAF was designed for the
Australian SKA Pathfinder telescope to demonstrate fast astronomical surveys
with a wide field of view for the Square Kilometre Array (SKA).Comment: 5 pages, 2 figures, accepted for publication in Electromagnetics in
Advanced applications (ICEAA), 2015 International Conference o
High-velocity OH megamasers in IRAS 20100-4156: Evidence for a Supermassive Black Hole
We report the discovery of new, high-velocity narrow-line components of the
OH megamaser in IRAS 20100-4156. Results from the Australian Square Kilometre
Array Pathfinder (ASKAP)'s Boolardy Engineering Test Array (BETA) and the
Australia Telescope Compact Array (ATCA) provide two independent measurements
of the OH megamaser spectrum. We found evidence for OH megamaser clumps at
409 and 562 km/s (blue-shifted) from the systemic velocity of the galaxy,
in addition to the lines previously known. The presence of such high velocities
in the molecular emission from IRAS 201004156 could be explained by a ~50 pc
molecular ring enclosing an approximately 3.8 billion solar mass black hole. We
also discuss two alternatives, i.e. that the narrow-line masers are dynamically
coupled to the wind driven by the active galactic nucleus or they are
associated with two separate galactic nuclei. The comparison between the BETA
and ATCA spectra provides another scientific verification of ASKAP's BETA. Our
data, combined with previous measurements of the source enabled us to study the
variability of the source over a twenty-six year period. The flux density of
the brightest OH maser components has reduced by more than a factor of two
between 1988 and 2015, whereas a secondary narrow-line component has more than
doubled in the same time. Plans for high-resolution VLBI follow-up of this
source are discussed, as are prospects for discovering new OH megamasers during
the ASKAP early science program.Comment: Accepted to MNRAS. Seven pages, three figure
Isolation of mesenchymal stem cells from bone marrow aspirate
Isolation of mesenchymal stem cells from bone marrow aspirat
The Performance and Calibration of the CRAFT Fly's Eye Fast Radio Burst Survey
Since January 2017, the Commensal Real-time ASKAP Fast Transients survey
(CRAFT) has been utilising commissioning antennas of the Australian SKA
Pathfinder (ASKAP) to survey for fast radio bursts (FRBs) in fly's eye mode.
This is the first extensive astronomical survey using phased array feeds
(PAFs), and a total of 20 FRBs have been reported. Here we present a
calculation of the sensitivity and total exposure of this survey, using the
pulsars B1641-45 (J1644-4559) and B0833-45 (J0835-4510, i.e.\ Vela) as
calibrators. The design of the survey allows us to benchmark effects due to PAF
beamshape, antenna-dependent system noise, radio-frequency interference, and
fluctuations during commissioning on timescales from one hour to a year.
Observation time, solid-angle, and search efficiency are calculated as a
function of FRB fluence threshold. Using this metric, effective survey
exposures and sensitivities are calculated as a function of the source counts
distribution. The implied FRB rate is significantly lower than the
\,sky\,day calculated using nominal exposures and
sensitivities for this same sample by \citet{craft_nature}. At the Euclidean
power-law index of , the rate is \,sky\,day above a threshold of \,Jy\,ms, while for the best-fit index for this sample of , it is
\,sky\,day above a threshold of \,Jy\,ms. This strongly suggests that these calculations be performed
for other FRB-hunting experiments, allowing meaningful comparisons to be made
between them.Comment: 21 pages, 15 figures, 2 tables, accepted for publication in PAS
Cold gas outflows from the Small Magellanic Cloud traced with ASKAP
Feedback from massive stars plays a critical role in the evolution of the
Universe by driving powerful outflows from galaxies that enrich the
intergalactic medium and regulate star formation. An important source of
outflows may be the most numerous galaxies in the Universe: dwarf galaxies.
With small gravitational potential wells, these galaxies easily lose their
star-forming material in the presence of intense stellar feedback. Here, we
show that the nearby dwarf galaxy, the Small Magellanic Cloud (SMC), has atomic
hydrogen outflows extending at least 2 kiloparsecs (kpc) from the star-forming
bar of the galaxy. The outflows are cold, , and may have formed
during a period of active star formation million years (Myr) ago. The
total mass of atomic gas in the outflow is solar masses, , or % of the total atomic gas of the galaxy. The inferred
mass flux in atomic gas alone, , is up to an order of magnitude greater than the star
formation rate. We suggest that most of the observed outflow will be stripped
from the SMC through its interaction with its companion, the Large Magellanic
Cloud (LMC), and the Milky Way, feeding the Magellanic Stream of hydrogen
encircling the Milky Way.Comment: Published in Nature Astronomy, 29 October 2018,
http://dx.doi.org/10.1038/s41550-018-0608-
WALLABY Early Science - I. The NGC 7162 Galaxy Group
We present Widefield ASKAP L-band Legacy All-sky Blind Survey (WALLABY) early
science results from the Australian Square Kilometre Array Pathfinder (ASKAP)
observations of the NGC 7162 galaxy group. We use archival HIPASS and Australia
Telescope Compact Array (ATCA) observations of this group to validate the new
ASKAP data and the data reduction pipeline ASKAPsoft. We detect six galaxies in
the neutral hydrogen (HI) 21-cm line, expanding the NGC 7162 group membership
from four to seven galaxies. Two of the new detections are also the first HI
detections of the dwarf galaxies, AM 2159-434 and GALEXASC J220338.65-431128.7,
for which we have measured velocities of and km s,
respectively. We confirm that there is extended HI emission around NGC 7162
possibly due to past interactions in the group as indicated by the
offset between the kinematic and morphological major axes for NGC 7162A, and
its HI richness. Taking advantage of the increased resolution (factor of
) of the ASKAP data over archival ATCA observations, we fit a tilted
ring model and use envelope tracing to determine the galaxies' rotation curves.
Using these we estimate the dynamical masses and find, as expected, high dark
matter fractions of for all group members. The
ASKAP data are publicly available.Comment: 20 pages, 11 figures, accepted for publication in MNRA
Field sources near the southern-sky calibrator PKS B1934-638: effect on spectral line observations with SKA-MID and its precursors
Accurate instrumental bandpass corrections are essential for the reliable
interpretation of spectral lines from targeted and survey-mode observations
with radio interferometers. Bandpass correction is typically performed by
comparing measurements of a strong calibrator source to an assumed model,
typically an isolated point source. The wide field-of-view and high sensitivity
of modern interferometers means that additional sources are often detected in
observations of calibrators. This can introduce errors into bandpass
corrections and subsequently the target data if not properly accounted for.
Focusing on the standard calibrator PKS B1934-638, we perform simulations to
asses this effect by constructing a wide-field sky model. The cases of ASKAP
(0.7-1.9 GHz), MeerKAT (UHF: 0.58-1.05 GHz; L-band: 0.87-1.67 GHz) and Band 2
(0.95-1.76 GHz) of SKA-MID are examined. The use of a central point source
model during bandpass calibration is found to impart amplitude errors into
spectra measured by the precursor instruments at the ~0.2-0.5% level dropping
to ~0.01% in the case of SKA-MID. This manifests itself as ripples in the
source spectrum, the behaviour of which is coupled to the distribution of the
array baselines, the solution interval, the primary beam size, the hour-angle
of the calibration scan, as well as the weights used when imaging the target.
Calibration pipelines should routinely employ complete field models for
standard calibrators to remove this potentially destructive contaminant from
the data, a recommendation we validate by comparing our simulation results to a
MeerKAT scan of PKS B1934-638, calibrated with and without our expanded sky
model.Comment: 11 pages, 10 figures, accepted for publication in MNRA
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