700 research outputs found
The Life and Times of the Parkes-Tidbinbilla Interferometer
The Parkes-Tidbinbilla took advantage of a real-time radio-link connecting
the Parkes and Tidbinbilla antennas to form the world's longest real-time
interferometer. Built on a minuscule budget, it was an extraordinarily
successful instrument, generating some 24 journal papers including 3 Nature
papers, as well as facilitating the early development of the Australia
Telescope Compact Array. Here we describe its origins, construction, successes,
and life cycle, and discuss the future use of single-baseline interferometers
in the era of SKA and its pathfinders.Comment: Accepted by Journal of Astronomical History & Heritage. arXiv admin
note: substantial text overlap with arXiv:1210.098
Adaptive Filters Revisited - RFI Mitigation in pulsar observations
Pulsar detection and timing experiments are applications where adaptive
filters seem eminently suitable tools for radio-frequency-interference (RFI)
mitigation. We describe a novel variant which works well in field trials of
pulsar observations centred on an observing frequency of 675 MHz, a bandwidth
of 64 MHz and with 2-bit sampling. Adaptive filters have generally received bad
press for RFI mitigation in radio astronomical observations with their most
serious drawback being a spectral echo of the RFI embedded in the filtered
signals. Pulsar observations are intrinsically less sensitive to this as they
operate in the (pulsar period) time domain. The field trials have allowed us to
identify those issues which limit the effectiveness of the adaptive filter. We
conclude that adaptive filters can significantly improve pulsar observations in
the presence of RFI.Comment: Accepted for publication in Radio Scienc
Robust correlators
Radio frequency interference (RFI) already limits the sensitivity of existing
radio telescopes in several frequency bands and may prove to be an even greater
obstacle for future generation instruments to overcome. I aim to create a
structure of radio astronomy correlators which will be statistically stable
(robust) in the presence of interference. A statistical analysis of the mixture
of system noise + signal noise + RFI is proposed here which could be
incorporated into the block diagram of a correlator. Order and rank statistics
are especially useful when calculated in both temporal and frequency domains.
Several new algorithms of robust correlators are proposed and investigated
here. Computer simulations and processing of real data demonstrate the efficacy
of the proposed algorithms
An Australia telescope survey for CMB anisotropies
We have surveyed six distinct `empty fields' using the Australia Telescope
Compact Array in an ultra-compact configuration with the aim of imaging, with a
high brightness sensitivity, any arcmin-scale brightness-temperature
anisotropies in the background radio sky. The six well-separated regions were
observed at a frequency of 8.7 GHz and the survey regions were limited by the
ATCA primary beams which have a full width at half maximum of 6 arcmin at this
frequency; all fields were observed with a resolution of 2 arcmin and an rms
thermal noise of 24 microJy/beam. After subtracting foreground confusion
detected in higher resolution images of the fields, residual fluctuations in
Stokes I images are consistent with the expectations from thermal noise and
weaker (unidentified) foreground sources; the Stokes Q and U images are
consistent with expectations from thermal noise.
Within the sensitivity of our observations, we have no reason to believe that
there are any Sunyaev-Zeldovich holes in the microwave sky surveyed. Assuming
Gaussian-form CMB anisotropy with a `flat' spectrum, we derive 95 per cent
confidence upper limits of Q_flat < 10--11 microK in polarized intensity and
Q_flat < 25 microK in total intensity. The ATCA filter function peaks at l=4700
and has half maximum values at l=3350 and 6050.Comment: 17 pages, includes 8 figures and 6 tables, accepted for publication
in MNRA
Compact Radio Cores in Seyfert Galaxies
We have observed a sample of 157 Seyfert galaxies with a 275 km baseline
radio interferometer to search for compact, high brightness temperature radio
emission from the active nucleus. We obtain the surprising result that compact
radio cores are much more common in Seyfert 2 than in Seyfert 1 galaxies, which
at first seems to be inconsistent with orientation unification schemes. We
propose a model, involving optical depth effects in the narrow-line region,
which can reconcile our result with the standard unified scheme. (Accepted for
publication in ApJ 1994 Sep 10)Comment: 21 pages and 7 figures, uuencoded tar-compressed postscript files,
ATP18
Model for Assessment of Endothelial Cell Function and Viability Using the MTT Dye Test and {3H}
A CAJM article on Model for assessment of endothelial cell function and viability.A highly specialised cell layer made of vascular endothelial cell (EC) lines all blood vessels and lymphatics.1 The function of this cell layer appears to vary according to anatomical site and size of the vessel.2 However, the basic function of supporting either anticoagulant orprocoagulant activities, depending on the local conditions and circumstances, are essentially similar. Any disruption of the equilibrium that exists between the endothelial cell and the circulating blood may result in clinically significant thrombosis or haemorrhage.3'4 Such pathophysiological insults include bacterial lipopolysaccharide (LPS) which may induce endotoxic septicaemia associated with disseminated intravascular coagulation,5 as well as the infusion of a variety of drugs into the vascular component.6
To investigate the effect of such agents and toxins on the endothelial cells, it is necessary to monitor metabolic and functional aspects of the cells’ behavior. This may provide an in vitro model for studying clinical conditions
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