1,809 research outputs found
Precious Little: Traces of Australian Place and Belonging
The Dissertation is a meditation on our relationship with this continent and its layered physical and psychological ‘landscapes’. It explores ways in which artists and writers have depicted our ‘thin’ but evolving presence here in the South, and references my own photographic work. The paper weaves together personal tales with fiction writing and cultural, settler and indigenous history. It identifies a uniquely Australian sense of 21st-century disquiet and argues for some modest aesthetic and social antidotes. It discusses in some detail the suppression of focus in photography, and suggests that the technique evokes not only memory, but a recognition of absence, which invites active participation (as the viewer attempts to ‘place’ and complete the picture). In seeking out special essences of place the paper considers the suburban poetics of painter Clarice Beckett, the rigorous focus-free oeuvre of photographer Uta Barth, and the hybrid vistas of artist/gardener Peter Hutchinson and painter Dale Frank. Interwoven are the insights of contemporary authors Gerald Murnane, W G Sebald and Paul Carter. A speculative chapter about the fluidity of landscape, the interconnectedness of land and sea, and Australia’s ‘deep’ geology fuses indigenous spirituality, oceanic imaginings of Australia, the sinuous bush-scapes of Patrick White, and the poetics of surfing. Full immersion is recommended
Detailed modelling of a large sample of Herschel sources in the Lockman Hole: identification of cold dust and of lensing candidates through their anomalous SEDs
We have studied in detail a sample of 967 SPIRE sources with 5σ detections at 350 and 500 μm and associations with Spitzer-SWIRE 24 μm galaxies in the HerMES-Lockman survey area, fitting theirmid- and far-infrared, and submillimetre, spectral energy distributions (SEDs) in an automatic search with a set of six infrared templates. For almost 300 galaxies,we havemodelled their SEDs individually to ensure the physicality of the fits. We confirm the need for the new cool and cold cirrus templates, and also of the young starburst template, introduced in earlier work. We also identify 109 lensing candidates via their anomalous SEDs and provide a set of colour–redshift constraints which allow lensing candidates to be identified from combined Herschel and Spitzer data. The picture that emerges of the submillimetre galaxy population is complex, comprising ultraluminous and hyperluminous starbursts, lower luminosity galaxies dominated by interstellar dust emission, lensed galaxies and galaxies with surprisingly cold (10–13 K) dust. 11 per cent of 500 μm selected sources are lensing candidates. 70 per cent of the unlensed sources are ultraluminous infrared galaxies and 26 per cent are hyperluminous. 34 per cent are dominated by optically thin interstellar dust (‘cirrus’) emission, but most of these are due to cooler dust than is characteristic of our Galaxy. At the highest infrared luminosities we see SEDs dominated by M82, Arp 220 and young starburst types, in roughly equal proportions
A SCUBA Scanmap of the HDF: Measuring the bright end of the sub-mm source counts
Using the 850 micron SCUBA camera on the JCMT and a scanning technique
different from other sub-mm surveys, we have obtained a 125 square arcminute
map centered on the Hubble Deep Field. The one-sigma sensitivity to point
sources is roughly 3 mJy and thus our map probes the brighter end of the sub-mm
source counts. We find 6 sources with a flux greater than about 12 mJy (>4
sigma) and, after a careful accounting of incompleteness and flux bias,
estimate the integrated density of bright sources N(>12 mJy)= 164 (+77/-58) per
square degree (68 per cent confidence bounds).Comment: 5 pages, 2 figures, Accepted for publication in MNRA
ISO observations and models of galaxies with Hidden Broad Line Regions
We present ISO mid-infrared spectrophotometry and far-infrared photometry of
galaxies with Hidden Broad Line Regions (HBLR). We also present radiative
transfer models of their spectral energy distributions which enable us to
separate the contributions from the dusty disc of the AGN and the dusty
starbursts. We find that the combination of tapered discs (discs whose
thickness increases with distance from the central source in the inner part but
stays constant in the outer part) and starbursts provide good fits to the data.
The tapered discs dominate in the mid-infrared part of the spectrum and the
starbursts in the far-infrared. After correcting the AGN luminosity for
anisotropic emission we find that the ratio of the AGN luminosity to the
starburst luminosity, L(AGN)/L(SB), ranges from about unity for IRAS14454-4343
to about 13 for IRAS01475-0740. Our results suggest that the warm IRAS colours
of HBLR are due to the relatively high L(AGN)/L(SB). Our fits are consistent
with the unified model and the idea that the infrared emission of AGN is
dominated by a dusty disc in the mid-infrared and starbursts in the
far-infrared.Comment: A&A accepeted, 8pages 2 Figures, final versio
LHC main dipole magnet circuits: sustaining near-nominal beam energies
Crossing the Franco-Swiss border, the Large Hadron Collider (LHC), designed to collide 7 TeV proton beams, is the world's largest and most powerful particle accelerator the operation of which was originally intended to commence in 2008. Unfortunately, due to an interconnect discontinuity in one of the main dipole circuit's 13 kA superconducting busbars, a catastrophic quench event occurred during initial magnet training, causing significant physical system damage. Furthermore, investigation into the cause found that such discontinuities were not only present in the circuit in question, but throughout the entire LHC. This prevented further magnet training and ultimately resulted in the maximum sustainable beam energy being limited to approximately half that of the design nominal, 3.5-4 TeV, for the first three years of operation (Run 1, 2009-2012) and a major consolidation campaign being scheduled for the first long shutdown (LS 1, 2012-2014).
Throughout Run 1, a series of studies attempted to predict the amount of post-installation training quenches still required to qualify each circuit to nominal-energy current levels. With predictions in excess of 80 quenches (each having a recovery time of 8-12+ hours) just to achieve 6.5 TeV and close to 1000 quenches for 7 TeV, it was decided that for Run 2, all systems be at least qualified for 6.5 TeV operation. However, even with all interconnect discontinuities scheduled to be repaired during LS 1, numerous other concerns regarding circuit stability arose. In particular, observations of an erratic behaviour of magnet bypass diodes and the degradation of other potentially weak busbar sections, as well as observations of seemingly random millisecond spikes in beam losses, known as unidentified falling object (UFO) events, which, if persist at 6.5 TeV, may eventually deposit sufficient energy to quench adjacent magnets.
In light of the above, the thesis hypothesis states that, even with the observed issues, the LHC main dipole circuits can safely support and sustain near-nominal proton beam energies of at least 6.5 TeV.
Research into minimising the risk of magnet training led to the development and implementation of a new qualification method, capable of providing conclusive evidence that all aspects of all circuits, other than the magnets and their internal joints, can safely withstand a quench event at near-nominal current levels, allowing for magnet training to be carried out both systematically and without risk. This method has become known as the Copper Stabiliser Continuity Measurement (CSCM). Results were a success, with all circuits eventually being subject to a full current decay from 6.5 TeV equivalent current levels, with no measurable damage occurring.
Research into UFO events led to the development of a numerical model capable of simulating typical UFO events, reproducing entire Run 1 measured event data sets and extrapolating to 6.5 TeV, predicting the likelihood of UFO-induced magnet quenches. Results provided interesting insights into the involved phenomena as well as confirming the possibility of UFO-induced magnet quenches. The model was also capable of predicting that such events, if left unaccounted for, are likely to be commonplace or not, resulting in significant long-term issues for 6.5+ TeV operation.
Addressing the thesis hypothesis, the following written works detail the development and results of all CSCM qualification tests and subsequent magnet training as well as the development and simulation results of both 4 TeV and 6.5 TeV UFO event modelling. The thesis concludes, post-LS 1, with the LHC successfully sustaining 6.5 TeV proton beams, but with UFO events, as predicted, resulting in otherwise uninitiated magnet quenches and being at the forefront of system availability issues
LHC Main Dipole Magnet Circuits: Sustaining Near-Nominal Beam Energies
Crossing the Franco-Swiss border, the Large Hadron Collider (LHC), designed to collide
7 TeV proton beams, is the world’s largest and most powerful particle accelerator –
the operation of which was originally intended to commence in 2008. Unfortunately, due
to an interconnect discontinuity in one of the main dipole circuit’s 13 kA superconducting
busbars, a catastrophic quench event occurred during initial magnet training, causing
significant physical system damage. Furthermore, investigation into the cause found that
such discontinuities were not only present in the circuit in question, but throughout the entire
LHC. This prevented further magnet training and ultimately resulted in the maximum
sustainable beam energy being limited to approximately half that of the design nominal,
3.5-4 TeV, for the first three years of operation (Run 1, 2009-2012) and a major consolidation
campaign being scheduled for the first long shutdown (LS 1, 2012-2014).
Throughout Run 1, a series of studies attempted to predict the amount of post-installation
training quenches still required to qualify each circuit to nominal-energy current levels.
With predictions in excess of 80 quenches (each having a recovery time of 8-12+ hours)
just to achieve 6.5 TeV and close to 1000 quenches for 7 TeV, it was decided that for
Run 2, all systems be at least qualified for 6.5 TeV operation. However, even with all interconnect
discontinuities scheduled to be repaired during LS 1, numerous other concerns
regarding circuit stability arose. In particular, observations of an erratic behaviour of magnet
bypass diodes and the degradation of other potentially weak busbar sections, as well as
observations of seemingly random millisecond spikes in beam losses, known as unidentified
falling object (UFO) events, which, if persist at 6.5 TeV, may eventually deposit sufficient
energy to quench adjacent magnets.
In light of the above, the thesis hypothesis states that, even with the observed issues,
the LHC main dipole circuits can safely support and sustain near-nominal proton beam
energies of at least 6.5 TeV.
Research into minimising the risk of magnet training led to the development and implementation
of a new qualification method, capable of providing conclusive evidence that
all aspects of all circuits, other than the magnets and their internal joints, can safely
withstand a quench event at near-nominal current levels, allowing for magnet training to
be carried out both systematically and without risk. This method has become known as
the Copper Stabiliser Continuity Measurement (CSCM). Results were a success, with all
iii
circuits eventually being subject to a full current decay from 6.5 TeV equivalent current
levels, with no measurable damage occurring.
Research into UFO events led to the development of a numerical model capable of
simulating typical UFO events, reproducing entire Run 1 measured event data sets and
extrapolating to 6.5 TeV, predicting the likelihood of UFO-induced magnet quenches. Results
provided interesting insights into the involved phenomena as well as confirming the
possibility of UFO-induced magnet quenches. The model was also capable of predicting
that such events, if left unaccounted for, are likely to be commonplace or not, resulting in
significant long-term issues for 6.5+ TeV operation.
Addressing the thesis hypothesis, the following written works detail the development
and results of all CSCM qualification tests and subsequent magnet training as well as the
development and simulation results of both 4 TeV and 6.5 TeV UFO event modelling. The
thesis concludes, post-LS 1, with the LHC successfully sustaining 6.5 TeV proton beams,
but with UFO events, as predicted, resulting in otherwise uninitiated magnet quenches and
being at the forefront of system availability issues
ISOPHOT 95 micron observations in the Lockman Hole - The catalogue and an assessment of the source counts
We report results from a new analysis of a deep 95 micron imaging survey with
ISOPHOT on board the Infrared Space Observatory, over a ~1 square degree area
within the Lockman Hole, which extends the statistics of our previous study
(Rodighiero et al. 2003). Within the survey area we detect sixty-four sources
with S/N>3 (roughly corresponding to a flux limit of 16 mJy). Extensive
simulations indicate that the sample is almost complete at fluxes > 100 mJy,
while the incompleteness can be quantified down to ~30 mJy. The 95 micron
galaxy counts reveal a steep slope below 100 mJy (alpha~1.6), in excess of that
expected for a non-evolving source population. In agreement with counts data
from ISO at 15 and 175 micron, this favours a model where the IR populations
evolve both in number and luminosity densities. We finally comment on some
differences found with other ISO results in this area.Comment: 4 pages, accepted by Astronomy and Astrophysics Lette
Submillimetre surveys: The prospects for Herschel
Using the observed submillimetre source counts, from 250-1200 microns
(including the most recent 250, 350 and 500 micron counts from BLAST), we
present a model capable of reproducing these results, which is used as a basis
to make predictions for upcoming surveys with the SPIRE instrument aboard the
Herschel Space Observatory. The model successfully fits both the integral and
differential source counts of submillimetre galaxies in all wavebands,
predicting that while ultra-luminous infrared galaxies dominate at the
brightest flux densities, the bulk of the infrared background is due to the
less luminous infrared galaxy population. The model also predicts confusion
limits and contributions to the cosmic infrared background that are consistent
with the BLAST results. Applying this to SPIRE gives predicted source confusion
limits of 19.4, 20.5 and 16.1mJy in the 250, 350 and 500 micron bands
respectively. This means the SPIRE surveys should achieve sensitivities 1.5
times deeper than BLAST, revealing a fainter population of infrared-luminous
galaxies, and detecting approximately 2600, 1300, and 700 sources per square
degree in the SPIRE bands (with one in three sources expected to be a high
redshift ultra-luminous source at 500 microns). The model number redshift
distributions predict a bimodal distribution of local quiescent galaxies and a
high redshift peak corresponding to strongly evolving star-forming galaxies. It
suggests the very deepest surveys with Herschel-SPIRE ought to sample the
source population responsible for the bulk of the infrared background.Comment: 5 pages, 4 figures, accepted for publication in MNRAS Letter
Submillimeter Observations of the Ultraluminous BAL Quasar APM 08279+5255
With an inferred bolometric luminosity of 5\times10^{15}{\rm \lsun}, the
recently identified z=3.87, broad absorption line quasar APM 08279+5255 is
apparently the most luminous object currently known. As half of its prodigious
emission occurs in the infrared, APM 08279+5255 also represents the most
extreme example of an Ultraluminous Infrared Galaxy. Here, we present new
submillimeter observations of this phenomenal object; while indicating that a
vast quantity of dust is present, these data prove to be incompatible with
current models of emission mechanisms and reprocessing in ultraluminous
systems. The influence of gravitational lensing upon these models is considered
and we find that while the emission from the central continuum emitting region
may be significantly enhanced, lensing induced magnification cannot easily
reconcile the models with observations. We conclude that further modeling,
including the effects of any differential magnification is required to explain
the observed emission from APM 08279+5255.Comment: 12 Pages with Two figures. Accepted for publication in the
Astrophysical Journal Letter
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