298 research outputs found
Review of water supply-demand options for South East Queensland
This independent review aims to assess the Queensland Government's proposed strategy for meeting the long-term water supply-demand balance for South East Queensland, of which the Traveston Crossing scheme is a major and controversial component. The review, conducted by a team from the ISF at the UTS and Cardno, concludes that a diverse portfolio of options can ensure supply security for South East Queensland (SEQ) well into the future, certainly to 2050. Such options include: increasing water supply availability (supply-side options); decreasing the demand for water (demand-side options); and meeting water supply needs during deep droughts (drought response options). A number of the elements of such a portfolio are already being implemented as part of the current Queensland Government strategy. With the extension and addition of low unit cost demand-side options and supply-side drought response readiness options, a clear conclusion of this study is that the proposed dam at Traveston Crossing on the Mary River is neither necessary nor desirable as a part of the portfolio for ensuring supply security to 2050. The increase in supply from this proposed dam will not assist in the short-term during the current severe drought in which water (from savings and supply) is needed over the next two to three years. Planned completion of the Traveston Crossing Dam Stage 1 is in 2012. Additional time will be needed for the dam to fill, which could take an additional two years, resulting in the yield from this source only potentially being available in 2014. Neither is the Traveston Crossing scheme needed for supply-demand balance in the longer term with the suite of other more appropriate drought response measures being implemented by the Queensland Government and strategy being proposed as part of this study. The proposed dam at Traveston Crossing on the Mary River represents a high total cost, high unit cost, high risk and high environmental and social impact option
A Mass Bound for Spherically Symmetric Black Hole Spacetimes
Requiring that the matter fields are subject to the dominant energy
condition, we establish the lower bound for the
total mass of a static, spherically symmetric black hole spacetime. ( and denote the area and the surface gravity of the horizon,
respectively.) Together with the fact that the Komar integral provides a simple
relation between and the strong energy condition,
this enables us to prove that the Schwarzschild metric represents the only
static, spherically symmetric black hole solution of a selfgravitating matter
model satisfying the dominant, but violating the strong energy condition for
the timelike Killing field at every point, that is, .
Applying this result to scalar fields, we recover the fact that the only black
hole configuration of the spherically symmetric Einstein-Higgs model with
arbitrary non-negative potential is the Schwarzschild spacetime with constant
Higgs field. In the presence of electromagnetic fields, we also derive a
stronger bound for the total mass, involving the electromagnetic potentials and
charges. Again, this estimate provides a simple tool to prove a ``no-hair''
theorem for matter fields violating the strong energy condition.Comment: 16 pages, LATEX, no figure
An Explanation for the Observed Weak Size Evolution of Disk Galaxies
Surveys of distant galaxies with the Hubble Space Telescope and from the
ground have shown that there is only mild evolution in the relationship between
radial size and stellar mass for galactic disks from z~1 to the present day.
Using a sample of nearby disk-dominated galaxies from the Sloan Digital Sky
Survey (SDSS), and high redshift data from the GEMS (Galaxy Evolution from
Morphology and SEDs) survey, we investigate whether this result is consistent
with theoretical expectations within the hierarchical paradigm of structure
formation. The relationship between virial radius and mass for dark matter
halos in the LCDM model evolves by about a factor of two over this interval.
However, N-body simulations have shown that halos of a given mass have less
centrally concentrated mass profiles at high redshift. When we compute the
expected disk size-stellar mass distribution, accounting for this evolution in
the internal structure of dark matter halos and the adiabatic contraction of
the dark matter by the self-gravity of the collapsing baryons, we find that the
predicted evolution in the mean size at fixed stellar mass since z~1 is about
15-20 percent, in good agreement with the observational constraints from GEMS.
At redshift z~2, the model predicts that disks at fixed stellar mass were on
average only 60% as large as they are today. Similarly, we predict that the
rotation velocity at a given stellar mass (essentially the zero-point of the
Tully-Fisher relation) is only about 10 percent larger at z~1 (20 percent at
z~2) than at the present day.Comment: 13 pages, 6 figures, accepted for publication in ApJ. Revised in
response to referee's comments to improve clariry. Results are unchange
Co-ordination between Rashba spin-orbital interaction and space charge effect and enhanced spin injection into semiconductors
We consider the effect of the Rashba spin-orbital interaction and space
charge in a ferromagnet-insulator/semiconductor/insulator-ferromagnet junction
where the spin current is severely affected by the doping, band structure and
charge screening in the semiconductor. In diffusion region, if the the
resistance of the tunneling barriers is comparable to the semiconductor
resistance, the magnetoresistance of this junction can be greatly enhanced
under appropriate doping by the co-ordination between the Rashba effect and
screened Coulomb interaction in the nonequilibrium transport processes within
Hartree approximation.Comment: 4 pages, 3 figure
A Study of the 't Hooft Model with the Overlap Dirac Operator
We present the results of an exploratory numerical study of two dimensional
QCD with overlap fermions. We have performed extensive simulations for U(N_c)
and SU(N_c) color groups with N_c=2, 3, 4 and coupling constants chosen to
satisfy the 't Hooft condition g^2 N_c =const=4/3. We have computed the meson
spectrum and decay constants, the topological susceptibility and the chiral
condensate. For U(N_c) gauge groups, our results indicate that the
Witten-Veneziano relation is satisfied within our statistical errors and that
the chiral condensate for N_f=1 is compatible with a non-zero value. Our
results exhibit universality in N_c and confirm once more the excellent chiral
properties of the overlap-Dirac operator.Comment: 18 pages, 4 figure
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Reasons for poor uptake of TB preventive therapy in South Africa
BACKGROUND: South Africa has one the highest TB and HIV burdens globally. TB preventive therapy (TPT) reduces the risk of TB disease and TB-related mortality in adults and children living with HIV and is indicated for use in TB-exposed HIV-negative individuals and children. TPT implementation in South Africa remains suboptimal.
METHODS: We conducted a pragmatic review of TPT implementation using multiple data sources, including informant interviews (n = 134), semi-structured observations (n = 93) and TB patient folder reviews in 31 health facilities purposively selected across three high TB burden provinces. We used case descriptive analysis and thematic coding to identify barriers and facilitators to TPT implementation.
RESULTS: TPT programme implementation was suboptimal, with inadequate monitoring even in health districts with well-functioning TB services. Health workers reported scepticism about TPT effectiveness, deprioritised TPT in practice and expressed divergent opinions about the cadres of staff responsible for implementation. Service- and facility-level barriers included ineffective contact tracing, resource shortages, lack of standardised reporting mechanisms and insufficient patient education on TPT. Patient-level barriers included socio-economic factors.
CONCLUSIONS: Improving TPT implementation will require radically simplified and more feasible systems and training for all cadres of health workers. Partnership with communities to stimulate demand driven service uptake can potentially facilitate implementation
VPR-Bench: An Open-Source Visual Place Recognition Evaluation Framework with Quantifiable Viewpoint and Appearance Change
Visual place recognition (VPR) is the process of recognising a previously visited place using visual information, often under varying appearance conditions and viewpoint changes and with computational constraints. VPR is related to the concepts of localisation, loop closure, image retrieval and is a critical component of many autonomous navigation systems ranging from autonomous vehicles to drones and computer vision systems. While the concept of place recognition has been around for many years, VPR research has grown rapidly as a field over the past decade due to improving camera hardware and its potential for deep learning-based techniques, and has become a widely studied topic in both the computer vision and robotics communities. This growth however has led to fragmentation and a lack of standardisation in the field, especially concerning performance evaluation. Moreover, the notion of viewpoint and illumination invariance of VPR techniques has largely been assessed qualitatively and hence ambiguously in the past. In this paper, we address these gaps through a new comprehensive open-source framework for assessing the performance of VPR techniques, dubbed “VPR-Bench”. VPR-Bench (Open-sourced at: https://github.com/MubarizZaffar/VPR-Bench) introduces two much-needed capabilities for VPR researchers: firstly, it contains a benchmark of 12 fully-integrated datasets and 10 VPR techniques, and secondly, it integrates a comprehensive variation-quantified dataset for quantifying viewpoint and illumination invariance. We apply and analyse popular evaluation metrics for VPR from both the computer vision and robotics communities, and discuss how these different metrics complement and/or replace each other, depending upon the underlying applications and system requirements. Our analysis reveals that no universal SOTA VPR technique exists, since: (a) state-of-the-art (SOTA) performance is achieved by 8 out of the 10 techniques on at least one dataset, (b) SOTA technique in one community does not necessarily yield SOTA performance in the other given the differences in datasets and metrics. Furthermore, we identify key open challenges since: (c) all 10 techniques suffer greatly in perceptually-aliased and less-structured environments, (d) all techniques suffer from viewpoint variance where lateral change has less effect than 3D change, and (e) directional illumination change has more adverse effects on matching confidence than uniform illumination change. We also present detailed meta-analyses regarding the roles of varying ground-truths, platforms, application requirements and technique parameters. Finally, VPR-Bench provides a unified implementation to deploy these VPR techniques, metrics and datasets, and is extensible through templates
The Evolution of Early-type Red Galaxies with the GEMS Survey: Luminosity-size and Stellar Mass-size Relations Since z=1
We combine HST/ACS imaging from the GEMS survey with redshifts and rest-frame
quantities from COMBO-17 to study the evolution of morphologically early-type
galaxies with red colors since z=1. We use a new large sample of 728 galaxies
with centrally-concentrated radial profiles (Sersic n>2.5) and rest-frame U-V
colors on the red sequence. By appropriate comparison with the local relations
from SDSS, we find that the luminosity-size (L-R) and stellar mass-size (M-R)
relations evolve in a manner that is consistent with the passive aging of
ancient stars. By itself, this result is consistent with a completely passive
evolution of the red early-type galaxy population. If instead, as demonstrated
by a number of recent surveys, the early-type galaxy population builds up in
mass by a factor of 2 since z=1, our results imply that new additions to the
early-type galaxy population follow similar L-R and M-R correlations, compared
to the older subset of early-type galaxies. Adding early-type galaxies to the
red sequence through disk fading appears to be consistent with the data.
Through comparison with models, the role of dissipationless merging is limited
to <1 major merger on average since z=1 for the most massive galaxies.
Predictions from models of gas-rich mergers are not yet mature enough to allow
a detailed comparison to our observations. We find tentative evidence that the
amount of luminosity evolution depends on galaxy stellar mass, such that the
least massive galaxies show stronger luminosity evolution compared to more
massive early types. This could reflect a different origin of low-mass
early-type galaxies and/or younger stellar populations; the present data is
insufficient to discriminate between these possibilities. (abridged)Comment: Submitted to ApJ, 23 pages, Latex using emulateapj5.sty and
onecolfloat.sty (included), 10 figures, version with full resolution figures
at http://www.astro.umass.edu/~dmac/Papers/ETevol.hires.p
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