9,297 research outputs found
Restoration of eucalypt grassy woodland: effects of experimental interventions on ground-layer vegetation
We report on the effects of broad-scale restoration treatments on the ground layer of eucalypt grassy woodland in south-eastern Australia. The experiment was conducted in two conservation reserves from which livestock grazing had previously been removed. Changes in biomass, species diversity, ground-cover attributes and life-form were analysed over a 4-year period in relation to the following experimental interventions: (1) reduced kangaroo density, (2) addition of coarse woody debris and (3) fire (a single burn). Reducing kangaroo density doubled total biomass in one reserve, but no effects on exotic biomass, species counts or ground cover attributes were observed. Coarse woody debris also promoted biomass, particularly exotic annual forbs, as well as plant diversity in one of the reserves. The single burn reduced biomass, but changed little else. Overall, we found the main driver of change to be the favourable growth seasons that had followed a period of drought. This resulted in biomass increasing by 67%, (mostly owing to the growth of perennial native grasses), whereas overall native species counts increased by 18%, and exotic species declined by 20% over the 4-year observation period. Strategic management of grazing pressure, use of fire where biomass has accumulated and placement of coarse woody debris in areas of persistent erosion will contribute to improvements in soil and vegetation condition, and gains in biodiversity, in the future.Funding and in-kind logistic support for this project was
provided by the ACT Government as part of an Australian Research
Council Linkage Grant (LP0561817; LP110100126). Drafts of the
manuscript were read by Saul Cunningham and Ben Macdonald
Shot Noise Suppression in Avalanche Photodiodes
We identify a new shot noise suppression mechanism in a thin (~100 nm)
heterostructure avalanche photodiode. In the low-gain regime the shot noise is
suppressed due to temporal correlations within amplified current pulses. We
demonstrate in a Monte Carlo simulation that the effective excess noise factors
can be <1, and reconcile the apparent conflict between theory and experiments.
This shot noise suppression mechanism is independent of known mechanisms such
as Coulomb interaction, or reflection at heterojunction interfaces.Comment: Phys. Rev. Lett., accepted for publicatio
Spin gaps and magnetic structure of NaxCoO2
We present two experiments that provide information on spin anisotropy and
the magnetic structure of NaxCoO2. First, we report low-energy neutron
inelastic scattering measurements of the zone-center magnetic excitations in
the magnetically ordered phase of Na0.75CoO2. The energy spectra suggest the
existence of two gaps, and are very well fitted by a spin-wave model with both
in-plane and out-of-plane anisotropy terms. The gap energies decrease with
increasing temperature and both gaps are found to have closed when the
temperature exceeds the magnetic ordering temperature T_m~22 K. Secondly, we
present neutron diffraction studies of Na0.85CoO2 with a magnetic field applied
approximately parallel to the c axis. For fields in excess of ~8T a magnetic
Bragg peak was observed at the (0,0,3) position in reciprocal space. We
interpret this as a spin-flop transition of the A-type antiferromagnetic
structure, and we show that the spin-flop field is consistent with the size of
the anisotropy gap.Comment: 9 pages, 7 figure
Radio Sources in the 2dF Galaxy Redshift Survey. I. Radio Source Populations
We present the first results from a study of the radio continuum properties
of galaxies in the 2dF Galaxy Redshift Survey, based on thirty 2dF fields
covering a total area of about 100 square degrees. About 1.5% of galaxies with
b(J) < 19.4 mag are detected as radio continuum sources in the NRAO VLA Sky
Survey (NVSS). Of these, roughly 40% are star-forming galaxies and 60% are
active galaxies (mostly low-power radio galaxies and a few Seyferts). The
combination of 2dFGRS and NVSS will eventually yield a homogeneous set of
around 4000 radio-galaxy spectra, which will be a powerful tool for studying
the distriibution and evolution of both AGN and starburst galaxies out to
redshift z=0.3.Comment: 14 pages, 7 figures, accepted for publication in PAS
The Interaction between the ISM and Star Formation in the Dwarf Starburst Galaxy NGC 4214
We present the first interferometric study of the molecular gas in the
metal-poor dwarf starburst galaxy NGC 4214. Our map of the 12CO(1-0) emission,
obtained at the OVRO millimeter array, reveals an unexpected structural wealth.
We detected three regions of molecular emission in the north-west (NW),
south-east (SE) and centre of NGC 4214 which are in very different and distinct
evolutionary stages (total molecular mass: 5.1 x 10^6 M_sun). These differences
are apparent most dramatically when the CO morphologies are compared to optical
ground based and HST imaging: massive star formation has not started yet in the
NW region; the well-known starburst in the centre is the most evolved and star
formation in the SE complex started more recently. We derive a star formation
efficiency of 8% for the SE complex. Using high--resolution VLA observations of
neutral hydrogen HI and our CO data we generated a total gas column density map
for NGC 4214 (HI + H_2). No clear correlation is seen between the peaks of HI,
CO and the sites of ongoing star formation. This emphasizes the irregular
nature of dwarf galaxies. The HI and CO velocities agree well, so do the
H-alpha velocities. In total, we cataloged 14 molecular clumps in NGC 4214. Our
results from a virial mass analysis are compatible with a Galactic CO-to-H_2
conversion factor for NGC 4214 (lower than what is usually found in metal-poor
dwarf galaxies).Comment: accepted for publication in the AJ (February 2001), full ps file at:
ftp://ftp.astro.caltech.edu/users/fw/ngc4214/walter_prep.p
A 4.8- and 8.6-GHz Survey of the Large Magellanic Cloud: I The Images
Detailed 4.8- and 8.6-GHz radio images of the entire Large Magellanic Cloud
with half-power beamwidths of 33" at 4.8 GHz and 20" at 8.6 GHz have been
obtained using the Australia Telescope Compact Array. A total of 7085 mosaic
positions were used to cover an area of 6 degrees on a side. Full polarimetric
observations were made. These images have sufficient spatial resolution (~8 and
5 pc, respectively) and sensitivity (3-sigma of 1 mJy/beam) to identify most of
the individual SNRs and H II regions and also, in combination with available
data from the Parkes 64-m telescope, the structure of the smooth emission in
that galaxy. In addition, limited data using the sixth antenna at 4.5 to 6-km
baselines are available to distinguish bright point sources (<3 and 2 arcsec,
respectively) and to help estimate sizes of individual sources smaller than the
resolution of the full survey. The resultant database will be valuable for
statistical studies and comparisons with x-ray, optical and infrared surveys of
the LMC with similar resolution.Comment: 28 pages, 10 figures, 2 tables, accepted for publication in the Feb
2005 A
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Thorium Energy Futures
The potential for thorium as an alternative or supplement to uranium in fission power generation has long been recognised, and several reactors, of various types, have already operated using thorium-based fuels. Accelerator Driven Subcritical (ADS) systems have benefits and drawbacks when compared to conventional critical thorium reactors, for both solid and molten salt fuels. None of the four options – liquid or solid, with or without an accelerator – can yet be rated as better or worse than the other three, given today's knowledge. We outline the research that will be necessary to lead to an informed choice
The impact of labial fixed appliance orthodontic treatment on patient expectation, experience, and satisfaction:An overview of systematic reviews
Background: Patient perception with fixed appliance orthodontic treatment is important to improve oral health-related quality of life.Objective: The main objective of this study was to evaluate the impact of labial fixed appliance orthodontic care on patient perception before, during, and after the treatment.Search methods: Relevant systematic reviews investigating patient perception with fixed appliance orthodontic treatment were identified by searching electronic databases: MEDLINE via OVID (1946 to 31 December 2018), EMBASE (1974 to 31 December 2018), AMED (Allied and Complementary Medicine Database; 1985 to November 2018), PubMed (inception to 31 December 2018), Web of Science (1900 to 2018), and PsychINFO (1806 to 31 December 2018). Ongoing systematic reviews were searched using Prospero and a grey literature search was undertaken using Google Scholar and OpenGrey (www.opengrey.eu/). No language restriction was applied.Selection criteria: Only studies investigating patient perception of fixed appliance orthodontic treatment were included.Data collection and analysis: Screening, quality assessment [using the AMSTAR 2 tool (A Measurement Tool to Assess Systematic Reviews)], and data extraction were performed by two authors independently. Information was categorized and narratively synthesized for the key findings.Results: A total of 163 articles investigating patient expectation, experience, and satisfaction with conventional ligation labial fixed orthodontic appliances were obtained. Of these, 152 observational or interventional studies were excluded, resulting in 11 eligible systematic reviews. Two were excluded as earlier reports of a Cochrane review. The quality of the reviews was variable (critically low, low, and moderate). The findings were as follows: aesthetics represents a primary motive for orthodontic treatment; a temporary deterioration in the quality of life occurs during the initial phases of treatment; gender and ethnicity factors do not have an impact on patient perception of treatment; and a positive relationship between orthodontist-patient-parent is important to achieve patient compliance and satisfaction.Conclusions: There is a lack of high-quality studies in terms of systematic reviews and meta-analyses for assessing patient perception with fixed appliance orthodontic treatment. The aesthetic impact of malocclusion is the main motive for seeking orthodontic treatment. Quality of life reduces during the initial stages of orthodontic treatment but improves in the later stages of treatment. Assessment before, during, and after orthodontic treatment is necessary to comprehensively assess patient perception at all stages of care.Trial registration: CRD42019122653. Conflict of Interest: None to declare.</p
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