8,695 research outputs found
Morphological budgeting in the Motueka River: an analysis of technique
Morphological budgeting is a key method for monitoring and studying sediment transfers within gravelly rivers. We assess the utility of traditional crossâsection approaches to budgeting using Digital Elevation Model (DEM) analysis. DEMs give a more accurate volume calculation within the
constraint of sampling frequency compared with cross sections, since a greater area of river bed is sampled. DEM volume calculation within the 1.7 km âThree Beachesâ reach in the upper Motueka revealed a net loss of 3219 m3 in this reach between 2008â2009. Comparisons of this value with cross sectionâbased volume calculations at a range of section spacing using (i) Mean Bed Level (MBL) analysis and (ii) DEMs generated from cross section data, suggest accuracy of the budget is maximised at a critical cross section spacing not exceeding 90 m. Careful positioning of cross sections could lengthen this distance further and is essential to accurately represent river channel morphology. MBL analysis using crossâsections in the reach monumented by Tasman District Council (TDC) for river monitoring underestimates the magnitude of net sediment transfers by c. 30%
Performance in the MRCP(UK) Examination 2003-4: analysis of pass rates of UK graduates in relation to self-declared ethnicity and gender
Background: Male students and students from ethnic minorities have been reported to underperform in undergraduate medical examinations. We examined the effects of ethnicity and gender on pass rates in UK medical graduates sitting the Membership of the Royal Colleges of Physicians in the United Kingdom [MRCP( UK)] Examination in 2003-4. Methods: Pass rates for each part of the examination were analysed for differences between graduate groupings based on self- declared ethnicity and gender.Results: All candidates declared their gender, and 84 - 90% declared their ethnicity. In all three parts of the examination, white candidates performed better than other ethnic groups (P < 0.001). In the MRCP(UK) Part 1 and Part 2 Written Examinations, there was no significant difference in pass rate between male and female graduates, nor was there any interaction between gender and ethnicity. In the Part 2 Clinical Examination (Practical Assessment of Clinical Examination Skills, PACES), women performed better than did men (P < 0.001). Non-white men performed more poorly than expected, relative to white men or non-white women. Analysis of individual station marks showed significant interaction between candidate and examiner ethnicity for performance on communication skills (P = 0.011), but not on clinical skills (P = 0.176). Analysis of overall average marks showed no interaction between candidate gender and the number of assessments made by female examiners (P = 0.151).Conclusion: The cause of these differences is most likely to be multifactorial, but cannot be readily explained in terms of previous educational experience or differential performance on particular parts of the examination. Potential examiner prejudice, significant only in the cases where there were two non- white examiners and the candidate was non- white, might indicate different cultural interpretations of the judgements being made
BOND: Bayesian Oxygen and Nitrogen abundance Determinations in giant H II regions using strong and semi-strong lines
We present BOND, a Bayesian code to simultaneously derive oxygen and nitrogen
abundances in giant H II regions. It compares observed emission lines to a grid
of photoionization models without assuming any relation between O/H and N/O.
Our grid spans a wide range in O/H, N/O and ionization parameter U, and covers
different starburst ages and nebular geometries. Varying starburst ages
accounts for variations in the ionizing radiation field hardness, which arise
due to the ageing of H II regions or the stochastic sampling of the initial
mass function. All previous approaches assume a strict relation between the
ionizing field and metallicity. The other novelty is extracting information on
the nebular physics from semi-strong emission lines. While strong lines ratios
alone ([O III]/Hbeta, [O II]/Hbeta and [N II]/Hbeta) lead to multiple O/H
solutions, the simultaneous use of [Ar III]/[Ne III] allows one to decide
whether an H II region is of high or low metallicity. Adding He I/Hbeta pins
down the hardness of the radiation field. We apply our method to H II regions
and blue compact dwarf galaxies, and find that the resulting N/O vs O/H
relation is as scattered as the one obtained from the temperature-based method.
As in previous strong-line methods calibrated on photoionization models, the
BOND O/H values are generally higher than temperature-based ones, which might
indicate the presence of temperature fluctuations or kappa distributions in
real nebulae, or a too soft ionizing radiation field in the models.Comment: MNRAS in press; 21 pages, 22 figures, 2 tables; code, data and
results available at http://bond.ufsc.b
Combined chips for atom-optics
We present experiments with Bose-Einstein condensates on a combined atom
chip. The combined structure consists of a large-scale "carrier chip" and
smaller "atom-optics chips", containing micron-sized elements. This allows us
to work with condensates very close to chip surfaces without suffering from
fragmentation or losses due to thermally driven spin flips. Precise
three-dimensional positioning and transport with constant trap frequencies are
described. Bose-Einstein condensates were manipulated with submicron accuracy
above atom-optics chips. As an application of atom chips, a direction sensitive
magnetic field microscope is demonstrated.Comment: 9 pages, 9 figure
Is the even distribution of insecticide-treated cattle essential for tsetse control? Modelling the impact of baits in heterogeneous environments
Background:
Eliminating Rhodesian sleeping sickness, the zoonotic form of Human African Trypanosomiasis, can be achieved only through interventions against the vectors, species of tsetse (Glossina). The use of insecticide-treated cattle is the most cost-effective method of controlling tsetse but its impact might be compromised by the patchy distribution of livestock. A deterministic simulation model was used to analyse the effects of spatial heterogeneities in habitat and baits (insecticide-treated cattle and targets) on the distribution and abundance of tsetse.
Methodology/Principal Findings:
The simulated area comprised an operational block extending 32 km from an area of good habitat from which tsetse might invade. Within the operational block, habitat comprised good areas mixed with poor ones where survival probabilities and population densities were lower. In good habitat, the natural daily mortalities of adults averaged 6.14% for males and 3.07% for females; the population grew 8.46in a year following a 90% reduction in densities of adults and pupae, but expired when the population density of males was reduced to <0.1/km2; daily movement of adults averaged 249 m for males and 367 m for females. Baits were placed throughout the operational area, or patchily to simulate uneven distributions of cattle and targets. Gaps of 2â3 km between baits were inconsequential provided the average imposed mortality per km2 across the entire operational area was maintained. Leaving gaps 5â7 km wide inside an area where baits killed 10% per day delayed effective control by 4â11 years. Corrective measures that put a few baits within the gaps were more effective than deploying extra baits on the edges.
Conclusions/Significance:
The uneven distribution of cattle within settled areas is unlikely to compromise the impact of insecticide-treated cattle on tsetse. However, where areas of >3 km wide are cattle-free then insecticide-treated targets should be deployed to compensate for the lack of cattle
Bragg spectroscopy of a strongly interacting Fermi gas
We present a comprehensive study of the Bose-Einstein condensate to
Bardeen-Cooper-Schrieffer (BEC-BCS) crossover in fermionic Li using Bragg
spectroscopy. A smooth transition from molecular to atomic spectra is observed
with a clear signature of pairing at and above unitarity. These spectra probe
the dynamic and static structure factors of the gas and provide a direct link
to two-body correlations. We have characterised these correlations and measured
their density dependence across the broad Feshbach resonance at 834 G.Comment: Replaced with published versio
Contact and sum-rules in a near-uniform Fermi gas at unitarity
We present an experimental study of the high-energy excitation spectra of
unitary Fermi gases. Using focussed beam Bragg spectroscopy, we locally probe
atoms in the central region of a harmonically trapped cloud where the density
is nearly uniform, enabling measurements of the dynamic structure factor for a
range of temperatures both below and above the superfluid transition. Applying
sum-rules to the measured Bragg spectra, we resolve the characteristic
behaviour of the universal contact parameter, , across the superfluid
transition. We also employ a recent theoretical result for the kinetic
(second-moment) sum-rule to obtain the internal energy of gases at unitarity.Comment: 5 pages, 4 figure
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