14 research outputs found
Heavy elements in Galactic and Magellanic Cloud HII regions: recombination-line versus forbidden-line abundances
We have obtained deep optical, long-slit spectrophotometry of the Galactic
HII regions M 17, NGC 3576 and of the Magellanic Cloud HII regions 30 Doradus,
LMC N11B and SMC N66, recording the optical recombination lines (ORLs) of CII,
NII and OII. Temperature-insensitive ORL C2+/O2+ and N2+/O2 ratios are obtained
for all nebulae except SMC N66. The ORL C2+/O2+ ratios show remarkable
agreement within each galactic system, while also being in agreement with the
corresponding CEL ratios. For all five nebulae, the O2+/H+ abundance derived
from multiple OII ORLs is found to be higher than the corresponding value
derived from the strong [OIII] 4959, 5007A CELs, by factors of 1.8--2.7 for
four of the nebulae. The LMC N11B nebula exhibits a more extreme discrepancy
factor for the O2+ ion, ~5. Thus these HII regions exhibit ORL/CEL abundance
discrepancy factors that are similar to those previously encountered amongst
planetary nebulae.
Our optical CEL O2+/H+ abundances agree to within 20-30 per cent with
published O2+/H+ abundances that were obtained from observations of infrared
fine-structure lines. Since the low excitation energies of the latter make them
insensitive to variations about typical nebular temperatures, fluctuations in
temperature are ruled out as the cause of the observed ORL/CEL O2+ abundance
discrepancies. We present evidence that the observed OII ORLs from these HII
regions originate from gas of very similar density (<3500 cm-3) to that
emitting the observed heavy-element optical and infrared CELs, ruling out
models that employ high-density ionized inclusions in order to explain the
abundance discrepancy. We consider a scenario whereby much of the heavy-element
ORL emission originates from cold (<=500 K) metal-rich ionized regions.Comment: 24 pages; 9 figures; accepted by Monthly Notices of the Royal
Astronomical Societ
Using geographically weighted regression to explore the spatially heterogeneous spread of bovine tuberculosis in England and Wales
An understanding of the factors that affect the spread of endemic bovine tuberculosis (bTB) is critical for the development of measures to stop and reverse this spread. Analyses of spatial data need to account for the inherent spatial heterogeneity within the data, or else spatial autocorrelation can lead to an overestimate of the significance of variables. This study used three methods of analysisâleast-squares linear regression with a spatial autocorrelation term, geographically weighted regression (GWR) and boosted regression tree (BRT) analysisâto identify the factors that influence the spread of endemic bTB at a local level in England and Wales. The linear regression and GWR methods demonstrated the importance of accounting for spatial differences in risk factors for bTB, and showed some consistency in the identification of certain factors related to flooding, disease history and the presence of multiple genotypes of bTB. This is the first attempt to explore the factors associated with the spread of endemic bTB in England and Wales using GWR. This technique improves on least-squares linear regression approaches by identifying regional differences in the factors associated with bTB spread. However, interpretation of these complex regional differences is difficult and the approach does not lend itself to predictive models which are likely to be of more value to policy makers. Methods such as BRT may be more suited to such a task. Here we have demonstrated that GWR and BRT can produce comparable outputs
Comparative Absorption and Emission Abundance Analyses of Nebulae: Ion Emission Densities for IC 418
Recent analyses of nebular spectra have resulted in discrepant abundances
from CNO forbidden and recombination lines. We consider independent methods of
determining ion abundances for emission nebulae, comparing ion emission
measures with column densities derived from resonance absorption lines viewed
against the central star continuum. Separate analyses of the nebular emission
lines and the stellar UV absorption lines yield independent abundances for
ions, and their ratio can be expressed in terms of a parameter n_e_{em}, the
``emission density'' for each ion. Adequate data for this technique are still
scarce, but separate analyses of spectra of the planetary nebula and central
star of IC 418 do show discrepant abundances for several ions, especially Fe
II. The discrepancies are probably due to the presence of absorbing gas which
does not emit and/or to uncertain atomic data and excitation processes, and
they demonstrate the importance of applying the technique of combining
emission- and absorption-line data in deriving abundances for nebulae.Comment: 25 pages, 3 figures, accepted for publication in PAS
Attitudes and behaviour towards convenience food and food waste in the United Kingdom
Households in the UK discard much food. A reduction in such waste to mitigate environmental impact is part of UK government policy. This study investigated whether household food waste is linked to a lifestyle reliant on convenience food in younger consumers. A survey of 928 UK residents aged 18-40 years and responsible for the household food shopping (male n = 278; female n = 650) completed an online questionnaire designed to measure attitudes to convenience food and to quantify household food waste. Cluster analysis of 24 food-related lifestyle factors identified 5 consumer groups. General linear modelling techniques were used to test relationships between the purchase frequency of convenience food and household food waste. From the cluster analysis, five distinct convenience profiles emerged comprising: âepicuresâ (n = 135), âtraditional consumersâ (n = 255), âcasual consumersâ (n = 246), âfood detached consumersâ (n = 151) and âkitchen evadersâ (n = 141). Casual consumers and kitchen evaders were the most reliant on convenience food and notably were the most wasteful. The demographic profile of kitchen evaders matched the population groups currently targeted by UK food waste policy. Casual consumers represent a new and distinct group characterised by âbuy a lot and waste a lotâ behaviour. Household size, packaging format, price-awareness and marketing all appear to influence levels of food waste. However, it seems that subtle behavioural and sociocultural factors also have impact. Further research is needed to elucidate the factors that mediate the positive association between the purchase of convenience food and reported food waste in order to inform food waste policy and initiatives
Properties of the ionized gas in HH202. II: Results from echelle spectrophotometry with UVES
We present results of deep echelle spectrophotometry of the brightest knot of
the HH202 in the Orion Nebula --HH202-S-- using the ultraviolet Visual Echelle
Spectrograph (UVES). The high spectral resolution has permitted to separate the
component associated with the ambient gas from that associated with the gas
flow. We derive electron densities and temperatures for both components, as
well as the chemical abundances of several ions and elements from collisionally
excited lines, including the first determinations of Ca^{+} and Cr^{+}
abundances in the Orion Nebula. We also calculate the He^{+}, C^{2+}, O^{+} and
O^{2+} abundances from recombination lines. The difference between the O^{2+}
abundances determined from collisionally excited and recombination lines --the
so-called abundance discrepancy factor-- is 0.35 dex and 0.11 dex for the shock
and nebular components, respectively. Assuming that the abundance discrepancy
is produced by spatial variations in the electron temperature, we derive values
of the temperature fluctuation parameter, t^2, of 0.050 and 0.016, for the
shock and nebular components, respectively. Interestingly, we obtain almost
coincident t^2 values for both components from the analysis of the intensity
ratios of He I lines. We find significant departures from case B predictions in
the Balmer and Paschen flux ratios of lines of high principal quantum number n.
We analyze the ionization structure of HH202-S, finding enough evidence to
conclude that the flow of HH202-S has compressed the ambient gas inside the
nebula trapping the ionization front. We measure a strong increase of the total
abundances of nickel and iron in the shock component, the abundance pattern and
the results of photoionization models for both components are consistent with
the partial destruction of dust after the passage of the shock wave in HH202-S.Comment: 23 pages, 7 figures. Accepted for publication in MNRA
Finishing the euchromatic sequence of the human genome
The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers âŒ99% of the euchromatic genome and is accurate to an error rate of âŒ1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead
The Turkish people : their social life, religious beliefs and institutions and domestic life
by Lucy M. J. Garnet