1,712 research outputs found
A comprehensive study of reported high metallicity giant HII regions. I. Detailed abundance analysis
We present long-slit observations in the optical and near infrared of
fourteen HII regions in the spiral galaxies: NGC 628, NGC 925, NGC 1232 and NGC
1637, all of them reported to have solar or oversolar abundances according to
empirical calibrations. For seven of the observed regions, ion-weighted
temperatures from optical forbidden auroral to nebular line ratios have been
obtained and for six of them, the oxygen abundances derived by standard methods
turn out to be significantly lower than solar. The other one, named CDT1 in NGC
1232, shows an oxygen abundance of 12+log(O/H) = 8.95+-0.20 and constitutes, to
the best of our knowledge, the first high metallicity HII region for which
accurate line temperatures, and hence elemental abundances, have been derived.
For the rest of the regions no line temperature measurements could be made
and the metallicity has been determined by means of both detailed
photoionisation modelling and the sulphur abundance parameter S_23. Only one of
these regions shows values of O_23 and S_23 implying a solar or oversolar
metallicity.
According to our analysis, only two of the observed regions can therefore be
considered as of high metallicity. The two of them fit the trends previously
found in other high metallicity HII regions, i.e. N/O and S/O abundance ratios
seem to be higher and lower than solar respectively.Comment: Accepted for publication by MNRA
Radiocarbon dating of methane and carbon dioxide evaded from a temperate peatland stream
Streams draining peatlands export large quantities of carbon in different chemical forms and
are an important part of the carbon cycle. Radiocarbon (14C) analysis/dating provides unique
information on the source and rate that carbon is cycled through ecosystems, as has recently
been demonstrated at the air-water interface through analysis of carbon dioxide (CO2) lost
from peatland streams by evasion (degassing). Peatland streams also have the potential to
release large amounts of methane (CH4) and, though 14C analysis of CH4 emitted by ebullition
(bubbling) has been previously reported, diffusive emissions have not. We describe methods
that enable the 14C analysis of CH4 evaded from peatland streams. Using these methods, we
investigated the 14C age and stable carbon isotope composition of both CH4 and CO2 evaded
from a small peatland stream draining a temperate raised mire. Methane was aged between
1617-1987 years BP, and was much older than CO2 which had an age range of 303-521 years
BP. Isotope mass balance modelling of the results indicated that the CO2 and CH4 evaded
from the stream were derived from different source areas, with most evaded CO2 originating
from younger layers located nearer the peat surface compared to CH4. The study demonstrates
the insight that can be gained into peatland carbon cycling from a methodological
development which enables dual isotope (14C and 13C) analysis of both CH4 and CO2 collected
at the same time and in the same way
Structural insight into the TRIAP1/PRELI-like domain family of mitochondrial phospholipid transfer complexes
The composition of the mitochondrial membrane is important for its architecture and proper function. Mitochondria depend on a tightly regulated supply of phospholipid via intra-mitochondrial synthesis and by direct import from the endoplasmic reticulum. The Ups1/PRELI-like family together with its mitochondrial chaperones (TRIAP1/Mdm35) represent a unique heterodimeric lipid transfer system that is evolutionary conserved from yeast to man. Work presented here provides new atomic resolution insight into the function of a human member of this system. Crystal structures of free TRIAP1 and the TRIAP1–SLMO1 complex reveal how the PRELI domain is chaperoned during import into the intermembrane mitochondrial space. The structural resemblance of PRELI-like domain of SLMO1 with that of mammalian phoshatidylinositol transfer proteins (PITPs) suggest that they share similar lipid transfer mechanisms, in which access to a buried phospholipid-binding cavity is regulated by conformationally adaptable loops
A comparative analysis of empirical calibrators for nebular metallicity
We present a new analysis of the main empirical calibrators of oxygen
abundance for ionised gas nebulae. With that aim we have compiled an extensive
sample of objects with emission line data including the near IR [SIII] lines
and the weak auroral lines which allow for the determination of the gas
electron temperature. For all the objects the oxygen abundances have been
derived in a homogeneus way, using the most recent sets of atomic coefficients
and taking into the account the effect of particle density on the temperature
of O. The residuals between directly and empirically-derived abundances as
a function of abundance have been studied. A grid of photo-ionisation models,
covering the range of physical properties of the gas, has been used to explain
the origin of the uncertainties affecting each abundance calibrator. The range
of validity for each abundance parameter has been identified and its average
uncertainty has been quantified.Comment: 16 pages, 26 figures, accepted for publication in MNRA
Fructose transport-deficient Staphylococcus aureus reveals important role of epithelial glucose transporters in limiting sugar-driven bacterial growth in airway surface liquid.
Hyperglycaemia as a result of diabetes mellitus or acute illness is associated with increased susceptibility to respiratory infection with Staphylococcus aureus. Hyperglycaemia increases the concentration of glucose in airway surface liquid (ASL) and promotes the growth of S. aureus in vitro and in vivo. Whether elevation of other sugars in the blood, such as fructose, also results in increased concentrations in ASL is unknown and whether sugars in ASL are directly utilised by S. aureus for growth has not been investigated. We obtained mutant S. aureus JE2 strains with transposon disrupted sugar transport genes. NE768(fruA) exhibited restricted growth in 10 mM fructose. In H441 airway epithelial-bacterial co-culture, elevation of basolateral sugar concentration (5-20 mM) increased the apical growth of JE2. However, sugar-induced growth of NE768(fruA) was significantly less when basolateral fructose rather than glucose was elevated. This is the first experimental evidence to show that S. aureus directly utilises sugars present in the ASL for growth. Interestingly, JE2 growth was promoted less by glucose than fructose. Net transepithelial flux of D-glucose was lower than D-fructose. However, uptake of D-glucose was higher than D-fructose across both apical and basolateral membranes consistent with the presence of GLUT1/10 in the airway epithelium. Therefore, we propose that the preferential uptake of glucose (compared to fructose) limits its accumulation in ASL. Pre-treatment with metformin increased transepithelial resistance and reduced the sugar-dependent growth of S. aureus. Thus, epithelial paracellular permeability and glucose transport mechanisms are vital to maintain low glucose concentration in ASL and limit bacterial nutrient sources as a defence against infection
Neon and Argon optical emission lines in ionized gaseous nebulae: Implications and applications
In this work we present a study of the strong optical collisional emission
lines of Ne and Ar in an heterogeneous sample of ionized gaseous nebulae for
which it is possible to derive directly the electron temperature and hence the
chemical abundances of neon and argon. We calculate using a grid of
photoionization models new ionization correction factors for these two elements
and we study the behaviour of Ne/O and Ar/O abundance ratios with metallicity.
We find a constant value for Ne/O, while there seems to be some evidence for
the existence of negative radial gradients of Ar/O over the disks of some
nearby spirals. We study the relation between the intensities of the emission
lines of [NeIII] at 3869 \AA and [OIII] at 4959 \AA and 5007 \AA. This relation
can be used in empirical calibrations and diagnostic ratios extending their
applicability to bluer wavelengths and therefore to samples of objects at
higher redshifts. Finally, we propose a new diagnostic using [OII], [NeIII] and
Hdelta emission lines to derive metallicities for galaxies at high z.Comment: 12 pages, 12 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Societ
The chemical composition of metal-poor emission-line galaxies in the Data Release 3 of the Sloan Digital Sky Survey
We have re-evaluated empirical expressions for the abundance determination of
N, O, Ne, S, Cl, Ar and Fe taking into account the latest atomic data and
constructing an appropriate grid of photoionization models with state-of-the
art model atmospheres. Using these expressions we have derived heavy element
abundances in the 310 emission-line galaxies from the Data Release 3 of
the Sloan Digital Sky Survey (SDSS)with an observed Hbeta flux F(Hbeta)> 1E-14
erg s^{-1} cm^{-2} and for which the [O III] 4363 emission line was detected at
least at a 2sigma level, allowing abundance determination by direct methods.
The oxygen abundance 12 + log O/H of the SDSS galaxies lies in the range from ~
7.1 (Zsun/30) to 8.5 (0.7 Zsun). The SDSS sample is merged with a sample of 109
blue compact dwarf (BCD) galaxies with high quality spectra, which contains
extremely low-metallicity objects. We use the merged sample to study the
abundance patterns of low-metallicity emission-line galaxies. We find that
extremely metal-poor galaxies (12 + log O/H < 7.6, i.e. Z < Zsun/12) are rare
in the SDSS sample. The alpha element-to-oxygen abundance ratios do not show
any significant trends with oxygen abundance, in agreement with previous
studies, except for a slight increase of Ne/O with increasing metallicity,
which we interpret as due to a moderate depletion of O onto grains in the most
metal-rich galaxies. The Fe/O abundance ratio is smaller than the solar value,
by up to 1 dex at the high metallicity end. (abridged)Comment: 17 pages, 12 figures. Accepted for publication in the Astronomy and
Astrophysic
The macro-economic effects of health co-benefits associated with climate change mitigation strategies
The UK government has specific targets for greenhouse gas (GHG) emission reduction to
lower the risk of dangerous climate change. Strategies to reduce GHG emissions are
sometimes perceived as expensive and difficult to implement but previous work has
demonstrated significant potential health co-benefits from ‘Active Travel and low carbon
driving’, ‘Housing Insulation/Ventilation’, and ‘Healthy Diet’ scenarios which may be
attractive to policymakers. Here a Computable General Equilibrium model is used to assess
the financial effects of such health co-benefits on the wider economy including changes in
labour force, social security payments and healthcare costs averted. Results suggest that for
all scenarios the financial impacts of the health co-benefits will be positive and increased
active travel in particular is likely to make a substantial contribution, largely due to health
care costs averted.
Strategies to reduce GHG emissions and improve health are likely to result in substantial and
increasing positive contributions to the economy which may offset some potential economic
costs and thereby be seen more favourably in times of economic austerity
Simplicity of eigenvalues in Anderson-type models
We show almost sure simplicity of eigenvalues for several models of
Anderson-type random Schr\"odinger operators, extending methods introduced by
Simon for the discrete Anderson model. These methods work throughout the
spectrum and are not restricted to the localization regime. We establish
general criteria for the simplicity of eigenvalues which can be interpreted as
separately excluding the absence of local and global symmetries, respectively.
The criteria are applied to Anderson models with matrix-valued potential as
well as with single-site potentials supported on a finite box.Comment: 20 page
Electoral management and the organisational determinants of electoral integrity
Achieving the ideals of electoral democracy depends on well-run elections. Persistent problems of electoral integrity in transitional and established democracies have prompted a burgeoning literature seeking to explain the determinants of electoral integrity around the world. However, the study of the organisations responsible for managing the electoral process has been limited to isolated national case studies. This article opens up an interdisciplinary and international research agenda on the global study of the organisational determinants of electoral integrity. It defines the concept of electoral management and provides a framework to understand how electoral management body (EMB) institutional design, EMB performance and electoral integrity are related. Findings from new data derived from cross-national surveys of EMBs are described, providing new insights into how elections are managed worldwide
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