775 research outputs found
The Impact of Biofuel Production on Food Security: A Briefing Paper with a Particular Emphasis on Maize-to-Ethanol Production
A multi-feedstock approach is crucial for sustainable biofuel production in South Africa. In respect of ethanol production, biofuel producers should be allowed to draw on a range of starch-based crops including maize. A multi-feedstock approach will enable producers to select crops best suited to the agro-climate of the regions where their plants are situated and to minimize logistic costs by sourcing crops grown closest to their plants. In recent months, plans to use maize to produce ethanol have raised concerns that this could jeopardize food security in South Africa.biofuel production, food security, maize, Food Security and Poverty, Resource /Energy Economics and Policy, Q10, Q27,
The Interaction Of Multiple Convection Zones In A-type Stars
A-type stars have a complex internal structure with the possibility of
multiple convection zones. If not sufficiently separated, such zones will
interact through the convectively stable regions that lie between them. It is
therefore of interest to ask whether the typical conditions that exist within
such stars are such that these convections zones can ever be considered as
disjoint.
In this paper we present results from numerical simulations that help in
understanding how increasing the distance between the convectively unstable
regions are likely to interact through the stable region that separates them.
This has profound implications for mixing and transport within these stars.Comment: 9 pages, 15 figures, Preprint accepted for publication in MNRA
Discovery of the first tau Sco analogues: HD 66665 and HD 63425
The B0.2 V magnetic star tau Sco stands out from the larger population of
massive OB stars due to its high X-ray activity, peculiar wind diagnostics and
highly complex magnetic field. This paper presents the discovery of the first
two tau Sco analogues - HD 66665 and HD 63425, identified by the striking
similarity of their UV spectra to that of tau Sco. ESPaDOnS spectropolarimetric
observations were secured by the Magnetism in Massive Stars CFHT Large Program,
in order to characterize the stellar and magnetic properties of these stars.
CMFGEN modelling of optical ESPaDOnS spectra and archived IUE UV spectra showed
that these stars have stellar parameters similar to those of tau Sco. A
magnetic field of similar surface strength is found on both stars, reinforcing
the connection between the presence of a magnetic field and wind peculiarities.
However, additional phase-resolved observations will be required in order to
assess the potential complexity of the magnetic fields, and verify if the wind
anomalies are linked to this property.Comment: 6 pages, 2 tables, 3 figures. Accepted for publication in MNRAS. The
definitive version will be available at www.blackwel-synergy.co
On the influence of Stark broadening on Si I lines in stellar atmospheres
We study the influence of Stark broadening and stratification effects on Si\i
lines in the rapidly oscillating (roAp) star 10 Aql, where the Si\i 6142.48 \AA
and 6155.13 \AA lines are asymmetrical and shifted. First we have calculated
Stark broadening parameters using the semiclassical perturbation method for
three Si\i lines: 5950.2 \AA, 6142.48 \AA and 6155.13 \AA. We revised the
synthetic sp$ calculation code taking into account both Stark width and shift
for these lines. From the comparison of our calculations with the observations
we found that Stark broadening + the stratification effect can explain
asymmetry of the Si\i 6142.48 \AA and 6155.13 \AA lines in the atmospere of
roAp star 10 Aql.Comment: Accepted to A&
Escape Behavior of Quantum Two-Particle Systems with Coulomb Interactions
Quantum escapes of two particles with Coulomb interactions from a confined
one-dimensional region to a semi-infinite lead are discussed by the probability
of particles remaining in the confined region, i.e. the survival probability,
in comparison with one or two free particles. For free-particle systems the
survival probability decays asymptotically in power as a function of time. On
the other hand, for two-particle systems with Coulomb interactions it shows an
exponential decay in time. A difference of escape behaviors between Bosons and
Fermions is considered as quantum effects of identical two particles such as
the Pauli exclusion principle. The exponential decay in the survival
probability of interacting two particles is also discussed in a viewpoint of
quantum chaos based on a distribution of energy level spacings.Comment: 10 pages, 7 figure
More illness in offspring of bipolar patients from the U.S. compared to Europe.
Background Evidence suggests that patients with bipolar disorder from the United States have an earlier age of onset and a more difficult course of illness than those from Germany and the Netherlands. These characteristics were related to a greater family burden of psychiatric illness and the experience of more psychosocial adversity in childhood. We hypothesized that this greater illness burden would extend to the offspring of the US patients. Methods 968 outpatients (average age 41) with bipolar illness gave informed consent for participation in a treatment outcome network and filled out a detailed questionnaire about their illness and family history of illness, including whether their offspring had a diagnosis of depression, bipolar disorder, alcohol or substance abuse, suicide attempt or “other” illness. Of those with children, 356 were from the US and 132 were from Europe. Results Compared to the Europeans, offspring of patients from the US had significantly (p\u3c0.001) more depression, bipolar disorder, drug abuse, and “other” illnesses. The number of illnesses in the offspring was related to the bipolar parent being from the US, having had childhood adversity, more than 20 prior episodes, and more parental psychiatric illness. Conclusions While the findings are limited by their basis on self report, the distribution of the percentages in the US offspring are similar to those of Axelson et al. (2015) who used direct interviews. The higher burden of illness in the offspring and their in directprogenitors from the US compared to Europe warrant new attempts at better treatment and prevention
HE 0557-4840 - Ultra-Metal-Poor and Carbon-Rich
We report the discovery and high-resolution, high S/N, spectroscopic analysis
of the ultra-metal-poor red giant HE 0557-4840, which is the third most
heavy-element deficient star currently known. Its atmospheric parameters are
T_eff = 4900 K, log g = 2.2, and [Fe/H]= -4.75. This brings the number of stars
with [Fe/H] < -4.0 to three, and the discovery of HE 0557-4840 suggests that
the metallicity distribution function of the Galactic halo does not have a
"gap" between [Fe/H] = -4.0, where several stars are known, and the two most
metal-poor stars, at [Fe/H] ~ -5.3. HE 0557-4840 is carbon rich - [C/Fe] = +1.6
- a property shared by all three objects with [Fe/H] < -4.0, suggesting that
the well-known increase of carbon relative to iron with decreasing [Fe/H]
reaches its logical conclusion - ubiquitous carbon richness - at lowest
abundance. We also present abundances (nine) and limits (nine) for a further 18
elements. For species having well-measured abundances or strong upper limits,
HE 0557-4840 is "normal" in comparison with the bulk of the stellar population
at [Fe/H] ~ -4.0 - with the possible exception of Co. We discuss the
implications of these results for chemical enrichment at the earliest times, in
the context of single ("mixing and fallback") and two-component enrichment
models. While neither offers a clear solution, the latter appears closer to the
mark. Further data are required to determine the oxygen abundance and improve
that of Co, and hence more strongly constrain the origin of this object.Comment: Submitted to Astrophysical Journal. 52 pages (41 text, 11 figures
Surface abundances of light elements for a large sample of early B-type stars - IV. The magnesium abundance in 52 stars - a test of metallicity
From high-resolution spectra a non-LTE analysis of the MgII 4481.2 A feature
is implemented for 52 early and medium local B stars on the main sequence (MS).
The influence of the neighbouring line AlIII 4479.9 A is considered. The
magnesium abundance is determined; it is found that log e(Mg) = 7.67 +- 0.21 on
average. It is shown that uncertainties in the microturbulent parameter Vt are
the main source of errors in log e(Mg). When using 36 stars with the most
reliable Vt values derived from OII and NII lines, we obtain the mean abundance
log e(Mg) = 7.59 +- 0.15. The latter value is precisely confirmed for several
hot B stars from an analysis of the MgII 7877 A weak line. The derived
abundance log e(Mg) = 7.59 +- 0.15 is in excellent agreement with the solar
magnesium abundance log e_sun(Mg) = 7.55 +- 0.02, as well as with the proto-Sun
abundance log e_ps(Mg) = 7.62 +- 0.02. Thus, it is confirmed that the Sun and
the B-type MS stars in our neighbourhood have the same metallicity.Comment: 9 pages, 6 figures. Has been accepted for publication at MNRA
Serum hyaluronic acid as a potential marker with a predictive value for further radiographic progression of hand osteoarthritis
SummaryObjectiveTo compare serum levels of hyaluronic acid (HA) between patients with erosive and non-erosive hand osteoarthritis (HOA), and investigate its association with morphological changes and radiographic progression over 2 years.MethodsFifty-five women with erosive and 33 women with non-erosive HOA were included in this study. All underwent clinical examination, which included assessment of pain, swelling, deformity and deviation of small hand joints and completed health assessment questionnaires. Serum levels of HA were measured by ELISA. Three-phase bone scintigraphy was performed at baseline. Radiographs of both hands were performed at baseline and after 2 years and scored according Kallman grading scale.ResultsSerum levels of HA were significantly higher in patients with erosive than with non-erosive HOA (P<0.01). It correlated significantly with the number of hand joints with deviations and deformities. HA adjusted for age and disease duration significantly correlated with radiographs at baseline and after 2 years in all patients with HOA (r=0.560 and r=0.542, P<0.01 for both correlations). Although there was an association between HA and radiographic score in erosive disease, after adjustment for confounders it remained no longer significant. HA adjusted for confounders correlated significantly with the late phase in all patients with HOA (r=0.412, P<0.01) and in patients with erosive disease (r=0.320, P<0.05).ConclusionHA is increased in patients with erosive HOA and could be proposed as a surrogate marker with a predictive value for further radiographic progression of HOA in general. Further investigation is necessary to confirm these results
Outbursts on normal stars. FH Leo misclassified as a novalike variable
We present high resolution spectroscopy of the common proper motion system FH
Leo (components HD 96273 and BD+07 2411B), which has been classified as a
novalike variable due to an outburst observed by Hipparcos, and we present and
review the available photometry. We show from our spectra that neither star can
possibly be a cataclysmic variable, instead they are perfectly normal late-F
and early-G stars. We measured their radial velocities and derived the
atmospheric fundamental parameters, abundances of several elements including
Fe, Ni, Cr, Co, V, Sc, Ti, Ca and Mg, and we derive the age of the system. From
our analysis we conclude that the stars do indeed constitute a physical binary.
However, the observed outburst cannot be readily explained. We examine several
explanations, including pollution with scattered light from Jupiter, binarity,
microlensing, background supernovae, interaction with unseen companions and
planetary engulfment. While no explanation is fully satisfactory, the scattered
light and star-planet interaction scenarios emerge as the least unlikely ones,
and we give suggestions for further study.Comment: 8 pages, 7 figures. Accepted for publication in A&
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