1,233 research outputs found
Instrumented indentation for determination of full range stress-strain curves
One common method for the determination of full range stress-strain curves by instrumented indentation is presented and validated for an aluminium alloy. This method relates properties describing the indentation force-depth curve with those describing the uniaxial stress-strain curve as traditionally obtained from a tensile test. The first aim of this paper is to explain the basic concepts of instrumented indentation. Next, the analysis method is presented and validated. This study ends with discussing the uniqueness of the obtained solution. It is concluded that accurate determination of stress-strain behaviour can be realized, but for certain materials two indentations are needed
Post-AGB stars in the Magellanic Clouds and neutron-capture processes in AGB stars
We explore modifications to the current scenario for the slow neutron capture
process in asymptotic giant branch (AGB) stars to account for the Pb deficiency
observed in post-AGB stars of low metallicity ([Fe/H] ~ -1.2) and low initial
mass (~ 1 - 1.5 Msun) in the Large and Small Magellanic Clouds. We calculated
the stellar evolution and nucleosynthesis for a 1.3 Msun star with [Fe/H]=-1.3
and tested different amounts and distributions of protons leading to the
production of the main neutron source within the 13C-pocket and proton
ingestion scenarios. No s-process models can fully reproduce the abundance
patterns observed in the post-AGB stars. When the Pb production is lowered the
abundances of the elements between Eu and Pb, such as Er, Yb, W, and Hf, are
also lowered to below those observed. Neutron-capture processes with neutron
densities intermediate between the s and the rapid neutron-capture processes
may provide a solution to this problem and be a common occurrence in low-mass,
low-metallicity AGB stars.Comment: 6 pages, 4 figures. To be published in Astronomy and Astrophysic
The lead discrepancy in intrinsically s-process enriched post-AGB stars in the Magellanic Clouds
Context: Our understanding of the s-process nucleosynthesis in asymptotic
giant branch (AGB) stars is incomplete. AGB models predict, for example, large
overabundances of lead (Pb) compared to other s-process elements in metal-poor
low-mass AGB stars. This is indeed observed in some extrinsically enhanced
metal-poor stars, but not in all. An extensive study of intrinsically s-process
enriched objects is essential for improving our knowledge of the AGB third
dredge-up and associated s-process nucleosynthesis. Aims: We compare the
spectral abundance analysis of the SMC post-AGB star J004441.04-732136.4 with
state-of-the-art AGB model predictions with a main focus on Pb. The low S/N in
the Pb line region made the result of our previous study inconclusive. We
acquired additional data covering the region of the strongest Pb line. Methods:
By carefully complementing re-reduced previous data, with newly acquired UVES
optical spectra, we improve the S/N of the spectrum around the strongest Pb
line. Therefore, an upper limit for the Pb abundance is estimated from a merged
weighted mean spectrum using synthetic spectral modeling. We then compare the
abundance results from the combined spectra to predictions of tailored AGB
evolutionary models from two independent evolution codes. In addition, we
determine upper limits for Pb abundances for three previously studied LMC
post-AGB objects. Results: Although theoretical predictions for
J004441.04-732136.4 match the s-process distribution up to tungsten (W), the
predicted very high Pb abundance is clearly not detected. The three additional
LMC post-AGB stars show a similar lack of a very high Pb abundance. Conclusion:
From our study, we conclude that none of these low-mass, low-metallicity
post-AGB stars of the LMC and SMC are strong Pb producers. This conflicts with
current theoretical predictions.Comment: 4 pages, 3 figure
Characteristic Angles in the Wetting of an Angular Region: Deposit Growth
As was shown in an earlier paper [1], solids dispersed in a drying drop
migrate to the (pinned) contact line. This migration is caused by outward flows
driven by the loss of the solvent due to evaporation and by geometrical
constraint that the drop maintains an equilibrium surface shape with a fixed
boundary. Here, in continuation of our earlier paper [2], we theoretically
investigate the evaporation rate, the flow field and the rate of growth of the
deposit patterns in a drop over an angular sector on a plane substrate.
Asymptotic power laws near the vertex (as distance to the vertex goes to zero)
are obtained. A hydrodynamic model of fluid flow near the singularity of the
vertex is developed and the velocity field is obtained. The rate of the deposit
growth near the contact line is found in two time regimes. The deposited mass
falls off as a weak power Gamma of distance close to the vertex and as a
stronger power Beta of distance further from the vertex. The power Gamma
depends only slightly on the opening angle Alpha and stays between roughly -1/3
and 0. The power Beta varies from -1 to 0 as the opening angle increases from 0
to 180 degrees. At a given distance from the vertex, the deposited mass grows
faster and faster with time, with the greatest increase in the growth rate
occurring at the early stages of the drying process.Comment: v1: 36 pages, 21 figures, LaTeX; submitted to Physical Review E; v2:
minor additions to Abstract and Introductio
Structural relations among implicit theories, achievement goals, and performance in writing
inexistenteinfo:eu-repo/semantics/publishedVersio
Short-term health effects in the general population following a major train accident with acrylonitrile in Belgium
Background: Following a train derailment, several tons of acrylonitrile (ACN) exploded, inflamed and part of the ACN ended up in the sewage system of the village of Wetteren. More than 2000 residents living in the close vicinity of the accident and along the sewage system were evacuated. A human biomonitoring study of the adduct N-2-cyanoethylvaline (CEV) was carried out days 14-21 after the accident.
Objectives: (1) To describe the short-term health effects that were reported by the evacuated residents following the train accident, and (2) to explore the association between the CEV concentrations, extrapolated at the time of the accident, and the self-reported short-term health effects.
Methods: Short-term health effects were reported in a questionnaire (n=191). An omnibus test of independence was used to investigate the association between the CEV concentrations and the symptoms. Dose-response relationships were quantified by Generalized Additive Models (GAMs).
Results: The most frequently reported symptoms were local symptoms of irritation. In non-smokers, dose-dependency was observed between the CEV levels and the self-reporting of irritation (p=0.007) and nausea (p=0.007). Almost all non-smokers with CEV concentrations above 100 pmol/g globin reported irritation symptoms. Both absence and presence of symptoms was reported by non-smokers with CEV concentrations below the reference value and up to 10 times the reference value. Residents who visited the emergency services reported more symptoms. This trend was seen for the whole range of CEV concentrations, and thus independently of the dose.
Discussion and conclusion: The present study is one of the first to relate exposure levels to a chemical released during a chemical incident to short-term (self-reported) health effects. A dose-response relation was observed between the CEV concentrations and the reporting of short-term health effects in the non-smokers. Overall, the value of self-reported symptoms to assess exposure showed to be limited. The results of this study confirm that a critical view should be taken when considering self-reported health complaints and that ideally biomarkers are monitored to allow an objective assessment of exposure
Sign-time distribution for a random walker with a drifting boundary
We present a derivation of the exact sign-time distribution for a random
walker in the presence of a boundary moving with constant velocity.Comment: 5 page
Internal rotation of red giants by asteroseismology
We present an asteroseismic approach to study the dynamics of the stellar
interior in red-giant stars by asteroseismic inversion of the splittings
induced by the stellar rotation on the oscillation frequencies. We show
preliminary results obtained for the red giant KIC4448777 observed by the space
mission Kepler.Comment: 3 pages, 4 figures, the 40th Liege International Astrophysical
Colloquium Liac40, 'Ageing low mass stars: from red giants to white dwarfs',
to be published on EPJ Web of Conference
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