992 research outputs found
A non-LTE study of neutral and singly-ionized iron line spectra in 1D models of the Sun and selected late-type stars
A comprehensive model atom for Fe with more than 3000 energy levels is
presented. As a test and first application of this model atom, Fe abundances
are determined for the Sun and five stars with well determined stellar
parameters and high-quality observed spectra. Non-LTE leads to systematically
depleted total absorption in the Fe I lines and to positive abundance
corrections in agreement with the previous studies, however, the magnitude of
non-LTE effect is smaller compared to the earlier results. Non-LTE corrections
do not exceed 0.1 dex for the solar metallicity and mildly metal-deficient
stars, and they vary within 0.21 dex and 0.35 dex in the very metal-poor stars
HD 84937 and HD 122563, respectively, depending on the assumed efficiency of
collisions with hydrogen atoms. Based on the analysis of the Fe I/Fe II
ionization equilibrium in these two stars, we recommend to apply the Drawin
formalism in non-LTE studies of Fe with a scaling factor of 0.1. For the Fe II
lines, non-LTE corrections do not exceed 0.01 dex in absolute value. The solar
non-LTE abundance obtained from 54 Fe I lines is 7.56+-0.09 and the abundance
from 18 Fe II lines varies between 7.41+-0.11 and 7.56+-0.05 depending on the
source of the gf-values. Thus, gf-values available for the iron lines are not
accurate enough to pursue high-accuracy absolute abundance determinations.
Lines of Fe I give, on average, a 0.1 dex lower abundance compared to those of
Fe II lines for HD 61421 and HD 102870, even when applying a differential
analysis relative to the Sun. A disparity between Fe I and Fe II points to
problems of stellar atmosphere modelling or/and effective temperature
determination.Comment: 19 pages, 8 figures, online material, accepted by A&
Primary stability of a press-fit cup in combination with impaction grafting in an acetabular defect model
The objectives of this study were to (a) assess primary stability of a press-fit cup in a simplified acetabular defect model, filled with compacted cancellous bone chips, and (b) to compare the results with primary stability of a press-fit cup combined with two different types of bone graft substitute in the same defect model. A previously developed acetabular test model made of polyurethane foam was used, in which a mainly medial contained defect was implemented. Three test groups (N = 6 each) were prepared: Cancellous bone chips (bone chips), tricalciumphosphate tetrapods + collagen matrix (tetrapods + coll), bioactive glass S53P4 + polyethylene glycol-glycerol matrix (b.a.glass + PEG). Each material was compacted into the acetabulum and a press-fit cup was implanted. The specimens were loaded dynamically in the direction of the maximum resultant force during level walking. Relative motion between cup and test model was assessed with an optical measurement system. At the last load step (3000 N), inducible displacement was highest for bone chips with median [25th percentile; 75th percentile] value of 113 [110; 114] ”m and lowest for b.a.glass + PEG with 91 [89; 93] ”m. Migration at this load step was highest for b.a.glass + PEG with 868 [845; 936] ”m and lowest for tetrapods + coll with 491 [487; 497] ”m. The results show a comparable behavior under load of tetrapods + coll and bone chips and suggest that tetrapods + coll could be an attractive alternative to bone chips. However, so far, this was found for one specific defect type and primary stability should be further investigated in additional/more severe defects
Observation of enhanced transmission for s-polarized light through a subwavelength slit
Enhanced optical transmission (EOT) through subwavelength apertures is
usually obtained for p-polarized light. The present study experimentally
investigates EOT for s-polarized light. A subwavelength slit surrounded on each
side by periodic grooves has been fabricated in a gold film and covered by a
thin dielectric layer. The excitation of s-polarized dielectric waveguide modes
inside the dielectric film strongly increases the s-polarized transmission.
Transmission measurements are compared with a coupled mode model and show good
qualitative agreement. Adding a waveguide can improve light transmission
through subwavelength apertures, as both s and p-polarization can be
efficiently transmitted.Comment: 11 pages, 3 figures, submitted to Applied Physics Letter
Theory of extraordinary optical transmission through subwavelength hole arrays
We present a fully three-dimensional theoretical study of the extraordinary
transmission of light through subwavelength hole arrays in optically thick
metal films. Good agreement is obtained with experimental data. An analytical
minimal model is also developed, which conclusively shows that the enhancement
of transmission is due to tunneling through surface plasmons formed on each
metal-dielectric interfaces. Different regimes of tunneling (resonant through a
''surface plasmon molecule", or sequential through two isolated surface
plasmons) are found depending on the geometrical parameters defining the
system.Comment: 4 pages, 4 figure
Positron lifetime measurements on neutronâirradiated InP crystals
Neutronâirradiated InP single crystals have been investigated by positronâlifetime measurements. The samples were irradiated with thermal neutrons at different fluences yielding concentrations for Snâtransmuted atoms between 2Ă1015 and 2Ă1018 cmâ3. The lifetime spectra have been analyzed into one exponential decay component. The mean lifetimes show a monotonous increase with the irradiation dose from 246 to 282 ps. The increase in the lifetime has been associated to a defect containing an Indium vacancy. Thermal annealing at 550â°C reduces the lifetime until values closed to those obtained for the asâgrown and conventionally doped InP [email protected] ; [email protected]
Non-LTE line formation for Pr II and Pr III in A and Ap stars
Non-LTE line formation for Pr II and Pr III is considered through a range of
effective temperatures between 7250 K and 9500 K. A comprehensive model atom
for Pr II/III is based on the measured and the predicted energy levels, in
total, 6708 levels of Pr II and Pr III. We describe calculations of the Pr II
energy levels and oscillator strengths for the transitions in Pr II and Pr III.
The influence of departures from LTE on Pr abundance determinations is
evaluated. At Teff >= 8000 K departures from LTE lead to overionization of Pr
II and to systematically depleted total absorption in the line and positive
abundance corrections. At the lower temperatures, different lines of Pr II may
be either weakened or amplified depending on the line strength. The non-LTE
effects strengthen the Pr III lines and lead to negative abundance corrections.
Non-LTE corrections grow with effective temperature for the Pr II lines, and,
in contrast, they decline for the Pr III lines. The Pr II/III model atom is
applied to determine the Pr abundance in the atmosphere of the roAp star HD
24712 from the lines of two ionization stages. In the chemically uniform
atmosphere with [Pr/H] = 3, the departures from LTE may explain only small part
(0.3 dex) of the difference between the LTE abundances derived from the Pr II
and Pr III lines (2 dex). We find that the lines of both ionization stages are
described for the vertical distribution of the praseodymium where the Pr
enriched layer with [Pr/H] > 4 exists in the outer atmosphere at log tau_5000 <
-4. The departures from LTE for Pr II/III are strong in the stratified
atmosphere and have the opposite sign for the Pr II and Pr III lines. Using the
revised partition function of Pr II and experimental transition probabilities,
we determine the solar non-LTE abundance of Pr as log (Pr/H) = -11.15\pm0.08.Comment: 17 pages, 4 tables, 11 figures, accepted for publication in A&
A Scoping Review: Overview of Current Respectful Maternity Care Research by Research Approach and Study Location
Introduction: Disrespectful care during childbirth contributes to poor health outcomes, perpetuates disparities, and encourages childbirth outside of healthcare facilities. To measure disrespectful care, investigators use many research approaches. Most research has focused on low/low-middle income countries. This scoping review aims to 1) summarize current research and research approaches to analyze whether these approaches identify the same types of mistreatment and 2) identify gaps in current research analyzing disrespectful care during childbirth.
Methods: Following PRISMA guidelines, this review utilized search terms to filter articles from the Pubmed database. Using specific criteria, articles were then excluded by title and abstract, then full article review. Included articles were organized by research approach and analyzed for study location and the presence of 9 types of mistreatment.
Results: 102 included articles were organized by research approach, including direct labor observation, survey, interview, and focus groups, yielding 144 total studies to account for articles with more than one research approach. Each research approach identified all 9 types of mistreatment, with neglect/abandonment, verbal mistreatment, and physical mistreatment reported the most. Low-income countries represented 134/144 studies, with most research centered in East Africa and India. High-income countries represented only 7% of research.
Discussion: This review is the first to organize current respectful maternity care research by research approach and study location. Analysis of study location shows gaps in research, particularly among high-income countries. Further research, particularly in high-income countries, is necessary to better this global health concern
The Hamburg/ESO R-process Enhanced Star survey (HERES) VI. The Galactic Chemical Evolution of Silicon
We determined the silicon abundances of 253 metal-poor stars in the
metallicity range , based on non-local thermodynamic
equilibrium (NLTE) line formation calculations of neutral silicon and
high-resolution spectra obtained with VLT-UT2/UVES. The
dependence of [Si/Fe] noticed in previous investigation is diminished in our
abundance analysis due to the inclusion of NLTE effects. An increasing slope of
[Si/Fe] towards decreasing metallicity is present in our results, in agreement
with Galactic chemical evolution models. The small intrinsic scatter of [Si/Fe]
in our sample may imply that these stars formed in a region where the yields of
type II supernovae were mixed into a large volume, or that the formation of
these stars was strongly clustered, even if the ISM was enriched by single SNa
II in a small mixing volume. We identified two dwarfs with
: HE 01313953, and HE 14301123. These
main-sequence turnoff stars are also carbon-enhanced. They might have been
pre-enriched by sub-luminous supernovae.Comment: 12 pages, 9 figures, 1 electronical table. Accepted by A &
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