1,237 research outputs found
Evolutionary history of four binary blue stragglers from the globular clusters \omega Cen, M55, 47 Tuc and NGC 6752
Context. Origin and evolution of blue stragglers in globular clusters is
still a matter of debate. Aims. The aim of the present investigation is to
reproduce the evolutionary history of four binary blue stragglers in four
different clusters, for which precise values of global parameters are known.
Methods. Using the model for cool close binary evolution, developed by one of
us (KS), progenitors of all investigated binaries were found and their
parameters evolved into the presently observed values. Results. The results
show that the progenitors of the binary blue stragglers are cool close binaries
with period of a few days, which transform into stragglers by rejuvenation of
the initially less massive component by mass transfer from its more massive
companion overflowing the inner critical Roche surface. The parameters of V209
from \omega Cen indicate that the binary is substantially enriched in helium.
This is an independent and strong evidence for the existence of the helium rich
subpopulation in this cluster.Comment: Accepted by Astronomy and Astrophysic
Shrinking binary and planetary orbits by Kozai cycles with tidal friction
At least two arguments suggest that the orbits of a large fraction of binary
stars and extrasolar planets shrank by 1-2 orders of magnitude after formation:
(i) the physical radius of a star shrinks by a large factor from birth to the
main sequence, yet many main-sequence stars have companions orbiting only a few
stellar radii away, and (ii) in current theories of planet formation, the
region within ~0.1 AU of a protostar is too hot and rarefied for a Jupiter-mass
planet to form, yet many "hot Jupiters" are observed at such distances. We
investigate orbital shrinkage by the combined effects of secular perturbations
from a distant companion star (Kozai oscillations) and tidal friction. We
integrate the relevant equations of motion to predict the distribution of
orbital elements produced by this process. Binary stars with orbital periods of
0.1 to 10 days, with a median of ~2 d, are produced from binaries with much
longer periods (10 d to 10^5 d), consistent with observations indicating that
most or all short-period binaries have distant companions (tertiaries). We also
make two new testable predictions: (1) For periods between 3 and 10 d, the
distribution of the mutual inclination between the inner binary and the
tertiary orbit should peak strongly near 40 deg and 140 deg. (2) Extrasolar
planets whose host stars have a distant binary companion may also undergo this
process, in which case the orbit of the resulting hot Jupiter will typically be
misaligned with the equator of its host star.Comment: Submitted to ApJ; 18 pages, 10 figure
Localisation of the human hSuv3p helicase in the mitochondrial matrix and its preferential unwinding of dsDNA
We characterised the human hSuv3p protein belonging to the family of NTPases/helicases. In yeast mitochondria the hSUV3 orthologue is a component of the degradosome complex and participates in mtRNA turnover and processing, while in Caenorhabditis elegans the hSUV3 orthologue is necessary for viability of early embryos. Using immunofluorescence analysis, an in vitro mitochondrial uptake assay and subâfractionation of human mitochondria we show hSuv3p to be a soluble protein localised in the mitochondrial matrix. We expressed and purified recombinant hSuv3p protein from a bacterial expression system. The purified enzyme was capable of hydrolysing ATP with a Km of 41.9 ”M and the activity was only modestly stimulated by polynucleotides. hSuv3p unwound partly hybridised dsRNA and dsDNA structures with a very strong preference for the latter. The presented analysis of the hSuv3p NTPase/helicase suggests that new functions of the protein have been acquired in the course of evolution
Econobiophysics - game of choosing. Model of selection or election process with diverse accessible information
We propose several models applicable to both selection and election processes when each selecting or electing subject has access to different information about the objects to choose from. We wrote special software to simulate these processes. We consider both the cases when the environment is neutral (natural process) as well as when the environment is involved (controlled process)
Effects of Fertilizers and Manures on Temporal Yield Variability of Winter Rye
The anticipated increases in environmental variability associated with climate change may lead to enhanced abiotic plant stresses (e.g. heat stress, drought stress, etc.) resulting in greater interâannual yield fluctuations and higher crop production risk. While there has been increasing attention to adaptation measures, there is little evidence available on how to change agronomic management strategies to maintain stable yields in winter rye production systems in Poland. This study uses rye yields from the unique Skierniewice Longâterm experiment (Poland) to examine for the firstâtime the longâterm effects of different nutrient regimes on crop yield stability from 1966 to 2015. Yields from six combinations of mineral fertilizers and lime (CaNPK, NPK,CaPK, CaNK, CaNP, Ca), with and without additional manure, were used to estimate the temporal yield variability of winter rye. A novel statistical approach based on a mixed model approach with REML (restricted maximum likelihood) stability parameter estimation was used. The results showed that the use of additional manure in âsubâoptimalâ mineral fertilizer treatments, such as Ca and CaPK (without mineral N), reduced the temporal yield variability of rye. In contrast, additional organic input led to more variable rye yields in already âoptimalâ treatments including mineral N (CaNPK and NPK), compared to those with no additional manure. Winter rye given CaNPK and NPK, without additional organic manure demonstrated high yield and low temporal yield variability. In contrast, yields of treatments with no mineral N (Ca and CaPK) and no additional manure supply were low and unstable. In addition, it was found that increasing soil organic carbon resulted in larger, more stable yields. These findings highlight the importance of ensuring rye crops receive sufficient fertilizer to maintain crop production levels and yield stability, especially in dry years. They also demonstrate the importance of avoiding the excessive use of organic manures when fertilizer inputs are sufficient to meet crop demand. Overall, the study provides novel insights about how to maintain grain yields and minimize temporal yield variation of rye in arable cropping systems, which will become increasingly important in a changing climate in Poland and in other temperate climate areas. This study also highlights the importance of soil organic carbon for improving the climate resilience of winter rye, while simultaneously meeting the demand for more sustainable management of the soil
Multimodal Imaging of Photoreceptor Structure in Choroideremia
Purpose
Choroideremia is a progressive X-linked recessive dystrophy, characterized by degeneration of the retinal pigment epithelium (RPE), choroid, choriocapillaris, and photoreceptors. We examined photoreceptor structure in a series of subjects with choroideremia with particular attention to areas bordering atrophic lesions. Methods
Twelve males with clinically-diagnosed choroideremia and confirmed hemizygous mutations in the CHM gene were examined. High-resolution images of the retina were obtained using spectral domain optical coherence tomography (SD-OCT) and both confocal and non-confocal split-detector adaptive optics scanning light ophthalmoscope (AOSLO) techniques. Results
Eleven CHM gene mutations (3 novel) were identified; three subjects had the same mutation and one subject had two mutations. SD-OCT findings included interdigitation zone (IZ) attenuation or loss in 10/12 subjects, often in areas with intact ellipsoid zones; RPE thinning in all subjects; interlaminar bridges in the imaged areas of 10/12 subjects; and outer retinal tubulations (ORTs) in 10/12 subjects. Only split-detector AOSLO could reliably resolve cones near lesion borders, and such cones were abnormally heterogeneous in morphology, diameter and density. On split-detector imaging, the cone mosaic terminated sharply at lesion borders in 5/5 cases examined. Split-detector imaging detected remnant cone inner segments within ORTs, which were generally contiguous with a central patch of preserved retina. Conclusions
Early IZ dropout and RPE thinning on SD-OCT are consistent with previously published results. Evidence of remnant cone inner segments within ORTs and the continuity of the ORTs with preserved retina suggests that these may represent an intermediate state of retinal degeneration prior to complete atrophy. Taken together, these results supports a model of choroideremia in which the RPE degenerates before photoreceptors
Binary coalescence from case A evolution -- mergers and blue stragglers
We constructed some main-sequence mergers from case A binary evolution and
studied their characteristics via Eggleton's stellar evolution code. Both total
mass and orbital angular momentum are conservative in our binary evolutions.
Some mergers might be on the left of the ZAMS as defined by normal surface
composition on a CMD because of enhanced surface helium content. The study also
shows that central hydrogen content of the mergers is independent of mass. As a
consequence, we fit the formula of magnitude and B-V of the mergers when they
return back to thermal equilibrium with maximum error 0.29 and 0.037,
respectively. Employing the consequences above, we performed Monte Carlo
simulations to examine our models in NGC 2682 and NGC 2660. In NGC 2682, binary
mergers from our models cover the region with high luminosity, but its
importance is much less than that of AML. Our results are well-matched to the
observations of NGC2660 if there is about 0.5Mo of mass loss in the merger
process.Comment: 14 pages, 12 figures. accepted by MNRA
X-ray rotational modulation of a supersaturated star in IC 2391
We present evidence of X-ray rotational modulation on VXR45, a young fast
rotator star, member of IC 2391. It is a dG9 spectral type star whose
rotational period and X-ray luminosity make it a supersaturated star. Our X-ray
observation, made with EPIC/PN on XMM-Newton, covers about two photometric
rotational periods. The detection of rotational modulation implies the presence
of structural inhomogeneities. Possible interpretations are presented and
discussed.Comment: 4 pages with 4 PostScript figures. Accepted for publication in
Astronomy & Astrophysics Letter
Correlation between different PBL assessment components and the final mark for MB ChB III at a rural South African university
Background. Problem-based learning (PBL) is now an accepted component of many medical school programmes worldwide. Our university also follows the PBL âSPICESâ model for MB ChB III. The assessment modalities used are the modified essay questions (MEQ), objective structured practical examination (OSPE), individualised process assessment (IPA) and tutorial continuous assessment (TUT). This study was done to compare
the studentsâ performances in individual assessment components with the final mark to determine the correlation between these parameters.
Materials and methods. The study was retrospective, descriptive and analytical, based on the integrated marks of all the MB ChB III students at Walter Sisulu University (WSU) in 2007. Assessment marks were stratified according to blocks and different types of assessment (MEQ, TUT, OSPE, IPA). Regression analysis was used to compute and scrutinise these vis-Ă -vis their correspondence with the final marks for each block.
Results. Three hundred and seventy-nine block assessment marks of 96 students from 4 blocks of MB ChB III were analysed and the correlation between the assessment components and final mark were compared. Regression analysis showed good correlation when analysing the assessment modality versus the final mark for the MEQs (r=0.93, 0.93, 0.94, 0.96), followed by OSPEs (r=0.71, 0.70, 0.76, 0.77) and IPAs (r=0.62, 0.51, 0.68,
0.77). However, correlation was not significant with the TUT.
Conclusion. There was good correlation between the studentsâ performance in the majority of assessment modalities and the final mark in the different blocks of the MB ChB III examination. There may be a need to make tutorial assessment methods more objective, partly by additional tutor training
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