992 research outputs found
The Hvar survey for roAp stars: II. Final results (Research Note)
The 60 known rapidly oscillating Ap (roAp) stars are excellent laboratories
to test pulsation models in the presence of stellar magnetic fields. Our survey
is dedicated to search for new group members in the Northern Hemisphere. We
attempt to increase the number of known chemically peculiar stars that are
known to be pulsationally unstable. About 40 h of new CCD photometric data of
21 roAp candidates, observed at the 1m Austrian-Croatian Telescope (Hvar
Observatory) are presented. We carefully analysed these to search for
pulsations in the frequency range of up to 10mHz. No new roAp star was detected
among the observed targets. The distribution of the upper limits for roAp-like
variations is similar to that of previoius similar efforts using
photomultipliers and comparable telescope sizes. In addition to photometric
observations, we need to consolidate spectroscopic information to select
suitable targets.Comment: 8 pages, 5 figures, accepted by Astronomy & Astrophysic
Is periodontitis and its treatment capable of changing the quality of life of a patient?
While clinical indicators, or so-called surrogate outcomes in periodontology, allow us to assess periodontal health and evaluate outcomes of periodontal therapy from a clinician's perspective, they cannot be used to evaluate patients' subjective perceptions of their health status or satisfaction with the received treatment. These can be assessed through patient-based outcomes, such as quality of life. The aim of this paper is to give an overview of the multidimensional concept of oral health-related quality of life (OHRQoL), its measures and association with plaque-induced, inflammatory periodontal diseases. Periodontitis and its clinical consequences, such as tooth loss, have a considerable negative effect on OHRQoL, while periodontal treatment and alleviation of the symptoms can lead to improvement in OHRQoL. Implant rehabilitation of missing teeth also seems to positively influence OHRQo
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The effect of one additional driver mutation on tumor progression
Tumor growth is caused by the acquisition of driver mutations, which enhance the net reproductive rate of cells. Driver mutations may increase cell division, reduce cell death, or allow cells to overcome density-limiting effects. We study the dynamics of tumor growth as one additional driver mutation is acquired. Our models are based on two-type branching processes that terminate in either tumor disappearance or tumor detection. In our first model, both cell types grow exponentially, with a faster rate for cells carrying the additional driver. We find that the additional driver mutation does not affect the survival probability of the lesion, but can substantially reduce the time to reach the detectable size if the lesion is slow growing. In our second model, cells lacking the additional driver cannot exceed a fixed carrying capacity, due to density limitations. In this case, the time to detection depends strongly on this carrying capacity. Our model provides a quantitative framework for studying tumor dynamics during different stages of progression. We observe that early, small lesions need additional drivers, while late stage metastases are only marginally affected by them. These results help to explain why additional driver mutations are typically not detected in fast-growing metastases.MathematicsOrganismic and Evolutionary Biolog
Swiss stone pine (Pinus cembra)
Technical guidelines are targeted to practical forest managers and provide summarized information on the biology and ecology of tree species, distribution ranges, importance and use, genetic knowledge, threats to genetic diversity and recommendations for long-term genetic conservation. For the full list of Technical guidelines produced, please visit http://www.euforgen.org/publications/technical_guidelines.htm
High levels of effective long-distance dispersal may blur ecotypic divergence in a rare terrestrial orchid
Background: Gene flow and adaptive divergence are key aspects of metapopulation dynamics and ecological speciation. Long-distance dispersal is hard to detect and few studies estimate dispersal in combination with adaptive divergence. The aim of this study was to investigate effective long-distance dispersal and adaptive divergence in the fen orchid (Liparis loeselii (L.) Rich.). We used amplified fragment length polymorphism (AFLP)-based assignment tests to quantify effective long-distance dispersal at two different regions in Northwest Europe. In addition, genomic divergence between fen orchid populations occupying two distinguishable habitats, wet dune slacks and alkaline fens, was investigated by a genome scan approach at different spatial scales (continental, landscape and regional) and based on 451 AFLP loci. Results: We expected that different habitats would contribute to strong divergence and restricted gene flow resulting in isolation-by-adaptation. Instead, we found remarkably high levels of effective long-distance seed dispersal and low levels of adaptive divergence. At least 15% of the assigned individuals likely originated from among-population dispersal events with dispersal distances up to 220 km. Six (1.3%) ‘outlier’ loci, potentially reflecting local adaptation to habitat-type, were identified with high statistical support. Of these, only one (0.22%) was a replicated outlier in multiple independent dune-fen population comparisons and thus possibly reflecting truly parallel divergence. Signals of adaptation in response to habitat type were most evident at the scale of individual populations. Conclusions: The findings of this study suggest that the homogenizing effect of effective long-distance seed dispersal may overwhelm divergent selection associated to habitat type in fen orchids in Northwest Europe
Exact solution of a two-type branching process: Clone size distribution in cell division kinetics
We study a two-type branching process which provides excellent description of
experimental data on cell dynamics in skin tissue (Clayton et al., 2007). The
model involves only a single type of progenitor cell, and does not require
support from a self-renewed population of stem cells. The progenitor cells
divide and may differentiate into post-mitotic cells. We derive an exact
solution of this model in terms of generating functions for the total number of
cells, and for the number of cells of different types. We also deduce large
time asymptotic behaviors drawing on our exact results, and on an independent
diffusion approximation.Comment: 16 page
The record-breaking rotational braking of the He strong CP star HD 37776
We study the long-term light and spectral variations in the He-strong
magnetic chemically peculiar star HD 37776 (V901 Ori) to search for changes of
its 1.5387 d period in 1976-2007. We analyze all published photometric
observations and spectrophotometry in the HeI 4026 A line. The data were
supplmented with 506 new (U)VB observations obtained during the last 2
observing seasons, 66 estimates of HeI equivalent widths on 23 CFHT
spectrograms and 35 of the 6-m Zeeman spectrograms. All the 1895 particular
observations heve been processed simultaneously. We confirm the previously
suspected increase of the period in HD 37776 which is a record-breaking among
CP stars. The mean rate of the period increase during the last 31 years is
0.541+-0.020 s per year. We interpret this ongoing period increase as the
slowing down of the star's surface rotation due to momentum loss through events
and processes in its magnetosphere.Comment: 3 pages, 1 figure, Proceedings of the "CP#AP Workshop", Vienna,
10.-14.Sept.2007, eds.J.Ziznovsky, J.Zverko, E.Paunzen, M.Netopil, will be
published in Contrib. Astron. Obs. Skalnate Ples
Constraining Disk Parameters of Be Stars using Narrowband H-alpha Interferometry with the NPOI
Interferometric observations of two well-known Be stars, gamma Cas and phi
Per, were collected and analyzed to determine the spatial characteristics of
their circumstellar regions. The observations were obtained using the Navy
Prototype Optical Interferometer equipped with custom-made narrowband filters.
The filters isolate the H-alpha emission line from the nearby continuum
radiation, which results in an increased contrast between the interferometric
signature due to the H-alpha-emitting circumstellar region and the central
star. Because the narrowband filters do not significantly attenuate the
continuum radiation at wavelengths 50 nm or more away from the line, the
interferometric signal in the H-alpha channel is calibrated with respect to the
continuum channels. The observations used in this study represent the highest
spatial resolution measurements of the H-alpha-emitting regions of Be stars
obtained to date. These observations allow us to demonstrate for the first time
that the intensity distribution in the circumstellar region of a Be star cannot
be represented by uniform disk or ring-like structures, whereas a Gaussian
intensity distribution appears to be fully consistent with our observations.Comment: 23 pages, 14 figures, accepted for publication in A
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