474 research outputs found
Fundamental properties of solar-like oscillating stars from frequencies of minimum : II. Model computations for different chemical compositions and mass
The large separations between the oscillation frequencies of solar-like stars
are measures of stellar mean density. The separations have been thought to be
mostly constant in the observed range of frequencies. However, detailed
investigation shows that they are not constant, and their variations are not
random but have very strong diagnostic potential for our understanding of
stellar structure and evolution. In this regard, frequencies of the minimum
large separation are very useful tools. From these frequencies, in addition to
the large separation and frequency of maximum amplitude, Y\i ld\i z et al.
recently have developed new methods to find almost all the fundamental stellar
properties. In the present study, we aim to find metallicity and helium
abundances from the frequencies, and generalize the relations given by Y\i ld\i
z et al. for a wider stellar mass range and arbitrary metallicity () and
helium abundance (). We show that the effect of metallicity is {
significant} for most of the fundamental parameters. For stellar mass, for
example, the expression must be multiplied by (Z/Z_{\sun})^{0.12}. For
arbitrary helium abundance, M \propto (Y/Y_{\sun})^{0.25} . Methods for
determination of and from pure asteroseismic quantities are based on
amplitudes (differences between maximum and minimum values of \Dnu) in the
oscillatory component in the spacing of oscillation frequencies. Additionally,
we demonstrate that the difference between the first maximum and the second
minimum is very sensitive to . It also depends on and small separation between the frequencies. Such a dependence leads us
to develop a method to find (and ) from oscillation frequencies. The
maximum difference between the estimated and model values is about 14 per
cent. It is 10 per cent for .Comment: 8 pages, 13 figures; published in MNRAS (2015
Comparison of Gaia and asteroseismic distances
Asteroseismology provides fundamental properties (mass, radius and effective
temperature) of solar-like oscillating stars using so-called scaling relations.
These properties allow the computation of the asteroseismic distance of stars.
We compare the asteroseismic distances with the recently released Gaia
distances for 74 stars studied in Y{\i}ld{\i}z et al. There is a very good
agreement between these two distances; for 64 of these stars, the difference is
less than 10 per cent. However, a systematic difference is seen if we use the
effective temperature obtained by spectroscopic methods; the Gaia distances are
about 5 per cent greater than the asteroseismic distances.Comment: 4 pages, 4 figures, accepted by MNRA
On the structure and evolution of planets and their host stars effects of various heating mechanisms on the size of giant gas planets
It is already stated in the previous studies that the radius of the giant
planets is affected by stellar irradiation. The confirmed relation between
radius and incident flux depends on planetary mass intervals. In this study, we
show that there is a single relation between radius and irradiated energy per
gram per second (), for all mass intervals. There is an extra increase in
radius of planets if is higher than 1100 times energy received by the
Earth (). This is likely due to dissociation of molecules. The tidal
interaction as a heating mechanism is also considered and found that its
maximum effect on the inflation of planets is about 15 per cent. We also
compute age and heavy element abundances from the properties of host stars,
given in the TEPCat catalogue (Southworth 2011). The metallicity given in the
literature is as [Fe/H]. However, the most abundant element is oxygen, and
there is a reverse relation between the observed abundances [Fe/H] and [O/Fe].
Therefore, we first compute [O/H] from [Fe/H] by using observed abundances, and
then find heavy element abundance from [O/H]. We also develop a new method for
age determination. Using the ages we find, we analyse variation of both radius
and mass of the planets with respect to time, and estimate the initial mass of
the planets from the relation we derive for the first time. According to our
results, the highly irradiated gas giants lose 5 per cent of their mass in
every 1 Gyr.Comment: 15 pages, 13 figures, 3 tables. Accepted by MNRA
Asteroseismic Investigation of 20 Planet and Planet-Candidate Host Stars
Planets and planet candidates are subjected to great investigation in recent
years. In this study, we analyse 20 planet and planet-candidate host stars at
different evolutionary phases. We construct stellar interior models of the host
stars with the MESA evolution code and obtain their fundamental parameters
under influence of observational asteroseismic and non-asteroseismic
constraints. Model mass range of the host stars is 0.74-1.55 .
The mean value of the so-called large separation between oscillation
frequencies and its variation about the minima show the diagnostic potential of
asteroseismic properties. Comparison of variations of model and observed large
separations versus the oscillation frequencies leads to inference of
fundamental parameters of the host stars. Using these parameters, we revise
orbital and fundamental parameters of 34 planets and four planet candidates.
According to our findings, radius range of the planets is 0.35-16.50
. The maximum difference between the transit and revised
radii occurs for Kepler-444b-f is about 25 per cent.Comment: 9 pages, 7 figures, 6 table
Fundamental properties of Kepler and CoRoT targets -- IV. Masses and radii from frequencies of minimum and their implications
Recently, by analysing the oscillation frequencies of 90 stars, Yildiz,
\c{C}elik Orhan & Kayhan have shown that the reference frequencies (, and ) derived from glitches due to He
{\scriptsize II} ionization zone have very strong diagnostic potential for the
determination of their effective temperatures. In this study, we continue to
analyse the same stars and compute their mass, radius and age from different
scaling relations including relations based on , and . For most of the stars, the masses computed using
and are very close to each other. For 38
stars, the difference between these masses is less than 0.024 .
The radii of these stars from and are even
closer, with differences of less than 0.007 . These stars may be
the most well known solar-like oscillating stars and deserve to be studied in
detail. The asteroseismic expressions we derive for mass and radius show slight
dependence on metallicity. We therefore develop a new method for computing
initial metallicity from this surface metallicity by taking into account the
effect of microscopic diffusion. The time dependence of initial metallicity
shows some very interesting features that may be important for our
understanding of chemical enrichment of Galactic Disc. According to our
findings, every epoch of the disc has its own lowest and highest values for
metallicity. It seems that rotational velocity is inversely proportional to 1/2
power of age as given by the Skumanich relation.Comment: 19 pages, 12 figure
Morphometric and morphological evaluation of mastoid emissary canal using cone-beam computed tomography
Objectives: This study aimed to determine mastoid emissary canal’s (MEC) and mastoid foramen (MF) prevalence and morphometric characteristics on cone-beam computed tomography (CBCT) images to underline its clinical significance and discuss its surgical consequences. Methods: In the retrospective analysis, two oral and maxillofacial radiologists analyzed the CBCT images of 135 patients (270 sides). The biggest MF and MEC were measured in the images evaluated in MultiPlanar Reconstruction (MPR) views. The MF and MEC mean diameters were calculated. The mastoid foramina number was recorded. The prevalence of MF was studied according to gender and side of the patient. Results: The overall prevalence of MEC and MF was 119 (88.1%). The prevalence of MEC and MF is 55.5% in females and 44.5% in males. MEC and MF were identified as bilateral in 80 patients (67.20%) and unilateral in 39 patients (32.80%). The mean diameter of MF was 2.4 ± 0.9 mm. The mean height of MF was 2.3 ± 0.9. The mean diameter of the MEC was 2.1 ± 0.8, and the mean height of the MEC was 2.1 ± 0.8. There is a statistical difference between the genders (p = 0.043) in foramen diameter. Males had a significantly larger mean diameter of MF in comparison to females. Conclusion: MEC and MF must be evaluated thoroughly if the surgery is contemplated. Radiologists and surgeons should be aware of mastoid emissary canal morphology, variations, clinical relevance, and surgical consequences while operating in the suboccipital and mastoid areas to avoid unexpected and catastrophic complications. CBCT may be a reliable imaging diagnostic technique
Nasopharynx evaluation in children of unilateral cleft palate patients and normal with cone beam computed tomography
OBJECTIVE: This study aimed to examine the morphological characteristics of the nasopharynx in unilateral Cleft lip/palate (CL/P) children and non-cleft children using cone beam computed tomography (CBCT). METHODS: A retrospective study consisted of 54 patients, of which 27 patients were unilateral CL/P, remaining 27 patients have no CL/P. Eustachian tubes orifice (ET), Rosenmuller fossa (RF) depth, presence of pharyngeal bursa (PB), the distance of posterior nasal spine (PNS)-pharynx posterior wall were quantitatively evaluated. RESULTS: The main effect of the CL/P groups was found to be effective on RF depth-right (p < 0.001) and RF depth-left (p < 0.001). The interaction effect of gender and CL/P groups was not influential on measurements. The cleft-side main effect was found to be effective on RF depth-left (p < 0.001) and RF depth-right (p  =  0002). There was no statistically significant relationship between CL/P groups and the presence of bursa pharyngea. CONCLUSIONS: Because it is the most common site of nasopharyngeal carcinoma (NPC), the anatomy of the nasopharynx should be well known in the early diagnosis of NPC
Incorporation of a global perspective into data-driven analysis of maritime collision accident risk
Ship collision accidents are one of the most frequent accident types in global maritime transportation. Nevertheless, conducting an in-depth analysis of collision prevention poses a formidable challenge due to the constraints of limited Risk Influential Factors (RIFs) and available datasets. This paper aims to incorporate a global perspective into a new data-driven risk model, scrutinize the root causes of collision accidents, and advance measures for their mitigation. Additionally, it seeks to analyze the spatial distribution and conduct a comprehensive comparative study on collision characteristics for both pre- and post-COVID-19, utilizing the real accident dataset collected from two reputable organizations: Global Integrated Shipping Information System (GISIS) and Lloyd's Register Fairplay (LRF). The research findings and implications encompass several crucial aspects: 1) the constructed model demonstrates its reliability and accuracy in predicting collision accidents, as evident from its prediction performance and various scenario analysis; 2) the most hazardous voyage segment for collision accidents is identified to provide valuable guidance to different stakeholders; and 3) the hierarchical significance of various ship types in the context of collision accident is highlighted regarding the most probable scenario for collision occurrences; 4) During the pandemic, the rise in collision probabilities, particularly involving older vessels and bulk carriers, implies heightened operational challenges or maintenance issues for these ship types; (5) The prominence of favorable and adverse sea conditions in collision reports underscores the significant influence of weather on accidents during the pandemic. These findings and implications help enhance safety protocols, ultimately reducing the frequency of collision accidents in the global maritime domain
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