347 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
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
Evaluation of the sealing ability of different root canal sealers: a combined SEM and micro-CT study
Extracorporeal shock waves enhance normal fibroblast proliferation in vitro and activate mRNA expression for TGF-β1 and for collagen types I and III
Background and purpose Extracorporeal shock waves (ESWs) are used to good effect in the treatment of soft tissue injuries, but the underlying mechanisms are still unknown. We therefore determined the effects of ESWs on normal fibroblasts in vitro, in order to assess treatment-induced cell response
Antibacterial Characterization of Novel Synthetic Thiazole Compounds against Methicillin-Resistant Staphylococcus pseudintermedius
Staphylococcus pseudintermedius is a commensal organism of companion animals that is a significant source of opportunistic infections in dogs. With the emergence of clinical isolates of S. pseudintermedius (chiefly methicillin-resistant S. pseudintermedius (MRSP)) exhibiting increased resistance to nearly all antibiotic classes, new antimicrobials and therapeutic strategies are urgently needed. Thiazole compounds have been previously shown to possess potent antibacterial activity against multidrug-resistant strains of Staphylococcus aureus of human and animal concern. Given the genetic similarity between S. aureus and S. pseudintermedius, this study explores the potential use of thiazole compounds as novel antibacterial agents against methicillin-sensitive S. pseudintermedius (MSSP) and MRSP. A broth microdilution assay confirmed these compounds exhibit potent bactericidal activity (at sub-microgram/mL concentrations) against both MSSA and MRSP clinical isolates while the MTS assay confirmed three compounds (at 10 μg/mL) were not toxic to mammalian cells. A time-kill assay revealed two derivatives rapidly kill MRSP within two hours. However, this rapid bactericidal activity was not due to disruption of the bacterial cell membrane indicating an alternative mechanism of action for these compounds against MRSP. A multistep resistance selection analysis revealed compounds 4 and 5 exhibited a modest (twofold) shift in activity over ten passages. Furthermore, all six compounds (at a subinihibitory concentration) demonstrated the ability to re-sensitize MRSP to oxacillin, indicating these compounds have potential use for extending the therapeutic utility of β-lactam antibiotics against MRSP. Metabolic stability analysis with dog liver microsomes revealed compound 3 exhibited an improved physicochemical profile compared to the lead compound. In addition to this, all six thiazole compounds possessed a long post-antibiotic effect (at least 8 hours) against MRSP. Collectively the present study demonstrates these synthetic thiazole compounds possess potent antibacterial activity against both MSSP and MRSP and warrant further investigation into their use as novel antimicrobial agents
One-year prevalence and the impact of migraine and tension-type headache in Turkey: a nationwide home-based study in adults
Several studies have shown that the prevalence of migraine and tension-type headache (TTH) varied between different geographical regions. Therefore, there is a need of a nationwide prevalence study for headache in our country, located between Asia and Europe. This nationwide study was designed to estimate the 1-year prevalence of migraine and TTH and analyse the clinical features, the impact as well as the demographic and socio-economic characteristics of the participant households in Turkey. We planned to investigate 6,000 representative households in 21 cities of Turkey; and a total of 5,323 households (response rate of 89%) aged between 18 and 65 years were examined for headache by 33 trained physicians at home on the basis of the diagnostic criteria of the second edition of the International Classification of Headache Disorders (ICHD-II). The electronically registered questionnaire was based on the headache features, the associated symptoms, demographic and socio-economic situation and history. Of 5,323 participants (48.8% women; mean age 35.9 ± 12 years) 44.6% reported recurrent headaches during the last 1 year and 871 were diagnosed with migraine at a prevalence rate of 16.4% (8.5% in men and 24.6% in women), whereas only 270 were diagnosed with TTH at a prevalence rate of 5.1% (5.7% in men and 4.5% in women). The 1-year prevalence of probable migraine was 12.4% and probable TTH was 9.5% additionally. The rate of migraine with aura among migraineurs was 21.5%. The prevalence of migraine was highest among 35–40-year-old women while there were no differences in age groups among men and in TTH overall. More than 2/3 of migraineurs had ever consulted a physician whereas only 1/3 of patients with TTH had ever consulted a physician. For women, the migraine prevalence was higher among the ones with a lower income, while among men, it did not show any change by income. Migraine prevalence was lower in those with a lower educational status compared to those with a high educational status. Chronic daily headache was present in 3.3% and the prevalence of medication overuse headache was 2.1% in our population. There was an important impact of migraine with a monthly frequency of 5.9 ± 6, and an attack duration of 35.1 ± 72 h, but only 4.9% were on prophylactic treatment. The one-year prevalence of migraine estimated as 16.4% was similar or even higher than world-wide reported migraine prevalence figures and identical to a previous nation-wide study conducted in 1998, whereas the TTH prevalence was much lower using the same methodology with the ICHD-II criteria
Apple polyphenol extract improves insulin sensitivity in vitro and in vivo in animal models of insulin resistance
Background:
Apple polyphenols could represent a novel nutritional approach in the management and control of blood glucose, especially in type 2 diabetics. The aim of this study was to test the therapeutic potential of an apple polyphenol extract (APE) in an insulin-resistant rat model and to determine the molecular basis of insulin sensitivity action in skeletal muscle cells.Methods:
Acute effect of APE on the postprandial hyperglycemic response was assayed in 15 week old obese Zucker rats (OZR), by using a meal tolerance test (MTT). The ability of APE to improve whole peripheral insulin sensitivity was also assayed in a chronic study by using the euglycemic-hyperinsulinemic clamp technique. To elucidate the molecular mechanisms, rat L6 myotubes were used. Glucose uptake was measured by using 2-[3H]-Deoxy-Glucose (2-DG) and specific inhibitors, as well as phosphorylation status of key kinases, were used to determine the implicated signaling pathway.Results:
In vivo study showed that nutritional intervention with APE induced an increase of insulin sensitivity with an increase of glucose infusion rate (GIR) of 45 %. Additionally, in vitro results showed a synergistic effect between APE and insulin as well as increased glucose uptake through GLUT4 translocation in muscle cells. This translocation was mediated by phosphatydil inositol 3-kinase (PI3K) and peroxisome proliferator-activated receptor-gamma (PPARγ) signaling pathways.Conclusions:
As a whole, this study describes the mechanisms involved in the insulin sensitizing effect of APE, which could be considered a promising ingredient for inclusion in nutritional products focused on the management of chronic diseases such as diabetes.This research was supported by funds from Abbott Laboratories S.A
- …