Fundamental properties of solar-like oscillating stars from frequencies of minimum Δν\Delta \nu : 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 ($Z$) and helium abundance ($Y$). 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 $Z$ and $Y$ 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 $Z$. It also depends on $\nu_{\rm min1}/\nu_{\rm max}$ and small separation between the frequencies. Such a dependence leads us to develop a method to find $Z$ (and $Y$) from oscillation frequencies. The maximum difference between the estimated and model $Z$ values is about 14 per cent. It is 10 per cent for $Y$.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 ($l_-$), for all mass intervals. There is an extra increase in radius of planets if $l_-$ is higher than 1100 times energy received by the Earth ($l_\oplus$). 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 ${\rm M}_\odot$. 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 $\mathrm{R}_{\oplus}$. 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

Advances in Metabolic Engineering of Saccharomyces cerevisiae for the Production of Industrially and Clinically Important Chemicals

Sustainable production of chemicals is of increasing importance, due to depletion of petroleum and environmental concerns. In addition to its importance in basic research as a simple, eukaryotic model organism, Saccharomyces cerevisiae has long been exploited in industry because of its physiological properties. And today, the development in genetic engineering toolbox and genome-scale metabolic models of S. cerevisiae has extended its application range to new products and bioprocesses. In addition, evolutionary engineering strategies have been useful in improving cellular properties of S. cerevisiae, such as tolerance to product toxicity and inhibitors. In this chapter, recent metabolic and evolutionary engineering studies that involve S. cerevisiae for the production of bulk chemicals and fine chemicals including flavours and pharmaceuticals are reviewed. It was shown that metabolic engineering particularly allowed the improvement of pharmaceuticals production, which will enable economic and large-scale production of many valuable pharmaceuticals. It is clear that S. cerevisiae will continue to be an important host for future metabolic engineering and metabolic pathway engineering applications to produce a variety of industrially and clinically important chemicals

Evaluation of type C fly ash in the production of composite material

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.In this study, the availability as a new composite material of the class C fly ashes which have negative effects on environment was investigated. First of all, the properties of fly ash and polypropylene have been identified. By making use of the obtained results, the availability of fly ash and polypropylene materials was investigated in production of a new composite material. For this purpose, by using type C fly ash of thermal power plants in mass ratios of 10% - 60%, a new composite material was produced. To determine mechanical and physical properties of the produced composite samples, thermal conductivity, compressive strength, water absorption capacity, and abrasive loss were performed. From the results, it was witnessed that both environmental problems can be reduced and economical profit can be achieved by means of energy saving.dc201

Rational design and direct fabrication of multi-walled hollow electrospun fibers with controllable structure and surface properties

Multi-walled hollow fibers with a novel architecture are fabricated through utilizing a direct,one-step tri-axial electrospinning process with a manufacturing methodology which does not require any post-treatments for the removal of core material for creating hollowness in the fiber structure. The hydrophilicity of both inner and outer layers’ solution needs to be dissimilar and carefully controlled for creating a two-walled/layered hollow fiber tructure with a sharp interface. To this end, Hansen solubility parameters are used as n index of layer solution affinity hence allowing for control of diffusion across the layers and the surface porosity whereby an ideal multi-walled hollow electrospun fiber is shown to be producible by tri-axial electrospinning process. Multi-walled hollow electrospun fibers with different inner and outer diameters and different surface morphology are successfully produced by using dissimilar material combinations for inner and outer layers (i.e., hydrophobic polymers as outer layer and hydrophilic polymer as inner layer). Upon using different material combinations for inner and outer layers, it is shown that one may control both the outer and inner diameters of the fiber. The inner layer not only acts as a barrier and thus provides an ease in the encapsulation of functional core materials of interest with different viscosities but also adds stiffness to the fiber. The structure and the surface morphology of fibers are controlled by changing applied voltage, polymer types, polymer concentration, and the evaporation rate of solvents. It is demonstrated that if the vapor pressure of the solvent for a given outer layer polymer is low, the fiber diameter decreases down to 100 nm whereas solvents with higher vapor pressure result in fibers with the outer diameter of up to 1 μm. The influence of electric field strength on the shape of Taylor cone is also monitored during the production process and the manufactured fibers are structurally investigated by relevant surface characterization techniques

Fundamental properties of Kepler and CoRoT targets -- IV. Masses and radii from frequencies of minimum Δν\Delta {\nu} and their implications

Recently, by analysing the oscillation frequencies of 90 stars, Yildiz, \c{C}elik Orhan & Kayhan have shown that the reference frequencies ($\nu_{\rm min0}$, $\nu_{\rm min1}$ and $\nu_{\rm min2}$) 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 $\nu_{\rm min0}$, $\nu_{\rm min1}$ and $\nu_{\rm min2}$. For most of the stars, the masses computed using $\nu_{\rm min0}$ and $\nu_{\rm min1}$ are very close to each other. For 38 stars, the difference between these masses is less than 0.024 ${\rm M}_\odot$. The radii of these stars from $\nu_{\rm min0}$ and $\nu_{\rm min1}$ are even closer, with differences of less than 0.007 ${\rm R}_\odot$. 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