2,283 research outputs found
Seismic analysis of 70 Ophiuchi A: A new quantity proposed
The basic intent of this paper is to model 70 Ophiuchi A using the latest
asteroseismic observations as complementary constraints and to determine the
fundamental parameters of the star. Additionally, we propose a new quantity to
lift the degeneracy between the initial chemical composition and stellar age.
Using the Yale stellar evolution code (YREC7), we construct a series of stellar
evolutionary tracks for the mass range = 0.85 -- 0.93 with
different composition (0.26 -- 0.30) and (0.017 -- 0.023).
Along these tracks, we select a grid of stellar model candidates that fall
within the error box in the HR diagram to calculate the theoretical
frequencies, the large- and small- frequency separations using the Guenther's
stellar pulsation code. Following the asymptotic formula of stellar -modes,
we define a quantity which is correlated with stellar age. Also, we
test it by theoretical adiabatic frequencies of many models. Many detailed
models of 70 Ophiuchi A have been listed in Table 3. By combining all
non-asteroseismic observations available for 70 Ophiuchi A with these
seismological data, we think that Model 60, Model 125 and Model 126, listed in
Table 3, are the optimum models presently. Meanwhile, we predict that the
radius of this star is about 0.860 -- 0.865 and the age is about
6.8 -- 7.0 Gyr with mass 0.89 -- 0.90 . Additionally, we prove that
the new quantity can be a useful indicator of stellar age.Comment: 23 pages, 5 figures, accepted by New Astronom
Asteroseismic study of solar-like stars: A method of estimating stellar age
Asteroseismology, as a tool to use the indirect information contained in
stellar oscillations to probe the stellar interiors, is an active field of
research presently. Stellar age, as a fundamental property of star apart from
its mass, is most difficult to estimate. In addition, the estimating of stellar
age can provide the chance to study the time evolution of astronomical
phenomena. In our poster, we summarize our previous work and further present a
method to determine age of low-mass main-sequence star.Comment: 2 pages, 1 figures, submitted to IAUS25
'Rapid fire' spectroscopy of Kepler solar-like oscillators
The NASA Kepler mission has been continuously monitoring the same field of
the sky since the successful launch in March 2009, providing high-quality
stellar lightcurves that are excellent data for asteroseismology, far superior
to any other observations available at the present. In order to make a
meaningful analysis and interpretation of the asteroseismic data, accurate
fundamental parameters for the observed stars are needed. The currently
available parameters are quite uncertain as illustrated by e.g. Thygesen et al.
(A&A 543, A160, 2012), who found deviations as extreme as 2.0 dex in [Fe/H] and
log g, compared to catalogue values. Thus, additional follow-up observations
for these targets are needed in order to put firm limits on the parameter space
investigated by the asteroseismic modellers. Here, we propose a metod for
deriving accurate metallicities of main sequence and subgiant solar-like
oscillators from medium resolution spectra with a moderate S/N. The method
takes advantage of the additional constraints on the fundamental parameters,
available from asteroseismology and multi-color photometry. The approach
enables us to reduce the analysis overhead significantly when doing spectral
synthesis, which in turn will increases the efficiency of follow-up
observations.Comment: 3 pages, 2 figures. Proceedings from Asteroseismology of Stellar
Populations in the Milky Way 2013 to appear in 'Astrophysics and Space
Science Proceedings
Hypersonic Separated Flows About "Tick" Configurations With Sensitivity to Model Design
This paper presents computational results obtained by applying the direct simulation Monte Carlo (DSMC) method for hypersonic nonequilibrium flow about "tick-shaped" model configurations. These test models produces a complex flow where the nonequilibrium and rarefied aspects of the flow are initially enhanced as the flow passes over an expansion surface, and then the flow encounters a compression surface that can induce flow separation. The resulting flow is such that meaningful numerical simulations must have the capability to account for a significant range of rarefaction effects; hence the application of the DSMC method in the current study as the flow spans several flow regimes, including transitional, slip, and continuum. The current focus is to examine the sensitivity of both the model surface response (heating, friction and pressure) and flowfield structure to assumptions regarding surface boundary conditions and more extensively the impact of model design as influenced by leading edge configuration as well as the geometrical features of the expansion and compression surfaces. Numerical results indicate a strong sensitivity to both the extent of the leading edge sharpness and the magnitude of the leading edge bevel angle. Also, the length of the expansion surface for a fixed compression surface has a significant impact on the extent of separated flow
Apparent digestibility of insect protein meals for rainbow trout
Insect meals are considered to be promising future ingredients for aquaculture feeds. In past feeding trials in rainbow trout, insect meals were included in diets only on the basis of their nutrients content and energy density without taking into account their biological availability due to the lack of their digestible values. Apparent digestibility (ADC) provides good indication of the bioavailability of nutrients and energy thus providing rational basis for the correct inclusion of feedstuffs. The aim of this research was to assess, in an in vivo trial on rainbow trout, the ADC of five full fat insect meals: one Tenebrio molitor (TM), two Hermetia illucens obtained through two different process (HI1 and HI2), one Musca domestica (MD), and one Alphitobius diaperinus (AD). Fish were fed a high-quality reference diet (R) and test diets obtained mixing the R diet with each of the test ingredients at a ratio of 70:30. Diets contained 1% celite as inert marker. Fish were fed to visual satiety twice a day and faecal samples collected using a continuous automatic device. Faeces were freeze dried and frozen (-20 \ub0C) until analyses. The ADC of dry matter, crude protein and ether extract of each insect meal diet were calculated. ADC for dry matter varied between 70.07 (HI1) and 80.85 (TM). ADC for protein was above 84% in all treatments and resulted the highest in MD, TM and AD treatments. Ether extract apparent digestibility significantly differed among diets with the highest value reported for TM treatment. All treatments reported values higher than 96%. Observed differences could be due to the insect species and meal treatment but in general, tested insect meals were highly digestible for rainbow trout. The results from this research could be useful to optimize the diet formulation
Effect of dietary supplementation with insect fats on growth performance, digestive efficiency and health of rabbits
Background: The present work aimed at evaluating the effect of the dietary replacement of soybean oil (S) by two types of insect fats extracted from black soldier fly larvae (H, Hermetia illucens L.) and yellow mealworm larvae (T, Tenebrio molitor L.) on growth performance, nutrient digestibility, blood parameters, intestinal morphology and health of growing rabbits. Methods: At weaning, 200 crossbred rabbits (36 days old) were allotted to five dietary treatments (40 rabbits/group): a control diet (C) containing 1.5% of soybean oil and four experimental diets where soybean oil was partially (50%) or totally (100%) substituted by H (H50 and H100) or T (T50 and T100) fats. Total tract digestibility was evaluated on 12 rabbits per treatment. The growth trial lasted 41 d and, at slaughtering (78 days old), blood samples were collected from 15 rabbits per treatment, morphometric analyses were performed on duodenum, jejunum and ileum mucosa, and samples of liver, spleen and kidney were submitted to histological evaluation. Results: No difference was observed between the control and the experimental groups fed insect fats in terms of performance, morbidity, mortality and blood variables. The addition of H and T fats did not influence apparent digestibility coefficients of dry matter, protein, ether extract, fibre fractions and gross energy. Gut morphometric indices and organ histopathology were not affected by dietary inclusion of H and T fats. Conclusions: H and T fats are suitable sources of lipid in rabbit diets to replace soybean oil without any detrimental effect on growth performance, apparent digestibility, gut mucosa traits and health
The Impact of Perceived Lottery Knowledge on Problem Lottery Playing: A Moderated Mediation Model
The study explored the mechanism of perceived lottery knowledge in predicting problem in lottery playing through a Moderated Mediation Model centering on overconfidence. A total of 972 Chinese football bettors from nine provinces completed a questionnaire survey. The result showed that: (1) perceived lottery knowledge could positively predict problem lottery playing; (2) perceived lottery knowledge influenced problem lottery playing directly and indirectly through overconfidence; (3) risk perception moderated the mediated path. The indirect effect was stronger for football bettors with low-risk perception than for those with high-risk perception. Implications of consumption and intervention for problem lottery players were discussed.
Keywords: football bettors, problem lottery playing, perceived lottery knowledge, overconfidence, risk perceptio
Magnetic ground state of the Ising-like antiferromagnet DyScO
We report the low temperature magnetic properties of the DyScO
perovskite, which were characterized by means of single crystal and powder
neutron scattering, and by magnetization measurements. Below
K, Dy moments form an antiferromagnetic structure
with an easy axis of magnetization lying in the -plane. The magnetic
moments are inclined at an angle of to the -axis. We
show that the ground state Kramers doublet of Dy is made up of primarily
eigenvectors and well separated by crystal field from the
first excited state at meV. This leads to an extreme Ising
single-ion anisotropy, . The transverse magnetic
fluctuations, which are proportional to , are
suppressed and only moment fluctuations along the local Ising direction are
allowed. We also found that the Dy-Dy dipolar interactions along the
crystallographic -axis are 2-4 times larger than in-plane interactions.Comment: 9 pages and 6 figures; to be published in Phys. Rev.
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