• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.77.4-78
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• 2016

Binary interactions may have significant impact on Pop III stellar evolution. Pop III single star evolution indicates that for primary masses less than $20M_{\odot}$, no significant binary mass transfer would occur before core helium exhaustion. We perform binary system evolution for various primary masses ($20M_{\odot}$ < $M_1$ < $60M_{\odot}$) and initial periods under same mass ratio $M_2/M_1=0.9$, and follow the evolution and mass transfer of the primary star. If binary mass transfer occurs during post main sequence, the primary star does not evolve into naked helium star and still contain significant hydrogen in the envelope. During the post mass transfer phase, the primary star evolves redward, and does not become sufficiently hot to enhance the number of ionizing photons, compared to the case of single star evolution for a given initial mass. This result implies that primary stars of massive Pop III binary systems would have little contribution to the reionization in the early universe. Given the large hydrogen content ($0.326-1.793M_{\odot}$), the primary stars that underwent stable mass transfers would explode as a Type IIb supernova, and it would be difficult for Pop III binary stars to produce Type Ib/c supernovae that look similar to those found in the local universe.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.53.2-53.2
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• 2021

Quasar luminosity function (QLF) shows the active galactic nucleus (AGN) demography as a result of the combination of the growth and the evolution of black holes, galaxies, and dark matter halos along the cosmic time. The recent wide and deep surveys have improved the census of high-redshift quasars, making it possible to construct reliable ultraviolet (UV) QLFs at 2 < z < 6 down to M1450 = -23 mag. By parameterizing these up-to-date observed UV QLFs that are the most extensive in both luminosity and survey area coverage at a given redshift, we show that the UV QLF has a universal shape, and their evolution can be approximated by a pure density evolution (PDE). In order to explain the observed QLF, we construct a model QLF employing the halo mass function, a number of empirical scaling relations, and the Eddington ratio distribution. We also include the outshining of AGN over its host galaxy, which made it possible to reproduce a moderately flat shape of the faint end of the observed QLF (slope of ~ -1.1). This model successfully explains the observed PDE behavior of UV QLF at z > 2, meaning that the QLF evolution at high redshift can be understood under the framework of halo mass function evolution. The importance of the outshining effect in our model also implies that there could be a hidden population of faint AGNs (M1450 > -24 mag), which are buried under their host galaxy light.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.2
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• pp.57-66
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• 2006

AA5182-polypropylene sandwich sheet was manufactured, and the mechanical properties evaluation was executed in order to identify $L{\ddot{u}}ders$ band that causes fabrication process problem and especially surface roughness. To identify formability, deformation behavior, plastic strain ratio (R-value) and pole figure were measured, and texture analysis was performed. In the case of sandwich sheet, the unstable deformation behavior has decreased. As well, for sandwich sheet, A1 skin could manage the most of load, and the elongation has improved about 45% more than that of A1 skin. The plastic strain ratio of A1 skin and sandwich panel, which indicates serration behavior, was obtained from instantaneous plastic strain ratio evaluation. Also, the planar anisotropy of sandwich sheet has decreased more than that of A1 skin. According to these results, the sandwich sheet produced lightening effect and could control unstable deformation characteristic, that is, surface roughness caused by $L{\ddot{u}}ders$ band. Furthermore, it was proved that the texture control of the rolling attachment of A1 skin is necessary to improve the formability of the sandwich panel.

• The Korean Journal of Nuclear Medicine Technology
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• v.18 no.1
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• pp.62-68
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• 2014

Purpose: After I-131 therapy, SPECT/CT is useful in identifying location of thyroid remnants and metastasis of thyroid cancers. An excessive uptake of thyroid leads to a ringing artifact in the SPECT images. The aim of this study is to investigate and suggest a proper post filters to remove ringing artifact and produce better image quality. Materials and Methods: A low-cost, customized thyroid-mimicking phantom, consisting of an acrylic bottle and a hollow sphere was used for SPECT/CT Discovery (GE Healthcare, USA). It was filled with I-131 solution. The ratio of hollow sphere to background were varied as 50:1, 200:1, 1000:1 and 4000:1. Acquired images were reconstructed by OSEM (2 iterations, 10 subsets) with and without Evolution (resolution recovery correction, GE). Three different post-filters were applied; Butterworth (cut off: 0.38 to 0.58 with intervals of 0.05), Hanning (cut off: 0.8 to 1 with intervals of 0.05) and Gaussian (FWHM: 3 to 5 with intervals of 0.5) filters. Contrast, background variability, air area variability, and full width half maximum (FWHM) were compared. Results: Higher contrasts were obtained from the SPECT images with Evolution than without Evolution. In the case of images without Evolution, image distortion such as star artifact was generated. For all sphere-to-background ratio, the Butterworth filter showed better constrasts and FWHMs than other two filters, but the ringing artifact was still generated in all studies except 50:1 and it was decreased as cutoff value was increased. The ringing artifact didn't appear with Hanning and Gaussian filters at all studies, however constrats and FWHMs with Gaussian was worse than Hanning filter. For the images having ringing artifacts, the background variability and air area variability were increased. Conclusion: In this study, we suggested that it is desirable to use Hanning filter when the ringing artifact is generated and to use Butterworth filter when ringing artifact is not generated in I-131 SPECT.

• Water Engineering Research
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• v.2 no.4
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• pp.243-259
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• 2001

Local phenomena around bridge piers and abutments are generally considered to be similar, nevertheless the presence of the incoming boundary layer on the side wall in the abutment case generates extra pressure gradients and consequently a more complex vortex pattern. In the literature, experimental data for bridge abutments are relatively scarce; in particular almost no data are available for the time evolution of the scour. In this work we present the results of several long duration (3 days longrightarrow5weeks) clear water scour laboratory tests around bridge abutments; the time evolution of the erosion process is analysed with respect to local and global characteristic values (maxima, volume, hole shape). In particular we analyse the effect of the constriction ratio b/B between the transversal obstacle dimension and the flume width: in many practical situations abutments (or piers) obstruct a significant portion of the channel, so that the average acceleration due to constriction is expected to increase the scour effects of the local acceleration around the obstacle. Measured values for maximum scour are poorly predicted by literature formulas. Scour depths are positively correlated with the constriction ratio, but increases are smaller than expected from literature indications. Experimental results show that models for bridge piers cannot be directly applied to abutments; in particular, time scales for the latter are significantly larger than for piers.

• Transactions of Materials Processing
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• v.24 no.6
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• pp.395-399
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• 2015

A microstructure-based finite element simulation was conducted to predict the plastic strain ratio (R-value) of a dual-phase (DP) steel. The representative volume elements (RVEs) concept was adopted for the image-based FE modeling and a 3D model was constructed using sequential 2D images. Each phase was considered with the von-Mises yield criterion and the Swift model. The Swift parameters were defined by the empirical equations based on the chemical composition. The developed model was applied to analyze the effect of residual stress on the R-value and stress distribution. In order to consider the residual stress development after cold rolling, 10 % compression was applied in the thickness direction and unloaded before the tensile stress was applied in the rolling direction. The results showed a reasonable prediction for the R-value evolution: a sharp increase at small strains was well described and a transition followed in the downward direction. The R-value evolution was analyzed using the stress distribution change on the π-plane

• Journal of the Korean Wood Science and Technology
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• v.23 no.4
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• pp.46-53
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• 1995

The anatomy of Korean diffuse-porous woods, 36 families, 75 genera, 145 species, 215 specimens was described and analyzed. Sixteen wood anatomical characters, habit and phenology factors were determined by simple correlation and principal component analysis. Strong positive correlations were found between vessel element length and fiber length, ray width and ray height, simple pits of fiber wall and paratracheal parenchyma distribution. The results of principal component analysis (PCA) disclose the primitive characteristics and the direction of xylem evolution of Korean diffuse-porous woods. The xylem evolution scenario for Korean dicotyledonous woods is considered to be developed in the direction of decreasing trends of vessel frequency, vessel element length, and length/diameter(L/D) ratio of vessel element but increasing trends of vessel diameter, fiber length/vessel element length(F/V) ratio, libriform wood fibers, simple perforation, and homogeneous ray composition. Increase of vessel diameter and decrease of vessel frequency seem to be related to the improvement of conductive efficiency, and increase of the vessel element length and occurrence of scalariform perforation in vessel element may be related to enhanced of conductive safety. Also the libriform wood fibers and ray features appear to have relationship with mechanical support and nutrient metabolism, respectively.

• Geomechanics and Engineering
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• v.20 no.1
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• pp.55-66
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• 2020

The damage or failure of coal rock is accompanied by energy accumulation, dissipation and release. It is crucial to study the energy evolution characteristics of coal rock for rock mechanics and mining engineering applications. In this paper, coal specimens sourced from the Xinhe mine located in the Jining mining area of China were initially subjected to uniaxial compression, and the micro-parameters of the two-dimensional particle flow code (PFC^2D) model were calibrated according to the experimental test results. Then, the PFC^2D model was used to subject the specimens to substantial uniaxial compression, and the energy evolution laws of coal specimens with various schemes were presented. Finally, the elastic energy storage ratio m was investigated for coal rock, which described the energy conversion in coal specimens with various arrangements of preformed holes. The arrangement of the preformed holes significantly influenced the characteristics of the crack initiation stress and energy in the prepeak stage, whereas the characteristics of the cumulative crack number, failure pattern and elastic strain energy during the loading process were similar. Additionally, the arrangement of the preformed holes altered the proportion of elastic strain energy U_e in the total energy in the prepeak stage, and the probability of rock bursts can be qualitatively predicted.

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.6
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• pp.128-134
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• 2005

In order to fabricate the aluminum alloys with good drawability, the textures evolution of the AA5182 sheets after rolling and annealing was studied. The measurement of the deformation textures was carried out for the sheets which were cold rolled with high reduction ratio by using the symmetric roll. In addition, the change of the recrystallization texture was investigated after heat-treatments of the rolled sheets with various heat treatment conditions. Rolling without lubrication and subsequent annealing led to the formation of favorable $rot-C_{ND}\;\{001\}<110>\;and\;{\gamma}-fiber ND//<111>$ textures in AA5182 sheets. From the results, the ${\gamma}$-fiber ND//<111> component well evolved during rolling at highest reduction ratio (over $90\%$, l/d parameter of 6.77). Among shear deformation textures, the ${\gamma}$-fiber ND//<111> was not rotated in holding time of $180\~7,200$ seconds at $350^{\circ}C$. The Monte-Carlo technique was used and could be representatively simulated these textures evolution during recrystallization.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.47.1-47.1
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• 2011

We studied the evolution of the two mass components system with NFW initial density distribution by direct integration of the Fokker-Planck equations. The low mass component is regarded the dark matter particles while the high mass component is assumed to be conglomerates of baryonic matter in order to depict the 'stars'. While the true mass ratio between these two types of particles should be extremely large, our adopted mass ratio is about 1000 beyond which the dynamical evolution and density distribution tend to converge. Since the dynamical evolution is dominated by the dynamical friction, the high mass component slowly moves toward the central part, and eventually undergoes the core collapse. The system reaches the core-collapse at about $7.1{\times}10^{-3}$ $t_{fh}$ in NFW models, where $t_{fh}$is the dynamical friction time at half-mass radius. The distribution of the high mass component is well fitted by the Sersic profiles or modified Hubble profile when the mass segregation is established. From these results, the surface brightness of elliptical galaxies may be explained by the high mass component experiencing dynamical friction by the dark matter particles. In order for the mass segregation to be effective within Hubble time, the mass of the luminous component should be greater than $10^5M_{\bigodot}$.