• KIEE International Transactions on Electrophysics and Applications
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• v.3C no.1
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• pp.19-22
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• 2003

The co-evaporated cathodes composed of A1 and CsF is adopted to enhance the electrical and the optical properties of organic light emitting diodes (OLEDs). The hole transport layer (HTL), made of 50nm thick N,N-dipheny1-N,N-bis(3-methylphenyl)-1,1-bipheny14,4-diamine (TPD), and the electron transport layer (ETL), made of 50nm thick tris(8-hydroxy-quinoline) aluminum (A1q$_3$), were deposited under the base pressure of 1.6$\times$10$^{-6}$ Torr. In depositing A1-CsF, the mass ratio of CsF is varied between 1 and 10wt%. OLEDs with co-evaporated cathodes have luminance of about 35,000cd/$m^2$, and external quantum efficiency of about 1.38%. Cs tends to diffuse into the organic layer and then re-forms Cs$^{+}$cation and free electron with the Cs-doped surface region.n.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.1
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• pp.17-24
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• 2013

The process of producing high precision and light weight product is always exposed to impact load or shock. Because of this, isolator device is required. To measure the response of the isolator, accelerometer is practically used. However, the measured response of the accelerometer is different to the response of the isolator. To predict the response of the accelerometer and the isolator, 2-DOF damped system with an input shock is modeled using numerical analysis. 1-DOF damped system with a base excitation is also used to predict the response of the isolator. The mass ratio, damping ratio, and natural frequency ratio are then varied. The predicted responses from the two modeling approaches are compared and large errors are found.

• Publications of The Korean Astronomical Society
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• v.7 no.1
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• pp.89-96
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• 1992

Recent spectroscopic observations indicate concentration of dark masses in the nuclei of nearby galaxies. This has been usually interpreted as the presence of massive black holes in these nuclei. Alternative explanations such as the dark cluster composed of low mass stars (brown dwarfs) or dark stellar remnants are possible provided that these systems can be stably maintained for the age of galaxies. For the case of low mass star cluster, mass of individual stars can grow to that of conventional stars in collision time scale. The requirement of collision time scale being shorter than the Hubble time gives the minimum cluster size. For typical conditions of M31 or M32, the half-mass radii of dark clusters can be as small as 0.1 arcsecond. For the case of clusters composed of stellar remnants, core-collapse and post-collapse expansion are required to take place in longer than Hubble time. Simple estimates reveal that the size of these clusters also can be small enough that no contradiction with observational data exists for the clusters made of white dwarfs or neutron stars. We then considered the possible outcomes of interactions between the black hole and the surrounding stellar system. Under typical conditions of M31 or M32, tidal disruption will occur every $10^3$ to $10^4$ years. We present a simple scenario for the evolution of stellar debris based on basic principles. While the accretion of stellar material could produce large amount of radiation so that the mass-to-light ratio can become too small compared to observational values it is too early to rule out the black hole model because the black hole can consume most of the stellar debris in time scale much shorter than mean time between two successive tidal disruptions. Finally we outline recent effort to simulate the process of tidal disruption and subsequent evolution of the stellar debris numerically using Smoothed Particle Hydrodynamics technique.

• Journal of The Korean Astronomical Society
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• v.56 no.1
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• pp.11-22
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• 2023

We report the result of a high-resolution spectroscopic study on seven magnesium (Mg) enhanced stars. The high Mg abundances in these stars imply that they were born in an environment heavily affected by the nucleosynthesis products of massive stars. We measure abundances of 16 elements including Mg and they show various abundance patterns implying their diverse origin. Three of our program stars show a very high Mg to Si ratio ([Mg/Si] ≈ 0.18-0.25), which might be well explained by fall-back supernovae or by supernovae with rapid rotating progenitors having an initial mass higher than about 20 M_⊙. Another three of our program stars have high light to heavy s-process element ratios ([Y/Ba] ≈ 0.30-0.44), which are consistent with the theoretical prediction of the nucleosynthesis in rapidly rotating massive stars with an initial mass of about M = 40 M_⊙. We also report a star having both high Y ([Y/Fe] = 0.2) and Ba ([Ba/Fe] = 0.28) abundance ratios, and it also shows the highest Zn abundance ratio ([Zn/Fe] = 0.27) among our sample, implying the nucleosynthesis by asymmetric supernova explosion induced by very rapid rotation of a massive progenitor having an initial mass between 20 M_⊙ ≲ M ≲ 40 M_⊙. A relative deficiency of odd-number elements, which would be a signature of the pair-instability nucleosynthesis, is not found in our sample.

• Current Photovoltaic Research
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• v.5 no.1
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• pp.9-14
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• 2017

The screen printing technique is one of process to form electrode for crystalline silicon solar cell and has been studied a lot, because it has many advantages such as low price, high efficiency and mass production due to simple and fast process. The reason why electrode formation is important is for influence of series resistance and amount of incident light in crystalline silicon solar cell. In this study, electrode was formed by screen printing method with various conditions like squeegee angle, printing speed, snap off, printing pressure. After optimizing various conditions, double printing method was applied to obtain low series resistance and high aspect ratio. As a result, we obtained electrode resistance 45.31 ohm, aspect ratio 4.38, shading loss 7.549% mono-crystalline silicon solar cell with optimal double screen printing condition.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.201-204
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• 2015

The common-envelope process is a complicated phase in binary evolution. A lot of effort has been dedicated to study the common-envelope stage, but many questions related to this process are yet to be answered. If one member of the binary survives the common-envelope phase, the binary will emerge as a white dwarf accompanied by a low-mass main sequence star in close orbit, often referred as a post common-envelope binary (PCEB). SDSS J0745+2631 is among the list of newly found PCEBs from the Sloan Digital Sky Survey (SDSS). This star is proposed to be a strong eclipsing system candidate due to the ellipsoidal modulation in its light curve. In this work, we aim to confirm the eclipsing nature of SDSS J0745+2631 and to determine the stellar and orbital parameters using the software Binary Maker 3.0 (BM3.0). We detected the primary eclipse in the light curve of SDSS J0745+2631 in our follow-up observation from January 2014 using the ULTRASPEC instrument at the Thai National Observatory. The data obtained on 7th and 8th January 2014 in g filter show an evident drop in brightness during the eclipse of the white dwarf, but this eclipse is less prominent in the data taken on the next night using a clear filter. According to our preliminary model, we find that SDSS J0745+2631 hosts a rather hot white dwarf with an effective temperature of 11500K. The companion star is a red dwarf star with a temperature of 3800K and radius of 0.3100 $R_{\odot}$. The red dwarf star almost fills its Roche lobe, causing a large ellipsoidal modulation. The mass ratio of the binary given by the Binary Maker 3.0 (BM3.0) model is M2/M1 = 0.33.

• Journal of The Korean Astronomical Society
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• v.10 no.1
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• pp.23-30
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• 1977

We have collected times of minimum light available in the literature for WZ Andromedae and analyzed the nature of the period variations. The O-C diagram of WZ And clearly shows that two abrupt changes near JD 2418000 and JD 2435000 are deduced by dp/p=$+4.24{\timesa}10^{-6}$ and dp/p=$-2.46{\times}10^{-6}$, respectively. For these period changes, we have introduced the equations which represent mass exchange in the close binery systems given by Biermann and Hall (1973), and the computation yieleled a mass flow of $7.42{\times}10^{-5}M$. from the hotter component to the cooler one. Due to the amount of mass flow, the period decrease may also be calculated. The theoritical new period after JD 2435000 became 0.69565858 days, which is in good agreement with the value 0.69566034 days found in the O-C diagram. In this computation, the mass ratio of WZ And suggested that the hotter star is the filling its Rochclooe, and thus WZ And is in Paczynski's stage II.

• Journal of Nutrition and Health
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• v.30 no.2
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• pp.201-209
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• 1997

The purpose of this study was to investigate the possible causal factors of obesity in women with child-bearing experiences in effects to provide optimal information for the prevention and/or treatment of obesity. Sventy one women with child-bearing experiences were divided into five groups based on the degree of obesity by BROCA method ; normal weight, overweight, and obesity which was further divided into three groups of light, moderate, and sever obesity. Various anthropomnetric measurements, overall eating habits, and dietery intakes were asessed for each groups. Out of eighteen anthropometric factors asociated with obesity, thirteen measurements were represented to be valid for the diagnosis of obesity. Body fat % which was analyzed by Bioelectrical Impedance fatnee Analyzer were 24.765, 28.05%, and 29.85 for normal, overweight, and obesity group respectively. WHR(waister to hip ratio) or BMI(body mass index) widely used index was also resulted to be valid as a predictor of obesity. Waist circumference which represents abdominal fat mass showed a good correlatin with body fat%. The analysis of dietary intakes suggested that the overintakes of total calorie may not be the only causal factor of obesity, rather the amount of daily protein, fat and carbohydrate intakes or the physical activity level would be more closely related with the prevalence of obesity. Further investigation considering more variety of food composition of diet and the activity level involving larger number of subjects would be needed.

• 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.

• Bulletin of the Korean Chemical Society
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• v.34 no.8
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• pp.2399-2402
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• 2013

The catalytic pyrolysis of cellulose was carried out over SAPO-11 for the first time. Pyrolyzer-gas chromatography/mass spectroscopy was used for the in-situ analysis of the pyrolysis products. The acid sites of SAPO-11 converted most levoglucosan produced from the non-catalytic pyrolysis of cellulose to furans. In particular, the selectivity toward light furans, such as furfural, furan and 2-methyl furan, was high. When the catalyst/cellulose ratio was increased from 1/1 to 3/1 and 5/1, the increase in the quantity of acid sites led to the promotion of deoxygenation and the resultant increase of the contents of light furan compounds. Because furans can be used as basic feedstock materials, the augmentation of the economical value of bio-oil through the catalytic upgrading over SAPO-11 is considerable.