• Journal of The Korean Astronomical Society
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• v.49 no.6
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• pp.289-293
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• 2016

We investigate the long-term spatial drift of the center and the temporal variation of the shutter delay time map of Y4KCam mounted on the CTIO 1.0 m telescope. We have collected shutter delay time maps over eight years as a part of our long-term survey program. We find that the center of the shutter delay time map can drift up to $450{\mu}m$, equivalent to ${\approx}30pixels$, on the CCD. This effect can result in a small amount of error in integration time without the proper shutter delay time correction, but it does not appear to cause any significant problems in photometric measurements. We obtain a mean shutter delay time of $69.1{\pm}0.8$ ms and find no temporal variation of the shutter delay time of Y4KCam over eight years, indicative of the mechanical stability of the shutter. We suggest that using a master shutter delay time correction frame would be sufficient to achieve high precision photometry, which does not exceed photometric errors ${\approx}1.7mmag$ across the CCD frame for exposure times longer than 1 s.

• Proceedings of the KSRS Conference
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• 2003.11a
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• pp.663-665
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• 2003

A field spectroradiometer SE-590 was used to measure the spectral reflectance of water body. The reflectance was calculated as the ratio of surface water radiance to the standard whiteboard radiance nearly measured at the same time. Water samples were taken simultaneously for determining their chlorophyll-a, suspended solid (SS) and transparency. The relationships between those water quality parameters and spectral reflectance were analy zed using stepwise multiple regression to derive optimal prediction models . The multiple regression was also applied to the SE-590 simulated SPOT bands. The SPOT image of the same day was also analyzed using the same method to compare the statistical results. It showed that the multiple regression models using the SE-590 reflectance data got the best water quality prediction results. The evaluated RMS error of chlorophyll-a, SS and transparency of water quality parameters were 0.57 ug/l, 0.2 mg/l and 0.17 m, respectively, and the RMS errors were 0.36 ug/l, 0.49 mg/l and 0.42 m for SPOT data, respectively. The SE-590 simulated SPOT three bands data obtained the worst results and the RMS errors were 1.77 ug/l, 0.49 mg/l and 0.37 m, respectively.

• Computers and Concrete
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• v.17 no.5
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• pp.629-638
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• 2016

Optimization of the concrete mixture design is a process of search for a mixture for which the sum of the cost of the ingredients is the lowest, yet satisfying the required performance of concrete. In this study, a statistical model was carried out to model a cost effective optimal mix proportioning of high strength self-compacting concrete (HSSCC) using the Response Surface Methodology (RSM). The effect of five key mixture parameters such as water-binder ratio, cement content, fine aggregate percentage, fly ash content and superplasticizer content on the properties and performance of HSSCC like compressive strength, passing ability, segregation resistance and manufacturing cost were investigated. To demonstrate the responses of model in quadratic manner Central Composite Design (CCD) was chosen. The statistical model showed the adjusted correlation coefficient R2adj values were 92.55%, 93.49%, 92.33%, and 100% for each performance which establish the adequacy of the model. The optimum combination was determined to be $439.4kg/m^3$ cement content, 35.5% W/B ratio, 50.0% fine aggregate, $49.85kg/m^3$ fly ash, and $7.76kg/m^3$ superplasticizer within the interest region using desirability function. Finally, it is concluded that multiobjective optimization method based on desirability function of the proposed response model offers an efficient approach regarding the HSSCC mixture optimization.

• Journal of Nutrition and Health
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• v.49 no.1
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• pp.59-62
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• 2016

Purpose: Zinc, a biomineral present within and outside cells, manages various cellular mechanisms. In this study, we examined whether zinc was involved in vascular smooth muscle cell (VSMC) calcification via regulation of calcification inhibitor protein, osteopontin (OPN). Methods: Rat aorta cell line (A7r5 cells) and primary vascular smooth muscle cells (pVSMCs) from rat aorta were cultured with phosphate (1-5 mM) and zinc ($0-15{\mu}M$) as appropriate, along with osteoblasts (MC3T3-E1) as control. The cells were then stained for Ca and P deposition for calcification examination as well as osteopontin expression as calcification inhibitor protein was measured. Results: Both Ca and phosphate deposition increased as the addition of phosphate increased. In the same manner, the expression of osteopontin was upregulated as the addition of phosphate increased in both cell types. When zinc was added, Ca and P deposition decreased in VSMCs, while it increased in osteoblasts. Conclusion: The results imply that zinc may prevent VSMC calcification by stimulating calcification inhibitor protein OPN synthesis in VSMCs.

• Journal of The Korean Astronomical Society
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• v.49 no.4
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• pp.145-155
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• 2016

The Sausage radio relic is the arc-like radio structure in the cluster CIZA J2242.8+5301, whose observed properties can be best understood by synchrotron emission from relativistic electrons accelerated at a merger-driven shock. However, there remain a few puzzles that cannot be explained by the shock acceleration model with only in-situ injection. In particular, the Mach number inferred from the observed radio spectral index, M_radio ≈ 4.6, while the Mach number estimated from X-ray observations, M_X−ray ≈ 2.7. In an attempt to resolve such a discrepancy, here we consider the re-acceleration model in which a shock of M_s ≈ 3 sweeps through the intracluster gas with a pre-existing population of relativistic electrons. We find that observed brightness profiles at multi frequencies provide strong constraints on the spectral shape of pre-existing electrons. The models with a power-law momentum spectrum with the slope, s ≈ 4.1, and the cutoff Lorentz factor, γ_e,c ≈ 3−5×10⁴, can reproduce reasonably well the observed spatial profiles of radio fluxes and integrated radio spectrum of the Sausage relic. The possible origins of such relativistic electrons in the intracluster medium remain to be investigated further.

• Journal of the Korean Ceramic Society
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• v.49 no.2
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• pp.167-172
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• 2012

Fine diamond powders are synthesized with a 420 ${\phi}$ cubic press and stack-cell composed of Kovar ($Fe_{54}Ni_{29}Co_{17}$) (or Kovar+7 ${\mu}m$-thick Zn electroplated) alloy and graphite disks. The high pressure high temperature (HPHT) process condition was executed at $1500^{\circ}C$ for 280 seconds by varying the nominal pressure of 5.7~10.6 GPa. The density of formation, size, shape, and phase of diamonds are determined by optical microscopy, field emission scanning electron microscopy, thermal gravimetric analysis-differential thermal ammnlysis (TGA-DTA), X-ray diffraction (XRD), and micro-Raman spectroscopy. Through the microscopy analyses, we found that 1.5 ${\mu}m$ super-fine tetrahedral diamonds were synthesized for Zn coated Kovar cell with whole range of pressure while ~3 ${\mu}m$ super-fine diamond for conventional Kovar cell with < 10.6 GPa. Based on $750^{\circ}C$ exothermic reaction of diamonds in TGA-DTA, and characteristic peaks of the diamonds in XRD and micro-Raman analysis, we could confirm that the diamonds were successfully formed with the whole pressure range in this research. Finally, we propose a new process for super-fine diamonds by lowering the pressure condition and employing Zn electroplated Kovar disks.

• BMB Reports
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• v.49 no.10
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• pp.527-528
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• 2016

In embryonic stem cells (ESCs), cell cycle regulation is deeply connected to pluripotency. Especially, core transcription factors (CTFs) which are essential to maintaining the pluripotency transcription programs should be reset during M/G1 transition. However, it remains unknown about how CTFs are governed during cell cycle progression. Here, we describe that the regulation of Oct4 by Aurora kinase b (Aurkb)/protein phosphatase 1 (PP1) axis during the cell cycle is important for resetting Oct4 to pluripotency and cell cycle related target genes in determining the identity of ESCs. Aurkb starts to phosphorylate Oct4(S229) at the onset of G2/M phase, inducing the dissociation of Oct4 from chromatin, whereas PP1 binds Oct4 and dephosphorylates Oct4(S229) during M/G1 transition, which resets Oct4-driven transcription for pluripotency and the cell cycle. Furthermore, Aurkb phosphormimetic and PP1 binding-deficient mutations in Oct4 disrupt the pluripotent cell cycle, lead to the loss of pluripotency in ESCs, and decrease the efficiency of somatic cell reprogramming. Based on our findings, we suggest that the cell cycle is directly linked to pluripotency programs in ESCs.

• Journal of the Korean institute of surface engineering
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• v.49 no.2
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• pp.191-195
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• 2016

Among the lithium metal oxides for hybrid-capacity, $Li_4Ti_5O_{12}(LTO)$ is an emerging electrode material as zero-stain material in volume change during the with the charging and discharging processes. However, LTO has a limitation of low ionic and electronic conductivity. To enhance the ionic and electronic properties of $Li_4Ti_5O_{12}(LTO)$, we synthesized the spherical LTO/CNT composite by sol-gel process for hybrid capacitors. CNT interconnection networks between CNT-LTO particles enhanced electronic conductivity and electrochemical charging/discharging properties. All of the LTO samples was observed to show the spinel structure and spherical morphology with the diameter of $5{\sim}10{\mu}m$. Especially, spherical LTO/CNT composite of the CNT-3 wt% showed the enhanced capacity from 110 mAh/g to 140 mAh/g at 10 C.

• Korean Journal of Metals and Materials
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• v.49 no.12
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• pp.945-949
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• 2011

The cycling characteristics of $MgH_2$ made by hydriding chemical vapor deposition method have been investigated. The particle size of $MgH_2$ made by HCVD was about $1{\mu}m$. The cycling experiment was performed by measuring hydrogen quantity absorbed at 673 K and under 35 atm of hydrogen pressure for 30 min. Up to 3 cycles the hydrogen storage capacity increased, but from 4 to 6 cycles the hydrogen storage capacity decreased rapidly. During this cycling test the particle size increased gradually from $1{\mu}m$ to $6{\mu}m$. This increase was due to sintering by the high reaction temperature and the heat of reaction during hydrogen absorption. From 7 to 30 cycles, the hydrogen storage capacity was maintained at 5.8 wt%. Even after 30 cycles, the plateau pressure was constant.

• Korean Journal of Metals and Materials
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• v.49 no.8
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• pp.601-607
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• 2011

The study investigated the influence of current density on the corrosion-protection properties of an AZ91 Mg alloy subjected to plasma electrolytic oxidation coating. The present coatings were carried out under an AC condition at three different current densities, i.e., 100, 150, and $200mA/cm^2$. From microstructural observations, the micro cracks connecting each micro pore were pronounced on the oxide surface of the samples coated at current densities higher than $150mA/cm^2$ since increasing the current density in this study led to an increment in the relative volume fraction of the MgO compound. Based on potentio dynamic polarization and immersion tests, the sample coated at a current density of $100mA/cm^2$ showed superior corrosion resistance.