• Korean Journal of Materials Research
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• v.21 no.7
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• pp.384-390
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• 2011

Ti-6Al-4V ELI (Extra Low Interstitial) alloy has been widely used as an alternative to bone due to its excellent biocompatibility. However, it still has many problems, including a high elastic modulus and toxicity. Therefore, nontoxic biomaterials with a low elastic modulus should be developed. However, the fabrication of a uniform coating is challenging. Moreover, the coating layer on Ti and Ti alloy substrates can be peeled off after implantation. To overcome these problems, it is necessary to produce bulk Ti and Ti alloy with hydroxyapatite (HA) composites. In this study, Ti, Nb, and Zr powders, which are biocompatible elements, were milled in a mixing machine (24h) and by planetary mechanical ball milling (1h, 4h, and 6h), respectively. Ti-35%Nb-7%Zr and Ti-35%Nb-7%Zr-10%HA composites were fabricated by spark plasma sintering (SPS) at $1000^{\circ}C$ under 70MPa using mixed and milled powders. The effects of HA addition and milling time on the biocompatibility and physical and mechanical properties of the Ti-35%Nb-7%Zr-(10%HA) alloys have been investigated. $Ti_2O$, CaO, $CaTiO_3$, and $Ti_xP_y$ phases were formed by chemical reaction during sintering. Vickers hardness of the sintered composites increases with increased milling time and by the addition of HA. The biocompatibilty of the HA added Ti-Nb-Zr alloys was improved, but the sintering ability was decreased.

• The Korean Journal of Petroleum Geology
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• v.3 no.1 s.4
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• pp.16-27
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• 1995

The Early Miocene Temblor Formation forms an important sandstone reservoir at Kettleman North Dome oil field, California. Sandstones are mostly arkosic in composition except deepest sandstones containing much volcanic rock fragments. Arranged in paragenetic sequence prior to feldspar alteration, the Temblor sandstones contain cements of early calcite, dolomite, quartz, albite, mixed-layer ohloriteismectite (C/S) and smectite, and anhydrite. Diagenetic changes associated with feldspar are albitization of plagioclase, late calcite and laumontite cementation and grain replacement, plagioclase dissolution, and kaolinite cementation. Plagioclase albitization and late calcite and laumontite cementation in Temblor sandstones occurred at the time of maximum burial with temperatures up to $130^{\circ}C$. Volcanic plagioclases were selectively albitized. Most diagenetic changes are interpreted to have occurred before the maior uplift which occurred within the last one million years ago. Since then to the time of hydrocarbon emplacement plagioclase dissolution and kaolinite cementation occurred. This reaction occurred in relatively closed system due to the occurrence of kaolinite next to the site of plagioclase dissolution. Unaltered part of volcanic plagioclase and plutonic plagioclase which escaped albitization during maximum burial were preferentially dissolved to make plagioclase porosity. Secondary porosity resulting from dissolution of plagioclase and carbonate and anhydrite cements was mainly produced by formation waters containing organic acids released during atagenesis of organic matter.

• Journal of the Korean Society for Heat Treatment
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• v.24 no.6
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• pp.318-326
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• 2011

This study has been performed to investigate the effect of Al addition on High Temperature Gas Nitriding (HTGN) in 13%Cr-0.16%C stainless steel with different Al contents of 0.54%, 1.76% and 2.36%, respectively. HTGN treatment was carried out at $1100^{\circ}C$ for 1 hr, 5 hrs and 10 hrs. Nitrogen-permeated surface layers showed round type carbides of $Cr_{23}C_6$ and needle type nitrides of AlN in the matrix of martensite, representing 600~700 Hv. And the thickness of the surface layer increased with increasing Al content and HTGN treatment time. The inner region that was not permeated nitrogen showed chromium carbides in the mixed phase of martensite and ferrite for the 0.53% Al alloyed steel, however chromium carbides in the matrix of ferrite single phase were shown for the steels with the addition of 1.76%Al and 2.36%Al, representing the hardness of ~200 Hv. During nitrogen permeation from surface to the interior, substitutional elements of Cr, Al and Si moved toward the surface and interstitial element of carbon also moved from interior to the surface. This movement of alloying elements leads high concentration of these elements at the outmost surface, subsequently the lowest peak of substitutional elements were shown in the vicinity of near surface. After showing the lowest peak, the high concentration region of Al and C were formed due to the continuous movement of Al toward the surface. The long discontinuous precipitates of $Cr_{23}C_6$ and AlN were formed along the outmost surface owing to the high concentration of these alloying elements.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.9
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• pp.422-430
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• 2016

We investigated the abundance and composition of the zooplankton community around Dokdo in the East Sea from 2006 to 2015. Zooplankton samples were collected in the surface mixed layer by vertical hauls using a standard type net at the monitoring stations. There were no clear long-term trends in the average temperature and salinity, but relatively low salinity was recorded in the summer of 2013 and 2015. The average abundances of zooplankton in the summer increased by two orders of magnitude from $317inds./m^3$ in 2008 to $10,242inds./m^3$ in 2015. This long-term increase was accompanied by a slight increase in the chlorophyll-a concentration and a decrease in the catch of potential crucial predators (anchovy, mackerel pike, squid, herring and horse mackerel) in the study area. The dominant zooplankton, accounting for most of the long-term increase, consisted of appendicularian (Oikopleura spp.), which showed a steady increase since 2012, summer species such as Noctiluca scintillans and the cladoceran Penilia avirostris, which showed an abrupt increase, and the copepod Paracalanus parvus s.l., which showed a rapid increase after its first occurrence in summer 2010. These results suggest that the long-term increase of zooplankton could be related to the increase in the concentration of prey and the decrease in the predation pressure of potential predators around Dokdo in the study area.

• Journal of the Korean Applied Science and Technology
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• v.34 no.4
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• pp.954-961
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• 2017

We investigated the purifications of PE-gal and CPN-gal, synthesized by transgalactosylation reaction using recombinant ${\beta}$-gal. The reaction mixture containing PE and PE-gal was first mixed with EA, and thereafter PE and PE-gal were distributed in two-phase (EA/water) system. In this system, PE and PE-gal was selectively moved into EA and water phase, respectively. Then, the water phase was collected, and silica gel chromatography was carried out using the collected water phase. Finally, we compared two purified PE-gal samples using HPLC and TLC analysis, in which the one was purified only by silica gel chromatography and the other was purified by EA extraction followed by silica gel chromatography. In the latter case, the residual PE was almost completely removed, whereas, in the former case, the residual PE was remained remarkably. Additionally, the purification yield of PE-gal was about 21% on the basis of mole. In the same purification protocol, CPN-gal was able to be purified using EA extraction followed by silica gel chromatography, in which the residual CPN was almost removed when CPN-gal was purified by EA extraction followed by silica gel chromatography.

• Journal of the Korean Geotechnical Society
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• v.34 no.2
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• pp.33-42
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• 2018

In this study, the EMI (electro-mechanical impedance) of a small piezoelectric sensor was applied for measuring a unit weight and cementation (strength) of sand. Three different sizes of uncemented Nakdong River sand were filled loosely or densely into a compaction mold. A piezoelectric sensor with 20 mm in diameter was installed within sand for impedance measurement. A small Nakdong River sand was mixed with cement ratios of 4, 8 12, 16% and then compacted into a specimen with 50 mm in diameter and 100 mm in height. The specimen consisted of 6 layers with a sensor at the third layer. The impedance signals for 3 days and unconfined compressive strength at the 3rd day were measured. As the unit weight of uncemented sand increased, the resonant frequency increased slightly from 102 to 105 kHz but a conductance at resonant frequency decreased. For cemented sands, as the curing time and cement ratio increased, the resonant frequency increased significantly from 129 to 266 kHz but the conductance at resonant frequency decreased. The unconfined compressive strength (UCS) of cemented sands was between 289 and 1,390 kPa for different cement ratios. The relationship of UCS and resonant frequency linearly increased but one with a conductance at resonant frequency was in inverse proportion.

• Korean Journal of Remote Sensing
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• v.21 no.4
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• pp.253-271
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• 2005

We have analyzed surface water temperature and seasonal stratification of lakes in the Han river system using time-series Landsat images and in situ measurement data. Using NASA equation, at-satellite temperature is derived from 29 Landsat-5 TM and Landsat-7 ETM+ images obtained from 1994 to 2004, and was compared with in situ surface temperature on river-type dam lakes such as Paro, Chuncheon, Euiam, Chongpyong, Paldang, and with 10m-depth temperature on lake-type dam lake Soyang. Although the in situ temperature at the time of satellite data acquisition was interpolated from monthly measurements, the number of images with standard deviation of temperature difference (at-satellite temperature - in situ interpolated temperature) less than $2^{\circ}C$ was 24 on which a novel statistical atmospheric correction could be applied. The correlation coefficient at Lake Soyang was 0.915 (0.950 after correction) and 0.951-0.980 (0.979-0.997 after correction) at other lakes. This high correlation implies that there exist a mixed layer in the shallow river-like dam lakes due to physical mixing from continuous influx and efflux, and the daily and hourly temperature change is not fluctuating. At Lake Soyang, an anomalous temperature difference was observed from April to July where at-satellite temperature is $3-5^{\circ}C$ higher than in situ interpolated temperature. Located in the uppermost part of the Han river system and its influx is governed only by natural precipitation, Lake Soyang develops stratification during this time with rising sun elevation and no physical mixture from influx in this relatively dry season of the year.

• Journal of IKEEE
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• v.25 no.3
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• pp.501-505
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• 2021

In this study, we fabricated amorphous indium-tin-gallium-zinc-oxide thin-film transistors (a-ITGZO TFTs) with gate dielectrics of HfO₂ and the mixed layers of HfO₂ and Al₂O₃, and investigated the effect of gate dielectric on electrical characteristics of a-ITGZO TFTs. When only HfO₂ was used as the gate dielectric, the mobility and subthreshold swing (SS) were 32.3 cm²/Vs and 206 mV/dec. For the a-ITGZO TFTs with gate dielectric made of HfO₂ and Al₂O (2:1, 1:1), the mobilities and SS were 26.4 cm²/Vs (2:1), 16.8 cm²/Vs(1:1), 160 mV/dec (2:1) and 173 mV/dec (1:1). On the other hand, the hysteresis window shown in transfer curves of the a-ITGZO TFTs was lessened from 0.60 to 0.09 V by the increase of Al₂O₃ ratio in gate dielectric, indicating that the interface trap density between the gate dielectric and channel layer decreases due to Al₂O₃.

• Applied Chemistry for Engineering
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• v.29 no.6
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• pp.759-764
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• 2018

3D porous carbon electrodes (cNPIM), prepared by solution casting of a polymer of intrinsic microporosity (PIM-1) followed by nonsolvent-induced phase separation (NIPS) and carbonization are presented. In order to effectively control the pore size of 3D porous carbon structures, cNPIM was prepared by varying the THF ratio of mixed solvents. The SEM analysis revealed that cNPIMs have a unique 3D macroporous structure having a gradient pore structure, which is expected to grant a smooth and easy ion transfer capability as an electrode material. In addition, the cNPIMs presented a very large specific surface area ($2,101.1m^2/g$) with a narrow micropore size distribution (0.75 nm). Consequently, the cNPIM exhibits a high specific capacitance (304.8 F/g) and superior rate capability of 77% in an aqueous electrolyte. We believe that our approach can provide a variety of new 3D porous carbon materials for the application to an electrochemical energy storage.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.80-85
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• 2019

Vanadium dioxide is a well-known metal-insulator phase transition material. Lots of researches of vanadium redox flow batteries have been researched as large scale energy storage system. In this study, vanadium oxide($VO_x$) thin films were applied to cathode for lithium ion battery. The $VO_x$ thin films were deposited on Si substrate($SiO_2$ layer of 300 nm thickness was formed on Si wafer via thermal oxidation process), quartz substrate by RF magnetron sputter system for 60 minutes at $500^{\circ}C$ with different RF powers. The surface morphology of as-deposited $VO_x$ thin films was characterized by field-emission scanning electron microscopy. The crystallographic property was confirmed by Raman spectroscopy. The optical properties were characterized by UV-visible spectrophotometer. The coin cell lithium-ion battery of CR2032 was fabricated with cathode material of $VO_x$ thin films on Cu foil. Electrochemical property of the coin cell was investigated by electrochemical analyzer. As the results, as increased of RF power, grain size of as-deposited $VO_x$ thin films was increased. As-deposited thin films exhibit $VO_2$ phase with RF power of 200 W above. The transmittance of as-deposited $VO_x$ films exhibits different values for different crystalline phase. The cyclic performance of $VO_x$ films exhibits higher values for large surface area and mixed crystalline phase.