• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 제35회 춘계학술대회
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• pp.207-214
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• 2002

Nano adhesion between SPM (scanning probe microscope) tips and $DDPO_{4}$ (dodecylphosphoric acid ester) and $ODPO_{4}$ (octadecylphosphoric acid ester) SAM (self-assembled monolayer) was experimentally studied. Tests were performed to measure the nano adhesion and friction in both AFM(atomic force microscope) and LFM(lateral force microscope) modes with the applied normal load. $DDPO_{4}$ and $ODPO_{4}$ SAM were formed on TiMe and TiOx surfaces. TiMe and TiOx were coated on the Si wafer by ion sputtering. Adhesion and friction of $DDPO_{4}$ and $ODPO_{4}$ SAM surfaces were compared with those of OTS (octadecyltrichlorosilane) SAM and DLC surfaces. $DDPO_{4}$ and $ODPO_{4}$ SAM converted the TiMe and TiOx surfaces to be hydrophobic. When the surface was hydrophobic, the adhesion and friction forces were found lower than those of bare surfaces. Work of adhesion was also discussed to explain how the surface was converted into hydrophobic. Results also showed that tribological characteristics of $DDPO_{4}$ and $ODPO_{4}$ had good properties in the adhesion, friction, wetting angle and work of adhesion. $DDPO_{4}$ and $ODPO_{4}$ SAM could be one of the candidates for the bio-MEMS elements.

• 한국진공학회지
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• 제18권3호
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• pp.164-175
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• 2009

전산 유체 역학 코드를 사용하여 안테나 내장형 유도 결합 플라즈마 시스템의 가스 유동 특성, 전력 흡수, 전자 온도, 전자 밀도, 화학종의 분포에 대해서 살펴보았다. 복잡한 현실적 3차원 시스템에 대한 안정한 수치해의 도출을 위해서 최적화된 격자생성 전략을 구사하였으며, 이를 이용하여 플라즈마 질화 시스템을 한 예로 전력 흡수, 가스 유동, 전자 온도, 전자 밀도, 화학종의 분포를 분석하였다. 금속 노출형 안테나의 경우 전력 도입부 쪽에 전력 흡수의 불균형이 모델에서 예측되었으며 유전체피복 안테나의 한 예에서 전력 흡수 표피 깊이가 실제 보고된 값인 53 mm와 잘 일치하는 50 mm로 예측되었다. 또한 수소연료 전지 분리판을 위한 고속 질화 공정용 시스템의 모델링에서도 산업용 대량 처리 시스템에 적절한 다중 분리판의 장입 간격을 가스 유동, 활발한 질화종인 질소 원자와 질소 분자 이온의 농도를 근거로 예측하였다.

• 정보과학회 논문지
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• 제41권9호
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• pp.605-610
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• 2014

현재 가상화 기술은 많은 연구를 통해 다양한 분야에서 널리 쓰이고 있다. 그러나 여전히 I/O 워크로드는 가상화로 인한 성능 저하로 인하여 가상화 분야에 적용되지 못하고 있다. 이전의 많은 연구에서 가상화 I/O 과정의 모드전환과 중복된 I/O 스택을 이러한 성능 저하의 원인으로 파악하고, 이를 해결하기 위한 기법을 제안하였으나 여전히 가상화 되지 않은 환경의 물리장치에 비해 낮은 성능을 보여주었다. 본 논문에서는 가상화 라이브러리를 사용하는 새로운 I/O 가상화 기법을 제안한다. 본 제안기법은 가상화 I/O 과정에서 발생하는 모드 전환을 완전히 제거하고 게스트 운영체제의 I/O 스택을 우회함으로써 /O 성능을 향상 시킨다. 네트워크 환경을 위한 프로토타입 구현을 통해 본 제안기법은 네트워크 처리량을 169% 향상시키며 네트워크 지연을 38% 감소시킴을 확인하였다.

• Journal of Plant Biology
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• 제17권4호
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• pp.158-162
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• 1974

Some ecological attributes of perennial plants and Pb contamination were analyzed for study plots near an entrance of Nevade Test Site at Mercury Valley, Nye County, Nevada. The surface of the desert pavement soil was composed of stones (1 to 4cm diameter). The underside of each stone was coated with coarse and fine sand (about 90%). The profiles of soil were constituted with the A-horizon and C-horizon only. The soil pH at the plots ranges from 7.6 to 8.5, C/N was 13 and cation exchange capacity showed 15me/100g. Nine species and 42 number of individuals were found in all plots. Franseria dumosa and Larrea divaricata were dominant species. The discrete clumps of vegetation were consisted of 9 species of common perennials and these were covered about 25% on desert pavement, on the other words, bare area without vegetation was about 75%. The size and spacing of the plants was irregular. Community coefficient as comparison between shrub species in these study area and those in near the low elevation desert indicated a low degree of similarity. Density, cover and productivity in the study plots as compared with those in the nearest study areas in Mercury Valley showed a higher value. The soils in the studied area involved high heavy metal contents in the plant tissue was higher than those of its soil. The leavds of Lycium andersonii tended to accumulate more Zn and Mo than those of the other species. Larrea divaricata leaves accumulated very high leaves of Fe and Ephedra nevadensis were generally high in Mn. Lead contamination was apparent in foliage of desert vegetation collected alongside the roadway, reflecting the variation in traffic volume. Lead contents greater than fifteen-fold of normal (low traffic) were found in plant foliage alongside the heavily traveled roadway. Lead content of old foliage by the heavily traveled roadway was as much as 129 ppm but that of new foliage 17 ppm only.

• 한국재료학회지
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• 제17권3호
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• pp.147-151
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• 2007

Cu-free multi-component sol, of which final oxide composition becomes $Bi_{1.9}Pb{0.35}SrCaO,\;Bi_{1.8}Pb_{0.2}SrCaO\;and\;Bi_{1.5}SrCaO$, respectively, was prepared through sol-gel route and coated on a bare Cu substrate. Starting materials were metal-alkoxides as follows.; [$Bi(OC_{2}H_{5})_{3}\;Pb(O^{1}C_{3}H_{7})_{2},\;Sr(O^{i}C_{3}H_{7})_{2},\;Ca(OC_{2}H_{5})_{2}$] as a reagent grade. Transparent light yellowish sol was obtained in the case of $Bi_{1.9}Pb_{0.35}SrCaO\;and\;Bi_{1.8}Pb_{0.2}SrCaO$ composition and $Bi_{1.5}SrCaO$ composition's sol was light greenish. Each sol was repeatedly dip-coated on Cu substrate four times and pre-heated at $400^{\circ}C$ and finally heat-treated in the range of $740{\sim}900^{\circ}C$. In the results, crystalline phases confirmed by XRD were (2201) orthorhombic and monoclinic phases. However, only $Bi_{1.9}Pb_{0.35}SrCaO_{x}$ composition showed pseudo-superconductive behavior after heat-treatment at $900^{\circ}C$ for 12 seconds and then onset temperature was 77 K, even though it did not exhibit zero resistance below Tc.

• 한국표면공학회지
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• 제41권6호
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• pp.255-263
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• 2008

Generally, deposition mechanism of diamond particle is mainly embedding effect in the kinetic spray process. Accordingly, in spite of high cost, helium gas was employed as process gas to get high diamond fraction in the composite coating. In this study, the deposition behavior of bronze/diamond by kinetic spray process was compared using different process gas (helium and nitrogen). Bare (mean size of $5{\mu}m$, $20{\mu}m$) and nickel coated diamond (mean size of $26{\mu}m$) were deposited on Al 6061-T6 substrate with fixed process temperature and pressure. For comparison with experimental results, plastic deformation behavior of nickel layer was simulated by finite element analysis (using ABAQUS/Explicit 6.7-2). The size, broken ratio, and fraction of diamond in the composite coating were analyzed through scanning electron microscopy and image analysis method. The uniform distribution and deposition efficiency of diamond particles in the coating layer could be achieved by tailoring the physical properties of the feedstock.

• 공업화학
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• 제31권5호
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• pp.581-584
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• 2020

The effect of a chemical pretreatment on the surface carbon was investigated using a scanning electron microscope (SEM) and electrochemical methods. Primitive carbon has a reducing power likely due to incompletely oxidized functional groups on the surface. We aim to control this reducing power by chemical treatment and apply for the spontaneous deposition of nanoparticles (NPs). Highly ordered pyrolytic graphite (HOPG) was initially treated with a reducing agent, NaBH4 or an oxidizing agent, KMnO₄, for 5 min. Subsequently, the pretreated carbon was immersed in a platinum (Pt) precursor. Unexpectedly, SEM images showed that the reducing agent increased spontaneous PtNPs deposition while the oxidizing agent decreased Pt loading more as compared to that of using bare carbon. However, the amount of Pt on the carbon obviously decreased by NaBH₄ treatment for 50 min. Secondly, spontaneous reduction on pretreated glassy carbon (GC) was investigated using the catalytic hydrogen evolution reaction (HER). GC electrode treated with NaBH4 for a short and long time showed small (onset potential: -640 mV vs. MSE) and large overpotential for the HER, respectively. Although the mechanism is unclear, the electrochemistry results correspond to the optical data. As a proof-of-concept, these results demonstrate that chemical treatments can be used to design the shapes and amounts of deposited catalytic metal on carbon by controlling the surface state.

• 청정기술
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• 제24권3호
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• pp.249-254
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• 2018

염료감응형 태양전지의 광전변환효율(${\eta}$) 향상을 위하여 수열합성한 $TiO_2$ 나노입자에 전기방사한 $TiO_2$, $SiO_2$, $ZrO_2$ 및 $SnO_2$ 나노파이버를 첨가하여 광전극에 적용하였다. $TiO_2$ 나노파이버를 첨가한 염료감응형 태양전지는 순수한 $TiO_2$ 나노입자에 비해 높은 전류밀도($J_{sc}$)를 나타내었고 이것은 나노파이버 구조로 인하여 염료에서 여기된 전지의 전달 특성이 용이하여 나타난 현상으로 생각된다. 또한 $SiO_2$ 나노파이버를 첨가한 염료감응형 태양전지의 경우, 순수한 $TiO_2$ 나노입자를 이용한 것에 비해 보다 높은 0.67 V의 개방전압($V_{oc}$)을 나타내었고 에너지 변환효율 또한 6.24%로 가장 높게 나타났다.

• 한국응용과학기술학회지
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• 제21권4호
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• pp.345-351
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• 2004

Highly ordered pure-silica MCM-41 materials possessing well-defined morphology have been successfully prepared with surfactant used as a template. The fabrication of mesoporous silica has received considerable attention due to the need to develop more efficient materials' for catalysis, separations, and chemical sensing. The surface modified MCM-41 was used as anadsorbent for biomolecules. Silica-supported organic groups and DNA adsorption on surface modified MCM-41 were investigated by FT-IR and UV-Vis spectrometer, respectively. The use of MCM-41 as the modification of electrode surfaces were investigated electrochemical properties of metal mediators with biomolecules. The modified ITO electrodes increased peak currents for a redox process of $[Ru(bpy)_3]^{2+}$ relative to the bare electrode. The electrochemical detection of DNA by cyclic voltammetry when the current is saturated in the presence of the mediator appeared more sensitive due to a higher catalytic current on the MCM-41 supported electrodes modified by carboxylic acid functional groups. The carboxyl or amine groups on the surface of MCM-41 interact and react with the $-NH_2$ groups of guanine and backbone, respectively. Highly ordered mesoporous materials with organic groups could find applications as DNA sensors.

• 한국세라믹학회지
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• 제44권7호
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• pp.362-367
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• 2007

Stent is a tiny structure made with either ceramic coating and/or bare metal. Being approximately $1{\sim}2 mm$ in diameter, it consists of holes, slots, or void space and is designed to cover entire medical lesions. Stent implantation into patients' arteries has been practiced for a little more than a decade in order to widen the blocked artery. The adoption of the stent has significantly improved the efficacy when compared with the previous medical practice by balloon angioplasty alone. Yet better biomedical performance of the stent is being demanded in order to eliminate the still existing problem of artery restenosis, which means the artery becomes narrowed again. Recent literature survey shows researches on ceramic coatings onto the stent surface, or material design to improve the mechanical response of the stent. This study focuses more on the material design and mechanical analysis. The results showed that the void configuration within the stent affects the mechanical response significantly. The rectangular shape was found to yield expansion at a relatively lower pressure than the elliptical slot for a slotted tube stent. The present results, when combined with research on coating at the stent surface, may provide stents with improved bio-medical performance.