• 한국재료학회지
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• 제22권3호
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• pp.130-135
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• 2012

We present a method of graphene synthesis with high thickness uniformity using the thermal chemical vapor deposition (TCVD) technique; we demonstrate its application to a grid supporting membrane using transmission electron microscope (TEM) observation, particularly for nanomaterials that have smaller dimensions than the pitch of commercial grid mesh. Graphene was synthesized on electron-beam-evaporated Ni catalytic thin films. Methane and hydrogen gases were used as carbon feedstock and dilution gas, respectively. The effects of synthesis temperature and flow rate of feedstock on graphene structures have been investigated. The most effective condition for large area growth synthesis and high thickness uniformity was found to be $1000^{\circ}C$ and 5 sccm of methane. Among the various applications of the synthesized graphenes, their use as a supporting membrane of a TEM grid has been demonstrated; such a grid is useful for high resolution TEM imaging of nanoscale materials because it preserves the same focal plane over the whole grid mesh. After the graphene synthesis, we were able successfully to transfer the graphenes from the Ni substrates to the TEM grid without a polymeric mediator, so that we were able to preserve the clean surface of the as-synthesized graphene. Then, a drop of carbon nanotube (CNT) suspension was deposited onto the graphene-covered TEM grid. Finally, we performed high resolution TEM observation and obtained clear image of the carbon nanotubes, which were deposited on the graphene supporting membrane.

• 한국안전학회지
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• 제28권5호
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• pp.5-9
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• 2013

Recently, eco-friendly sources of energy by fuel cells that use hydrogen as an energy source has emerged as the next generation of energy to solve the problem of environmental issues and exhaustion of energy. A solid oxide fuel cell(SOFC) classified based on the type of ion transfer mediator electrolyte has actively being researched. However, the reliability according to the thermal cycle is low during the operation of the fuel cell, and deformation problem comes from the difference in thermal expansion coefficient between the electrode material, the components made of ceramic material is also brittle, which means disadvantages in terms of the strength. Therefore, in this study, considering the states of the manufacturing and operating of SOFC single cells, the stress analyses in the each of the interfacial layer between the anode, electrolyte and the cathode were performed to get the basic data for reliability assessment of SOFC. The obtained results show that von Mises stress according to the thickness direction on operating state occurred maximum stress value in the electrolyte layer. And also the stresses inside the active area on a distance of 1 ${\mu}m$ from the electrode interface were estimated. Futhermore the evaluation was done for the variation of the stress according to the stage of the operation divided into three stages of manufacturing, stack, and operating.

• 한국정보통신학회논문지
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• 제17권9호
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• pp.2127-2132
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• 2013

화학적 증착방법으로 구리기판 위에 그래핀을 형성하고 일반적인 전사방법을 이용하여 그래핀 박막을 제작하였다. 메탄과 수소 가스의 유량비에 따른 특성에 대하여 라만 분석법을 이용하여 조사하였다. 메탄의 유량이 많을수록 그래핀의 형성이 잘 이루어지는 것을 확인하였다. 수소의 양이 증가할수록 D ($1350cm^{-1}$), G ($1580cm^{-1}$) 대역이 증가하였으며, 상대적으로 메탄의 유량비가 증가할수록 2D ($2700cm^{-1}$)의 픽이 강도가 증하였다. D ($1350cm^{-1}$)은 결함과 관련되어 있는 픽이다. 그래핀의 단층확인은 G/2D의 비율이 작을수록 그래핀이 단일박막임을 알 수 있고, 200도에서 열처리 후 0.55의 값을 나타내는 것을 확인하였다. 그래핀 채널 트랜지스터를 제작한 결과 p 형 반도체로서의 전달특성이 나타나는 것을 확인하였다.

• 한국전산유체공학회지
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• 제17권4호
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• pp.16-23
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• 2012

Current display manufacturing processes apply thermal treatment of glass backplanes widely for hydrogen degassing, crystallization of thin-films, tempering, forming, and precompaction. Estimation of the characteristics of transient heating stages and thermal non-uniformities on a single glass substrate or in a stack of glasses are extremely helpful to understand non-homogeneity of mechanical and electronic features of nano/micro structures of end products. Based on simple heat transfer models and using an electric muffle furnace, temperature variations in a glass stack were predicted and measured for glass backplanes of $1.5{\times}1.85m^2$ in size and 0.7 mm in thickness. Except for the period of putting glass backplanes into the furnace, thermal radiation was the major heating mechanism for the treatment and theoretical predictions agreed well to the experimental temperatures on the backplanes. Using the theoretical model, thermal fields for a glass stack of glass-size, $2.2{\times}2.5m^2$, and of the number of sheets, 1 to 12, were calculated for practical design and manufacturing of the muffle furnace for large-scale displays, e.g. up to $8^{th}$ generation.

• 대한기계학회논문집A
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• 제34권10호
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• pp.1455-1462
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• 2010

초고온가스로에서 생성된 $950^{\circ}C$ 정도의 초고온 열을 이용하여 수소를 경제적이며 또한 대량으로 생산하기 위한 시스템이 원자력수소생산시스템이며, 이 시스템에서 공정열교환기는 초고온 열과 황-요오드 공정을 통해 수소를 생산하는 핵심 기기이다. 한국원자력연구원에서는 초고온가스로에 사용될 기기에 대한 성능시험을 위해 헬륨가스루프를 구축하고 공정열교환기 시제품을 제작하였다. 본 연구는 공정열교환기 시제품을 헬륨가스루프에서 시험하기 전에 미리 공정열교환기 시제품의 고온 구조건전성을 평가하기 위한 작업의 일환으로 공정열교환기 시제품에 대한 고온구조해석 모델링, 열해석 및 열팽창해석 결과들을 정리한 것이다. 해석 결과는 공정열교환기 시제품 성능시험 장치 설계에 반영할 것이다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.221-221
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• 2013

Striving to replace the well known silicon nanocrystals embedded in oxides with solution-processable charge-trapping materials has been debated because of large scale and cost effective demands. Herein, a silicon quantum dot-polystyrene nanocomposite (SiQD-PS NC) was synthesized by postfunctionalization of hydrogen-terminated silicon quantum dots (H-SiQDs) with styrene using a thermally induced surface-initiated polymerization approach. The NC contains two miscible components: PS and SiQD@PS, which respectively are polystyrene and polystyrene chains-capped SiQDs. Spin-coated films of the nanocomposite on various substrate were thermally annealed at different temperatures and subsequently used to construct metal-insulator-semiconductor (MIS) devices and thin film field effect transistors (TFTs) having a structure p-$S^{++}$/$SiO_2$/NC/pentacene/Au source-drain. C-V curves obtained from the MIS devices exhibit a well-defined counterclockwise hysteresis with negative fat band shifts, which was stable over a wide range of curing temperature ($50{\sim}250^{\circ}C$. The positive charge trapping capability of the NC originates from the spherical potential well structure of the SiQD@PS component while the strong chemical bonding between SiQDs and polystyrene chains accounts for the thermal stability of the charge trapping property. The transfer curve of the transistor was controllably shifted to the negative direction by chaining applied gate voltage. Thereby, this newly synthesized and solution processable SiQD-PS nanocomposite is applicable as charge trapping materials for TFT based memory devices.

• Journal of Microbiology and Biotechnology
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• 제28권9호
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• pp.1482-1492
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• 2018

Fusarium oxysporum trypsin (FOT) is a fungal serine protease similar to mammal trypsin. The FOT could be successfully expressed in Pichiapastoris by engineering the natural propeptide APQEIPN. In this study, we constructed two recombinant enzymes with engineered amino acid sequences added to the N-terminus of FOT and expressed in P. pastoris. The N-terminal residues had various effects on the structural and functional properties of trypsin. The FOT, and the recombinants TE (with peptide YVEF) and TS (with peptide YV) displayed the same optimum temperature ($40^{\circ}C$) and pH (8.0). However, the combinants TE and TS showed significantly increased thermal stability at $40^{\circ}C$ and $50^{\circ}C$. Moreover, the combinants TE and TS also showed enhanced tolerance of alkaline pH conditions. Compared with those of wild-type FOT, the intramolecular hydrogen bonds and the cation ${\pi}$-interactions of the recombinants TE and TS were significantly increased. The recombinants TE and TS also had significantly increased catalytic efficiencies (referring to the specificity constant, $k_{cat}/K_m$), 1.75-fold and 1.23-fold than wild-type FOT. In silico modeling analysis uncovered that the introduction of the peptides YVEF and YV resulted in shorter distances between the substrate binding pocket (D174, G198, and G208) and catalytic triad (His42, Asp102, and Ser180), which would improve the electron transfer rate and catalytic efficiency. In addition, N-terminal residues modification described here may be a useful approach for improving the catalytic efficiencies and characteristics of other target enzymes.

• Corrosion Science and Technology
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• 제16권3호
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• pp.100-108
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• 2017

In this investigation corrosion behavior of newly developed high-pressure die cast Al-Ni (N15) and Al-Ni-Ca (NX1503) alloys was studied in 3.5% NaCl solution. The electrochemical corrosion behavior was evaluated using open circuit potential (OCP) measurement, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) techniques. Potentiodynamic polarization results validated that NX1503 alloy exhibited lower corrosion current density ($i_{corr}$) value ($5.969{\mu}A/cm^2$) compared to N15 ($7.387{\mu}A/cm^2$). EIS-Bode plots revealed a higher impedance (${\mid}Z{\mid}$) value and maximum phase angle value for NX1503 than N15 alloy. Equivalent circuit curve fitting analysis revealed that surface layer ($R_1$) and charge transfer resistance ($R_{ct}$) values of NX1503 alloy was higher compared to N15 alloy. Immersion corrosion studies were also conducted for alloys using fishing line specimen arrangement to simultaneously measure corrosion rates from weight loss ($P_W$) and hydrogen volume ($P_H$) after 72 hours and NX1503 alloy had lower corrosion rate compared to N15 alloy. The addition of Ca to N15 alloy significantly reduced the Al3Ni intermetallic phase and further grain refinement may be attributed for reduction in the corrosion rate.

• 한국독성학회:학술대회논문집
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• 한국독성학회 2002년도 국제심포지움
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• pp.59-72
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• 2002

The anticarcinogenic effects of epicatechin(EC) and ginsenoside Rb2(Rb2), which are major components of green tea and Korea ginsen, respectively, were investigated using a model system of gap junctional intercellular communication (GJIC) in WB-F344 rat liver epithelial cells. 12-O-Tetradecanoylphorbol-13-accetate (TPA) and hydrogen preoxide, known as cancer promoters, inhibited GJIC in the epithelial cells as determined by the scrape loading/dye transfer assay, fluorescence redistribution assay after photobleaching, and immunofluorescent staining of connexin 43 using a laser confocal microscope. The inhibition of GJIC by TPA and H2O2 was prevented with treatment of Rb2 or Ec. The effect of EC on GJIC was stronger in TPA-treated cells than in H2O2-treated cells, while the effect of Rb2 was opoosite to that of EC. EC, at the concentration of 27.8$\mu$g/ml, prevented the TPA-induced GJIC inhibition by about 60%. Rb2, at the concentration of 277$\mu$g/ml, recovered the H2O2-induced GJIC inhibition by about 60%. These results suggest that Rb2 and EC may prevent human cancers by preventing the down-regulation of GJIC during the cancer promotion phase and that the anticancer effect of green tea and Korea ginseng may come from the major respective conponents, EC and Rb2.

• 한국화재소방학회논문지
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• 제30권6호
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• pp.23-30
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• 2016

본 연구는 화학물질 운송 화학사고를 대상으로 각 연도별 사고현황, 사고유형, 사고원인 등의 화학사고 특성을 분석하였다. 그 결과 77건의 운송 화학사고 중 74건이 유 누출 유형에 의한 사고였으며, 사고 원인으로는 41건이 교통사고에 의한 화학사고였다. 또한, 사고다발 화학물질 조사에서는 46건의 사고가 유해화학물질에 의한 사고인 것으로 조사되었다. 화학물질 운송 화학사고의 예방 및 대응을 위해서는 화학물질 유 누출과 화학물질의 운송 교통사고에 의한 화학사고에 대한 예방책의 보완이 필요하며, 운송 화학사고가 발생되었을 경우 방재가 시스템적으로 신속히 이루어질 수 있도록 범국가적이고 체계적인 화학물질 운송안전 시스템을 구축하여 화학물질 운송에 적용하는 것이 필요하다.