• 한국주조공학회지
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• 제16권6호
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• pp.550-555
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• 1996

A stochastic model, based on the coupling of the finite volume(FV) method for macroscopic heat flow calculation and a two-dimensional cellular automaton(CA) model for treating microstructural evolution was applied-for the prediction of microstructural evolution in squeeze casting. The interfacial heat transfer coefficient at the casting/die interface was evaluated as a function of time using an inverse problem method in order to provide a quantitative simulation of solidification sequences under high pressure. The effects of casting process variables on the formation of solidification grain structures and on the columnar to equiaxed transition of an Al-4.5wt%Cu alloy in squeeze casting were investigated. The calculated solidification grain structures were in good agreement with those obtained experimentally.

• 한국광학회:학술대회논문집
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• 한국광학회 2000년도 제11회 정기총회 및 00년 동계학술발표회 논문집
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• pp.156-157
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• 2000

The amplification method using evanescent wave coupling has a long history and has been widely used as a new lasing method, especially, in the waveguide optics$^{(1)}$ . In particular, it has been observed experimentally that when the light wave propagating in a dielectric medium is totally reflected at the planar interface between the dielectric and a pumped active medium, the reflectance may be greater than unity, i.e., amplification is possible$^{(2)}$ . There were several attempts by other authors to explain this enhanced internal reflection (EIR) classically$^{(3)}$ . They commonly introduced a complex refractive index for the active medium with its imaginary part being negative, and this scheme was also used to describe an amplification process in a waveguide having active-cladding region$^{(4)}$ . However these theories are phenomenological, using macroscopic constants, and therefore a microscopic theory is needed to understand EIR in a fundamental level. (omitted)

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2002년도 금형가공 심포지엄
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• pp.225-230
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• 2002

As in most metal forming processes, die and lubrication are of vital importance in hydrostatic extrusion. An efficient die design and lubrication system selection reduce the pressure required for a given reduction ratio by lowering friction at the billet-die interface. In contrast to the conventional macroscopic extrusion, fine-wire fabrication requires higher extrusion pressure and effect of friction is much more significant. Forming fine Au, Ag, and Cu wire with hydrostatic extrusion process in cold condition, the effect of extrusion die angle, lubrication and billet's initial diameter was studied.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.3-3
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• 2011

Graphene has been attracting much attention owing to its fascinating physical properties such as quantum electronic transport, a tunable band gap, extremely high mobility, elasticity, thermal conductivity, mechanical strength and so on. There have been many efforts to utilize these outstanding properties of graphene for macroscopic applications such as transparent conducting films useful for flexible/stretchable electronics. However, the scale and the quality graphene need to be further enhanced for practical applications by developing more efficient synthesis, transfer, and doping methods. In this tutorial, the recent advances in graphene synthesis and applications will be reviewed, and discuss the future directions of graphene research.

• 한국분말재료학회지
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• 제14권6호
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• pp.399-404
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• 2007

The Cu-based bulk metallic glass (BMG) composite was fabricated by spark plasma sintering (SPS) using of gas-atomized metallic glass powders and ductile brass powders. No defect such as pores and cavities was observed at the interface between the brass powder and the metallic glass matrix, suggesting that the SPS process caused a severe viscous flow of the metallic glass and brass phases in the supercooled liquid region, resulting in a full densification. The BMG composites shows some macroscopic plasticity after yielding, although the levels of strength decreased.

• 한국세라믹학회지
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• 제43권4호
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• pp.247-252
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• 2006

Joining Yittria Stabilized Zirconia (YSZ) to NiCr metal was fabricated using YSZ/NiCr Functionally Graded Materials (FGM) Interlayer by hot pressing process. Microscopic observations demonstrate that the composition and microstructure of YSZ/NiCr FGM distribute gradually in stepwise way, eliminating the macroscopic ceramic/metal interface such as that in traditional ceramic/metal joint. The thermal characteristics of this YSZ/FGM/NiCr joint were studied by thermal shock testing and therml barrier testing. Thermal shock test was conducted by gas burner rig. Acoustic Emission (AE) monitoring was performed to analyze the microfracture behavior during the thermal shock test. It could be confirmed that FGM was the excellent performance of thermal shock/barrier resistance at above $1000^{\circ}C$.

• Journal of Advanced Marine Engineering and Technology
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• 제20권3호
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• pp.11-18
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• 1996

Liquid droplets of water and argon surrounded by their vapor have been simulated by the milecular dynamics method. To explore the surface phenomena of clusters, each molecule is classified into 'liquid', 'surface', or 'vapor' with respect to the number of neighbor molecules. The contribution of a 'surface' molecule of the water cluster to the far infrared spectrum is almist the same as that of the 'liquid' molecule. Hence, the liquid-vapor interface is viewed as geometrically and temporally varying boundary of 'liquid' molecules with only a single layer of 'surface' molecules that might have different characteristics from the 'liquid' molecules. The time scale of the 'phase change' of each molecule is estimated for the argon cluster by observing the instantancous kinetic and potential energies of each molecule. To compare the feature of clusters with macroscopic droplets, the temperature dependence of the surface tension of the argon cluster is estimated.

• 한국재료학회지
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• 제22권8호
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• pp.390-396
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• 2012

Ag pastes added to Bi-oxide frits have been applied to the electrode material of Si solar cells. It has been reported that frits induce contacts between the Ag electrodes and the Si wafer after firing. During firing, the control of interfaces among Ag, the glass layer, and Si is one of the key factors for improving cell performance. Specifically, the thermo-physical properties of frits considerably influence Ag-Si contact. Therefore, the thermal properties of frits should be carefully controlled to enhance the efficiency of cells. In this study, the interface structures among Ag electrodes, glass layers, and recrystallites on an $n^+$ emitter were carefully analyzed with the thermal properties of lead-free frits. First, a cross-section of the area between the Ag electrodes and the Si wafer was studied in order to understand the interface structures in light of the thermal properties of the frits. The depth and area of the pits formed in the Si wafer were quantitatively calculated with the thermal properties of frits. The area of the glass layers between the Ag electrodes and Si, and the distribution of recrystallites on the $n^+$ emitter, were measured from a macroscopic point of view with the characteristics of the frits. Our studies suggest that the thermophysical properties should be controlled for the optimal performance of Si solar cells; our studies also show why cell performance deteriorated due to the high viscosity of frits in Ag pastes.

• KIEE International Transactions on Electrophysics and Applications
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• 제3C권6호
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• pp.216-219
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• 2003

A new class of carbosiloxane dendrimer (G4-48PyP) terminated with 4-pyridylpropano I was synthesized and its possible application to functional thin films was examined through metal complexation and Langmuir-Blodgett (LB) technique. The highly concentrated periphery pyridyl groups of G4-48PyP were exposed on aq. aluminum ions at the air-water interface. The monolayers showed stability up to ca. 50 mN/m of surface pressure. When the subphase became acidic or alkaline, the monolayers changed to condensed phase. The presence of aluminum ions also caused reduction of the molecular area. The macroscopic images of the monolayers were monitored by Brewster angle microscopy (BAM) and only the images of dendrimer aggregates could be observed after the monolayer collapse. The surface images of the monolayer LB film were scanned by atomic force microscopy (AFM). The convex structures of single and aggregate molecules were directly observed. The structures of Langmuir-Blodgett (LB) films were characterized by FT-IR, UV-Vis, and X-ray photoelectron spectroscopy (XPS). The UV-Vis spectrum of the aluminum ion-complexed LB film showed additional band around 670nm, which was not found in the spectra of dendrimer itself or aq. aluminum ions. XPS spectra also supported the incorporation of aluminum ions into the LB films.

• Korean Chemical Engineering Research
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• 제49권3호
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• pp.361-366
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• 2011

몬테칼로 시뮬레이션 방법을 사용하여 유기화합물의 열역학적 물성을 예측하는 새로운 분자 시뮬레이션 소프트웨어를 개발하였다. 분자 구조, 분자간 포텐셜 에너지 함수와 엄밀한 통계역학적 원리로부터 많은 분자들을 포함한 계의 거동에 대한 확률 분포를 구하고 거시적인 계의 열역학적 물성을 계산한다. 본 연구에서 개발된 소프트웨어 cheMC는 윈도우즈 플랫폼에 기반하여 사용자 접근성이 좋고, 가시화 도구 및 차트 생성 기능 등 직관적인 인터페이스로 시뮬레이션 관리가 쉽다. 분자 시뮬레이션은 기존의 상태 방정식을 사용한 열역학 물성 연구를 보완하고, 향후 그 역할이 점점 더 커질 것으로 기대된다.