• 한국광물학회지
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• 제16권1호
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• pp.91-106
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• 2003

Na-장석(Amelia albite)의 등온가열 실험에 대한 XRD 분석 결과는 $1073^{\circ}C$의 가열 시료에서 격자상수의 급격한 변화를 보여주는데, 이는 Al과 Si의 비배열(disordering)과 가열된 시료의 급랭에 의한 격자 변형 때문이라고 본다. $1073^{\circ}C$에서는 약 7일 간의 가열에 의해 저온 알바이트에서 고온 알바이트로 상전이한 반면, $924^{\circ}C$에서는 Al-Si의 비배열 속도가 느려서 140일 동안 가열된 시료도 초기 단계의 중간단계 알바이트 상태로 남아 있었다. TEM 분석 결과는 가열된 시료에서 100∼200$\AA$ 크기의 트위드(tweed) 구조가 형성됨이 특징적인데, 이 구조의 발달 및 변화는 고온($1073^{\circ}C$)과 저온 ($923^{\circ}C$)의 가열 시료가 다름이 드러났다. 즉, 전자는 국부적으로 알바이트 쌍정과 유사한 미세구조로 전이한데 반해, 후자는 보다 넓은 지역에 걸쳐 알바이트 쌍정면이 우세한 도메인 구조로 전이하였다. 가열에 의한 Al과 Si의 비배열과 급랭에 의한 응력 때문에 격자의 불안정(lattice instability)이 증가하게 되는데 이를 완화시키기 위하여 태아 단계의 쌍정 구조(알바이트 쌍정과 pericline 쌍정)를 형성되는 것이 트위드 구조의 원인이라고 본다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 춘계학술대회 초록집
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• pp.62.1-62.1
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• 2011

The wind can be stronger and steadier further from shore, but water depth is also deeper. Then bottom-mounted towers are not feasible, and floating turbines are more competitive. There are additional motions in an offshore floating wind turbine, which results in a more complex aerodynamics operating environment for the turbine rotor. Many aerodynamic analysis methods rely on blade element momentum theory to investigate aerodynamic load, which are not valid in vortex ring state that occurs in floating wind turbine operations. So, vortex lattice method, which is more physical, was used in this analysis. Floating platform's prescribed positions were calculated in the time domain by using floating system RAO and waves that are simulated using JONSWAP spectrum. The average value of in-plane aerodynamic force increase, but the value of out-of-plane force decrease. The maximum variation aerodynamic force abruptly increases in severe sea state. Especially, as the pitch motion of the barge platform is large, this motion should be avoided to decrease the aerodynamic load variation.

• 한국재료학회지
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• 제17권7호
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• pp.386-389
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• 2007

The dielectric properties of $(Ba_{0.5}Sr_{0.5})TiO_3$ ferroelectric thin films have been investigated according to the substrates in order to optimize the their properties. MgO, r-plane sapphire, and poly-crystalline sapphire (Alumina) substrates have been used to deposite $(Ba_{0.5}Sr_{0.5})TiO_3$ ferroelectric thin films by RF magnetron sputtering. The BST thin films deposited on the single crystal (100)MgO substrates have high tunability and low dielectric loss. These results are caused by a low misfit between the lattice parameters of the BST films and the substrate. The BST films deposited on r-plane sapphire have relatively high misfit, and the tunability of 17% and dielectric loss of 0.0007. To improve the dielectric properties of the BST films, the post-annealing methods has been introduced. The BST films deposited on (100)MgO, (1102)r-plane sapphire, and poly-crystalline sapphire substrates have best properties in post-annealing conditions of $1050^{\circ}C$, $1100^{\circ}C$, and $1150^{\circ}C$, respectively. The different optimal post-annealing conditions have been found according to the different misfits between the films and substrates, and thermal expansion coefficients. Moreover, the films deposited on alumina substrate which is relatively cheap have a good tunability properties of 23% by the post-annealing.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.436-436
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• 2011

Recently, spintronic devices with submicron structures are widely investigated to take advantage of their unique micromagnetic properties. In this work, we study the temperature dependence of exchange bias in bilayer anti-dot arrays made by depositing Co (40 nm)/Ni (5 nm) ferromagnetic bilayer on Si substrate to form anti-dot arrays with a diameter $1{\mu}m$. The anti-dot patterning was done only for the upper Co layer, while the Ni underlayer was kept unperforated. The temperature dependences of magnetoresistance (MR) and exchange bias were studied along magnetic easy and hard axes. The in-plane MR measurements were performed using a physical-property measurement system (PPMS ; Quantum Design Inc.) at various temperatures. The standard in-line four-point probe configuration was used for the electrical contacts. As temperature was varied, the MR data were obtained in which in-plane field (H=3 kOe) was applied in the directions along the hard and the easy axes with respect to the lattice plane. The temperature dependences of magnetic anisotropy and exchange bias were also studied along the magnetic easy and hard axes. As temperature decreases, the single peak splits into two peaks. While no exchange bias was observed along the magnetic easy axis, the exchange bias field steadily increased with decreasing temperature along the magnetic hard axis. These results were interpreted in connection with the magnetic anisotropy and the effect of the anti-dots in pinning domain wall motion along the respective direction.

• 한국구조물진단유지관리공학회 논문집
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• 제15권3호
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• pp.88-98
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• 2011

조적조 구조물은 전 세계적으로 중 저층 주거시설, 상업시설, 종교용 건축물, 학교, 관공서 등의 용도로 폭넓게 사용되어 왔다. 그러나 조적벽체는 조적개체와 모르타르의 이질재료를 접착하여 쌓는 방식의 구조벽체로 지진과 같은 횡력 발생 시 접착력을 잃거나 미끄러지면서 파괴될 수 있다. 본 연구는 이러한 문제점을 해결하고자 조적식 구조물의 내진보강 기법을 제안하였으며, 진동대 실험을 통하여 내진 성능을 검증하였다. 진동대 실험 결과, 본 연구에서 제안한 내진보강 기법을 이용한 벽체는 한국 건축설계 기준이 제시하는 내진 기준인 0.14g와 미국 IBC에서 제시하는 내진 기준인 0.4g에서 모두 최종 파괴에 도달하지 않았다. 그러나, 0.14g 이상의 지진을 경험한 면외방향 실험체의 경우 급격한 강성저하가 관찰되어, 적절한 보수 보강이 필요할 것으로 예측된다.

• Transactions on Electrical and Electronic Materials
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• 제10권2호
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• pp.40-43
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• 2009

The authors fabricated a nanopatterned surface on a GaN thin film deposited on a sapphire substrate and used that as an epitaxial wafer on which to grow an InGaN/GaN multi-quantum well structure with metal-organic chemical vapor deposition. The deposited GaN epitaxial surface has a two-dimensional photonic crystal structure with a hexagonal lattice of 230 nm. The grown structure on the nano-surface shows a Raman shift of the transverse optical phonon mode to $569.5\;cm^{-1}$, which implies a compressive stress of 0.5 GPa. However, the regrown thin film without the nano-surface shows a free standing mode of $567.6\;cm^{-1}$, implying no stress. The nanohole surface better preserves the strain energy for pseudo-morphic crystal growth than does a flat plane.

• 대한수학교육학회지:수학교육학연구
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• 제8권1호
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• pp.137-144
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• 1998

A common geoboard puzzel serves as the point of departure for an investigation that lends itself to whole-group discussion with a class of prospective secondary school teachers. Students are provided with opportunities to devise and carry out problem-solving strategies (called 'heuristics' by Polya); exploit inerrelationships among geometry, arithmetic and algebra; formulate generalizations and conjectures; plan and execute an computational project; construct mathematical arguments to establish theorems; and find counter-examples to dispose of a false conjecture. In recent tears, Eugene F. Krause wrote two papers having the same title except for the numeral In that papers he arrives at an theorem about the sizes of squares with lattice point vertices in the coordinate plane, In this paper we follow a different path genearlization to coordinate 3-space

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 추계학술대회 초록집
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• pp.184.1-184.1
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• 2010

Floating wind turbines have been suggested as a feasible solution for going further offshore into deeper waters. However, floating platforms cause additional unsteady motions induced by wind and wave conditions, so that it is difficult to predict annual energy output of wind turbines by using conventional power prediction method. That is because sectional inflow condition on a rotor plane is varied by unsteady motion of floating platforms. Therefore, aerodynamic simulation using Vortex Lattice Method(VLM) were used to investigate the influence of motion on the aerodynamic performance of a floating offshore wind turbine. Simulation with individual motion of offshore platform were compared to the case of onshore platform and carried out according to the wave height and the wave angular frequency.

• 한국표면공학회지
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• 제28권2호
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• pp.92-100
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• 1995

To increase the capacity of positive electrode materials for matching the high capacity negative electrode materials in alkaline rechargeable batteries, high-density nickel hydroxide powders were made through a continuous process from nickel sulfate reacted with ammonia and sodium hydroxidc. The effect of operating conditions on structure, shape, size distribution, apparent density and tap density of powders were investigated. Crystal structure of nickel hydroxide powder was hcp according to Bravais Lattice. The increase of mean residence time promoted the growth of (101) plane. The shape of powder was nearly spherical. Their size was in the range of $2~50\mu\textrm{m}$. The size distribution of the powders prepared was narrower than that of commercially obtained nickel hydroxide. Apparent density and tap density were 1.6~1.7g/cc and 2.0~2.1g/cc, respectively.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2003년도 추계학술발표강연 및 논문개요집
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• pp.122-122
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• 2003

In recent years, there has been increasing interest in quasi one-dimensional nanostructural systems, because of their numerous potential applications in various areas, such as materials sciences, electronics, optics, magnetism and energy storage. Specifically, zinc oxide (ZnO) is recognized as one of the most promising oxide semiconductor materials, because of its good optical, electrical, and piezoelectrical properties. The ZnO nanorods were synthesized using vapor-solid (VS) mechanism on soda lime glass substrate without the presence of metal catalyst. ZnO nanorods were prepared thermal evaporation of a Zn powder at 500. As-fabricated ZnO nanorods had an average diameter and length of 40nm and 3$\mu\textrm{m}$. Transmission electron microscopy revealed that the ZnO nanorods were single crystalline with the growth direction perpendicular to the (101) lattice plane. The influences of reaction time on the formation of the ZnO nanorods were investigated. The Photoluminescence measurements showed that the ZnO nanorods had a strong ultraviolet emission at around 380nm and a green emission at around 500nm.