• 전기화학회지
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• 제2권4호
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• pp.237-241
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• 1999

펄스전착법에 의한 구리박막의 특성과 via hole 충진 특성을 연구하였다. 특히 구리박막의 특성에 미치는 첨가제의 영향을 중점적으로 다루었다. 펄스 전류와 첨가제를 사용하여 전착한 구리박막은 83.4 MPa이하의 낮은 인장응력을 가졌으며 높은 Cu (111) 우선 배향성을 나타냈다. Superfilling에 의해 최고 $0.25{\mu}m, 6: 1$ 정도의 고 종횡비를 가지는 via hole에 결함 없이 성공적으로 충진할 수 있었으며 미세 구조를 관찰한 결과 쌍정에 의한 변형이 일어났음을 알 수 있었다. $500^{\circ}C$에서 1시간 동안 진공열처리를 했을 경우 두께의 $1\~2$배에 달하는 결정립을 가지는 bamboo구조를 나타냈으며 이때 전기비저항은 $1.8\~2.0{\mu}{\Omega}{\cdot}cm$을 나타냈다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 Techno-Fair 및 추계학술대회 논문집 전기물성,응용부문
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• pp.148-149
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• 2007

We present the design and fabrication prcoess of a two-axis tilting micromirror device driven by the electrostatic vertical comb actuator. A high aspect-ratio comb actuator is fabricated by multiple DRIE process in order to achieve large scan angle. The proposed fabrication process enables a mirror to be fabricated on the wafer-scale. By bonding a double-side polished (DSP) wafer and a silicon-on-insulator (SOI) wafer together, all actuators on the wafer are completely hidden under the reflectors. Nickel lines are embedded on a Pyrex wafer for the electrical access to numerous electrodes of mirrors. An anodic bonding step is implemented to contact electrical lines with ail electrodes on the wafer at a time. The mechanical angle of a fabricated mirror has been measured to be 1.9 degree and 1.6 degree, respectively, in the two orthogonal axes under driving voltages of 100 V. Also, a $8{\times}8$ array of micromirrors with high fill-factor of 70 % is fabricated by the same fabrication process.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.75.2-75.2
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• 2013

Atomic layer deposition (ALD), utilizing self-limiting surface reactions, could offer promising perspectives for future efficient energy conversion devices. The capabilities of ALD for surface/interface modification and construction of novel architectures with sub-nanometer precision and exceptional conformality over high aspect ratio make it more valuable than any other deposition methods in nanoscale science and technology. In the context, a variety of researches on fabrication of active materials for energy conversion applications by ALD are emerging. Among those materials, one-dimensional nanotubular titanium dioxide, providing not only high specific surface area but also efficient carrier transport pathway, is a class of the most intensively explored materials for energy conversion systems, such as photovoltaic cells and photo/electrochemical devices. The monodisperse, stoichiometric, anatase, TiO2 nanotubes with smooth surface morphology and controlled wall thickness were fabricated via low-temperature template-directed ALD followed by subsequent annealing. The ALD-grown, anatase, TiO2 nanotubes in alumina template show unusual crystal growth behavior which allows to form remarkably large grains along axial direction over certain wall thickness. We also fabricated dye-sensitized solar cells (DSCs) introducing our anatase TiO2 nanotubes as photoanodes, and studied the effect of blocking layer, TiO2 thin films formed by ALD, on overall device efficiency. The photon convertsion efficiency ~7% were measured for our TiO2 nanotubebased DSCs with blocking layers, which is ~1% higher than ones without blocking layer. We also performed open circuit voltage decay measurement to estimate recombination rate in our cells, which is 3 times longer than conventional nanoparticulate photoanodes. The high efficiency of our ALD-grown, anatase, TiO2 nanotube-based DSCs may be attributed to both enhanced charge transport property of our TiO2 nanotubes photoanode and the suppression of recombination at the interface between transparent conducting electrode and iodine electrolytes by blocking layer.

• Journal of Welding and Joining
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• 제27권6호
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• pp.68-73
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• 2009

Recently, as titanium and titanium alloys are being increasingly used in wide areas, there are on-going researches to obtain high quality weld zone. In particular, growing interest is being drawn to laser welding, which involves low heat input and large aspect ratio in various welding processes and can facilitate shield in atmospheric condition compared with electron beam welding. The first report covered the analysis of embrittlement by the bead color of weld zone through quantitative analysis of oxygen and nitrogen and measurement of hardness as basic experiment to apply laser welding to titanium. Results indicated that the element that affect embrittlement the most was nitrogen, and as embrittlement and oxygenation go on, bead color changed to silver, gold, brown, blue and gray. This study performed butt welding of pure titanium and STS304 by using 1kW CW Nd:YAG laser, and to find out basic physical properties, evaluated welding performance by laser output, welding speed, root gap and misalignment etc, and examined mechanical properties through tensile stress and Erichsen test. The reason particles of pure titanium welded metal and HAZ are greater than STS304 is because they are pure metal and do not include many impure elements that work as nuclei in case of resolidification, thus becoming coarse columnar crystals eventually. In addition, the reason STS304 requires more energy during welding than pure titanium is because the particle size of base metal is smaller.

• 한국항공우주학회지
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• 제47권2호
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• pp.98-106
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• 2019

인간동력항공기의 날개는 고세장비의 형상을 가지고 있어 큰 굽힘변위가 발생한다. 본 논문에서는 고세장비 형상의 날개가 가지는 구조적인 한계를 붙임각을 변경함으로써 개선하고자 하였다. 날개의 익형 및 단면형상을 고정시킨 후 동일 수준의 양력 발생을 만족시킨다는 전제하에 붙임각의 변경에 따른 날개 끝단의 굽힘변위 변화 경향을 관측하였다. 이를 위해 유한날개의 양력, 항력, 모멘트 하중을 날개의 각 섹션에 분포시켰다. 그리고 EDISON의 "geometrically exact beam (GEB)" 프로그램과 "Variational Asymptotic Beam Sectional Analysis (VABS)" 단면해석 프로그램을 사용하여 변경된 설계안의 구조 안전도를 평가하였다. 또한, 다물체 동역학 해석 프로그램 DYMORE를 이용하여 본 논문에서 예측한 날개의 끝단 변위 예측값을 비교 검증하였다.

• 한국산업융합학회 논문집
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• 제25권5호
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• pp.791-797
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• 2022

Using the fatigue limit (△σ_unsm) and residual stress (σ_r) of the UNSM smooth specimen, the harmless maximum crack depth (α_hml) according to the crack aspect ratio (As) was evaluated. α_hml evaluated the reliability in the relationship between the minimum crack depth (α_NDI1, α_NDI2) detectable by nondestructive inspection(NDI) and the crack depth (α₂₅, α₅₀) that reduces the fatigue limit by 25% and 50%. All α_hml was determined by the crack depth. The α_hml of 80N UNSM with high σ_r and high △σ_unsm was found to be large. σ_r in the depth direction had a much effect on α_hml. Since α_hml>α₅₀(As=0.6-0.1) and α_hml>α₂₅, α₂₅ and α₅₀(some range) can secure the safety and reliability. Since α_hml<α₅₀ (As=1. 0-0. 6), it cannot be made harmless by UNSM. So safety and reliability cannot be secured. α_NDI1 and α_NDI2 are larger than α₂₅, α₂₅ cannot be detected by NDI. α_NDI1 and α_NDI2 are smaller than α₅₀, α₂₅ can detected by NDI.

• 대한토목학회논문집
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• 제30권3D호
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• pp.313-321
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• 2010

본 연구는 부산시의 주택순환과정을 살펴보기 위해 가구의 생애주기에 따른 주거이동 특성을 분석하였는데, 설문조사는 부산시 거주 만 40세 이상의 성인들을 대상으로 결혼 이후 현재까지의 주거이동에 대한 주거경력을 조사하였다. 통계자료 분석의 결과와 설문조사 결과는 모든 항목에서 유사한 결과를 보였는데 이를 정리하면 다음과 같다. 설문대상자들이 현재 거주하고 있는 주택을 살펴보면, 주택유형은 아파트가 절대적으로 높은 비율을 차지하고 있으며, 주택의 점유형태는 자가소유이며, 주택규모는 30평형대, 거주기간은 6년 이상 10년 미만이다. 주택자금마련 방법은 저축과 은행대출이 대다수를 차지하고 있는데, 현재 가구의 소득만으로는 자가소유의 희망주택을 마련하는 것이 불가능함에도 불구하고 주택금융을 활용하여 내집마련을 하는 주거문화는 임대료를 지불하고 임차소유를 하는 외국과는 다소 다른 우리의 주거문화이다. 그러나 주거만족도의 측면에서 주거이동은 주택규모를 확장시키고 점유형태를 변화시켰기 때문에 주거이동으로 인해 대부분의 가구가 주거의 질이 향상되었다고 인식하고 있으며, 현재의 주거에 대해 매우 높은 만족감을 보인다.

• Nuclear Engineering and Technology
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• 제55권10호
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• pp.3775-3786
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• 2023

Mixing Vane Grid (MVG) is one of the most important structures in fuel assembly due to its high performance in mixing the coolant and ultimately increasing Critical Heat Flux (CHF), which avoids the temperature rising suddenly of fuel rods. To evaluate the mixing performance of the MVG, a Total Diffusion Coefficient (TDC) mixing coefficient is defined in the subchannel analysis code. Conventionally, the TDC of the spacer grid is obtained from the combination of experiments and subchannel analysis. However, the processing of obtaining and determine a reasonable TDC is much challenging, it is affected by boundary conditions and MVG geometries. In is difficult to perform all the large and costing rod bundle tests. In this paper, the CFD method was applied in TDC analysis. A typical 5 × 5 MVG was simulated and validated to estimate the mixing performance of the MVG. The subchannel code was used to calculate the TDC. Firstly, the CFD method was validated from the aspect of pressure drop and lateral temperature distribution in the subchannels. Then the effect of boundary conditions including the inlet temperature, inlet velocities, heat flux ratio between hot and cold rods and the arrangement of hot and cold rods on MVG mixing and TDC were studied. The geometric effects on mixing are also carried out in this paper. The effect of vane pattern on mixing was investigated to determine which one is the best to represent the grid's mixing performance.

• Archives of Metallurgy and Materials
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• 제63권3호
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• pp.1433-1437
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• 2018

Neodymium-Iron-Boron (Nd-Fe-B) magnets are considered to have the highest energy density, and their applications include electric motors, generators, hard disc drives, and MRI. It is well known that a fiber structure with a high aspect ratio and the large specific surface area has the potential to overcome the limitations, such as inhomogeneous structures and the difficulty in alignment of easy axis, associated with such magnets obtained by conventional methods. In this work, a suitable heat-treatment procedure based on single-step and multistep treatments to synthesize sound electrospun Nd-Fe-B-O nanofibers of Φ572 nm was investigated. The single-step heat-treated (directly heat-treated at 800℃ for 2 h in air) samples disintegrated along with the residual organic compounds, whereas the multistep heat-treated (sequential three-step heat-treated including three steps;: dehydration (250℃ for 30 min in an inert atmosphere), debinding (650℃ for 30 min in air), and calcination (800℃ for 1 h in air)) fibers maintained sound fibrous morphology without any organic impurities. They could maintain such fibrous morphologies during the dehydration and debinding steps because of the relatively low internal pressures of water vapor and polymer, respectively. In addition, the NdFeO3 alloying phase was dominant in the multistep heat-treated fibers due to the removal of barriers to mass transfer in the interparticles.

• Structural Engineering and Mechanics
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• 제91권5호
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• pp.487-502
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• 2024

This study introduces a novel 'multi-mushroom' structural system designed to improve seismic performance in lowrise buildings. Traditional low-rise structures tend to favor sliding over rocking due to their smaller aspect ratios despite the rocking system's superior seismic response reduction. Rocking designs allow structures to pivot at their base during seismic events, reducing damage by dissipating energy. The proposed multi-mushroom system divides the building into four equal sections with small gaps in between, each capable of independent rocking. Numerical analyses are conducted using scaled earthquake records from far- and near-source events to evaluate this system's performance. The results indicated that the multimushroom system significantly reduces plastic hinge formation compared to conventional designs. The system also demonstrated enhanced beam performance and a robust base girder, contributing to reduced collapse vulnerability. The 3-story model exhibited the most favorable behavior, effectively mitigating peak roof drift values, where the rocking system achieved a 21% reduction in mean roof displacement for near-field records and 15% for far-field records. However, the 5-story configuration showed increased roof displacement, and the 7-story model recorded higher incidences of collapse prevention (CP) hinges, indicating areas for further optimization. Overall, the multi-mushroom system enhances seismic resilience by minimizing plastic hinge formation and improving structural integrity. While the system shows significant promise for low-rise buildings, challenges related to roof displacement and inter-story drift ratio in taller structures necessitate further research. These findings suggest that the multi-mushroom system offers a viable solution for seismic risk reduction, contributing to safer and more sustainable urban development in earthquake-prone areas.