• 한국주조공학회지
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• 제27권6호
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• pp.243-249
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• 2007

The effect of Re addition and solidification rate on the directional solidification behavior of Ni-Al model alloy has been investigated. Directional solidification (DS) were carried out using the modified Bridgman furnace with various solidification rates. The solid/liquid interface during directional solidification was preserved by quenching the specimen after the desired volume fraction of original liquid was solidified. The equilibrium partition coefficients of Al and Re Were estimated by measuring the compositions at the quenched solid/liquid interface. Then, the effect of Re addition on the elemental segregation behavior was carefully analyzed. The differential scanning calorimetry results showed that the Re addition results in increased ${\gamma}'$ solvus and freezing range of the alloy. It was also shown that the primary dendrite arm spacing gradually decreases with increasing the Re content, while the secondary dendrite arm spacing appears to be independent on the Re content. The compositional analyses clearly revealed that the segregation of Al increased with increasing the Re content and solidification rate, while that of Re was found to be independent on the solidification rate in the range of $10{\sim}100{\mu}m/s$ due to its sluggish diffusion rate in the Ni solid solution.

• 콘크리트학회지
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• 제4권1호
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• pp.89-96
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• 1992

콘크리트의 내동해성은 일반적으로 공기량이나 기포조직 및 분포에 따라 크게 영향을 받으며 콘크리트의 강도와도 관련이 있는 것으로 알려져 있다. 본 연구에서는 고강도콘크리트의 동결융해 저항성에 미치는 공기량 및 기포조직 특히 간격계수의 영향에 관한 실험적 연구로서 우선 압축강도는 Non-AE콘크리트를 대상으로 400-500kg/$\textrm{cm}^2$를 목표로 하였고, 실험결과 내구성지수가 10~20%정도에 불과하므로 다음단계로 공기량 2~12%인 AE콘크리트로 하여 내구성 향상을 도모하였다. 이 때 단위시멘트량, 물\ulcorner시멘트비등을 변화시킨 20종류의 콘크리트 배합에 대해 500cycle까지 동결융해시험을 실시하였다. 결론적으로 동결융해의 저항성은 물\ulcorner시멘트비 보다는 공기량과 더 밀접한 관계가 있었고 임계내구성지수에 대응하는 간격계수는 물\ulcorner시멘트비에 따라 다르다는 사실을 알 수 있었다.

• 미생물학회지
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• 제41권4호
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• pp.239-245
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• 2005

Transformation-associated recombination (TAR) 클로닝 법은 복잡한 게놈으로부터 염색체 내의 특정부위나 유전자를 선택적으로 분리할 수 있다. 이 방법은 목적 유전자에 근접한 작은 게놈DNA 염기서열 정보를 필요로 한다. 이 기술은 효모의 spheroplast transformation을 시키는 동안 목적으로 하는 유전자의 5' 또는 3' 서열을 포함하고 있는 TAR vector와 게놈DNA사이에서 일어나는 상동성재조합에 의해 이루어진다. 본 연구에서는 plasmid 모델시스템을 이용하여 target hooks 내에 존재하는 비상동성 염기서 열이 상동성재조합에 미치는 영향을 조사하였다. plasmid에 존재하는HIS3유전자와 변형시킨 his3-TRP1-his3 단편 사이의 상동성재조합의 효율은 $Ura^+$ 형질전환체의 형질분석에 의해 이루어졌다. $Ura^+$ 형질전환체의 수는 7종류의 서로 달리 변형된 his3-TRP1-his3 단편들을 사용하였을 매 거의 동일하게 나타났다. 그러나 $Trp^+His^+$ positive recombinants의 빈도는 변형된 his3-TRP1-his3 단편 내에 비상동성 영역에 부정확한 간격을 지닐 때 현저한 감소를 나타내었다. 이러한 결과로서, 부정확한 간격이 target hook과 substrate DNA 사이에 일어나는 상동성재조합을 방해하는 것으로 사료된다. 그러므로 이종간의 상동유전자를 클로닝 할 때에는 target hook내의 비상동성 염기서열이 존재한다면 이것이 정확한 간격을 지니는지 여부를 중요란 요인으로 고려해야 한다.

• 광물과 암석
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• 제35권1호
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• pp.51-64
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• 2022

포항 금광동층 함식물화석층 암석의 효과적인 보존을 위하여 구성암석의 특징과 보존처리제 적용을 인공풍화시험을 통해 살펴보았다. 화석지 구성암석은 규조토성 규질이암으로 팽윤성 광물인 스멕타이트를 약간 함유하고 있으며, 엽층리가 발달되어 있다. 화석지 암석은 물과 반응 후 팽윤성 광물의 d₀₀₁ 층간간격이 증가하였다. 에틸실리케이트 암석강화제를 적용한 후 시편의 경도는 향상되었으나 팽윤성 광물의 층간간격은 감소하였다. 팽윤저지제를 선처리한 후 강화제를 처리하였을 때 광물 층간간격의 변화는 강화제만을 처리하였을 때와 유사하여 팽윤저지제의 효과는 거의 없었다. 보존약품이 처리된 암석에 수분이 닿았을 경우, 강화제 또는 팽윤저지제를 선처리한 후 강화제를 처리한 암석 모두 엽층리 간격이 확대되었으나, 습기만 접했을 때는 변화가 적었다. 또한 보존처리 후 노천에 그대로 위치하여 풍화를 받게 되면, 약품이 처리되지 않은 암석에 비해 약간 느리게 발생하기는 하지만, 매우 빠른 시간 내에 엽층리면의 분리와 암석의 분말화가 발생하는 결과를 보였다. 화석지 암석의 원활한 보존을 위해서는 보존약품의 처리가 필요하나, 강우를 접하고 동결융해과정을 거치면 그 효과는 매우 빠른 시간에 소멸되기 때문에 약품처리에 상관없이 암석에 직접적인 강우의 접촉을 막는 것이 우선적으로 요구된다.

• 전자공학회논문지A
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• 제30A권7호
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• pp.60-74
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• 1993

Experiments of RIE of tungsten films using SF$_{6}$ plasma were conducted to investigate the effect of process parameters on etch rate, uniformity, anisotropy, and selectivity. As power increased, the etch rate increased. Maximum etch rate was obtained at 200mtorr As interelectrode spacing increased the etch rate increased for P < 200mtorr while it decreased for P> 200mtorr. Etch rate was maximum at 20 sccm gas flow rate. As substrate temperature increased, the etch rate increased and activation energy was 0.046 eV. In addition, maximum etch rate was acquired at 20% $O_{2}$ addition. The etch rate slightly increased when Ar was added up to 20% while it continuously decreased when N$_{2}$ was added. Uniformity got improved as pressure decreased and was less than 4% for P <100mtorr. Mass spectrometer was utilized to analyze gas composition and S and F peaks were observed from XPS analysis with increasing power. The anisotropy was better for smaller power and spacing, and lower pressure and temperature. It improved when CH$_{4}$ was added and anisotropic etch profile was obtained when about 10% $O_{2}$ was added. The selectjvity was better for smaller power larger pressure and spacing, and lower temperature. Especially. low temperature processing was proposed as a novel method to improve the anisotropy and selectivity.

• 한국전기전자재료학회논문지
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• 제27권4호
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• pp.209-216
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• 2014

The screen printed technique is one of the electrode forming technologies for crystalline silicon solar cell. It has the advantage that can raise the production efficiency due to simple process. The electrode technology is the core process because the electrode feature is given a substantial factor (for solar cell efficiency). In this paper, we tried to change conditions such as squeegee angle $55{\sim}75^{\circ}$, snap off 0.5~1.75 mm, printing pressure 0.6~0.3 MPa and 1.6~2.0 mm finger spacing. As a result, the screen printing process showed an improved performance with an increased height higher finger height. Optimization of fabrication process has achieved 17.48% efficiency at screen mesh of 1.6 mm finger spacing.

• Journal of Mechanical Science and Technology
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• 제19권9호
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• pp.1801-1810
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• 2005

The effect of longitudinal thin rectangular riblets aligned with the flow direction on turbulent channel flow has been investigated using direct numerical simulation. The thin riblets have been modeled using the immersed boundary method (IBM) where the velocities at only one set of vertical nodes at the riblets positions are enforced to be zeros. Different spacings, ranging between 11 and 43 wall units, have been simulated aiming at getting the optimum spacing corresponding to the maximum drag reduction while keeping the height/spacing ratio at 0.5. Reynolds number based on the friction velocity ${\mu}_\tau$ and the channel half depth $\delta$ is set to 150. The flow is driven by adjusted pressure gradient so that the mass flow rate is kept constant in all the simulations. This study shows similar trend of the drag ratio to that of the experiments at the different spacings. Also, this research provides an optimum spacing of around 17 wall units leading to maximum drag reduction as experimental data. Explanation of drag increasing/decreasing mechanism is highlighted.

• 한국재료학회지
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• 제26권11호
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• pp.590-597
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• 2016

In this study, six kinds of low-carbon steel specimens with different ferrite-pearlite microstructures were fabricated by varying the Nb content and the transformation temperature. The microstructural factors of ferrite grain size, pearlite fraction, interlamellar spacing, and cementite thickness were quantitatively measured based on optical and scanning electron micrographs; then, Charpy impact tests were conducted in order to investigate the correlation of the microstructural factors with the impact toughness and the ductile-brittle transition temperature (DBTT). The microstructural analysis results showed that the Nb4 specimens had ferrite grain size smaller than that of the Nb0 specimens due to the pinning effect resulting from the formation of carbonitrides. The pearlite interlamellar spacing and the cementite thickness also decreased as the transformation temperature decreased. The Charpy impact test results indicated that the impact-absorbed energy increased and the ductile-brittle transition temperature decreased with addition of Nb content and decreasing transformation temperature, although all specimens showed ductile-brittle transition behaviour.

• 대한기계학회논문집B
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• 제29권11호
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• pp.1199-1208
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• 2005

The flow fields including velocities, turbulence intensities, Reynolds shear stress and turbulent kinetic energy were investigated using particle image velocimetry(PIV) to study the flow characteristics around two square cylinders in a tandem arrangement. The experiments were carried out in the range of the spacing from 1.0 to 4.0 widths of cylinder, Reynolds number of 5.3$\times$10$^{3}$ and 1.6$\times$10$^{4}$ respectively. Discontinuous jumping at the drag coefficient variation was found for two cylinders simultaneously when the spacing between two cylinders is varied. This phenomenon is attributed to a sudden change of the flow pattern which depends on the reattachment of the shear layer separated from the upstream cylinder. Near such a critical spacing, the changes of the flow fields as well as the effect of Reynolds number were studied in detail.

• 패션비즈니스
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• 제6권2호
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• pp.93-109
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• 2002

This study measured the accompanying rating, recall, and recognition of advertisements, which were run with different methods of spacing in the magazines. To achieve this objective the study chose a qualitative research and performed a reliable test. After the survey was completed, the advertisement recall test was performed. In addition, two days later, the recognition test was performed to the survey respondents and data on the memory of respondents on the advertisements was collected. As a result, rating, recall and recognition of the advertisement's were significantly different by the various forms of advertisements in the magazines. In the advertisement rating and recall by the advertisement printing forms, rather than the regular printing form of running the target advertisement for two pages in a role and the irregular printing form, the continuous printing form was confirmed to be more effective. In addition to that, in the form of running continuous target advertisements for six pages in a role, the effects of the advertisements recall and the recognition were increased. A continuous printing form had higher outcomes on the rating, recall and recognition of advertisements. Therefore, conclusively, it gave more effects in increasing the memory of the advertisement for the consumers. The conclusion of the study provided suggestions on the forms of advertisement to stimulate the memory of consumers in the magazine advertisement.