• Metals and materials international
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• 제24권6호
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• pp.1333-1345
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• 2018

The effect of manganese sulfide (MnS) inclusions on the machinability of free-cutting steel is based on their morphology, size and distribution. Furthermore, the plasticity of MnS is high during the hot working caused different characterization of MnS. In this study, the deformation behavior of MnS in 1215MS steel after a thermomechanical process was investigated at 1323 K. The microstructures of MnS inclusions were characterized by optical microscopy, scanning electron microscopy, energy-dispersive spectrometry, and electron backscattering diffraction (EBSD). As the thickness reduction of the inclusions increased from 10 to 70%, their average aspect ratio increased from 1.20 to 2.39. In addition, the deformability of MnS inclusions was lower than that of the matrix. The possible slip systems of A, B, C, and D plane traces were (${\bar{1}}0{\bar{1}}$)[${\bar{1}}01$], ($10{\bar{1}}$)[101], (011)[$01{\bar{1}}$], and (110)[$1{\bar{1}}0$]. Furthermore, the EBSD measurements suggested that slip planes in MnS inclusions occur on {110} planes.

• 소성∙가공
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• 제32권6호
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• pp.360-366
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• 2023

This study is concerned with the surface quality of products according to the material and coating condition of the forming tool in incremental sheet forming. Three forming tools, SKD11 with and without diamond-like-coating (DLC) and polymer tool tip, were used to form conical and pyramidal geometries to take into account the influence of friction between the forming tool and the sheet on the surface quality including geometric accuracy of deformed samples. Each test was performed using SUS304 with a thickness of 0.4 mm according to different incremental depths per lap of 0.5 mm, 1.0 mm, and 1.5 mm for the contour tool path, considering the increase in normal force which is associated with the frictional behavior during local deformation. The surface quality was then investigated through surface roughness measured with KEYENCE VR-6000 and relative strain distribution including deformed shape analyzed with ARGUS which is a non-contact optical strain measurement system. Differences between 3D CAD surfaces and captured geometry from experiments were evaluated to compare the effect of friction on geometric accuracy. From comparisons of experimental results, it was revealed that the polymer-based tool tip can improve surface quality and geometric accuracy by reducing the undesired material flow due to local friction in the increment sheet forming process.

• 한국전기전자재료학회논문지
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• 제36권5호
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• pp.500-504
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• 2023

In this study, the heteroepitaxial thin film growth of β-Ga₂O₃ was studied according to the position of the susceptor in mist-CVD. The position of the susceptor and substrate was moved step by step from the center of the hot zone to the inlet of mist in the range of 0~50 mm. It was confirmed that the average thickness increased to 292 nm (D1), 521 nm (D2), and 580 nm (D3) as the position of the susceptor moved away from the center of the hot zone region. The thickness of the lower region of the substrate is increased compared to the upper region. The surface roughness of the lower region of the substrate also increased because the nucleation density increased due to the increase in the lifetime of the mist droplets and the increased mist density. Therefore, thin film growth of β-Ga₂O₃ in mist-CVD is performed by appropriately adjusting the position of the susceptor (or substrate) in consideration of the mist velocity, evaporation amount, and temperature difference with the substrate, thereby determining the crystallinity of the thin film, the thickness distribution, and the thickness of the thin film. Therefore, these results can provide insights for optimizing the mist-CVD process and producing high-quality β-Ga₂O₃ thin films for various optical and electronic applications.

• Journal of Microbiology and Biotechnology
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• 제16권12호
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• pp.1968-1976
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• 2006

Recombinant E. coli ACV 1003 (recA:: lacZ) was used to measure low concentrations of DNA-damaging chemicals, which produce $\beta$-galactosidase via an SOS regulon system. Very low $\beta$-galactosidase activities of less than 0.01 unit/ml, $\beta$-galactosidase produced through an SOS response corresponding to the 10 ng/ml (ppb) of DNA damaging chemicals in the environment, can be rapidly determined by using an alternative interferometric biosensor with optically flat thin films of porous silicon rather than by the conventional time-consuming Miller's enzyme assay as well as the ELISA method. fu order to enhance the sensitivity in the interferometry, it needs to obtain more uniform distribution and higher biolinking efficiency, whereas interferometric sensing is rapid, cheap, and advantageous in high throughput by using a multiple-well-type chip. In this study, pore size adjusted to 60 nm for the target enzyme $\beta$-galactosidase to be bound on both walls of a Si pore and a calyx crown derivative was apllied as a more efficient biolinker. Furthermore, anti-$\beta$-galactosidase was previously functionalized with the biolinker for the target $\beta$-galactosidase to be specifically bound. When anti-$\beta$-galactosidase was bound to the calyx-crown derivative-linked surface, the effective optical thickness was found to be three times as high as that obtained without using anti-$\beta$-galactosidase. The resolution obtained was very similar to that afforded by the time-consuming ELISA method; however, the reproducibility was still unsatisfactory, below 1 unit $\beta$-galactosidase/ml, owing to the microscopic non-uniform distribution of the pores in the etched silicon surface.

• 대기
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• 제23권4호
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• pp.519-526
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• 2013

This study aims to analyze the vertical distribution of Asian dust measured by LIDARs at three weather stations in Baengnyeongdo (BND), Munsan (MS), and Gunsan (GS) during 10~11 May 2010, and thereby investigate their effectiveness. Asian dust passed through from central to south-western part of Korea. Although dust particles were detected over the surface in MS and GS, LIDAR data showed that the Asian dust with non-spherical particles was observed in all of the three regions. It seems that the naked-eye observation could not detect dust over the surface of BND due to the temperature inversion below a height of 0.45 km. During the Asian dust events, the duration time of dust presented 9.5 hr (BND), 19.5 hr (MS), and 24.5 hr (GS), respectively with the longest time in GS, whereas dust altitudes ranged from 0.4 to 1.3 km (BND), 0.1 to 2.8 km and 4.1 to 4.2 km (MS), and 0.2 to 2.0 km (GS), respectively, while showing the highest altitude in MS. Aerosol optical thickness (AOT) retrieved by LIDAR and skyradiometer (SR), located close to the LIDAR sites, was compared. MS (LIDAR) and Seoul (SR) attained the AOT of 0.64 and 0.50, and GS (LIDAR) and Gongju (SR) attained the AOT of 0.38 and 0.54, respectively. As SR-derived angstrom exponents (AE) during the time period determined as Asian dust by LIDAR data were 0.17 in Seoul (near MS) and 0.30 in Gongju (near GS), it can be said that the characteristics of dust particles were appeared. During the study period, depolarization ratio could serve as a useful indicator to determine dust aerosol. But, it still seems essential to conduct further investigation with longer period of data to better describe the discrepancy of AOT between LIDARs and SR.

• 한국광학회지
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• 제17권2호
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• pp.149-158
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• 2006

가우스 괄호법을 이용한 굴절능 배치 방법과 등가렌즈 설계법으로 기존에 설계한 반도체와이어 본딩 검사용 다중배치 현미경 광학계에 대한 공차 분석을 하였다. 축상 대칭 공차인 곡률과 두께에 대한 공차는 회절 한계에 의한 초점심도 내에서 후방초점거리(BFL)가 변하도록 결정하였고, 축 비대칭 공차인 decenter와 tilt에 대한 공차는 0.7 field에서 공간주파수 50 lp/mm에서의 MTF(Modulation Transfer Function) 변화가 5% 이내가 되도록 시행착오 방법으로 정하였다. 이 결과 공차분포확률에 관계없이 MTF의 감소율이 5% 미만 되는 곳에 가장 많은 확률로 공차가 분포하므로 위와 같은 방법으로 공차를 부여하면 원하는 본 광학계의 결상 성능을 만족시킬 수 있음을 확인하였다.

• 한국재료학회지
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• 제20권11호
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• pp.617-622
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• 2010

We have studied methods to save Si source during the fabrication process of crystalline Si solar cells. One way is to use a thin silicon wafer substrate. As the thickness of the wafers is reduced, mechanical fractures of the substrate increase with the mechanical handling of the thin wafers. It is expected that the mechanical fractures lead to a dropping of yield in the solar cell process. In this study, the mechanical properties of 220-micrometer-solar grade Cz p-type monocrystalline Si wafers were investigated by varying saw-damage etching conditions in order to improve the flexural strength of ultra-thin monocrystalline Si solar cells. Potassium hydroxide (KOH) solution and tetramethyl ammonium hydroxide (TMAH) solution were used as etching solutions. Etching processes were operated with a varying of the ratio of KOH and TMAH solutions in different temperature conditions. After saw-damage etching, wafers were cleaned with a modified RCA cleaning method for ten minutes. Each sample was divided into 42 pieces using an automatic dicing saw machine. The surface morphologies were investigated by scanning electron microscopy and 3D optical microscopy. The thickness distribution was measured by micrometer. The strength distribution was measured with a 4-point-bending tester. As a result, TMAH solution at $90^{\circ}C$ showed the best performance for flexural strength.

• 대한기계학회논문집
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• 제14권6호
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• pp.1652-1660
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• 1990

본 연구에서는 원관내에서 복사에 관여하는 고온의 가스유동에 의한 복사열전 달과 대류열전달간의 상호작용에 대해 실험과 수치해석을 통하여 고찰하고자 한다. 실험으로는 프로판가스의 화염생성에 의한 속도, 온도 및 벽면에서의 열유속분포를 측 정하고, 수치적으로는 냉염(cold flame) 상태서 측정한 난류요동성분과 연소시의 입구 속도와 온도를 초기조건으로 하여 밀도와 점성계수의 온동에 따른 변화를 고려한 K-.epsilon. 모델과 구조화근사법 및 최근에 개발되어 사용되기 시작한 Weighted Sum of Gray Gas- es모델을 사용하여 속도, 온도 및 열유속 분포를 계산하여 수치해석의 결과와 실험결 과를 비교함으로써 모델의 타당성을 검증하고, 복사에 의한 열전달량과 대류에 의한 열전달량을 분리하여 각 모드가 온도분포 및 열유속분포에 미치는 영향을 고찰하고자 한다.

• 한국광학회지
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• 제12권1호
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• pp.61-66
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• 2001

두께가 얇은 기록매질을 사용하는 디스크형 홀로그래픽 메모리에서 비초점 Fourier aus 홀로그램을 저장할 때 홀로그램 당면적 저장밀도 및 기록 면에서의 빔세기분포 등을 조사하였다. 정확한 Fourier 면 홀로그램을 기록할때에는 2진 데이터를 표현하는 공간 광 변조기의 화소 피치가 클수록 면적 저장 밀도가 증가하지만, 비초점 Fourier 면 홀로그램을 저장할 때에는 면적 저장밀도를 최대로 하는 최적의 화소 피치가 존재함을 보였다. 일반적으로 홀로그램당 면적 저장밀도를 높이기 위해서는 데이터 영상을 집속하는 Fourier 변환 렌즈의 f/#가 가급적 작아야 한다. 이 경우 기록면에서의 빔세기 분포뿐만 아니라 기록면적이 비초점율에 따라 매우 민감하게 변하게 된다. 따라서 정확한 Fourier 면 홀로그램을 기록한다. 할지라도 최대의 면적 저장밀도를 얻기 위해서는 매질의 두께에 따른 비초점율의 영향을 고려해야 한다.

• 한국광학회지
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• 제3권4호
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• pp.227-233
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• 1992

분할디스크형 글라스레이저 증폭기를 개발하기 위하여 이를 해석 설계할 수 있는 시뮬레이션 코드를 작성했다. 레이저매질에서의 열부하를 감소시키고, 플래시램프의 방사스펙트럼과 레이저글라스의 흡수 스펙트럼 간의 결합효율을 높이기 위해서는 전류밀도를 2000-4000A/$\textrm{cm}^{2}$로 유지하여 단파장에서의 방사에너지를 줄여야 한다. 디스크 증폭기에서 같은 부피를 갖는 매질을 3등분하여 냉각표면적을 3배로 늘렸을 때 온도상승치는 30% 정도로 떨어졌다. 단면펌핑 분할 디스크형 증폭기의 설계에서는 각 글라스 간의 $Nd^{3+}$ 도핑율에 차등을 주어야 하고 플래시램프 앞에 있는 매질의 흡수계수 $\alpha$ 와 두께 d의 곱인 $\alpha$d가 0.26 전후가 적절하다는 것을 알았다.