• 한국정밀공학회지
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• 제13권3호
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• pp.70-79
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• 1996

In off-line process optimization, process parameters are controlled such that the process is robust against changes in equipment conditions and incoming materials. The off-line methods, however, are not effective when the changes are so large that process parameters need to be adjusted. On-line control can respond to such large changes, but process uniformity has not been controlled on-line due to the difficulties in modeling. This paper is aimed at developing a new on-line control methodology where the uniformity is controlled effectively. The process variability is categorized based on the physical considerations, and the process parameters are classi- fied considering their effects on the categorized process variabilities. On-line control is performed with the properly selected process parameters so that robustness may not be degraded. The developed methodology is applied to the single wafer plasma etching processes, which resulted in both higher within-a-wafer uniformity and compens- ation of the incoming material non-uniformity.

• Structural Engineering and Mechanics
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• 제91권2호
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• pp.149-161
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• 2024

In the world, the construction science and technology industry has developed strongly thanks to the application of Ultra-High Performance Concrete (UHPC) technology, with a strength greater than 150 Mpa and unprecedented durability. compared to previous materials. However, this technology can build special structures but has limited use in construction because it is not commercially feasible to replace regular concrete in most structural types due to material costs. high, lack of availability, limited design standards, complex manufacturing and maintenance techniques. This article examines the composition of UHPC materials and their performance in composite structures with conventional concrete, a promising choice for promoting the development of UHPC technology in construction. It is based on the combined use of UHPC as a covering layer around normal concrete or as an inner core to increase the strength of normal concrete, create a slender structure and reduce the cost and repair of construction works. Construction and transport infrastructure are degraded. Manufacturing costs are expected to be reduced with composite construction due to the advantages of combined materials.

• 한국잠사곤충학회지
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• 제52권2호
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• pp.159-164
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• 2014

본 연구는 누에 숙잠 혈림프를 발효를 통하여 화장품으로서의 기능성과 피부 침투력을 증진시기고자 수행되었다. 누에 숙잠 혈림프를 대량 정제하여 이를 이용하여 2종의 Bacillus균을 이용하여 4주간 발효하였으며, 이들 발효산물의 분자량 및 세포 독성, 항산화, 티로시나아제 활성 억제 효과를 확인하였다. 1. 누에 숙잠 혈림프 단백질의 분자량이 커서(70 kDa) 정제물의 용해도가 낮다는 문제가 제기되어 단백질의 저분자화를 위해 바실러스속 균주 2종(B. subtilis 10854, B. amyloliquefaciens M27)으로 4주간 발효시켰다. 그 결과, 혈림프 발효액의 단백질은 현저하게 분자량이 저하되었으며, 바실러스속 균주 중 B. amyloliquefaciens M27이 단백질 분해 능력이 더 뛰어난 것으로 나타났다. 2. 누에 숙잠 혈림프 정제물을 바실러스속 균주 2종(B. subtilis 10854, B. amyloliquefaciens M27)으로 발효하여 발효액의 세포독성을 멜라닌세포의 세포 생존율을 측정하여 확인한 결과, 발효액의 $12.5{\sim}50{\mu}g/mL$ 농도 범위에서 세포 독성이 나타나지 않았고 세포 생존율이 증가하는 결과를 보였다. 3. 누에 숙잠 혈림프, 혈림프 발효물의 DPPH 자유라디칼 소거 활성을 정한 결과, 농도 의존적으로 항산화력이 증가하였고 혈림프 발효액은 양성대조군인 비타민 C와 유사한 활성 정도를 나타내었다. 분자량 저하 효과가 더 우수했던 Bacillus amyloliquefaciens M27균주를 이용하여 4주간 발효시키며 발효기간별 DPPH 자유라디칼 소거 활성을 측정한 결과, 2주 이상 발효시켰을 때 약 5% 이상 자유라디칼 소거 활성 능력이 증가함을 나타내었다. 4. 티로시나아제 활성 억제효과는 대조군에 비해 혈림프와 혈림프 발효액 처리군 모두에서 나타났으며, amyloliquefaciens M27를 이용한 발효액의 경우 미백효과가 더욱 뚜렷하였다.

• 비파괴검사학회지
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• 제24권4호
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• pp.325-330
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• 2004

원자력발전소에는 여러 종류의 케이블이 전력공급, 감시 및 제어신호의 전달을 위해 열악한 환경하에서 이용되고 있다. 발전소의 안전한 운전을 위해서 이 케이블이 어느 정도 열화 되었는지 확인할 필요가 있다. 특히, 원자력발전소의 수명 연장과 더불어 저압 케이블을 장기간 사용함에 따라서 저압케이블의 열화를 평가하기 위한 방법이 필요하게 되었다 저압케이블의 열화를 측정하는 파라미터로는 주변 온도, 절연재질의 경도, 파단시 연신률(EAB, Elongation At Breaking Point) 등이 있다. 그러나, 온도나 경도를 계측하는 검사는 정량적인 판단기준의 설정이 곤란하고 진단의 정밀도가 낮으며, 부분적으로 샘플링하는 방법은 샘플링되는 케이블에 연결된 부하를 정전시켜야 하고 장소와 시간적인 제약이 있으며, 전기적 측정법은 노화 초기부터 중기까지의 열화정도를 확인하기 어렵다. 본 연구에서는 재료의 열화에 따라서 초음파의 음속이 변화한다는 이론적인 배경(1,2)을 바탕으로 저압 케이블 재료의 열화에 따른 초음파의 음속을 측정하였다. 이를 위해, 원자력발전소에서 사용되는 저압케이블을 가속 열화시켰으며, 저압케이블의 피복재에서 초음파의 음속을 측정할 수 있는 장비를 개발하여, 초음파의 음속측정 후 인장시험을 통해 파단시 연신률을 측정하였다. 파단시 연신률이 증가함에 따라서 음속이 선형적으로 감소하였으며, 초음파의 음속은 열화의 정량적 평가 파라미터로서의 사용 가능성을 확인할 수 있었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 하계학술대회 논문집
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• pp.54-54
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• 2009

Ag thick film has been used for electrode materials with the excellent conductivity. Ag electrode is used in screen-printed silicon solar cells as a electrode material. Compared to photolithography and buried-contact technology, screen-printing technology has the merit of fabricating low-priced cells and enormous cells in a few hours. Ag paste consists of Ag powders, vehicles and additives such as frits, metal powders (Pb, Bi, Zn). Frits accelerate the sintering of Ag powders and induce the connection between Ag electrode and Si wafer. Thermophysical properties of frits and reactions among Ag, frits and Si influence on cell performance. In this study, Ag pastes were fabricated with adding different kinds of frits. After Ag pastes were printed on silicon wafer by screen-printing technology, the cells were fired using a belt furnace. The cell parameters were measured by light I-V to determine the short-circuit current, open-circuit voltage, FF and cell efficiency. In order to study the relationship between the reactivity of Ag, frit, Si and the electrical properties of cells, the reaction of frits and Si wafer on was studied with thermal properties of frits. The interface structure between Ag electrode and Si wafer were also measured for understanding the reactivity of Ag, frit and Si wafer. The excessive reactivity of Ag, frit and Si wafer certainly degraded the electrical properties of cells. These preliminary studies suggest that reactions among Ag, frits and Si wafer should optimally be controlled for cell performances.

• 한국환경과학회지
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• 제20권5호
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• pp.555-564
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• 2011

This study examines the potential restoration of abandoned channels of the Mangyeong River in South Korea. To analyze the morphological changes and equilibrium conditions, a flow duration analysis was performed to obtain the discharge of 255 m3/s with a recurrence interval of 1.5 year. It is a gravel-bed stream with a median bed diameter of 36 mm. The reach-averaged results using HEC-RAS showed that the top width is 244 m, the mean flow depth is 1.11 m, the width/depth ratio is very high at 277, the channel velocity is 1.18 m/s, and the Froude number is also high at 0.42. The hydraulic parameters vary in the vicinity of the three sills which control the bed elevation. The total sediment load is 6,500 tons per day and the equivalent sediment concentration is 240 mg/l. The Engelund-Hansen method was closer to the field measurements than any other method. The bed material coarser than 33 mm will not move. The methods of Julien-Wargadalam and Lacey gave an equilibrium channel width of 83 m and 77 m respectively, which demonstrates that the Mangyeong River is currently very wide and shallow. The planform geometry for the Mangyeong River is definitely straight with a sinuosity as low as 1.03. The thalweg and mean bed elevation profiles were analyzed using field measurements in 1976, 1993 and 2009. The measured profiles indicated that the channel has degraded about 2 m since 1976. The coarse gravel material and large width-depth ratio increase the stability of the bed material in this reach.

• 소성∙가공
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• 제29권2호
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• pp.103-112
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• 2020

This study explores the effects of different pre-machining conditions on the deposition characteristics and mechanical properties of austenitic stainless steel samples repaired using direct energy deposition (DED). In the DED repair process, defects such as pores and cracks can occur at the interface between the substrate and deposited material. In this study, we varied the shape of the pre-machined zone for repair in order to prevent cracks from occurring at the slope surface. After repairs by the DED process, macro-scale cracks were observed in samples that had been pre-machined with elliptic and trapezoidal grooves. In addition, it was not possible to completely prevent micro-crack generation on the sloped interfaces, even in the capsule-type grooved sample. From observation of the fracture surfaces, it was found that the cracks around the inclined interface were due to a lack of fusion between the substrate and the powder material, which led to low tensile properties. The specimen with the capsule-type groove provided the highest tensile strength and elongation (respective of 46% and 571% compared to the trapezoidal grooved specimen). However, the tensile properties were degraded compared to the non-repaired specimen (as-hot rolled material). The fracture characteristics of the repaired specimens were determined by the cracks at the sloped interfaces. These cracks grew and coalesced with each other to form macro-cracks, they then coalesced with other cracks and propagated to the substrate, causing final fracture.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2009년도 정기총회 및 동계학술연구발표회
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• pp.192-192
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• 2009

Magnetic and magnetotransport properties of (1-x) $La_{0.7}Sr_{0.3}MnO_3-xRE_2O_3$ (RE=La, Nd) (x = 0.025, 0.05, 0.075, 0.1, 0.2, 0.3) composite polycrystalline samples were systematically studied. Samples were prepared using conventional solid-state reaction. LSMO and $RE_2O_3$ react at high temperature and become chemically compatible. The ferromagnetic-paramagnetic transition temperatures ($T_c$) of the LSMO-$Nd_2O_3$ composite samples were decreased 313K~349K with increasing x, while the $T_c$ values of the LSMO-$La_2O_3$ composite samples were almost unaltered in the range of 355K~358K, representing that the ferromagnetism of LSMO might be more seriously degraded by Nd substitution on the ($La_{0.7}Sr_{0.3}$) site. However, LSMO-$RE_2O_3$ composite samples exhibit greatly enhanced low field magnetoresistance (LFMR) and dMR/dH value without an appreciable increase in its resistivity. Remarkably improved LFMR properties are attributed to LSMO grain boundaries acting as effective spin-dependent scattering centers. The relationship among the $RE_2O_3$ addition, microstructure, magnetic and magnetotransport properties will be discussed in this paper.

• 대한기계학회논문집A
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• 제32권9호
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• pp.740-753
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• 2008

The conventional Split Hopkinson Pressure Bar (C-SHPB) technique with aluminum pressure bars to achieve a closer impedance match between the pressure bars and the specimen materials such as hot temperature degraded POM (Poly Oxy Methylene) and PP (Poly Propylene) to obtain more distinguishable experimental signals is used to obtain a dynamic behavior of material deformation under a high strain rate loading condition. An experimental modification with Pulse shaper is introduced to reduce the nonequilibrium on the dynamic material response during a short test period to increase the rise time of the incident pulse for two polymeric materials. For the dynamic stress strain curve obtained from SHPB experiment under high strain rate, the Johnson-Cook model is applied as a constitutive equation, and we verify the applicability of this constitutive equation to the probabilistic reliability estimation method. The methodology to estimate the reliability using the probabilistic method such as the FORM and the SORM has been proposed, after compose the limit state function using Johnson-Cook model. It is found that the failure probability estimated by using the SORM is more reliable than those of the FORM, and the failure probability increases with the increase of applied stress. Moreover, it is noted that the parameters of Johnson-Cook model such as A and n, and applied stress affect the failure probability more than the other random variables according to the sensitivity analysis.

• Composites Research
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• 제23권1호
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• pp.44-50
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• 2010

본 연구에서는 염수 침수 실험과 염수 분무 실험이라는 두 가지의 실험을 위그선의 구조재료로 사용될 3가지 다른 복합재료 시스템에 대해서 해수와의 접촉에 의한 물성저하를재현하기 위해 수행하였다. 140일간 염수환경하에서 노화시킨 후 탄소섬유 복합재료와유리섬유 복합재료의 인장, 압축, 전단 강성과 강도 및 층간 전단 강도를 측정하였다. 기본 물성파의 비교를 통해서 염수환경이 복합재료의 기계적 물성에 미치는 영향이 평가되었다. 실험을 통해 염수 분무환경과 침수 환경의 차이는 거의 영향을 미치지 않음을 확인하였다. 탄소섬유 복합재료의 경우 인장 물성에 적은 손실이 발생한 반면 유리섬유 복합재료에서는 인장물성의 저하률이 탄소섬유 복합재료에 비해서 큼을 확인하였다. 그리고 모재 지배적 물성들의 큰 물성저하가 관찰되었다. 이를 통해, 염수는 복합재료의 섬유와 모재 사이의 계면을 퇴화시키고, 또한 모재 자체 물성과 유리섬유의 물성을 저하시킬 수 있음을 확인하였다.