• 한국해양공학회지
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• 제4권1호
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• pp.110-119
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• 1990

This study is concerned about the stress concentration factor measurement by photoelastic method, for the case of two circular holes arrangement in 3mm semi-infinite plate under tensile load, the ratio of those two circular holes diameter, the ratio of distance apart from circular holes to breadth and the two holes arrangement angle with loading direction were varied. Besides, the measured stress concentration by photoelastic method around one circular hole was compared with that by strain-gage method.

• Journal of Biosystems Engineering
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• 제1권1호
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• pp.64-72
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• 1976

This experimental work was carried out to investigate the fatigue bending strength on various shapes and sizes of notches of the domestically manufactured steel plate. The notch types tested were a circular hole, U-and V-notches. The S-N diagram for different notch shapes were discussed in relation to plan bending strength and stress concentration factor of notches .The results of the experiments are summarized as follows : (1) The difference between stress concentration factor and notch factor was greater as the radium of notch root became smaller, and these values approached to an identical value as the radium of notch root increased. (2) It was shown that the plane bending fatigue limit of bar without notch for the hotrolled steel having the tensile strength of 33.1kg/$mm^2$was 17.0kg/$mm^2$. (3) U-and V-notch had a greater effect of stress concentration factor on the endurance limit, but O-hole showed the same effect only for $\o\pm2mm$. (4) For the same radius of notch root, U-notch showed a lower value of fatigue limit compared to V-notch and O-hole.

• Biomolecules & Therapeutics
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• 제26권4호
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• pp.380-388
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• 2018

Neural stem cells (NSCs) have the ability to self-renew and differentiate into multiple nervous system cell types. During embryonic development, the concentrations of soluble biological molecules have a critical role in controlling cell proliferation, migration, differentiation and apoptosis. In an effort to find optimal culture conditions for the generation of desired cell types in vitro, we used a microfluidic chip-generated growth factor gradient system. In the current study, NSCs in the microfluidic device remained healthy during the entire period of cell culture, and proliferated and differentiated in response to the concentration gradient of growth factors (epithermal growth factor and basic fibroblast growth factor). We also showed that overexpression of ASCL1 in NSCs increased neuronal differentiation depending on the concentration gradient of growth factors generated in the microfluidic gradient chip. The microfluidic system allowed us to study concentration-dependent effects of growth factors within a single device, while a traditional system requires multiple independent cultures using fixed growth factor concentrations. Our study suggests that the microfluidic gradient-generating chip is a powerful tool for determining the optimal culture conditions.

• ALGAE
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• 제17권2호
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• pp.105-115
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• 2002

Influences of vrious environmental factors on the eutrophication of Nakdong River were analyzed statistically using water samples collected from 1 January, 1999, to 30 September, 2001 at Namji area. The relationships between the concentration of chlorophyll α (eutrophication index) and environmental factors and were analyzed to develop a statistical model which can predict the status of eutrophication. The concentation of chlorophyll α ranged from 66.2 mg · $m^{-3}$ to 70.8 mg · $m^{-3}$ during dry winter season and the average concentration during this study period was 35.5 mg · $m^{-3}$ Namji area of Nakdong River was in the hypereutrohic stage in terms of water quality. Stephanodiscus sp. and Aulacoseria granulata var. angustissima were dominant species during the witnter to spring time and summer to autumn period, respectively. Based on the correlation analysis and the analysis of variance between chlorophyll α concentration and environmental factors, significantly high positive relationships were found in the order of BOD> pH> COD > KMnO₄ consumption > DO > conductivity > alkalinity. In contrast to these factors, significantly negrative relationships were found as in the order of $PO₄^{3-}-P$ >water level>the rate of Namgang-dam discharge > NH₃-N> the rate of Andong-dam discharge> the rate of Hapchoen-dam discharge. Based on the factors analysis of environmental factors on the concentration of chlorophyll α, we obtained five factors as follows. The first factor included water level, pH, turbiditiy, conductivity, alkalinity and the rate of Namgang-dam discharge. The second factor included water temperature DO, NH₄+-N, NO₃- -N. The third factor included KMnO₄ consumption COD and BOD. The fourth factor included the rate of Andong-dam discharge, the rate of Hapcheon-dam discharge, and the rate of Imha-dam discharge. The final factor included T-N T-P and $PO₄^{3-}-P$ > concentration. We derived two statistica models that can predict the occurrence of eutrophication based on the factors by factor analysis, using regression analysis. The first model is the stepwise regression model whose independent variables are the factors produced by factor analysis : chl α (mg · $m^{-3}$ = 42.923+(18.637 factor 3) + (-17.147 factor 1) + (-12.095 factor 5) + (-4.828 factor 4). The second model is the alternative stepwise regression model whose independent variables are the sums of the standardized main component variables:chl α (mg · $m^{-3}$ = 37.295+(7.326 Zfactor 3) + (-2.704 Zfactor 1)+(-2.341 Zfactor 5).

• 한국기후변화학회지
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• 제8권3호
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• pp.231-237
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• 2017

In this study, the $N_2O$ emission factor of the facility was developed by measuring the kiln type pyrolysis melting facility. This used PAS (Photoacoustic Spectroscopy) method and measured the $N_2O$ emission concentration. From March 2016 to April 2016, it was measured over a total of two times and $N_2O$ concentrations were measured continuously for 24 hours using a 24 hour continuous measuring instrument (LSE-4405). The measured $N_2O$ emission concentration of the pyrolysis melting facility was 0.263 ppm on average and the emission concentration distribution in the range of 0.013~0.733 ppm was obtained. Therefore, the $N_2O$ emission factor of the kiln-type pyrolysis melting facility was estimated to be $0.829gN_2O/ton$-Waste. As a result of comparing the $N_2O$ emission factor of the thermal kiln type pyrolysis melting facility and the previous study, previous studies were about 18 times higher. It is estimated that this is due to the difference of furnace temperature, oxygen concentration and denitrification facilities. It is considered that the study of the emission factor of pyrolysis melting facility is an important factor in improving the credibility of greenhouse gas inventory in waste incineration sector.

• 한국항공운항학회지
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• 제28권3호
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• pp.41-51
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• 2020

This research is accomplished to verify objectively how flight instructor's transformative leadership affects student pilot's psychological stabilities and learning satisfactions. Flight instructor's transformative leadership factor divided into individual consideration, intellectual stimulus and charisma from exploring factor analysis. Psychological stability factor subdivided into happiness, concentration and satisfaction. Learning satisfaction factor subdivided into participation, recommendation, persistence, accomplishment and relationship. According to the analysis of flight instructor's transformative leadership effect on psychological stability, it showed that it has statistical significance on happiness, concentration and satisfaction. It also has positive influence on happiness and concentration. The result from regression analysis showed that individual consideration and charisma affected happiness and concentration in order. However, satisfaction from individual consideration, intellectual stimulus and charisma didn't show statistical significance to student pilot's satisfaction. Analysis of flight instructor's transformative leadership on student pilot's learning satisfaction showed statistical significance between them. Intellectual stimulus and charisma had positive influence on student pilot's learning satisfaction. Regression analysis showed charisma and intellectual affect student pilot's learning satisfaction in order.

• 한국토양비료학회지
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• 제47권6호
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• pp.518-524
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• 2014

Heavy metal pollution in agricultural field near at the abandoned metal mines has been a critical issue in Korea. In particular, bioaccumulation in plants can have detrimental effect on human health. Main objective of this research was to examine arsenic (As) concentration in soil with varied extraction methods and to determine bioaccumulation and biological transfer factor in different crops. Results showed that bioaccumulation ratio of As for total contents in soil was ordered leafy and stem vegetables (1.19%) > fruit bearing vegetables (0.79%) > pulses (0.40%) > root vegetables (0.36%) with different crop species. Among 6 different extraction methods, all of extraction methods showed high correlation ($R^2=0.87-0.97$) except DTPA ($R^2=0.25$) when comparing As concentration in soil extracted with different extractants and As concentration in each crops. Calculated biological transfer factor was ranged 0.002-0.018 depending on crop species. Overall, concentration of As in crops can be varied and best management practice for minimizing bioaccumulation of As should be considered depending on crop species.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.381-388
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• 2003

The material deficiencies in the form of pre-existing defects can initiated cracks and fractures. The stress distribution and fatigue crack initiation life of engineering materials may be associated with the size, the shape and the relative location of defects contained in the component. The objective of this study is to investigate the effect of arbitrarily located hole defect around the rivet hole of a wing section in monolithic aluminum and Al/GFRP laminates under cyclic bending moment during a service load. The stress distribution and the fatigue crack initiation behavior near a rivet hole of on the relationships between stress concentration factor ($K_t$) and relative position of defects were considered. The test results indicated the features of different stress field. Therefore, the stress concentration factor ($K_t$) and the fatigue crack initiation behavior was illustrated different behavior according to each position of hole defect around the rivet hole in monolithic aluminum and Al/GFRP laminates.

• 대한조선학회논문집
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• 제33권3호
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• pp.1-7
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• 1996

용접이음부재에서 피로강도에 큰 영향을 미치는 용접부의 응력집중계수를 추정하였다. 여기서는 하중전달형 십자필렛용접이음부를 그 대상으로 하였다. 필렛용접이음부에서 토우파괴를 일으키는 피로균열발생부인 용접토우부의 응력집중계수를 구하기 위해 인장하중하에서 토우부의 적정 요소 크기를 검토하고 여러 파라메타들의 값을 변화시켜 유한요소 응력해석을 수행하였다. 즉 용접토우부의 형상인 토우각 및 곡률반경의 영향과 용입부족부 길이의 변화를 동시에 고려한 응력집중계수를 정량적으로 구하였다. 그리고 그 결과를 이용하여 응력집중계수 추정식을 유도하였다.

• 한국지반공학회논문집
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• 제18권5호
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• pp.133-141
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• 2002

암반파괴의 가장 큰 영향을 미치는 인장강도는 등방의 암석과 횡등방의 암석의 경우는 분명히 다를 것이다. 본 논문에서는 일축압축강도시험에서 횡등방 암석의 탄성정수를 구하고, 간접인장강도시험을 통하여 횡등방 암석의 인장강도와 인장파괴 거동을 분석하였다. 일축압축시험에서 구한 이방성 탄성정수와 간접인장강도시험에서 얻어진 변형률로 시료중앙의 응력집중계수를 구하여, 등방으로 가정하여 구한 인장강도 값과 이방성일때의 인장강도 값을 비교 분석하였다. 실험 결과 횡등방성 암석의 응력집중계수는 층리면의 각도에 따라서 등방재료의 응력집중계수와는 크거나 작은 값을 나타내었다. 횡등방 암석의 인장강도 산정시 등방의 응력집중계수를 사용하는 것은 층리면이 이루는 각도에 따라 인장강도의 과대 혹은 과소 평가됨을 알 수 있었다.