• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.5
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• pp.329-337
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• 2016

As a turbulence-enhancing device, a mixing vane, which is installed at a spacer grid of the fuel assembly, plays an important role in improving convective heat transfer by generating either swirl flow in the subchannels or cross flow between the fuel rod gaps. Therefore, both the geometric configuration and the arrangement pattern of a mixing vane are important factors in determining the performance of a mixing vane. In this study, in order to examine the flow-distribution features inside a $5{\times}5$ fuel assembly with split-type mixing vanes, which was used in the benchmark calculation of the OECD/NEA, we conduct simulations using the commercial computational fluid dynamics software, ANSYS CFX R.14. We compare the predicted results with measured data obtained from the MATiS-H (Measurement and Analysis of Turbulent Mixing in Subchannels-Horizontal) test facility. In addition, we discuss the effect of the split-type mixing vanes on the flow pattern inside the fuel assembly.

• Applied Chemistry for Engineering
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• v.3 no.1
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• pp.138-147
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• 1992

Chemically-modified electrodes were fabricated and their electrocatalytic behaviors have been investigated. As a modifying layer, poly-[1-methyl-3-(pyrrol-1-ylmethyl) pyridinium] was electropolymerized onto Pt electrodes under constant current. The thickness of the polymer film was controlled by means of total charge consumed during the electropolymerization. SEM was used to measure the thickness. There was a linear relationship between the passed charge and the film thickness. Ferro/ferricyanide, used as an electron mediator in this study, was rapidly ion-exchanged into the polymer layer with its concentration of 1.2~1.3M. It was found that electrooxidation of ascorbic acid is catalyzed by incorporated ferri/ferrocyanide couple. Kinetic parameters for electrooxidation were determined by RDE experiments. The results indicate that the present system corresponds to ER+S case based on the Saveant theory. Improving methods have been proposed to be R+S case which is ideal for electrocatalysis.

• Journal of the Korean Institute of Intelligent Systems
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• v.21 no.2
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• pp.260-267
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• 2011

This paper proposes a method for segmenting objects from the background in IR(Infrared) images based on GrabCut algorithm. The GrabCut algorithm needs the window encompassing the interesting known object. This procedure is processed by user. However, to apply it for object recognition problems in image sequences. the location of window should be determined automatically. For this, we adopted the Otsu' algorithm for segmenting the interesting but unknown objects in an image coarsely. After applying the Otsu' algorithm, the window is located automatically by blob analysis. The GrabCut algorithm needs the probability distributions of both the candidate object region and the background region surrounding closely the object for estimating the Gaussian mixture models(GMMs) of the object and the background. The probability distribution of the background is computed from the background window, which has the same number of pixels within the candidate object region. Experiments for various IR images show that the proposed method is proper to segment out the interesting object in IR image sequences. To evaluate performance of proposed segmentation method, we compare other segmentation methods.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.8
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• pp.743-749
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• 2015

In this paper, we describe the dynamic tumble-stability analysis of a seabed-walking robot named Crabster (CR200) in forward-incident currents. CR200 is designed to be operated in tidal-current conditions, and its body shape is also designed to minimize hydrodynamic resistances considering hydrodynamics. To analyze its tumble stability, we adopt the dynamic stability margin of a ground-legged robot and modify the definition of the margin to consider tidal-current effects. To analyze its dynamic tumble stability, we use the estimated hydrodynamic forces that act on the robot in various tidal-current conditions, and analyze the dynamic tumble-stability margin of the robot using the estimated results obtained for the various tidal-current conditions. From the analyses, we confirm the improved tumble stability of the robot according to the movement of the tumble axis caused by the supporting points of the legs.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.120-120
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• 2018

반도체 소자나 디스플레이 패널 제조 공정에 가장 많이 사용되는 진공 펌프인 터보 분자 펌프는 오일을 사용하지 않고, 설치 방향이 자유로우며 넓은 작동 압력 영역을 가지고 있어서 고가임에도 불구하고 점점 더 사용 영역을 넓혀 가고 있다. 상하의 두 곳에 회전축을 지지하는 베어링이 필요한데, 기계식 금속 베어링을 채용하는 경우에는 반드시 윤활유를 공급해 주어야 하고, 고온, 부식성 또는 산화성 가스의 배기 시에는 퍼지 가스로 비활성인 질소나 알곤등을 이용하여 보호를 해주어야 한다. 반면, 자기 베어링을 채택한 모델은 윤활의 걱정에서 자유로울 수 있기 때문에 채용이 늘어나고 있다. 동일극의 반발력이나 반대극의 인상력을 이용한 구조를 갖게 되는데 갑작스러운 입구 쪽 압력의 증가 시에는 자석 끼리 부딪치는 일이 발생하고 이로 인해서 로터 모듈 전체에 큰 손상을 갖게 되므로 한 곳 정도에 비상용 터치 다운 베어링을 기계식으로 윤활제 없이 설치하기도 한다. 기본적으로 자기 베어링 방식은 로터 모듈의 부상과 제어를 위해서 3축 또는 5축 제어를 하게 되는데 여기에는 전자석의 전류를 미세하게 조정하여 피드백 하는 시스템을 활용하기 때문에 외부에서의 자기장이 일정값 이상 침투하게 되면 제어 회로의 기능에 문제를 일으키게 된다. 또한 축 방향에 수직인 자기장의 강도가 높아지면 고속으로 회전하는 금속 블레이드가 자속을 자르게 되므로 표면에 와전류가 발생하여 문제가 된다. 터보 분자 펌프는 회전자와 고정자 간격이 1 mm 이내로 작아서 약간의 진동이라도 발생하면 회전자와 고정자 간에 충돌이 일어나고 이는 곧 파손으로 이어진다. 그림 1에는 파손 원인 분석을 위한 회전자 모듈의 수치 해석용 모델의 일부를 나타내었고, 그림 2에는 실제로 외부 자기장에 의한 파손이 발생한 사례의 자기 베어링 모듈의 사진을 나타내었다. 본 발표에서는 외부 자기장의 형태에 따라 제어 자기장에 미치는 영향을 CFD-ACE+(ESI corp)를 활용하여 해석하였다.

• Journal of the Korean Society for Railway
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• v.12 no.5
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• pp.732-737
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• 2009

Wind tunnel testing on the real-scale pantograph for high-speed train has been conducted to investigate the aerodynamic characteristic of the pantograph at high-speed. The mid-scale subsonic wind tunnel of Korea Airforce Acamedy with 3.5m width, 2.45m height, and 8.8m length test section has been employed. The test model has been supported above 50cm height from the bottom of test section using vertical strut to eliminate the boundary layer generated from the bottom of the test section. The height of the pantograph has been varied in three cases, in both of the normal running and reverse running modes. The resultant lift forces of the pantograph to catenary system in all the cases have been measured and the relation between the test conditions and the lift forces have been extensively analyzed.

• Journal of KIISE:Databases
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• v.29 no.1
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• pp.1-14
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• 2002

Association rule discovery is a method of mining for the associated item set on large databases based on support and confidence threshold. The discovered association rules can be applied to the marketing pattern analysis in E-commerce, large shopping mall and so on. The association rule discovery makes multiple scan over the database storing large transaction data, thus, the algorithm requiring very high overhead might not be useful in real-time association rule discovery in dynamic environment. Therefore this paper proposes an active candidate set management model based on trigger and incremental update mechanism to overcome non-realtime limitation of association rule discovery. In order to implement the proposed model, we not only describe an implementation model for incremental updating operation, but also evaluate the performance characteristics of this model through the experiment.

• Proceedings of the Korea Society of Poultry Science Conference
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• 2003.11a
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• pp.101-102
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• 2003

This experiment was conducted to investigate the effect of restricted feeding to pullet on growth pattern and body composition. Conventional diets(C) was formulated by NRC recommendation, and one of restricted diet started from seven to seventeen week of age(T1), and another started from twelve to seventeen(T2) with adjusted eighty percentage amount of conventional diet. Body weight decreased with starting restriction of feeding comparing to the C(P＜0.05), but reached to similar weight in all treatments at twenty week regardless restriction. All of birds started to lay egg around 1,400 to 1,450gram of body weight though the age was in order of C, T2 and T1. Fat contents of restricted group in the body were less than that of C around one thousand gram of body weight. And the tendency of body fat was similar to the first egg. After twenty week, all content of body composition were similar in all treatments. The proportion of intestinal organ weight was higher in T1 than others during restriction.

• Journal of Preventive Medicine and Public Health
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• v.34 no.4
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• pp.437-443
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• 2001

Objectives : This study was peformed to assess the association between the social support and blood pressure(BP) in a rural community. Methods : A cross-sectional survey, comprising a health examination including BP, height and weight and a questionnaire-based interview which investigated social support, demographic factors, smoking, drinking, and etc. was peformed between February 10th and March 5th, 1998. The survey included 318 persons who were over than 30-year-old in the rural community of Kwangju, Republic of Korea. We excluded persons who taking antihypertensive medications or who provided incomplete information; we subsequently analyzed the data from 284 persons. In order to test the hypothesis of an association between BP and social support controlling confounders such as age, educational level, working time, body mass index, smoking and drinking, the data was analyzed using multiple linear regression analysis. Results : The subjects were composed of 109(38.4%) males and 175(61.6%) females with mean ages of 62.0 years and 61.1 years, respectively. The hypertension prevalence was 41.3% among males and 45.1% among females. In the correlation analysis, higher total social support scores correlated significantly with lower systolic BP in both males and females. The hypertension prevalence increased significantly with the decreasing of the social support in males. In multiple regression analysis, systolic and diastolic blood pressure showed a negative association with social support in both males and females, although this was not statistically significant. Conclusions : Larger and broader studies are required in the future in order to identify the association between the social support and BP.

• Korean Journal of Social Welfare Studies
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• no.39
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• pp.29-56
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• 2008

The purpose of this study was to find out correlation and predictors of posttraumatic growth of North Korean refugees in South Korea in 7years. This survey was conducted on 105 North Korean refugees in 7 years with questions on depression, anxiety, socio-demographic characteristics, personal & social variables, psychological trauma in North Korea, stress experience in South Korea. The influence of these variables was analysed. Result indicated that education in North Korea and living period in the 3rd country iwas associated with PTG. Date for escaping from North Korea, depression, acculturative stress in South Korea, hope for future, social support from South Korean, perceived satisfaction had correlation with PTG. And Date for escaping from North Korea, living period in the 3rd country, social support from South Korean, acculturative stress in South Korea predicted PTG of North Korean refugees. Finally, social political intervention and mental health service programs for North Korean refugees were discussed.