• 한국해양공학회지
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• 제25권2호
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• pp.85-91
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• 2011

Many protection methods such as surface coating, electric protection, or other methods have been applied to the numerous steel structures widely used in continental and marine areas to control their corrosion, which is done from an economic point of view. Most of these steel structures are primarily protected by coating methods. However, some steel piles under seawater are protected by the electric protection method, that is, either using an impressed current or a sacrificial anode method. Furthermore, environmental contamination may cause a severely corrosive environment, which, in turn, causes the accelerated corrosion of steel structures. Subsequently, coated steel structures could deteriorate more rapidly than the designed lifetime because of the acid rain caused by air pollution, etc. Therefore, a coating of marine paint exposed to seawater, that is, underwater hardening painting, is increasingly required to be fast drying as well as highly corrosion resistant. In this study, five types of underwater hardening paints were prepared with different resin series and additives. Their corrosion and water resistances were investigated using electrochemical methods such as corrosion potential, polarization curves, impedance and cyclic voltammogram measurements, etc. Even though it is generally accepted that the corrosion resistance of bare steel tends to increase with a shift of the corrosion potential in the noble direction, the corrosion resistance of a sample with a coating exhibited a relatively better tendency when it had a lower corrosion potential in this study. The corrosion current density was also decreased with a decrease in the diffusion limiting current density, which may mean that there is some relationship between corrosion and water resistance. The S sample of the ceramic resin series showed the relatively best corrosion and water resistance among those of samples, while the worst corrosion and water resistance were observed for the R sample of the epoxy resin series. The corrosion and water resistance of those samples tended to deteriorate with an increase in the immersion days, and their corrosion and water resistances were considered to be apparently improved by the types of resin and additives.

• 조명전기설비학회논문지
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• 제17권6호
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• pp.113-118
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• 2003

비선형 부하는 고조파 발생원으로 고조파 전압원과 고조파 전류원의 두종류로 분류된다. 직렬동조필터는 개인용 컴퓨터 부하와 같이 직류 캐패시터가 있는 비선형 부하로 고조파 전압원에 매우 효과적으로 고조파를 저감시킨다. 병렬동조필터는 교류 구동장치와 같이 직류 리액터가 있는 비선형 부하로 고조파 전류원에 적합하다. 본 논문에서는 직렬 및 병렬 동조 필터의 고조파 저감 특성과 비교를 검토하고 실험하였다. 국제 고조파 관리 기준인 IEC 1000-3-2 으로 직렬 및 병렬 동조필터의 고조파 저감 효과를 평가하고자 한다.

• Asian Pacific Journal of Cancer Prevention
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• 제17권sup1호
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• pp.55-63
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• 2016

Smoking and harmful drinking dramatically increase health risks but little is known about their cooccurrence and factors that influence this co-habit, limiting development and implementation of appropriately targeted prevention interventions. This study was conducted among youth aged 10-24 years old in the Chi Linh Demographic - Epidemiological Surveillance System (CHILILAB DESS). The total numbers in the first, second and third rounds in 2006, 2009 and 2013 were 12,406, 10,211, and 7,654, respectively. A random-effects logit model controlling for both time-variant and time-invariant variables was applied to explore factors associated with current smoking, harmful drinking, and occurrence of smoking and harmful drinking together. We found dramatically increasing trends in current smoking, harmful drinking and co-occurrence among youth. Our results indicate similar health problems among youth in peri-urban areas in Vietnam. Demographic characteristics (older age, being male, being unmarried, and having informal work) appeared to be predictors for smoking and drinking behaviour. Besides, peer and family members had significant influence on smoking, whereas having a close-friend who was smoking was the most important variable. The results suggested that smoking and harmful drinking should not be solved with separate, stand-alone interventions but rather with integrated efforts.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2009년도 춘계학술대회 논문집
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• pp.97-100
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• 2009

배전계통에서 전력수요의 증가와 분산전원의 증가로 대용량 변압기의 적용이 불가피하게 되었다. 하지만, 대용량 변압기로 교체할 경우 배전계통에 고장발생시 고장전류의 크기가 증가되어 기존에 설치된 차단기 및 보호기기의 차단용량 초과로 인해 교체에 따른 경제적 비용 상승이 우려된다. 따라서, 대용량 변압기의 교체시 고장전류 증가 문제를 해결하기 위한 방안 중 하나로 초전도한류기를 설치하는 방안을 검토하고 있다. 초전도 한류기는 평상시에 초전도 상태인 영 저항이므로 전력손실이 발생하지 않으며, 고장 발생시 치로 인한 신속한 저항 발생으로 고장전류를 빠르게 감지 및 제한함으로써 기존에 설치된 차단기의 차단 용량이하로 감소시켜 줄뿐만 아니라 계통의 안정도를 향상시킬 수 있다. 그러나, 초전도한류기는 도입위치에 따라 ��치 발생시 초전도한류기의 저항 크기가 다르게 되며, 고장전류 제한효과 및 보호협조를 고려한 적정의 한류기 저항 설정이 필요하다. 이에 대한 선행연구로서, 본 논문에서는 모의 배전계통에 초전도한류기를 적용하였을 경우 도입위치에 따라 전류제한, 모선 전압강하, 초전도한류기의 전력부담을 실험을 통하여 비교 분석하였다. 분석을 통해 초전도한류기를 피더에 설치하였을 경우 전류제한 효과, 모선 전압강하 보상효과는 가장 우수하였으나 가장 많은 전력부담을 갖는 것을 확인할 수 있었다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.2004-2005
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• 2007

고온 초전도체를 이용한 자속구속형 사고전류제한기는 1차권선과 2차권선을 감는 방향이나 감은 횟수의 비율에 따라서 부하전류용량과 전류제한용량이 다르다. 부하전류용량은 사고 발생 시 최초의 전류 제한 레벨과 밀접하게 관련이 되는데 자속구속형 사고전류제한기에서 최초의 전류 제한 레벨은 인덕턴스에 의해서 결정되기 때문이다. 전류제한용량은 사고전류제한기의 임피던스와 관계된다. 이 논문에서 자속구속형 사고전류제한기의 변압기 특성을 변화시키면서 부하전류용량과 전류제한용량의 변화를 살펴보았다.

• 한국초전도ㆍ저온공학회논문지
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• 제9권4호
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• pp.37-40
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• 2007

As power demands increase, development of the superconducting fault current limiter (SFCL) is being watched with interest. Many types of SFCLs using various superconducting materials have been developed. Especially, the FCL using coated conductor (CC) has been investigated actively at present. CCs have many advantages for the FCL application. YBCO materials used in CCs have a high n-value, and it is relatively easy to choose a matrix of the CC for high resistivity. If the CC has high resistivity, high voltage can be applied to the CC. Then total length of the CC used in SFCL, which has effects on total price and volume of the SFCL, can be reduced. Short circuit tests of two different types of CCs in the liquid nitrogen bath and its sub-cooled condition were performed and analyzed. An effect of high resistivity of the CC and cooling methods on fault current limiting characteristics could be verified in this paper.

• 소성∙가공
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• 제18권7호
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• pp.538-543
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• 2009

The cowl cross bar of an automobile is a frame component that is installed inside the cockpit module to provide a guide surface, to which functional components for electricity and air condition are attached. In the recent years, the geometries of cowl cross bars are getting more complex in order to meet the demands of a wide variety of embedded functional components and the reduced weight of frame parts with enhanced mechanical and noise/vibration characteristics. There for, welding processes between tubes with different diameters are widely conducted while the welded parts are experiencing various problems such as undermined appearance, low production efficiency and poor mechanical characteristics. Therefore, this paper seeks to develop an one-piece forming process which eliminate welding process for the cowl cross bar by applying the tube drawing process. However, it was predicted that a conventional tube drawing can not be applied directly to the current part since the area reduction ratio of the drawing process reaches 51.7% which exceeds the general limiting value. Therefore, in this study, a combined drawing process which adds a compressive force to a tensile force of the conventional drawing process was proposed and 2-stage drawing process was designed by using CAE analyses. In addition, drawing tryouts were carried out by using the manufactured combined drawing machine in order to verify the designed process.

• 한국산학기술학회논문지
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• 제20권6호
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• pp.14-18
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• 2019

반도체의 전도성은 주로 케리어에 의해서 결정된다. 전도성이 높아지려면 케리어의 수가 많고 에너지 내의 트랩 준위를 만들어서 케리어들이 낮은 에너지로도 금지대역을 넘어설수 있도록 하는 도핑기법을 주로 사용한다. 케리어들은 결정질 결합구조를 갖으며, 계면불일치에 의하여 전도성이 떨어지는 경향도 있지만 대체적으로 고농도 도핑은 이동도를 높이는 대표적인 방법에 속한다. 하지만 비정질 결합구조에서도 전도성이 높아지는 현상이 나타나며, 본 연구에서는 트래핑현상과는 다른 터널링 현상에 의한 공간전하제한 전류가 흐르면서 전도성이 향상되고 이동도가 높아지는 현상에 대하여 관찰하였다. 비정질구조에서는 케리어수가 낮고 저항이 높아지며, 커패시턴스의 on/off 특성이 향상되면서 이동도가 높아지는 것을 확인하였다. ZTO 박막은 150도에서 열처리한 경우 커패시턴스의 on/off 특성이 향상되었으며, 충전과 방전하는 실험에서는, 충전과 방전되는 형상에 있어서 시간차이가 있었으며, n형과 p형의 구분이 없었으며, 공핍층과 같은 비정질 결합구조를 보여주었다. 비정질 결합구조는 전위장벽으로 볼 수 있으며, 전위장벽은 공간전하제한전류가 흐르게 되는 원천이기도 하며, 터널링현상에 의한 전도현상이 나타나는 원인이 된다. 따라서 비정질구조에서 이동도가 증가하는 현상이 나타났으며, 케리어가 희박함에도 불구하고 전도성이 증가하는 것을 확인하였다.

• 전력전자학회논문지
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• 제24권6호
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• pp.411-418
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• 2019

Light-triggered thyristors (LTTs) are essential components in high-power applications, such as HVDC transmission and several pulsed-power applications. Generally, LTT fabrication includes a deep diffusion of aluminum as a p-type dopant to form a uniform p-base region, which needs careful concern for contamination and additional facilities in silicon semiconductor manufacturing factories. We fabricated 4-inch 5,000 V LTTs with boron implantation and diffusion process as a p-type dopant. The LTT contains a main cathode region, edge termination designed with a variation of lateral doping, breakover diode, integrated resistor, photosensitive area, and dV/dt protection region. The doping concentration of each region was adjusted with different doses of boron ion implantation. The fabricated LTTs showed good light triggering characteristics for a light pulse of 905 nm and a blocking voltage (V_DRM) of 6,500 V. They drove an average on-state current (I_TAVM) of 2,270 A, peak nonrepetitive surge current (I_TSM) of 61 kA, critical rate of rise of on-state current (di/dt) of 1,010 A/㎲, and limiting load integral (I²T) of 17 MA²s without damage to the device.

• 한국생활과학회지
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• 제16권2호
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• pp.315-331
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• 2007

The purpose of this study is to examine current situations about and factors related to expenditures of private education among pre-school children and to provide policy implications useful for future pre-school children education. The subjects of the study were parents of pre-school children under seven years of age, who lived in Seoul and Incheon area. The survey was conducted using parent questionnaire. The major findings of the study are: First, 86.8% of parents of pre-school children use private education and the average expenditure on it was 154, 446 won. Second, major factors determining their private education expenditure are educational level of parents, parents' job characteristics, household income, and region. Third, the most important reason for using private education among parents is to improve and excel in academic performance of their children. Forth, the higher the parents' expected returns from private education are, the higher the expenditure level of private education is. Fitth, the results of the logistic regressions showed that parents' attitudes toward private education was the most important factor in determining household economic burden associated with private education. The odds were 5 times greater for the parent group with strong desire for private education than for the parent group without it and 1.2 times greater for the parent group with high-expected returns from private education than the parent group without it. In conclusion, systematic, universal educational policies need to be developed to provide and support all the parents with pre-school children, given that their current economic burden is substantial. By providing such support, we can help parents focus on public education. This study examining current situations about and determining factors related to private education expenditures among pre-school children collected data limiting only Seoul and Inchoen area, therefore, future studies need to include data collected nationwide for generalizability of the findings. As well, development of more elaborated survey instruments and analytical methods would advance our understanding in the field.