• Proceedings of the KIPE Conference
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• 2020.08a
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• pp.233-235
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• 2020

본 논문은 40 kV 나노초 펄스발생을 위한 모듈형 solid-state Marx modulator(SSMM) 설계에 대해 기술한다. 가속기 및 플라즈마 어플리케이션과 같은 다양한 응용분야에 요구되는 전압 및 전류 사양을 만족시키기 위해 10 kV(출력 전압), 50 ns(펄스폭), 20 ns(상승&하강 시간), 100 kHz(반복률)의 사양을 만족하는 단위모듈기반으로 모듈형 설계를 제안한다. 독립적인 제어가 가능한 4개의 단위모듈을 기반으로 제안된 SSMM은 임의의 출력 파워 및 임피던스를 만족시킬 수 있는 장점을 가지고 있다. 예를 들어, 모든 단위모듈의 위상을 같게 했을 때 출력전압을 증가시킬 수 있으며 각 모듈의 위상을 지연하였을 경우는 펄스의 반복률을 크게 높일 수 있다. 개발된 SSMM은 직렬 스택 MOSFET의 스위칭 성능을 향상시키기 위해 게이트 구동 회로는 동기 신호와 구동 전력을 제공하는 1 턴 변압기로 설계되었다. 출력 펄스의 폭과 하강시간을 최소화하기 위해 다이오드 대신 기생 커패시턴스에 저장된 에너지를 빠르게 방출하는 액티브 풀다운 회로가 적용되었다. 또한, 출력 펄스의 빠른 상승을 달성하기 위해 게이트의 라인 인덕턴스를 최소화하고 모든 게이트 신호의 동기화는 필수적이다. 개발된 ns급 펄스전원장치는 단위모듈을 기반으로 최대 펄스전압이 40 kV 까지 출력이 가능하며 이에 대한 상세설계 및 구현은 실험결과를 바탕으로 검증한다.

• Journal of Labour Economics
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• v.25 no.2
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• pp.1-32
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• 2002

This paper investigates how real wages adjust to regional and cyclical shocks in the Korean labor market. Major findings are as follows. First, like most longitudinal studies in this literature, we find that real wages are strongly procyclical and more procyclical for men than for women. Second, consistent with the theory prediction of efficiency wages, both permanent and transitory components of real wages are negatively correlated with the local unemployment rate. Third, when overall and local unemployment rates compete in a wage equation (our preferred specification), current wages are dominantly affected by the overall rate, and the effect of the local rate is rather small. This rejects the Blanchflower and Oswald's hypothesis that wages are primarily determined by local labor market conditions. Finally, no lagged effects on wages are detected in the overall or local unemployment rate.

• Journal of The Korean Association For Science Education
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• v.41 no.5
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• pp.401-414
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• 2021

The purpose of this study is to explore the cognitive achievement characteristics by group of achievement levels in the PISA 2018 science domain compared to the results of the PISA 2015, and to compare and analyze the 'epistemic' knowledge in the revised curriculum 2009 and in the revised curriculum 2007. The average correctness rates in PISA 2015 and PISA 2018 were analyzed by sub category of the evaluation frame in the PISA scientific domain. In the competencies domain, especially, the average correct answer rates of 'evaluating and designing scientific inquiry' were the lowest in medium and lower groups, but the rates rose in all achievement groups compared to PISA 2015, which is encouraging. Although the answer rates were low for both 'living system' knowledge and 'epistemic' knowledge in the knowledge domain, the average answer rates of the upper and middle groups increased in 'epistemic' knowledge compared to PISA 2015. The changes in the curriculum experienced by students participating in PISA were analyzed in relation to the 'evaluating and designing scientific inquiry' competency and 'epistemic' knowledge, which increased in average correct answer rates. In terms of understanding science, the "What is science?" unit that explicitly presents epistemic knowledge, and nature of model in inquiry activities, were explicitly presented in the revised curriculum 2009. In terms of understanding the process of justifying scientific knowledge, the number of inquiry activities increased, scientific explanations based on experimental results strengthened, and the "Science and Human Civilization" unit was introduced to help students to understand STS while simultaneously conducting arguments. These findings confirm the educational performance of groups by achievement level in the PISA 2018 scientific domain and suggest that the direction of education relates to epistemic knowledge in Korea's Science curriculum.

• Economic and Environmental Geology
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• v.43 no.5
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• pp.523-528
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• 2010

With the financial crisis from USA had negative impacts on the real economy, base metals price on LME was downward in 4 quarter of 2008. Following the deepest global downturn in recent history, economic growth solidified and broadened to advanced countries and simultaneously the price of base metal on LME showed a rising curve over 2009. There are three factors supported an upward tendency of base metal's price. The First factor is the US economy recovery, the second factor is the weak dollar, the third factor is the chinese base metal demand. Among the factors, the last one is a major factor. Therefore, this study analyze the factor of the movement of price of base metal with linear regression analysis. The result of analysis show that the chinese GDP growth has effect on the recent upward base metal price. Despite the result, the upward movement is difficult to be sustained without the full recovery of advanced economies.

• Journal of the Korean Data and Information Science Society
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• v.25 no.6
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• pp.1361-1369
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• 2014

This research is for analyzing the change rate of housing rent price index produced by KAB (Korea Appraisal Board) in the monthly periodical, Survey on Housing Monthly Rent. The index is a very important and useful indicator to understand and diagnose the house rental market. However, the index is criticized in that it tends to decline when the price level of Jeonse (i.e., a typical type of dwellings in Korea, generally leased on a deposit basis for 1 or 2 years) is highly going up, which is inconsistent with the actual economic sentiment of tenants. We verify the reason why such phenomenon occurs and suggest a simple but novel method to analyze properly the change rate of the index. The main findings are as follows. The key factor to trigger the problem is the use of the conversion rate for Jeonse-to-monthly rent for constructing the rent price indexes. We separate the effect of the conversion rate out of the change rate of the index and quantify the adjusted real change rate showing an increase of the rent price level which is masked by the conversion rate before.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.9
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• pp.4342-4348
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• 2013

The present study was intended to reveal the relationships between serum lipid levels and various factors of obesity and blood pressure. The study subjects were 1,838 adult women measured at a mass health screening during the period from January through December, 2011. TC, TG, HDL-C, LDL-C, SBP, DBP, degree of obesity, body fat rate were measured and the relation between these obesity and blood pressure measurements to serum lipid levels were studied. As a results, TC, TG, LDL-C, body fat rate and degree of obesity increased linearly with advancing age. TC, TG and LDL-C increased linearly with increasing blood pressure, and these values were higher in hypertension group than that of normal group. TC, TG and SBP increased linearly with increasing degree of obesity, and these values were higher in obesity group than that of normal group. HDL-C decreased linearly with increasing degree of obesity, and these values were lower in obesity group than that of normal group. TC, TG, HDL-C, degree of obesity, body fat rate was positive correlation with each others, but these values negatively correlated to HDL-C. Principal component analysis, showed that subjects could be divided into the group having the hypertensive group(1st principal component), the obesity group(2nd principal component), the hyperlipidemia group(3rd principal component), and HDL-C(4th principal component). In multiple regression analysis, age, TC, TG and body fat rate were affected to HDL-C. Above results suggest that higher the degree of obesity and blood pressure, the higher the serum lipid levels.

• Proceedings of the Korea Contents Association Conference
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• 2007.11a
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• pp.310-314
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• 2007

In these days we can often see examples of suicide. Nowaday suicide becomes a serious social problem in Korean Society. Suicide rate is rapidly increasing. The number of suicides increase continuously from 3,157 in 1990 to 10,688 in 2006. And the annual suicide rate rapidly went up in 1996 and hit the highest in 2005. Furthermore the level of ssuicide which is of ten leading causes of death is rising steadily. In 2006, suicide rate becomes the 2nd level among all ccountries in OECD.

• Proceedings of the Korean Institute Of Construction Engineering and Management
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• 2006.11a
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• pp.435-439
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• 2006

The purposes of study is to propose a new method contract price adjustment in construction projects. The research method of this study includes a case analysis and questionnaire survey. The results of this study are as follows: 1) For improvement method of contract amount adjustment, enactment for legislation pertaining to computation methods such as military's organization through total unit cost, and price flexibility computation at the point of design modification were presented. 2) Arithmetic formulas for cases in which volume is deleted or modified below the price flexibility exemption amount or in which there is no change to quantity, at the occurrence of design modification resulting from price flexibility, were proposed.

• Journal of the Korean Wood Science and Technology
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• v.37 no.4
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• pp.293-299
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• 2009

In manufacturing the crack-free carbonized boards using fiberboards, shrinking ratio, weight loss and density variation of carbonized boards at each carbonization temperature were investigated. Fiberboards with thickness of 3, 4.5, 6, and 18 mm were carbonized while pressed with pressure plates at different temperature from $400^{\circ}C$ to $1,000^{\circ}C$ using a ordinary laboratory furnace. Either of crack or twist was not observed in fiberboards by adapting the pressing carbonization method. The ratios of shrinkage of length, width, and thickness were 10~25%, 12~25%, and 28~48%, respectively, and shrinkage ratio of thickness was higher than those of length and width with increasing the carbonization temperature. Weight loss tended to increase with increasing the carbonization temperature, but low correlation between weight loss in thickness of fiberboards and carbonization temperature was observed. Density of 3 mm carbonized hardboard had the highest value and it tended to increase with increasing the carbonization temperature.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.7
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• pp.1433-1438
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• 2009

The purpose of this study is to investigate how the ignition spark timing conversion influences the engine performance of LPG/Gasoline Bi-Fuel engine. We propose the control system which can advance the ignition spark timing in LPG fuel mode more than used in gasoline fuel mode. In order to investigate the engine performance during combustion, engine performance are sampled by data acquisition system, for example cylinder pressure, pressure rise rate and heat release rate, while change of the rpm(1500, 2000) and the ignition timing advance($5^{\circ}$,$10^{\circ}$,$15^{\circ}$,$20^{\circ}$) As the result, between 1500rpm and 2000rpm, the cylinder pressure and pressure rise rate was increased when the spark ignition was advanced but pressure rise rate at $20^{\circ}$was smaller value. Also, the heat release rate at 1500rpm was increased but it was lower around $20^{\circ}$at 2000rpm.