• Journal of Mechanical Science and Technology
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• 제15권12호
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• pp.1623-1629
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• 2001

This parer presents a CVT line pressure control strategy for the increased shift speed. Firstly, an algorithm to increase the CVT shift speed is suggested based on a modified CVT shift dynamics and shift speed maps are constructed. In addition, simplified dynamic models of the line pressure and the ratio control valve are derived by considering the CVT shift dynamics, and low level control algorithms for the ratio and the line pressure control are proposed. Using the shift speed maps and the simplified dynamic models of the CVT system, shift performance is investigated. It is found from the experimental and simulation results that improved shift speed can be achieved by increasing the lilly pressure.

• Journal of Electrical Engineering and Technology
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• 제12권5호
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• pp.1902-1915
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• 2017

This paper presents the evaluation of a three-phase three-level DC-DC converter which achieves the soft switching condition for all switches in the circuit and uses the phase-shift PWM strategy to adjust electric power at the output side. According to the analysis, the operation modes can be categorized into two cases: in the first case, where the phase shift angle is less than 120 degrees and in the second case, where the phase shift angle is more than 120 degrees. The outer switches of the circuit operate under ZVS condition and the inner switches operate under ZVZCS condition. It has been discovered that under ZCS condition of the inner switches, when the blocking capacitors decrease, they make the voltage across the blocking capacitor higher so the current reduce rapidly. A three-phase three-level DC-DC converter has a maximum efficiency of 93.5% when its load is of 5.7 kW. The results from the experiment have been compared to the results obtained by the $MATLAB^{(R)}$ simulator in order to confirm the validity of the proposed converter.

• Journal of Korean Biological Nursing Science
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• 제2권2호
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• pp.81-89
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• 2000

To determine the optimal rotational shift system, the effect of the direction of the rotational work shifting on the nocturnal rhythm of plasma melatonin were investigated in nursing students. Two groups of nine volunteers participated as experimental subjects, and two nursing students participated as a control group. The directions of the rotational work shift were as follows: CW(clockwise)-shift were rotated in the direction of day shift(3 days), evening shift(3 days), off duty(1 day) and night shift(5 days), and CCW(conuterclockwise)-shift were done in the reverse direction. Plasma melatonin concentrations was measured by radioimmunoassay. The results were as follows : The plasma melatonin levels were kept low at night and in the following morning in the CW night shift workers, whereas the level started to increase at 05 : 00 hr in two workers of four CCW shift workers. These result suggests that the shift rotation in the CW direction is more acceptable in terms of the adaptation of hormonal rhythms. These results indicate that the CCW rotation of shift work is somewhat better than CCW rotation for the adaptation to shift work on hormonal aspects in nurses.

• 한국해안·해양공학회논문집
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• 제32권5호
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• pp.322-330
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• 2020

부산, 목포 지점의 평균해수면(MSL)과 고극조위, 저극조위 자료의 이상자료 시계열 모델링을 수행하였다. 시계열 모델은 계절성분을 포함하는 SARIMA 모형이며, 일시적인 변화에 해당하는 이상자료(Additive Outlier, AO)와 영구적인 변화를 의미하는 기준고도 변화(Level Shift, LS)를 모델에 포함하였으며, AIC 기준에 의거하여 최적 모델을 선정하였다. 이상자료 모형의 매개변수 추정은 R 프로그램 'tsoutliers' 패키지('tso' 함수)를 이용하였다. 선정 모형을 이용하여 이상자료와 기준고도 변화 진단에 적용한 결과, 부산의 월 단위 고극조위 자료에서 2003, 2012년 발생한 태풍 매미(MAEMI), 산바(SANBA)에 의한 일시적인 수위상승을 65.5, 29.5 cm 정도로 추정하였으며, 목포의 월 단위 평균해수면 자료에서는 1983년의 영산강 하굿둑 건설 사업에 의한 기준고도 변화를 21.2 cm 정도로 추정하였다. 한편 본 연구에서 구성한 모형은 모형의 편향을 유발하는 이상자료의 영향을 포함하며, 모형에 의한 RMS 오차는 연간 자료를 사용한 경우, 부산은 MSL 1.95 cm, 고극조위, 저극조위 각각 5.11 cm, 6.50 cm이며, 목포의 경우에는 큰 조차의 영향으로 MSL 2.01 cm, 고극조위, 저극조위 각각 11.80 cm, 9.14 cm로 부산보다 다소 높게 나타났다.

• Journal of Korean Biological Nursing Science
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• 제19권3호
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• pp.206-213
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• 2017

Purpose: The purpose of the study was to compare salivary cortisol levels, self-reported occupational stress, and anxiety before duty to those after duty in the shift and regular work nurses, and the relationships among them. Methods: Thirty nurses working in a tertiary hospital participated in the study. Salivary specimens were collected before and after daytime duty for 2 days. The occupational stress and state anxiety were also evaluated using self-report questionnaires. Results: The average level of salivary cortisol was $0.40{\mu}g/dL$ before duty and $0.20{\mu}g/dL$ after duty in Korean nurses. Overall levels of salivary cortisol, self-reported occupational stress, and anxiety were higher in shift working nurses than regular working nurses. In shift working nurses, the salivary cortisol gap between before and after duty was attenuated on the first day of daytime duty. Significant positive correlation was found between the level of cortisol before duty and anxiety after duty. Conclusion: Strategies to alleviate occupational stress and anxiety are needed for shift working nurses, especially for those with elevated levels of cortisol. It seems to require 3days to recover from attenuated cortisol rhythm during nighttime duty in shift working nurses.

• Journal of Mechanical Science and Technology
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• 제14권4호
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• pp.418-425
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• 2000

Recently, many passenger cars have adopted automatic transmissions for shifting gears, and thus the smooth and precise control of gear shifts of passenger car automatic transmissions has become more and more essential for the riding comfort of vehicles equipped with automatic transmissions. In this article, a neural network-based supervisor for an automotive shift controller considering the throttle opening, variations in throttle opening, and the driving load is presented. For using the driving load information, an observer-based driving load estimation algorithm is proposed. A proportional-integral-derivative controller along with an open loop controller is used as a low level controller for controlling the gear shifts, and a supervisory controller for properly adapting the shift control parameters of the low level shift controller is designed using ANFIS. To evaluate the control performance of the proposed supervisor-based shift controller, both simulation studies and experimental studies are performed for various shifting situations.

• Safety and Health at Work
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• 제9권4호
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• pp.421-426
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• 2018

Background: The purpose of this study was to investigate the effect of shift work on occupational safety in various industrial sectors. The study analyzes the effects of shift work on the health of workers by considering factors such as the workplace environment and welfare. Methods: Focusing on the $4^{th}$ Korean Working Conditions Survey, this study used an ordinary least-square multiple regression analysis. The dependent variable was the annual frequency of injuries reported by workers. Independent variables were categorized as demographic, shift work, workplace environment, and welfare variables. The analysis was conducted on two levels: 1) Shift work and nonshift work groups were compared, and 2) Shift work was compared with fixed and rotating shifts. Results: For the entire group, age, a low level of education, work hours, and daily and dispatch work negatively impacted the frequency of injuries. Shift work was negatively affected by workplace environment and welfare factors. In the shift group, the frequency of injuries was lower than that of regular workers, and the higher the autonomy in the choice of work hours, the lower the frequency of injuries. Furthermore, shift workers in Korea have more extended work hours (49.25 h/week) than other workers (46.34 h/week). Conclusion: Overall, welfare factors such as workplace satisfaction and worke-life balance reduced the frequency of injuries. The effect of shift work was limited, but it was confirmed that shift worker autonomy could reduce the frequency of injuries.

• 한국컴퓨터정보학회:학술대회논문집
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• 한국컴퓨터정보학회 2008년도 제39차 동계학술발표논문집 16권2호
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• pp.207-210
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• 2009

Edge detection is an important process in low level image processing. But many proposed methods for edge detection are not very robust to the image noise and are not flexible for different images. To solve the both problems, an algorithm is proposed which eliminate the noise by mean shift algorithm in advance, and then adaptively determine the double thresholds based on gradient histogram and minimum interclass variance, With this algorithm, it can fade out almost all the sensitive noise and calculate the both thresholds for different images without necessity to setup any parameter artificially, and choose edge pixels by fuzzy algorithm.

• 전력전자학회논문지
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• 제11권6호
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• pp.520-528
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• 2006

동일한 변압기를 사용하는 공통암 타입의 절연형 다중레벨 인버터에서 스위칭 주파수를 저감하기 위해 새로운 위상변위제어기법을 제안 하였다. 제안된 스위칭 방식은 인버터의 각 암이 기본주파수당 한번만을 스위칭을 하는 스텝 펄스파 방식을 사용하여 동일한 스위칭 주파수를 유지할 수 있다. 제안된 스위칭 방식의 타당성을 검증하기 위해 기존의 동일변압기를 이용한 멀티레벨 인버터의 스위칭 패턴과 제안된 위상변위 제어방식을 이용한 멀티레벨 인버터의 스위칭 패턴을 시뮬레이션하고 실험을 통해 비교 하였다.

• 한국전기전자재료학회논문지
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• 제22권7호
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• pp.580-583
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• 2009

This paper introduces a gate drive IC for power modules with shoot-through immunity. A new approach uses a bootstrap diode as a high-side voltage bias and a level shift function at the same time. Therefore, the gate drive circuit becomes a simple and low-cost without conventional level shift functions such as HVIC(High-Voltage IC), optocoupler and transformer. The proposed gate drive IC is designed and fabricated using the Dongbu-Hitek's 0.35um BD350BA process. It has been tested and verified with IGBT modules.