• Journal of Power Electronics
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• v.15 no.1
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• pp.235-245
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• 2015

This paper proposes a reactive current assignment and control strategy for a doubly-fed induction generator (DFIG) based wind-turbine generation system under generic grid voltage sag or swell conditions. The system's active and reactive power constrains during grid faults are investigated with both the grid- and rotor-side convertors (GSC and RSC) maximum ampere limits considered. To meet the latest grid codes, especially the low- and high-voltage ride-through (LVRT and HVRT) requirements, an adaptive reactive current control scheme is investigated. In addition, a torque-oscillation suppression technique is designed to reduce the mechanism stress on turbine systems caused by intensive voltage variations. Simulation and experiment studies demonstrate the feasibility and effectiveness of the proposed control scheme to enhance the fault ride-through (FRT) capability of DFIG-based wind turbines during violent changes in grid voltage.

• Journal of the Korean Society for Nondestructive Testing
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• v.12 no.2
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• pp.14-20
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• 1992

Stress analysis has been performed using computer program ANSYS in the pressurizer surge line in accordance with ASME Sec. III in order to predict possibility of fatigue failure due to thermal stratification phenomena in pipes connected to reactor coolant system of nuclear power plants. Highly vulnerable area to crack generation has been chosen by the analysis of fatigue due to thermal stress in pressurizer surge line. This kind of result can be helpful to choose the location requiring intensive care during inservice inspection of nuclear power plants.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.497-501
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• 2001

Unbundled power quality service is paid much attention under the circumstances of deregulation and diversification of needs of customers for quality and price of electric power. Moreover, distributed generators (DGs) such as photovoltaic generations and wind turbines will be introduced to distribution system more and more, and reverse flow of active power has possibility to cause new problems in the distribution system such as voltage rise of distribution line and protection problem. Flexible, Reliable and Intelligent Electrical eNergy Delivery System, which is called FRIENDS, has been proposed as one of promising distribution system for such requirements, and intensive studies are under way. One of features of the system is introducing Quality Control Center (QCC) into the system for unbundled power quality service and easy installation of DGs. Two types of QCCs for such purposes are proposed, and simulation results are shown in this paper.

• Journal of the Korean Data and Information Science Society
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• v.28 no.3
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• pp.669-684
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• 2017

Mediation models are widely used in many fields of research and have recently gained attention in epidemiology. The mediation proportion is a standard measure to evaluate what part of the total exposure effect on an outcome may be explained by a particular mediator and to examine how important that pathway is relative to the overall exposure effect. A common question is how large a sample size is needed to achieve high statistical power or, equivalently, what magnitude of effect can be detected. Current power and sample size calculations for mediation analysis are limited and additional research is needed. We therefore propose a computer-intensive power analysis using the mediation proportion. We conduct simulation studies to calculate statistical powers and sample sizes. And then, we illustrate our power analysis using an example from the Adult Health Study of atomic-bomb survivors and demonstrate that the method is relatively straightforward to understand and compute.

• Journal of Power Electronics
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• v.10 no.2
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• pp.132-137
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• 2010

Interleaving techniques are widely used to reduce input/output ripples and to increase the power capacity of boost converters operating in critical conduction mode. Two types of phase-shift control schemes are studied in this paper, the turn-on time shifting method and the turn-off time shifting method. It is found that although the turn-off time shifting method exhibits better performance, it suffers from sub-harmonic oscillations at high input voltages. To solve this problem, an intensive quantitative analysis of the sub-harmonic oscillation phenomenon is made in this paper. Based upon that, a novel modified turn off time shifting control scheme for interleaved boost converters operating in critical conduction mode is proposed. An important advantage of this scheme is that both the master phase and the slave phase can operate stably in critical conduction mode without any oscillations in the full input voltage range. This method is implemented with a FPGA based digital PWM control platform, and tests were carried out on a two-phase interleaved boost PFC converter prototype. Experimental results demonstrated the feasibility and performance of the proposed phase-shift control scheme.

• Vacuum Magazine
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• v.1 no.4
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• pp.10-13
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• 2014

Since the development of 9.7% efficient long-term stable solid state perovskite solar cell in 2012, intensive study on perovskite solar cell has been performed. As a result, power conversion efficiency (PCE) has reached 20.1%. In-dept study on perovskite light absorber enabled understanding of origin of superb photovoltaic performance of perovskite solar cell. In this article, historical evolutions of perovskite solar cell along with key physical properties enabling high PCE are presented. Several important results for development of high efficiency perovskite solar cell are introduced. Finally, in-present research issues and future direction for solving these issues are discussed.

• Journal of the HCI Society of Korea
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• v.9 no.2
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• pp.13-21
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• 2014

Jump-rope is a simple and effective exercise, but its intensive exercise load and monotonous pattern make it difficult to perform consistent workout. On the other hand, jumping rope accompanies large amount of kinetic energy which can be converted into electrical energy. In this study, we designed and implemented a self-powered jump-rope which can support the low-power embedded Bluetooth system inside it. The embedded system wirelessly transmits the acceleration data measured during jumping-rope exercise to a smartphone. We also developed a smartphone app which can count the number of jumps and provide real-time feedback with sound and animated graphic effects in a game context. Pilot test using the prototype smart jump-rope verified that it can be useful to motivation for the jump-rope exercise and make the exercise more effective by providing users with precise information about their exercise. We expect that the developed self-powered jump-rope will change the exercise from an intensive physical activity into electricity-generating fun experience combined with smartphone game, which maximize the benefit of the consistent jump-rope exercise.

• Journal of Korean Clinical Nursing Research
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• v.19 no.3
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• pp.383-394
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• 2013

Purpose: This study was conducted to investigate the effects of preparatory nursing information and information offering by SMS on anxiety and nursing satisfaction among family members of ICU (Intensive Care Unit) inpatients. It utilized a quasi-experimental research design with a non-equivalent and non-synchronized control group. Methods: The experimental group and the control group were offered a booklet guiding ICU and were offered face-to-face information by nurses using Power Point. The experimental group was additionally offered SMS (short message service) message on patient's safety at night every morning during the hospital stay between 8 and 9 am. All participants in the experimental group and the control group were measured in reference to anxiety at the point of hospitalization and were surveyed anxiety and nursing satisfaction on the third day of hospital stay. Results: The anxiety demonstrated no significant difference between the groups, while the nursing satisfaction was significantly higher in the experimental group than that of the control group. Conclusion: Proving direct information and indirect information via SMS message were considered effective in improving the family member's satisfaction with nursing care. The frequencies of SMS message and the contents of the message and information need to be defined and specified in the given population.

• Journal of Korean Critical Care Nursing
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• v.12 no.2
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• pp.39-49
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• 2019

Purpose : The purpose of this study was to identify the extent to which intensive care unit (ICU) nurses' perceptions of life-sustaining treatment decisions and "a good death" affect attitudes toward terminal care. Method : Participants included 109 ICU nurses from three university hospitals. Data were collected using structured questionnaires, and collected data were analyzed using a t-test, ANOVA, the $Scheff{\acute{e}}$ test, Pearson correlation coefficients, and a multiple regression analysis (SPSS 24.0 program). Results : Perceptions of life-sustaining treatment decisions and a sense of closeness (a constituent for the awareness of "a good death") were positively correlated with terminal care attitudes. The factors affecting terminal care attitudes were a clinical career in ICU (${\beta}=.20$, p =.035), a sense of closeness(${\beta}=.19$, p =.041), and the perception of a life-sustaining treatment decision (${\beta}=.22$, p =.017). This finding indicates that more than 10 years of experience in ICU, a greater sense of closeness, and a higher view of life-sustaining treatment decisions results in more positive attitudes toward terminal care. The explanatory power of these variables on terminal care attitudes was 14% (F=6.84, p < .001, Adj $R^2=.140$). Conclusion : A sense of closeness and the perception of life-sustaining treatment decisions were identified as the factors affecting terminal care attitudes. Thus, various programs must be developed to raise awareness among ICU nurses of "a good death" and perceptions of life-sustaining treatment decisions.

• The Research Journal of the Costume Culture
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• v.28 no.4
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• pp.508-526
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• 2020

This study has established a fashion illustration education plan using the contour drawing that fosters observational ability and enables creative drawing. This study developed two illustration curriculum proposals consisting of 15 weeks, combining literature and case studies. The researchers organized a step-by-step teaching plan that utilizes contour drawing according to the three stages of fashion illustration classes: foundation courses, general courses, and intensive courses. When the contour drawing is used at the beginning stage of the foundation courses of fashion illustration, it can be used as a technique to reduce the fear of students about practical skills, induce interest in illustration, and cultivate observation ability about objects. In general process, it is combined with various tools and coloring materials to strengthen expression power, and it is possible to produce detailed expressions and illustrations about human body and clothing. In intensive courses, it is expanded to the production of creative works with new aesthetics through digital techniques and mixed materials. As such, the contour drawing is expanded in various ways according to the learning contents and goals of each step, and is flexibly adjusted according to the learning content. Contour drawing has the effect of acquiring observation and expression ability, and it is analyzed as a technique that enables the production of creative illustration of students.