• Proceedings of the KIPE Conference
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• 2020.08a
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• pp.320-321
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• 2020

본 논문은 AC 계통 불평형 발생 시 출력전력의 동요를 저감시키기 위한 POD 전략을 수행하는 MMC-HVDC 시스템의 내부 동적상태를 분석하였다. POD 전략을 통해서 MMC 출력전류의 역상분을 제어하여 계통에 주입되는 유효 전력의 발진을 제거함으로써, MMC-HVDC 시스템이 연계된 인근 계통에 공급 신뢰도를 향상시킬 수 있다. POD 전략에서 유효 전력만 출력할 경우, MMC의 각 상에는 동일한 전력이 흐른다. 반면, 계통 전압 보상을 위해서 무효 전력을 동시에 공급할 경우, 각 상에 흐르는 전력은 불균형해지기 때문에 MMC의 암전류 불평형이 발생하여 스위치 소자의 정격 용량 및 열 스트레스를 증가 시켜 MMC의 안정성을 저해시킨다. 본 논문은 POD 전략을 수행하기 위해서 무효 전력이 MMC 암 전류에 미치는 영향을 분석하였으며, 200 MW MMC-HVDC 모델을 바탕으로 PSCAD/EMTDC 시뮬레이션 툴을 이용하여 분석 결과를 검증하였다.

• Journal of Korean Academy of Nursing
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• v.45 no.5
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• pp.752-760
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• 2015

Purpose: The purpose of this study was to examine the moderating mediation effect of self-esteem on the relations among adolescents' abuse experiences, depression and anxiety, and suicidal ideation. Methods: The participants were selected using secondary data from a population in the 2012 Korea Welfare Panel Survey (KOWEPS). Data were analyzed using SPSS 15.0 and SPSS Macro, and bootstrapping and hierarchical regression analysis were performed to analyze multilevel models. Results: First, analysis of the mediating effect of the adolescents' abuse showed that there was significant mediating influence between suicidal ideation and depression and anxiety. Second, hierarchical regression analysis showed that self-esteem had significant mediation effect on depression and anxiety in adolescents' suicidal ideation. Third, SPSS Macro showed that self-esteem also significantly moderated the mediating effect of adolescents' abuse experiences on suicidal ideation through depression and anxiety. Conclusion: The study results suggest that in future research on adolescent's abuse experience, the risk of suicide in depression and anxiety scores should be selected through evaluation of each individual's self-esteem scale. Coping strategies with immediate early intervention should be suggested.

• Safety and Health at Work
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• v.9 no.4
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• pp.427-433
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• 2018

Background: The purpose of this study was to identify the influence of workers' perceived workload, accident experiences, supervisors' safety leadership, and an organization's safety climate on the cognitive and emotional risk perception. Methods: Six hundred and twenty employees in a variety of manufacturing organizations were asked to complete to a questionnaire. Among them, a total of 376 employees provided valid data for analysis. To test the hypothesis, correlation analysis and hierarchical regression analysis were used. Statistical analyses were conducted using IBM SPSS program, version 23. Results: The results indicated that workload and accident experiences have a positive influence and safety leadership and safety climate have a negative influence on the cognitive and emotional risk perception. Workload, safety leadership, and the safety climate influence perceived risk more than accident experience, especially for the emotional risk perception. Conclusion: These results indicated that multilevel factors (organization, group, and individual) play a critical role in predicting individual risk perceptions. Based on these results, therefore, to reduce risk perception related with unsafe behaviors and accidents, organizations need to conduct a variety of safety programs that enhance their safety climate beyond simple safety-related education and training. Simultaneously, it needs to seek ways to promote supervisors' safety leadership behaviors (e.g., site visits, feedback, safety communication, etc.). In addition, it is necessary to adjust work speed and amount and allocate task considering employees' skill and ability to reduce the workload for reducing risk perception.

• Child Health Nursing Research
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• v.29 no.1
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• pp.84-95
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• 2023

Purpose: This study aimed to conduct a concept analysis of health-related quality of life in children with epilepsy to promote conceptual clarification and facilitate mutual understanding of the concept. Methods: Walker and Avant's concept analysis method was adopted. Results: Health-related quality of life in children with epilepsy consists of six attributes: health status, inner strength, close relationships, resource-rich community, social acceptance, and changeability. According to the ecological system paradigm, these attributes are structured into five dimensions: organism, microsystem, macrosystem, exosystem, and chronosystem. These dimensions provide a comprehensive approach to the relationship between children with epilepsy and their environment. Epilepsy and interactions with multilevel ecological systems that are directly and indirectly related to children with epilepsy precede the concept, followed by positive and negative affective responses. Conclusion: The findings of this study may support effective communication in various practice settings, thereby contributing to the health and well-being of children with epilepsy, as well as the development and expansion of interventions to improve their health-related quality of life.

• 한국사회정책
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• v.25 no.2
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• pp.125-163
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• 2018

Social and health problems related to drinking are serious. Drinking behavior is affected not only by personal factors but also by environment factors. The purpose of this study is to find out how the alcoholic beverage stores in community influence the drinking behaviors of individuals after adjusting the individual level variables and provide it as basic data for alcohol related regulatory policies. In order to identify the factors affecting drinking behavior, we conducted a multilevel logistic regression analysis with high-risk drinking and current drinking as dependent variables. Individual-level data provided by 2015 community health survey from respondents of urban residents, and regional level data provided by the National Statistical office. The variables such as age, education level, and income level were used as individual level variables and the number of basic living allowances, divorce rate, and the number of pubs were used as community level variables. According to the research results, after controlling all variables, the number of bar, retail per $1km^2$ in residential area effect on current drinking. But, they are not effect on high risk drinking. In the high risk drinking, only the divorce rate effect on drinking behavior. As a result of the stratified analysis, there was no difference in the current drinking. But, it shows that the higher the number of retail stores and the total alcohol availability, the higher risk drinking behavior in the 60s. The results of this study suggest that policies aimed not only on individuals but also on the local environment are necessary.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.13 no.1
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• pp.27-34
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• 2013

This paper deals with the performance anlysis of CCA adaptive equalization algorithm, that is used for reduction of intersymbol interference at the receiving side which occurs in the time dispersive communication channel. Basically, this algorithm is borned for the solving phase unrecovery problem in the CMA equalizer, and the comines the concept of DDA (Decision Directed Algorithm) and RCA (Reduce Constellation Algorithm). The DDA has a stable convergence characteristics in unilevel signal, but not in the number of levels in multilevel signal such as QAM, so it has unstable problem. The RCA does not provide reliable initial convergence. And even after convergence, the equalization noise due to the steady state misadjustment exhibited by it is very high as compared to DDA. For the solving the abovemensioned point, the CCA adaptive eualization alogorithm has borned. In order to performance analysis of CCA algorithm, the recovered signal constellation that is the output of the equalizer, the convergence characteristic by the residual isi and MD (maximum distortion), the SER characteristic are used by computer simulation and it was compared with the DDA, RCA respectively. As a result of simulation, the DDA has superior performance than other algoithm, but it has a convergence unguarantee and unstability in the multilevel signal. In order to solving this problem, the CCA has more good performance than RCA in every performance index.

• Korean Journal of Social Welfare
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• v.63 no.2
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• pp.81-107
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• 2011

The purpose of the study is to examine the effect of error management culture and psychological capital on job satisfaction and organizational commitment from social workers. This study was focused on the relationship between error management culture, psychological capital and job satisfaction and organizational commitment, controlled organizational fairness. The data was collected from social workers in Seoul, Kyunggi areas using stratified sampling method. A total of 564 social workers and 89 human service organizations were finally used for multilevel analysis. The survey had conducted for 18 days, from October 27 to November 13 in 2009 by mail. The major finding of this study are as follows. First, interaction effect between error management culture and psychological capital was significant job satisfaction and organizational commitment in positive direction. Second, main effect of error management culture in human service organizations was positively significant job satisfaction and organizational commitment on social workers. So it was important to enhance the level of error management culture in order to increase the job satisfaction and organizational commitment. Third, main effect of psychological capital on social workers was positively significant job satisfaction and organizational commitment. According to the results of this study, it was suggested the theoretical and practical implications for increasing and strengthen the error management culture and psychological capital.

• Journal of Korean Neurosurgical Society
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• v.65 no.4
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• pp.549-557
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• 2022

Objective : This study analyzed the risk factors in patients who developed distal junctional kyphosis (DJK) after posterior cervical fusion. Methods : We retrospectively analyzed the clinical and radiographic outcomes of 64 patients, aged ≥18 years (51 and 13 male and female patients, respectively), who underwent single-staged multilevel (3-6 levels) posterior cervical fusion surgery due to multiple cervical spondylotic myelopathy. The surgeries were performed by a single spinal surgeon between January 2012 and December 2017. Demographic data, clinical outcomes, and radiological results were collected. We divided the patients into a DJK group and a non-DJK group according to the presence of DJK and investigated the risk factors by comparing the differences between the two groups. Results : Of the 64 patients, 13 developed DJK. No significant differences in clinical results were observed between the two groups before and immediately after the surgery. At the final follow-up, a higher visual analog score for neck pain was observed in the DJK group compared to the non-DJK group (p<0.01). The DJK group had a significantly lower T1 slope and a significantly higher C2-7 sagittal vertical axis (SVA) before surgery compared to the non-DJK group (p=0.03 and p<0.01, respectively). Immediately after surgery, the difference between the two groups decreased and no significant difference was observed. However, at the last follow-up, a significantly higher C2-7 SVA was observed in the DJK group (p<0.01). At the last follow up, there is no discrepancy in T1S-CL. In multiple logistic regression analysis, preoperative higher C2-7 SVA and preoperative lower T1 slope were identified as independent risk factors (p=0.03 and p<0.01, respectively). As a result, it was confirmed that DJK occurred along the process of returning to preoperative values. Conclusion : DJK can be considered to be caused by cervical misalignment due to excessive change in the surgical site in patients with low T1 slope and high C2-7 SVA before surgery. This also affects the clinical outcome after surgery. It is recommended to refrain from excessive segmental lordosis changes during multilevel cervical post fusion surgery, especially in patients with a small preoperative T1 slope and a large SVA value.

• Journal of Korean Public Health Nursing
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• v.31 no.3
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• pp.492-504
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• 2017

Purpose: This study aims to investigate the effect of employment of elderly over 65 years on elderly depression using the "Nation Elderly Survey 2014". Methods: The subjects were 10,451 elderly aged 65 or older who were selected from 16 cities and provinces via multilevel stratified sampling method. In an effort to represent well the nation's elderly population, composite sample analysis method was used for the study, and a hierarchical logistic regression analysis was performed to identify those factors affecting the depression among the elderly population. Results: The factors affecting the depression were education level, household income, Perceived health status, smoking, drinking, physical activity, body mass index and employment status. It was found that the unemployed persons were 1.68 times more likely to be depressed than those who remain employed. Conclusion: Where the average life expectancy is getting longer and the poverty rate of elderly is high, employment activities of the elderly are of great significance in terms of ensuring economic stability as well as in lowering medical expenses through reduction of depression. Therefore, it is necessary to increase the employment rates of the elderly for economic, social and healthcare perspectives.

• Journal of Power Electronics
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• v.9 no.2
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• pp.133-145
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• 2009

In this paper a modular high performance MV-to-LV rectifier based on a cascaded H-bridge rectifier is presented. The proposed rectifier can directly connect to the medium voltage levels and provide a low-voltage and highly-stable DC interface with the consumer applications. The input stage eliminates the necessity for heavy and bulky step-down transformers. It corrects the input power factor and maintains the voltage balance among the individual DC buses. The second stage includes the high frequency parallel-output DC/DC converters which prepares the galvanic isolation, regulates the output voltage, and attenuates the low frequency voltage ripple ($2f_{line}$) generated by the first stage. The parallel-output converters can work in interleaving mode and the active load-current sharing technique is utilized to balance the load power among them. The detailed analysis for modeling and control of the proposed structure is presented. The validity and performance of the proposed topology is verified by simulation and experimental results.