• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.4
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• pp.817-824
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• 2000

This paper presents circuit DQ modeling and analysis of operating characteristics of hybrid cascade multilevel PWM rectifier, especially five-level, without isolation transformers. The circuit DQ transformation changes the original three-phase time varying circuit to stationary equivalent one by employing the synchronously rotating transformation matrix. As a result of circuit DQ modeling, the operating characteristics and some useful design relationships for the system are obtained with ease. That is, the analytic equations for DC voltages and active/reactive power supplied by source with respect to control variables are Presented. Moreover, the DC voltages for the multilevel output generation may be directly built up from AC utility source and the important control equation ensuring 5-level output voltage is obtained. Finally, to confirm the validity of the analysis, MATLAB simulations are carried out and the simulation results show good agreements between analytic predictions and the simulated waveforms.

• International conference on construction engineering and project management
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• 2015.10a
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• pp.294-298
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• 2015

In the United States, the completion of Construction Work Zone (CWZ) impact assessments for all federally-funded highway infrastructure improvement projects is mandated, yet it is regarded as a daunting task for state transportation agencies, due to a lack of standardized analytical methods for developing sounder Transportation Management Plans (TMPs). To circumvent these issues, this study aims to create a spatiotemporal modeling framework, dubbed "SWAT" (Spatiotemporal Work zone Assessment for TMPs). This study drew a total of 43,795 traffic sensor reading data collected from heavily trafficked highways in U.S. metropolitan areas. A multilevel-cluster-driven analysis characterized traffic patterns, while being verified using a measurement system analysis. An artificial neural networks model was created to predict potential 24/7 traffic demand automatically, and its predictive power was statistically validated. It is proposed that the predicted traffic patterns will be then incorporated into a what-if scenario analysis that evaluates the impact of numerous alternative construction plans. This study will yield a breakthrough in automating CWZ impact assessments with the first view of a systematic estimation method.

• Education of Primary School Mathematics
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• v.23 no.4
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• pp.175-189
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• 2020

The purpose of the present study was to investigate the structural relationships between elementary teachers' mathematics instruction, teachers' mathematics teaching efficacy, students' mathematical interest, and mathematics achievement. To achieve this goal, we used TIMSS 2015 Korean data and implemented multilevel structural equation modeling given that student data were nested within the school data. The findings reveled that at the student level, the instructional quality rated by students positively affected student mathematical interest. Additionally, student mathematical interest positively affected student mathematics achievement. Although the direct effect of instructional quality on student mathematics achievement was insignificant, the total was significant. At the school level, there were positive direct effects of instructional quality and teacher's mathematics teaching efficacy on student mathematical interest. The direct effects of instructional quality, teachers' mathematics teaching efficacy, and student mathematical interest on mathematics achievement were not significant. However, the total effects of instructional quality and teachers' mathematics teaching efficacy on mathematics achievement were significant. Based on the results, we discussed the implications of the study.

• 한국노년학
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• v.39 no.4
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• pp.977-996
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• 2019

The current study aimed to examine the gender differences in trajectories of nine successful aging indicators (chronic disease, depression, activities of daily living, instrumental activities of daily living, mini mental state examination, social activity, personal contact, health satisfaction, and general life satisfaction) with age, controlling the effect of education. The data were from the Korean Longitudinal Study of Aging, which had been conducted biennially from 2006 to 2016. The sample included 822 men and 1,236 women who responded to all of the panel surveys and were 65 years old or above in 2006. Multilevel modeling analyses showed that older men had fewer chronic diseases; lower levels of depression; higher levels of activities of daily living, cognitive function, and social activity; and better perceived health satisfaction and general life satisfaction at age 65 years compared to women. However, both men and women showed increase in the number of chronic diseases and depression level, and decrease in physical, cognitive, and social functions with age. In addition, perceived health and life satisfaction also decreased after the age of 65. The trajectories of most of the indicators were non-linear, and markedly increased or decreased around mid-70s. Study limitations and implications were further discussed.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.4 no.2
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• pp.55-70
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• 1994

본 논문은 데이타베이스의 동적 기능을 모형화하기 위해서 동적 규칙을 사건과 동적 규칙 객체로 취급하여 개념적 스키마에 표현하는 동적 객체지향 데이타 모델을 제안한다. 제안된 모델에서 정적 구조와 동적 구조에 대한 개념들을 정의하고 모형화 과정에서 사용자의 이해도를 증진시키는 모델의 구성요호에 대한 그래픽 다이어그램을 제시하였다. 그리고 동적 규칙이 데이타베이스 구조에 포함됨으로써 발생가능한 정보의 불법적인 노출 또는 변경을 방지하기 위해서 BLP모델의 보안 정책을 확장하여 제안된 모델에 대한 11가지 종류의 다단계 보안 성질들을 정의하였다. 또한, 정의된 다단계 보안 성질들이 타당한가를 조사하기 위해서 패트리네트를 확장하여, 보안 성질의 검증작업을 수행하였다.

• Journal of Korean Society of Transportation
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• v.21 no.4
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• pp.145-154
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• 2003

Multilevel and Multivariate Structural Equation Mpdel is applied to handle the hierarchical nature of the data and explain complex relationship among socioeconomic factors of individuals and household, activity participation, and travel behavior using Puset Sound Transportation Panel data. From analysis, variations of individual activity participation and travel behavior can be divided into two categories : Within-household variation and Between-households variation. Empirical results show that the interdependency index(p) of variables for household members within a household is between 0.13 and 0.33 indicating high interdependency. These results suggest that Multilevel and Multivariate SEM approach is an appropriate modeling methodology and gives additional information for activity participation and travel behavior. Also most of personal and household characteristics influence on activity participation and travel behavior within a household as well as between households.

• Journal of Preventive Medicine and Public Health
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• v.47 no.5
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• pp.258-265
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• 2014

Objectives: To examine whether the nursing practice environment at the hospital-level affects the job satisfaction and turnover intention of hospital nurses. Methods: Among the 11 731 nurses who participated in the Korea Health and Medical Workers' Union's educational program, 5654 responded to our survey. Data from 3096 nurses working in 185 general inpatient wards at 60 hospitals were analyzed using multilevel logistic regression modeling. Results: Having a standardized nursing process (odds ratio [OR], 4.21; p<0.001), adequate nurse staffing (OR, 4.21; p<0.01), and good doctor-nurse relationship (OR, 4.15; p<0.01), which are hospital-level variables based on the Korean General Inpatients Unit Nursing Work Index (KGU-NWI), were significantly related to nurses' job satisfaction. However, no hospital-level variable from the KGU-NWI was significantly related to nurses' turnover intention. Conclusions: Favorable nursing practice environments are associated with job satisfaction among nurses. In particular, having a standardized nursing process, adequate nurse staffing, and good doctor-nurse relationship were found to positively influence nurses' job satisfaction. However, the nursing practice environment was not related to nurses' turnover intention.

• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.6
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• pp.526-534
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• 2022

The modular multilevel converter (MMC) has been widely applied to various industrial areas because of its various advantages and structural characteristics. Therefore, many methods for synthesizing the output voltage of MMC have been studied. Among these methods, phase-shifted pulse width modulation (PSPWM) is frequently used in MMC systems because it has diverse merits, such as excellent output qualities even with a small number of cells and uniform power distribution among cells. In this study, the total harmonic distortion (THD) of the output voltage is analyzed in accordance with the number of cells in one arm of a single-delta bridge cell MMC in order to compare PSPWM methods in terms of the THD of the output voltage. The physical characteristics of the triangle and sawtooth carrier waves used for the PSPWM and the mathematical modeling of output voltage are introduced. Then, the obtained results are verified through real-time simulation of a 1 MW single-delta bridge cell MMC system.

• Journal of Korean Academy of Nursing
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• v.50 no.3
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• pp.333-348
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• 2020

Purpose: The present study investigated the association between nurse staffing and health outcomes among psychiatric inpatients in Korea by assessing National Health Insurance claims data. Methods: The dataset included 70,136 patients aged 19 years who were inpatients in psychiatric wards for at least two days in 2016 and treated for mental and behavioral disorders due to use of alcohol; schizophrenia, schizotypal and delusional disorders; and mood disorders across 453 hospitals. Nurse staffing levels were measured in three ways: registered nurse-to-inpatient ratio, registered nurse-to-adjusted inpatient ratio, and nursing staff-to-adjusted inpatient ratio. Patient outcomes included length of stay, readmission within 30 days, psychiatric emergency treatment, use of injected psycholeptics for chemical restraint, and hypnotics use. Relationships between nurse staffing levels and patient outcomes were analyzed considering both patient and system characteristics using multilevel modeling. Results: Multilevel analyses revealed that more inpatients per registered nurse, adjusted inpatients per registered nurse, and adjusted inpatients per nursing staff were associated with longer lengths of stay as well as a higher risk of readmission. More adjusted inpatients per registered nurse and adjusted inpatients per nursing staff were also associated with increased hypnotics use but a lower risk of psychiatric emergency treatment. Nurse staffing levels were not significantly associated with the use of injected psycholeptics for chemical restraint. Conclusion: Lower nurse staffing levels are associated with negative health outcomes of psychiatric inpatients. Policies for improving nurse staffing toward an optimal level should be enacted to facilitate better outcomes for psychiatric inpatients in Korea.

• International Journal of Human Ecology
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• v.16 no.1
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• pp.25-35
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• 2015

The primary purpose of this study was to examine to what extent adolescents' daily self-evaluation mediates the effect of experiencing intimacy in parent-adolescent interactions on positive peer interactions the next day, even after controlling for gender and grade level. We employed a daily diary method for seven days in a sample of 452 Korean adolescents, collecting checklist data at the end of each day. Data were analyzed by using hierarchical linear modeling. According to moderated multilevel mediation analyses, the variance of self-evaluation explained 83% of the variance in the lagged effect of parental intimacy on the next day peer interaction even after the upper-level effects of gender and grade level were accounted for. Forth graders were more likely than 7th graders to have a more positive view of themselves when they experienced parental intimacy the previous day. Girls were less likely to experience positive peer interactions when they perceived less intimacy with their parents the day before. Results suggested that it would be most effective for peer relationship programs to teach parents and adolescents how to experience intimacy in their daily interactions, particularly in ways that help adolescents to think more positively about themselves. It would be helpful for parents to learn about various ways to compliment and encourage the adolescent child in everyday conversations. Lastly, findings in grade level differences also suggest that these programs might be especially effective for 4th graders more than 7th graders.