• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.2
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• pp.133-141
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• 2020

The use of high-gain-voltage step-up converters for distributed power generation systems is being popularized because of the need for new energy generation and power conversion technologies. In this study, a new constructed high-gain-boost DC-DC converter was proposed to coordinate low voltage output DC sources, such as PV or fuel cell systems, with high DC bus (380 V) lines. Compared with traditional boost DC-DC converters, the proposed converter can create higher gain and has wider input voltage range and lower voltage stress for power semiconductors and passive elements. Moreover, the proposed topology produces multilevel DC voltage output, which is the main advantage of the proposed topology. Steady-state analysis in continuous conduction mode of the proposed converter is discussed in detail. The practicability of the proposed DC-DC converter is presented by experimental results with a 300 W prototype converter.

• 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 Preventive Medicine and Public Health
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• v.56 no.6
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• pp.504-514
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• 2023

Objectives: This study investigated the relationship between prescribing institutions and medication adherence among patients newly diagnosed with hypertension and diabetes. Methods: This study investigated patients with new prescriptions for hypertension and diabetes in Korea in 2019 with using data collected from general health screenings. A multilevel logistic regression model was applied to explore the relationship between patients' first prescribing institution and their medication adherence, defined as a medication possession ratio (MPR) over 80%. Results: The overall adherence rates were 53.7% and 56.0% among patients with hypertension and diabetes, respectively. The intra-class correlation coefficients were 13.2% for hypertension and 13.8% for diabetes (p<0.001), implying that the first prescribing institution had a significant role in medication adherence. With clinics as the reference group, all other types of hospitals showed an odds ratio (OR) less than 1.00, with the lowest for tertiary hospitals (OR, 0.30 for hypertension; 0.45 for diabetes), and the next lowest in health screening specialized clinics (OR, 0.51 for hypertension; 0.46 for diabetes). Among individual-level variables, female sex, older age, higher insurance premium level, and residing in cities were positively associated with adherence in both the hypertension and diabetes samples. Conclusions: This study showed that the prescribing institution had a significant relationship with medication adherence. When the first prescribing institution was a clinic, newly diagnosed patients were more likely to adhere to their medication. These results highlight the important role played by primary care institutions in managing mild chronic diseases.

• The Journal of the Korea Contents Association
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• v.13 no.5
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• pp.342-353
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• 2013

Objectives: It attempted to analyze influencing factors on the utilization of outpatient services which were adopted to predisposing, enabling, and need factors in Anderson model. Methods: The current study analyzed "2007 Korean National Health Nutrition Survey" data, which selected 3,335 people nationwide by proportional systematic sampling. This study analyzed data of persons who used outpatient services in two weeks. It adopted Anderson Model to control contextual factors including socioeconomic factors. The study compared means and fitted logistic regression models and multilevel model. Results: The logistic regression model showed that persons purchased private medical insurance were less likely to use outpatient services than the persons did not purchase private medical insurance. Persons with hypertension and diabetes mellitus, overweight, and problem drinkers were more likely to use outpatient services. Persons with high school graduates or higher in education level and experience of accidents or intoxications were more likely to use outpatient services according to the multilevel analysis of mixed model which treated region as random effect. Conclusion: Higher level of perceived stress increased the probability to use outpatient service than lower level of perceived stress. As number of days a person had exercised increased, the probability to use outpatient service decreased. Overweight and problem alcohol drinking increased the probability of outpatient service use. Further research should be conducted to find more factors influencing outpatient service use.

• Korean Journal of Health Education and Promotion
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• v.29 no.2
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• pp.83-91
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• 2012

Objectives: This study is to examine that drinking problems among university students were accounted for not only by student's individual characteristics but alcohol policy and environmental characteristics of the university in which students were enrolled. Method: Secondary data analysis was employed in which variables under study were derived from a raw data of a nationwide representative sample in 2009. Raw data under analysis included 3,665 students from 63 universities across Korea. Organizational and environmental characteristics of the university were collected from university administrators while individual characteristics and drinking behavior from the students in using self-administrated questionnaire. Multilevel regression analyses were employed to describe alcohol policy effects on students's drinking problems measured by AUDIT by using HLM7.0. Results: ICCs indicate that variation in drinking problem depends on alcohol policy of university. Multilevel regression models identified statistically significant factors in explaining variance of drinking problems. Group means on drinking problem are affected by indicators representing alcohol policy with level of drinking problem of student being decreased in accordance to level of availability of alcohol on campus. Conclusions: It is concluded that drinking problems among university students were associated with both individual characteristics and alcohol policy of the university they enrolled. This study supports policy belief that interventions at environmental as well as individual level are required to prevent drinking problem among university students.

• Journal of the Korean Data and Information Science Society
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• v.24 no.6
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• pp.1285-1296
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• 2013

The fundamental concerns of this paper are to analyze the effects of student course evaluation using subject characteristic and student characteristic variables. We use a 2-level hierarchical linear model since the data structure of subject characteristic and student characteristic variables is multilevel. Four models we consider are as follows; (1) null model, (2) random coefficient model, (3) mean as outcomes model, (4) intercepts and slopes as outcomes model. The results of the analysis were given as follows. First, the result of null model was that subject characteristics effects on course evaluation had much larger than student characteristics. Second, the result of conditional model specifying subject and student level predictors revealed that class size, grade, tenure, mean GPA of the class, native class for level-1, and sex, department category, admission method, mean GPA of the student for level-2 had statistically significant effects on course evaluation. The explained variance was 13% in subject level, 13% in student level.

• 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.

• Journal of Preventive Medicine and Public Health
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• v.43 no.3
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• pp.245-256
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• 2010

Objectives: This study aims to compare quality indicators for the hemodialysis services between patients with health insurance and those with medical aid. Methods: This study used data from sampled hospitals that provided a hemodialysis service. A total of 2287 patients were selected, and the information for hemodialysis service has been granted from medical record reviews. A multi-level regression analysis was used to examine the differences in process and outcome indicators for hemodialysis between patients with health insurance and those with medical aid. Process indicators were defined as: frequency of hemodialysis, hemodialysis time, erythropoietin (EPO) use, measurement of hemodialysis dose at least once a month, measurement of phosphate at least once every three months, and measurement of albumin at least once every three months. Outcome indicators were defined as: hemodialysis adequacy, anemia management, blood pressure management, and calcium, phosphate and nutrition management. The total scores for outcome indicators ranged from 0 (worst) to 4 (best). Results: There was a significant difference in the measurement of hemodialysis dose at least once a month between patients with health insurance and those with medical aid (OR 0.66, 95% CI = 0.43 - 0.99). However, frequency of hemodialysis, hemodialysis time, EPO use, measurement of phosphate at least once every three months, measurement of albumin at least once every three months, hemodialysis adequacy management, Hb${\geq}$11 g/dL, blood pressure within the range of 100-140 /60-90 mmHg, calcium x phosphate${\leq}$55 $g^2/dL^2$ and albumin${\geq}$4 g/dL were not significantly different between the groups. Conclusions: There were no significant differences in outcome indicators for hemodialysis between the groups. Further studies are warranted into the mechanism that results in no differences in the outcome indicators for hemodialysis.

• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.4
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• pp.271-276
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• 2021

Arc fault detector based on multilevel DWT with analysis of high-frequency noise components over 100 kHz is proposed in this study to improve the performance in detecting serial arcs and distinguishing them from inverter noise in PV systems. PV inverters generally operate at a frequency range of 20-50 kHz for switching operation and maximum power tracking control, and the effect of these frequency components on the signal for arc detection leads to negative arc detection. High-speed ADC and multilevel DWT are used in this study to analyze frequency components above 100 kHz. Such high frequency components are less influenced by inverter noise and utilized to detect as well as separate DC series arc from inverter noise. Arc detectors identify the input current of PV inverters using a Rogowski coil. The sensed signal is filtered, amplified, and used in 800kSPS ADC and DWT analysis and arc occurrence determination in DSP. An arc detection simulation facility in UL1699B was constructed and AFD tests the proposed detector were conducted to verify the performance of arc detection and performance of distinction of the negative arc. The satisfactory performance of the arc detector meets the standard of arc detection and extinguishing time of UL1699B with an arc detection time of approximately 0.11 seconds.

• Proceedings of the IEEK Conference
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• 2001.09a
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• pp.69-72
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• 2001

본 논문에서는 디지털 통신 시스템의 블라인드 등화에 있어서, 다중레벨 modulus를 기준 신호로 사용하여 등화기의 탭 계수 갱신 식에 사용되는 오차 신호를 형성함으로써 등화기의 블라인드 수렴 특성을 개선한 다중레벨 modulus 알고리즘들의 성능을 분석하였다. 다중경로 채널 하에서 QAM 신호점에 대해 컴퓨터 모의실험을 통하여 단일/다중레벨 modulus 알고리즘(SMMA)과 기존의 modified constant modulus algorithm(MCMA) 및 최근에 제안된 다중레벨 modulus 알고리즘(MMA) 등의 블라인드 수렴 및 정상 상태 성능을 비교하였다.