• The Transactions of the Korean Institute of Electrical Engineers D
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• v.49 no.8
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• pp.467-472
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• 2000

A three-level decoupled sliding mode controller is developed to achieve asymptotic stability for a class of sixth-order nonlinear systems. The sixth-order system is decoupled into three subsystems according to the structure of the whole system. Each subsystem has a separate control target in the form of a sliding surface. The information of the third sliding surface is transferred to the second one through an intermediate variable and the information of the second sliding surface is transferred to the first one through another intermediate variable. Consequently, the controller designed on the basis of the first sliding surface can make three subsystems move toward their sliding surfaces, respectively. The three-level decoupled sliding mode controller is applied to the double-inverted pendulum problem where the zero stable states are required.

• Restorative Dentistry and Endodontics
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• v.19 no.1
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• pp.85-96
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• 1994

In this study, 24 curved resin blocks were prepared by one of the following four methods: 1) Conventional technique using K-flexo files 2) Step-back technique using K-flexo files 3) Crown-down technique using K-flexo files 4) Canal Master instrumentation using Canal Master Resin blocks were sectioned, photographed, and evaluated the mean centering ratio and the mean area of dentin removed before and after the instrumentation. The results were as follows : I. the mean centering ratio 1. In the level 1 and level 3, there was no significant difference in the mean centering ratio. 2. In the level 2, Step-back technique showed the worst mean centering ratio among the tested groups(p<0.001) and there was no significant difference between the other three groups. 3. In the level 4, Canal Master instrumentation and Step-back technique showed better mean centering ratio than the other two techniques(p<0.001) and there was no significant difference between the two techniques. II. the mean area of dentin removed 1. In the level l and level 3, there was no significant difference in the mean area of dentin removed. 2. In the level 2, Canal Master instrumentation removed less dentin than the other three techniques(P<0.01). 3. In the level 4, Crown-down technique removed less dentin than the other three techniques(P<0.05).

• Health Policy and Management
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• v.6 no.1
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• pp.191-210
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• 1996

This study purported to acquire information necessary to improve the operational efficiency of general hospitals. It tried to determine major indices which represent managerial performance of general hospitals and to identify the managerial characteristics of general hospital which affect the major financial indices. 201 hospitals which were subject to standardization audit by the Korean Hospital Association were investigated and 80 hospitals were finally chosen for this study. Their financial and managerial data during the period between January 1991 and December 1991 were collected. Considering financial indices in this study were the ration of net income to total asset, income growth rate, and quick ration. The results of study are summarized as followings. First. The ration of net income to total assets and quick ration were highly related to managerial characteristics of general hospitals. Therefore, the standardization of three financial indices should be needed to systematically check the operational efficiency of general hospitals. Second, the sample hospitals can be classified as four groups on the basis of their financial indices' level. 4 of those hospitals(5.0%) showed high level of performance in terms of three financial indices and 27 of them(33.7%) showed that they are highly related to only two financial indices. 34 hospitals(42.5%) showed they have high level of relationship with only one indices and 15 hospitals(18.8%) showed very weak performance level with three indices. In addition, there is no hospitals to show mid-range level of managerial performance in relation to all three financial indices. Third, there is no significant relationship between three financial indices and the managerial characteristics of hospitals such as the number of beds, type of operation, location of hospitals, and etc. However, in the case of hospitals which have high level of managerial performance, they have more specialists and medical support personnel in comparison to low performance hospitals. They also have high level of bed occupancy rate and average length of stay(ALOS). In conclusion, the study showed the standardization of 3 financial indices are necessary to systematically evaluate the managerial performance of general hospitals and provide more accurate operational information for each hospital. To do so, it is necessary to focus on management side of hospital such as the effective human resource management and quality enhancement of medical treatment.

• Journal of Electrical Engineering and Technology
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• v.12 no.1
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• pp.78-90
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• 2017

This paper presents the design of closed loop controllers operating a single-phase AC-DC three-level converter for improving power quality at AC mains. Closed loop inhibits outer voltage controller and inner current controller. Simulations of three level converter with three different voltage and current controller combinations such as PI-Hysteresis, Fuzzy-Hysteresis and Fuzzy tuned PI-Hysteresis are carried out in MATLAB/Simulink. Performance parameters such as input power factor and source current total harmonic distortion (THD) are considered for comparison of the three controller combinations. The fuzzy-tuned PI voltage controller with hysteresis current controller combination provides a better result, with a source-current THD of 0.93% and unity power factor without any source side filter for the three level converter. For load variations of 25% to 100%, a THD of less than 5% is obtained with a maximum value of only 1.67%. Finally, the fuzzy-tuned PI voltage with hysteresis controller combination is implemented in a Xilinx Spartan-6 XC6SLX25 FPGA board for experimental validation of power quality enhancement. A prototype 100 W, 0-24-48 V as output converter is considered for the testing of controller performance. A source-current THD of 1.351% is obtained in the experimental study with a power factor near unity. For load variations of 25% to 100%, the THD is found to be less than 5%, with a maximum value of only 2.698% in the experimental setup which matches with the simulation results.

• Proceedings of the KIPE Conference
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• 2011.11a
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• pp.63-64
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• 2011

The inevitable calculation time delay of digital controller especially degrades the voltage control performance of three-phase UPS systems. This paper proposes time delay compensators based on the Smith-predictor for both voltage and current controllers of three-level NPC inverters. The PSIM-based simulation results show that the proposed controller with delay compensator gives improved voltage control performance with respect to time delay.

• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.4
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• pp.376-382
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• 2014

This paper proposes the pulse width modulation (PWM) control strategy for low-speed operation in the three-level neutral-point-clamped (NPC) inverters based on the bootstrap gate drive circuit. As a purpose of the cost reduction, several papers have paid attention to the bootstrap circuit applied to the three-level NPC inverter. However, the bootstrap gate driver IC cannot generate the gate signal to the IGBT for low-speed operation, because the bootstrap capacitor voltage decreases under the threshold level. For low-speed operation, the dipolar and partial-dipolar modulations can be the effective solution. However, these modulations have drawbacks in terms of the switching loss and THD. Therefore, this paper proposes the PWM control strategy to operate the inverter at low-speed and to minimize the switching loss and harmonics. The experimental results are presented to verify the validity on the proposed method.

• Journal of Power Electronics
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• v.16 no.6
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• pp.2085-2098
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• 2016

Laminated busbars with a low stray inductance are widely used in NPC three-level inverters, even though some of them have poor performances in heat equilibrium and overvoltage suppression. Therefore, a theoretical method is in need to establish an accurate mathematical model of laminated busbars and to calculate the impedance and stray inductance of each commutation loop to improve the heat equilibrium and overvoltage suppression performance. Firstly, an equivalent circuit of a NPC three-level inverter laminated busbar was built with an analysis of the commutation processes. Secondly, on the basis of a 3D (three dimensional) cubical thermal model and mirror circulation theory, a supersymmetric mirror circulation 3D cubical thermal model was built. Based on this, the laminated busbar was decomposed in 3D space to calculate the equivalent resistance and stray inductance in each commutation loop. Finally, the model and analysis results were put into a busbar design, simulation and experiments, whose results demonstrate the accuracy and feasibility of the proposed method.

• Restorative Dentistry and Endodontics
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• v.23 no.2
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• pp.682-689
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• 1998

The purpose of this study was to evaluate the sealing ability of the Microseal$^{(R)}$, which was new obturation system made by Tycom company, U.S.A. Forty-five extracted single-rooted human teeth were resected at cemento-enamel junction and divided three groups. All canals were prepared using Profile system, and then each group was obturated by lateral condensation technique (group 1), vertical condensation technique (group 2) and Microseal$^{(R)}$ condensation technique (group 3) with root canal sealer. Teeth were immersed in resorcinol-formaldehyde resin for 5 days at $4^{\circ}C$ and the resin was allowed to polymerize completely for 4 days at room temperature. Teeth were resected horizontally at 1 mm (level I), 2 mm (level II), 3 mm (level III) from the anatomical root apex using low speed microtome and examined with Image analyzer (IBASR, Zeiss co., Germany.) at ${\times}25$ magnification. The gab between the canal wall and the filling material, which was filled with the resin, was measured at each of the three levels. Each ratio of leakage was expressed percentage by calculating the ratio of the area of the resin to the total area of the canal and was analyzed statistically (one-way ANOVA). The results were as follows; 1. The mean ratio of leakage (%) was 6.46% at group 1, 3.06% at group 2, 11.27% at group 3. 2. When evaluating the ratio of leakage at the three levels, there was level I> level II> level III in all groups. Especially, the difference between level I and level III was statistically significant (p<0.05). 3. When evaluating the ratio of leakage at the three groups, there was group 3> group 1> group 2 at all levels. Especially the difference between group 2 and group 3 was statistically significant (p<0.05).

• The Transactions of the Korean Institute of Power Electronics
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• v.14 no.6
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• pp.472-480
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• 2009

This paper describes the overmodulative SVPWM technique and harmonics analyses of three phase NPC type three-level inverter to the modulation index. Three phase NPC type three-level inverter adopted SVPWM to extend the linear region to 0.907, moreover, the following voltage compensation using Fourier series was adopted in the region of overmodulation to make it work to six-step level. PD type of multi carrier method is used with the double Fourier series for the analysis of output power harmonics characteristic. Simulation was performed by PSIM, and the harmonics characteristics of 3-level inverter in each region are analyzed. The side band harmonics of carrier frequency are dominant in the linear region, but these harmonic components are decreased as the inveter goes to overmodulation region, and the harmonics due to the fundamental frequency is increased gradually at the same time. The harmonic analyses are verified through the simulation and experimental results under the same condition.

• Journal of Nutrition and Health
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• v.40 no.8
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• pp.684-692
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• 2007

This study was performed to investigate the effect of chongkukjang intake on lipid metabolism and liver function in ethanol consumed rats. Twenty one Sprague-Dawley male rats aging 4 weeks old were used as experimental animals, which were divided into three dietary groups; casein diet(CA), soybean diet(SB) and chongkukjang diet(CJ). Alcohol was consumed with water as 25%(v/v) ethanol solution. After 4 weeks of experimental period, rats were sacrificed to get blood and liver samples for analysis of lipids, lipid peroxides, antioxidative enzymes and biochemical indices of liver function. The mean body weight, food intake and liver index were not significantly different among three groups. Serum level of total lipid, triglyceride and total cholesterol of chongkukjang diet group was the lowest among three groups although the difference was not significant. HDL-cholesterol level was significantly(p<0.05) higher in chongkukjang diet group than that of casein diet group. LDL-cholesterol level of chongkukjang and soybean diet group was significantly(p<0.05) lower than that of casein diet group respectively. Liver TBARS of chongkukjang and soybean diet group was significantly(p<0.05) lower than that of casein diet group respectively. The superoxide dismutase activity of chongkukjang diet group was significantly(p<0.05) higher than that of casein diet group. Catalase activity was not significantly different among three groups. As indices of liver function, glutamic oxaloacetic transminase(GOT), glutamic pyruvic transminase(GPT), $\gamma$-glutamyl transpeptidase($\gamma$-GTP) and lactate dehydrogenase(LDH) were not significantly different among three groups. Serum alcohol concentration and activities of alcohol dehydrogenase(ADH) and aldehyde dehydrogenase(ALDH) were not significantly different among three groups. The chongkukjang diet seems to give a beneficial effect for improving lipid metabolism by increasing HDL-cholesterol level and SOD activity while reducing liver TBARS level. However, effect on liver function has to be investigated further.