• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.1
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• pp.31-40
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• 2014

This paper describes an optimal configuration for multi-central inverters in a medium-voltage (MV) grid, which is suitable for large-scale photovoltaic (PV) power plants. We theoretically analyze a proposed common-mode equivalent model for problems associated with multi-central transformerless-type three-phase full bridge(3-FB) PV inverters employing two-winding MV transformers. We propose a synchronized PWM control strategy to effectively reduce the common-mode voltages that may simultaneously occur. In addition, we propose that the existing 3-FB topology may also have the configuration of a multi-central inverter with a two-winding MV transformer by making a simple circuit modification. Simulation and experimental results of three 350kW PV inverters in a multi-central configuration verify the effectiveness of the proposed synchronization control strategy. The modified transformerless-type 3-FB topology for a multi-central PV inverter configuration is verified using an experimental prototype of a 100kW PV inverter.

• Journal of Sasang Constitutional Medicine
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• v.19 no.3
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• pp.242-256
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• 2007

1. Objectives Purpose of this study is to prove anti-aging and anti-oxidative effects of Gongjinhugwon-dan decoction. 2. Methods The SD rats used in this experiment were 6, 18, and 36 weeks old. Each age group was again divided into three groups. These nine groups consisted of 8 rats each. One group was given no treatment, another group was dosed $200{\mu}l$ of normal saline daily, and the last group was dosed $200{\mu}l$ of 1 % Gongjinhugwon-dan and saline mixture. At the conclusion of the experiment, the age groups were relabelled accordingly (10 weeks, 22 weeks, and 40 weeks). After 4 weeks, change of weight and liver markers were measured. Serum LDL cholesterol, total bilirubin, albumin, glucose, GOT and GPT levels were observed in order to check the hematological modification. Also, each organ tissue was biopsied in order to measure the SOD activity and the glutathione content change. 3. Results & Conclusions Aging did not cause any significant change in GOT and LDH, but GPT and albumin levels showed increase after GHD intake. Serum GPT was lower in the experimental group. Serum total bilirubin of the 40 w GHD group was significantly increased. The populations of dendritic cells in the spleens of the GHD groups were significantly increased. The levels of GSH in the liver of the 40 w GHD group and in the kidney of 22w-GSD were significantly increased in comparison with those of the normal groups. The degenerative change of brain tissue was decreased in the 40 w GHD group compared with those of the 40w normal group and the 40 w saline group. These results suggest that anti-oxidative GSH concentration of liver and kidney in rats treated with GHD showed significant increase in the 40 w GHD group. GHD was effective on increasing anti-oxidative substance in liver and dendritic cells in spleen, thus helping immune system and preventing cell mutation and degenerative change of brain tissues. Further studies and clinical investigation with GHD is needed.

• Journal of Power Electronics
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• v.13 no.2
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• pp.322-328
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• 2013

This paper presents a modified Current Source Parallel Resonant Push-pull Inverter (CSPRPI) for single phase induction heating applications. One of the most important problems associated with current source parallel resonant inverters is achieving ZVS in transient intervals. This paper shows that a CSPRPI with the integral cycle control method has dynamic ZVS. According to this method, it is the Phase Locked Loop (PLL) circuit that tracks the switching frequency. The advantages of this technique are a higher efficiency, a smaller package size and a low EMI in comparison with similar topologies. Additionally, the proposed modification results in a low THD of the ac-line current. It has been measured as less than %2. To show the validity of the proposed method, a laboratory prototype is implemented with an operating frequency of 80 kHz and an output power of 400 W. The experimental results confirm the validity of the proposed single phase induction heating system.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.147-149
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• 2001

In order to understand the influence of the modification of deformation texture on the formation of annealing texture, the evolution of texture during the clock rolling and the subsequent annealing was investigated by employing X-ray texture measurements and microstructure observation. The $\beta$-fiber orientations were proved to be quite unstable during the clock rolling. The clock rolled texture having uniform orientation densities along $\{011\}//ND$ fiber resulted in the randomization of annealing texture. This indicated that the operation of both the oriented nucleation and the oriented growth was effectively suppressed in the clock-rolled specimen during recrystallization.

• Journal of computational fluids engineering
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• v.19 no.4
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• pp.75-79
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• 2014

In the paper, a study on the analysis of the effects of trailing edge thickness on the aerodynamic characteristics of an airfoil is described. In this research, modification of the formula representing NACA symmetric airfoil is studied to change the airfoil shape with different trailing edge thickness of user's choice. According to the result of aerodynamic characteristics, as the trailing edge thickness increases the maximum lift coefficient increases while the lift-to-drag ratio decreases. In this paper flow calculation results are demonstrated and the analysis on those results and findings on the effects of non-zero thickness of trailing edge are suggested.

• Proceedings of the KSME Conference
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• 2001.06c
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• pp.257-262
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• 2001

This paper describes a specialized CAD system for injection mold design, which has been developed using the application procedure interfaces of Unigraphics. The system consists of modeling modules that are mutually independent and can be accessed without any predefined sequence. In addition, the design process modeling capability proposed in this paper facilitate mold redesign process caused by modification of part shape.

• Transactions of the Korean Society of Automotive Engineers
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• v.3 no.3
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• pp.90-96
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• 1995

In general, natural gas engine converted from gasoline engine has disadvantage of power decrease. In order to increase power output in natural gas engine, the improvement of in-cylinder flow motion has been believed as the most effective method. In this study, the geometry of combustion chamber in 4 valve DOHC natural gas engine is modified, and in-cylinder flow patterns is analyized. Also engine performance is evaluated according to the modification of in-cylinder flow motion.

• Journal of Korean Society for Quality Management
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• v.12 no.2
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• pp.15-24
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• 1984

Since W.A. Shewhart (1931) developed the quality control method using the control chart, many theoretical and empirical works about such an analytical method have been done. However there are two major methods relating to the control chart analysis; the conventional 3 sigma control method and the warning limit method which has been suggested as a modification of the former. The conventional 3 sigma method requires to take a remedial action only when a quality characteristic is beyond the control limit (3 sigma). However, once a quality characteristic is over the control limit, searching and repairing an assignable cause requires time consuming job and high costs. Therefore if we set the warning limit between the central line and the control limit, we will be able to take remedial measures before too late. In spite of its advantage, much attention has not been paid to use the control chart with warning limit in Korean industries. The main object of this study is to examine improvement of quality and productivity when the control chart with warning limit is used.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.10
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• pp.1802-1806
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• 2007

Nowadays, many configurations and applications of small atmospheric plasma source have been investigated with growing interest, as it provides the bacteria inactivation, the surface modification and removal of unwanted small regions, and so on. In this paper, the non-thermal micro plasma source under atmospheric pressure by means of submicrosecond pulse voltage waveforms is suggested. Plasma operates in helium is appears as a small (sub-mm) glow at the tip of a plasma gun. Electrical measurements show that the plasma source operates at low voltage (about 500V) and the power consumption is about 1W at 25kHz. Moreover, the emission spectrum shows the relatively higher emission intensity of oxygen particles than those of helium and nitrogen.

• Bulletin of the Korean Mathematical Society
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• v.33 no.3
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• pp.455-463
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• 1996

In [3] and [4], Kitahara, Pak and the author obtained the conformally invariant tensor $B_0$, which is an algebraic Hermitian analogue of the Weyl conformal curvature tensor W in the Riemannian geometry, by the decomposition of the curvature tensor H of the Hermitian connection and the notion of semi-curvature-like tensors of Tanno (see[7]). In [5], the author defined a conformally invariant tensor $B_0$ on a Hermitian manifold as a modification of $B_0$. Moreover he introduced the notion of local conformal Hermitian-flatness of Hermitian manifolds and proved that the vanishing of this tensor $B_0$ together with some condition for the scalar curvatures is a necessary and sufficient condition for a Hermitian manifold to be locally conformally Hermitian-flat.