• Journal of Physiology & Pathology in Korean Medicine
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• v.17 no.1
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• pp.118-122
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• 2003

Oxidative stress and its consequent lipid peroxidation exert harmful effects, which have been currently involved in the generation of carbon tetrachloride (CCl₄)-induced fibrosis(cirrhosis). In this study, it was investigated whether dried extract of 田螺(Concha Cipangopaludinae; CC) has liver functional improvement, antioxidative and antifibrotic effect in rats those were induced liver fibrosis by CCl₄ administration. The female Sprague-Dawley rats were divided into 3 groups(Normal, AC, AC-CC) and were observed in 6 weeks. Except for normal group, liver fibrosis(cirrhosis) in rats were developed by CCl₄ administration(0.8 ㎖/rat/week). And the rats were treated with prepared CC(p. o. 2 ㎖/day/rat). At the time of sacrifice, the liver, kidney and spleen were weighed and the ratio of organ weight/body weight was calculated. The MDA, hyp and biochemical parameters(AST, ALT, ALP, t-bili) were measured in sera and liver tissue of rats. The strong yellow color of urine was observed in all CCl₄-treated group compared with normal group, but jaundice didn't appear in CCl₄-treated group. The mortality of CCl₄-treated group is very low(<13%) during 6 weeks of observation time. The ratio of liver/body as well as the weight of liver in CCl₄-treated rats significantly increased compared with that in normal group(p<0.001). The level of clinical parameters in sera of all liver fibrosis(cirrhosis) developed rats were significantly higher than that of normal group(p<0.001-0.05). Especially the value of BUN, ALP, t-bilirubin in AC-CC group showed 20.9%, 19.6%, 47.9% lower than that in AC group. The content of hyp in CCl₄-treated rats was significantly higher than normal group(p<0.001～<0.05), and showed 12.2% lower value in the AC-CC group than AC group(p<0.05). The production of lipid peroxidation(MDA) in sera and liver tissue significantly increased under the fibrotic(cirrhotic) condition(p<0.001～<0.05). Especially the MDA value of AC-CC group in sera significantly 46.5% decreased compared with that of AC group(p<0.05), and the MDA value of AC-CC in liver tissue showed 21.4% lower than that of AC group. Concha Cipangopaludinae can be improved hepatic function, and maybe have effect of liver protection, antioxidation and antifibrosis.

• Journal of the Institute of Convergence Signal Processing
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• v.3 no.3
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• pp.70-75
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• 2002

This paper proposes new single stage power factor correction (PFC) full bridge converter. The proposed converter is combined previous ZVS full bridge DC/DC converter with two inductors, two diodes, two magnetic coupling transformer for PFC. This process of power is isolated from the source and also regulate stable DC output voltage in a category. In this topology, the voltage stress of main switches is reduced by zero voltage switching. Moreover, the proposed converter doesn't need active PFC switch and auxiliarly circuits, like control and gating board, so it could decrease the size and cost and increase the efficiency.

• Journal of Power Electronics
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• v.9 no.6
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• pp.823-834
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• 2009

This paper proposes a high-efficiency single-stage ac/dc converter. The proposed converter features low voltage stresses and reduced switching losses. It operates at the boundary of discontinuous- and continuous-conduction modes by employing variable switching frequency control. The turn-on switching loss of the switch can be reduced by turning it on when the voltage across it is at a minimum. The voltage across the bulk capacitor is independent of the output loads and maintained within the practical range for the universal line input, so the problem of high voltage stress across the bulk capacitor is alleviated. Moreover, the voltage stress of the output diodes is clamped to the output voltage, and the output diodes are turned off at zero-current. Thus, the reverse-recovery related losses of the output diodes are eliminated. The operational principles and circuit analysis are presented. A prototype circuit was built and tested for a 150 W (50V/3A) output power. The experimental results verify the performance of the proposed converter.

• Journal of the Korean Society of Industry Convergence
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• v.3 no.2
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• pp.131-139
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• 2000

Gear train in the automobile to be used for controlling gas flow in automobiles consists of spur gears with involute tooth type in multiple stages. This spur gear is designed considering to the high power transfer efficiency, bending stress and contact stress in the static and dynamic analysis. The torque has been increased simultaneously the angular velocity has been decreased through the stages after being supplied by AC synchronous motor. This apparatus is controlled by electrical devices such as the PIC microprocessor, hall sensor and other electric components. By comparing the preset data of PIC microcomputer which is supplied by external DC electric power with the value set of hall sensor which detects the rotation angle position, PIC microcomputer thus controls AC motor and gear train according to the program algorithm which includes the on-off control and PWM motor driving method. As the result of the experiment such as performance, fatigue, torque test, we can conclude that this system is superior to the same and familiar foreign systems.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.1701-1703
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• 2006

Here we describe a novel driving scheme in the form of negative AC bias stress (NAC) to compensate shift in the threshold voltage for hydrogenated amorphous silicon (${\alpha}$-Si:H) thin film transistor (TFT) for AMOLED applications. This scheme preserves the threshold voltage shift of ${\alpha}$-Si:H TFT for infinitely long duration of time(>30,000 hours) and thereby overall performance, without using any additional TFTs for compensation. We briefly describe about the possible driving schemes in order to implement for real time AMOLED applications. We attribute most of the results based on concept of plugging holes and electrons across the interface of the gate insulator in a controlled manner.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.507-510
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• 2002

In economical points of view, AC loss of high temperature superconducting devices is considered as a serious problem that must be solved. Expecially, in case of HTS cables, HTS tapes are wound helically on the former to reduce AC loss. Critical characteristics of HTS tapes, however, are influenced by mechanical stress as well as electrical, temperature, and magnetical factors. The purpose of this study is to investigate the over current characteristics of HTS tapes given mechanical stress when they are wound on the former. We prepared HTS tapes with the pitch angle 20$^{\circ}$, length 25cm as well as tapes with pitch angle 0$^{\circ}$. When current of over 200A$\_$rms/ was applied, we found out that there are differences to the rate of resistance increase between the case of pitch angle 20$^{\circ}$and that of 0$^{\circ}$. The rate of resistance variation in HTS tapes of pitch angle 20$^{\circ}$increased more slowly than that of pitch angle 0$^{\circ}$. As a result, we concluded that if critical characteristics of HTS tapes are degraded by any external factor, when over current is applied, the current limiting characteristics in HTS tapes won't be able to be expected any more.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.6
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• pp.623-628
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• 2010

This paper presents a wind-power-driven portable power source based on piezoelectric effect. Positive piezoelectric effect is one of efficient and widely used mechanisms for converting mechanical energy to electrical energy. However, for this mechanism, a periodic mechanical stress with a high frequency, as in the case of AC, has to be exerted; such stress cannot be exerted by the natural wind in the environment. The natural wind has a constant velocity with slow and irregular variations, as in the case of DC. In this paper, we propose a novel and simple mechanism to convert mechanical energy into electrical energy. The DC-like wind flow is passed through a propeller to convert it to an AC-like wind flow; the resultant AC-like periodic flow induces vibrations in a piezoelectric cantilever, thereby, generating electrical power. This system is expected to be one of practical solutions for wireless energy supply to ubiquitous sensor networks (USNs).

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.2
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• pp.190-195
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• 2009

This paper introduces experimental investigates of an electrical accident of the distributing cable termination with simulated a shoddy construction. We prepared two termination kites, one is built-in type, the other is heat contraction type. Also, we manufactured cable termination that have simulated defect by badness construction and investigated their insulation characteristics such as ac (35[kV], 1[min]) and impulse (95[kV], $1.2{\times}50[{\mu}s]$) withstand test. The influence of defects such as thickness decrease, the gap between stress-con of housing and semiconductor and heating time on insulating properties of the termination have been studied. The thickness decrease of an insulator decreases ac breakdown strength suddenly and the breakdown traces of the insulator that is damaged by knife displayed elliptic shape. The gap of between stress-con and semiconductor deteriorates dielectric strength of insulator seriously. In heat contraction type, the ac breakdown voltage became low when the heating time is short.

• Horticultural Science & Technology
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• v.33 no.2
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• pp.259-267
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• 2015

This study was conducted to comparatively evaluate antioxidant capacity (AC) of seven cultivars of kiwifruit (Actinidia spp.) and their protective effects on neuronal PC-12 cells. The contents of total phenolics (TP) and total flavonoids (TF) of kiwifruits were also examined. Five cultivars of kiwifruit, Actinidia chinensis (cv. Haehyang and cv. Haegeum), A. eriantha (cv. Bidan), A. arguta ${\times}$ A. deliciosa (cv. Mansoo), and A. arguta (cv. Chiak), were bred in Korea, while two cultivars, A. deliciosa (cv. Hayward) and A. linguiensis (accession number 041AE), originated from New Zealand and China, respectively. Skin extracts of kiwifruit showed higher TP, TF, and AC than flesh extracts. The highest levels of TP and AC were found in cv. Bidan flesh extract among cultivars studied, but the TF content of cv. Bidan flesh extract was the lowest. The kiwifruit bred in Korea had higher AC than their counterparts. AC of kiwifruit had a highly positive linear correlation with TP and TF. The flesh extracts from cv. Hayward, cv. Haehyang, and cv. Haegeum significantly (p < 0.05) prevented PC-12 cells from oxidative stress induced using $H_2O_2$ compared to a control with $H_2O_2$ only. Overall, our results suggest that kiwifruit bred in Korea may offer a good source of antioxidants and serve as functional materials.

• Journal of the Korean Society of Safety
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• v.27 no.4
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• pp.7-12
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• 2012

In this study, the solidification characteristics inside the AC7A casting material was analyzed using the numerical analysis method and was verified using the experimental method by the pre-heated temperature conditions of metal casting device. For the numerical analysis, "COMSOL Multiphysics", the commercial code based on the finite element analysis(FEA), was used in order to predict the thermal deformation of the AC7A casting material including temperature, displacement and stress distribution. Also, in order to verify the results calculated by the numerical analysis, the experiment for temperature measurement inside the AC7A casting material was performed using the K-type thermocouple under the same condition of numerical analysis method. In the numerical results, thermal deformation inside AC7A casting material was well-suited for manufacturing products when the pre-heated temperatures of the metal casting device was $250^{\circ}C$. When the results of the temperature distribution were experimentally measured and were compared with those of the numerical result, it appeared that there was some temperature difference because of the latent heat by phase change heat transfer. However, the result of cooling temperature and patterns were almost similar except for the latent heat interval. The solidification characteristics was closely related to the temperature difference between the surface and inside of the casting.