• Journal of the Korean Society of Visualization
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• v.11 no.1
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• pp.48-52
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• 2013

This paper presents experimental observation of asymmetric electrohydrodynamic flow generated around a pair of symmetric coplanar electrodes. Electrodes are attached on the bottom of the cavity containing a dielectric liquid, i.e., a mixture of dodecane and 0.5% wt Span80. In the first experiment, an AC voltage of 1500 V is applied with the frequency varying in the range 10~500 hz and the left electrode being grounded. The flow patterns show that the center line of vortices is unexpectedly tilted to the left side. If the right side electrode is grounded, the center line is tilted to the right side. The magnitude of the fluid velocity shows an irregular variation with the frequency in the range 10 Hz~100 Hz, beyond which it simply decays. In the second experiment, we applied fixed AC with 1000 V and 60 Hz superposed by DC voltage varying in the range -1000 V ~ +1000 V. The center line of the flow pattern is tilted to the right side with positive DC voltage and to the left side with negative DC. We have managed to show that the flow pattern can be symmetric with a suitable combination of DC and AC, e.g., DC 850 V plus AC 1000 V with the frequency 10 Hz.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.1
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• pp.53-60
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• 2010

This paper dealt with the acoustic detection of partial discharge (PD) in insulation oil for insulation diagnostics of oil immersed transformers. Electrode systems such as needle to plane, plane to plane, and floating were fabricated to simulate some defects in transformers. A wide band acoustic emission(AE) sensor with the frequency ranges of 100 kHz~1 MHz and a narrow band AE sensor with the resonant frequency of 140 kHz were used in the experiment. Also, a decoupler and an amplifier were designed to detect and amplify the acoustic signal only. The decoupler separates acoustic signal from DC source without any distortion, and the amplifier has the gain of 40 dB in frequency ranges of 11 kHz~4 MHz. In the experiment, frequency components and propagation characteristics of acoustic signal were analyzed, and an algorithm of positioning of PD occurrence by the time difference of arrival was proposed. From the results, the frequency components of the acoustic signal exist from 50 kHz to 200 kHz and the positioning error of PD calculated by three AE sensors was within 1%.

• The korean journal of orthodontics
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• v.53 no.5
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• pp.307-316
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• 2023

Objective: To evaluate the effects of an electric toothbrush with vibrational frequencies of 125 Hz and 150 Hz on the orthodontic tooth movement (OTM) rate and the production of prostaglandin E2 (PGE2). Methods: Out of thirty patients (aged 18-25 years; 16 females and 14 males), ten patients each formed Group A and B, who used electric toothbrushes with 125 Hz and 150 Hz vibrations, respectively. The remaining ten patients (Group C) served as the control group and did not use electric toothbrushes. The rate of OTM and levels of PGE2 using microcapillary pipettes were calculated before the start of retraction (T0), on the 30th day (T1), on the 60th day (T2), and on the 90th day (T3) from the start of retraction in all the groups. Results: There was a statistically significant difference in the mean OTM values and PGE2 levels in all three groups at different time intervals, with the maximum difference seen in Group B compared to Group A and least in Group C at T1, T2 and T3. Conclusions: The rate of OTM and levels of PGE2 were highest in patients who used an electric toothbrush with 150 Hz mechanical vibration compared to those who used an electric toothbrush with 125 Hz mechanical vibration and least in patients who did not use an electric toothbrush. Mechanical vibration led to an increase in the PGE2 levels and accelerated the OTM.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1960-1962
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• 2004

In this paper, we have studied shielding characteristics of high conductivity or high permeability materials on ELF magnetic fields generated from single or three phase AC line. Perm alloy has been selected as high permeability material and copper as high conductivity material. Four-plate shield (square section) was considered as a shielding shape. We found copper showed stable shielding effects more than perm alloy.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1360-1365
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• 2007

A linear compressor used in a refrigerator has higher energy efficiency than other compressors. On the other hand, its vibration level has still been much severe. Changing the characteristics of connecting parts may reduce the vibration level of linear compressor. The piston, body and shell are assumed to be rigid. These rigid bodies are connected by coil springs and flexible loop pipe. This paper derived the mathematical model by combining the equation of motion of rigid parts and flexible parts. The variation of vibration level according to the change of connecting parts was investigated.

• Proceedings of the KIEE Conference
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• 2003.04a
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• pp.79-81
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• 2003

최근 전력계통에 연결된 비선형 장치가 부하의 큰 부분을 차지하고 있다. 비선형 장치는 계통전류에 고조파를 발생시키고 기본파 전류에 의한 도체 손실에 고조파 전류손이 더해져서 도체의 온도를 상승시킨다. 도체의 온도 상승에 관한 연구는 주로 정현파 60Hz 전류에 기초해서 통전 용량을 계산하고 그에 따른 손실을 계산하였다. 본 논문에서는 GIS 모선에 고조파 전류가 포함되는 경우 고조파의 영향에 따른 통전 용량을 계산한다. 즉, GIS 모선에 주파수의 영향에 따른 손실비를 구하고, 유한 요소 해석을 통해 계산된 GIS 모선의 고조파에 따른 손실값을 정현파 60Hz 전류일 때에 계산된 손실값과 비교한다. 이 결과는 GIS 모선의 정확한 통전용량을 예측하는데 사용될 것이다.

• The Korean Journal of Pain
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• v.14 no.2
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• pp.261-265
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• 2001

Radiofrequency thermocoagulation of the gasserian ganglion is a safe procedure that can be controlled well and provides satisfactory pain relief from trigeminal neuralgia with low risk. Here the authors report a case of radiofrequency thermocoagulation performed on a recurred trigeminal neuralgia patient, with particular attention to the V3 area. The patient was treated with microvascular decompression 7 years previous, which lead to untolerable side effects from carbamazepine medication. Following the paresthesia and masseter muscle contracture test at 50 Hz-0.06 volt and 2 Hz-0.5 volt respectively, RF lesionings were performed for 60 sec at $60^{\circ}C$ and 70 sec at $70^{\circ}C$. One week after the procedure, the pain was reduced with a mild hypoesthesia in the V2 area. After 6 months, the pain recurred. Therefore, we performed the same procedure again. After 8-months of follow-up, there has been no pain or complications.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2007.05a
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• pp.291-294
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• 2007

This paper preserts the characteristics of leakage currents flowing through 18 kV zinc oxide (ZnO) surge arrester under the mixed DC and AC voltages. The I-V curves of ZnO surge arrester were measured as a function of the voltage ratio K The I-V curves under the mixed DC and AC voltages lay between the pure DC and AC characteristics, and the cross-over phenomenon in I-V curves was observed at the low current region As a result, the increase of DC component to mixed voltages causes the increase of resistive component of total leakage current th ZnO surge arrester.

• Journal of Korea Multimedia Society
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• v.7 no.12
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• pp.1650-1656
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• 2004

In this paper, a multi-adaptive filter is proposed for removing EOG and the 60 Hz power supply noise from EEG measured in the frontal lobe and the feedback output control method is implemented for biofeedback. The multi-adaptive filter has been implemented on the TMS320C6711 DSP system and the feedback output control algorithm has been realized by calculating the ratio of alpha wave on the TMS320C31 DSP system with real time performance. Through the experiment using the implemented multi-adaptive filter and feedback output controller, we demonstrate that the proposed adaptive filter effectively removes EOG and the 60 Hz power supply noise from the measured EEG in the frontal lobe and the feedback algorithm controls the level of stimulation by the ratio of the alpha wave.

• Proceedings of the KIEE Conference
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• 2001.07b
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• pp.1281-1283
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• 2001

An investigation into power conditioners that interface with photovoltaic array and utilities has been completed. The rating for this investigation is residential system(3-5kW) that interface with a 220V single phase utility connection. As the result of this investigation, a 3kW high frequency PWM IGBT inverter feeding a high frequency isolation transformer with a sinusoidal current wave was selected. The output of the transformer rectified with a diode bridge rectifier four IGBT, used as 60Hz switched, reverse the polarity of the rectified current on every other half cycle of the utility voltage. Even though the high frequency link system used more power semiconductors a net size, weight, and parts cost saying result compared to the other systems due to elimination of 60Hz transformer.