• 대한기계학회논문집
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• 제19권9호
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• pp.2154-2164
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• 1995

In this study, a dielectric cure monitoring system which consists of an electric circuit, a sensor and a personal computer was developed to on-line monitor the dielectric properties of carbon fiber epoxy composite materials. Also, the kinetic model of carbon fiber epoxy composite materials was developed by curve fitting of differential scanning calorimetry data. The start and end points of cure and the relationship between the dissipation factor and the degree of cure were obtained by comparing the dissipation factor from the dielectric properties with the degree of cure from the DSC data. The relationship between the dissipation factor and the degree of cure was tested under various temperature profiles.

• 센서학회지
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• 제20권2호
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• pp.71-76
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• 2011

To characterize the relationship between the stage of hepatic fibrosis and bioimpedance, several electric parameters were estimated in rats with $CCl_4$-induced liver fibrosis. Thirty three Sprague-Dawley rats were intraperitoneally injected with a $CCl_4$-mineral oil mixture (1:1, 0.2 mL/100 g) twice a week for 8 weeks. The resistance(R), reactance(X), impedance(Z), and dissipation factor(D) between 1 kHz and 100 kHz were then evaluated in the livers of the rats under pentobarbital anesthesia using an HP4294A Impedance Analyzer. The rats were killed 2, 4, 6, and 8 weeks later, and their livers were classified in accordance with Ishak's scoring system. R, X, and Z changed in accordance with the progression of hepatic fibrosis and the changes were greater at lower frequencies than at higher frequencies. In comparison, the D spectrum was biphasic; D increased initially then decreased with increasing frequency. All of the parameters(R, X, Z, and D) changed in accordance with the stage of fibrosis in the livers, but D changed specifically with the progression of fibrosis. These results indicate that hepatic fibrosis may be evaluated by determining the changes in D.

• 한국항행학회논문지
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• 제24권4호
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• pp.261-266
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• 2020

항공기 장착물에 KW급 전력변환장치가 탑재되는 경우, 전력 변환 시 발생하는 대량의 발열에 대한 방열설계가 고려되어야 한다. 적절한 방열을 하지 못하는 경우, 장비 오작동 및 화재의 우려가 발생하며 이는 항공기 운항에 있어 치명적인 요인이 될 수 있다. 본 논문은 항공기 장착물에 탑재되는 KW급 전력변환장치의 방열설계에 관하여 기술하였다. 전산해석을 통한 설계 및 제작 후 시험을 수행하였으며, 고전력 변환에 따른 발열부품의 급격한 발열 현상을 확인하여 해석 모델을 보정하였다. 모델 보정 후 방열구조가 개선된 형상으로 설계를 개선하였으며, 미 군사규격인 MIL-STD-810G 의 고온동작 시험을 수행하여 개선된 형상의 타당성을 검증하였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 추계학술대회 논문집 Vol.15
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• pp.296-299
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• 2002

In this paper, a hexagon-type piezoelectric transformer was investigated to increase the output power. The length of its side was 14mm and 17.5mm, respectively. The piezoelectric ceramics was composed to PZT-PMN-PSN. This composition showed the characteristics which had an about 1500 of the mechanical Q-factor, 0.55 of the electromechanical coupling coefficient, $320{\times}10^{-12}C/N$ of the piezoelectric constant $d_{31}$, 0.3 % of the dissipation factor, etc. The voltage step-up ratio increased with increasing the load resistance, $R_{L}$, so it reached 80 with $R_{L}$ of $1M{\Omega}$ and was proportion to the length of side of the hexagon-type piezoelectric transformer. Also, the output power increased with increasing the size of the hexagon-type piezoelectric transformer.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 E
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• pp.2101-2103
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• 1999

The insulation condition of stator windings was measured by dissipation factor($tan{\delta}$) test in the six high voltage motors(rated 6.6kV) which had been in service for two years. The ${\Delta}tan{\delta}$ of motor D and E was higher than that of the rest motors. The specimens were drawn out from stator windings of the high voltage motor and their were analyzed using scanning electron microscope (SEM). SEM result shows that large voids are present in the interface both turn insulation and groundwall insulation.

• Tribology and Lubricants
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• 제30권6호
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• pp.378-383
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• 2014

This study predicts the of the hysteretic friction of a rubber block sliding on an SMA asphalt road. The friction of filled rubber on a rough surface is primarily determined by two elements:the viscoelasticity of the rubber and the multi-scale perspective asperities of the road. The surface asperities of the substrate exert osillating forces on the rubber surface leading to energy dissipation via the internal friction of the rubber when rubber slides on a hard and rough substrate. This study defines the power spectra at different length scales by using a high-resolution surface profilometer, and uses rubber and road surface samples to conduct friction tests. I consider in detail the case when the substrate surface has a self affine fractal structure. The theory developed by Persson is applied to describe these tests through comparison with the hysteretic friction coefficient relevant to the energy dissipation of the viscoelastic rubber attributable to cyclic deformation. The results showed differences in the absolute values of predicted and measured friction, but with high correlation between these values. Hence, the friction prediction model is an appropriate tool for separating the effects of each factor. Therefore, this model will contribute to clearer understanding of the fundamental principles of rubber friction.

• 전자공학회논문지D
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• 제35D권5호
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• pp.1-10
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• 1998

A GaAs MMIC composed of VCO (voltage controlled oscillator) and mixer for PCS receiver has been developed using 1.mu.m ion implanted GaAs MESFET process. The VCO consists of a colpitts-type oscillator with a dielectric resonator and the circuit configuration of the mixer is a dual-gate type with an asymmetric combination of LO and RF FETs for the improvement of intermodulation characteristics. The common-source self-biasing is used in all circuits including a buffer amplifier and mixer, achieving a single power supply (3V) operation. The total power dissipation is 78mW. The VCO chip shows a phase noise of-99 dBc/Hz at 100KHz offset. The combined VCO/mixer chip shows a flat conversion gain of 2dB, the frequency-tuning factor of 80MHz/volts in the varacter bias ranging from 0.5V to 0.5V , and output IP3 of dBm at varactor bias of 0V. The fabricated chip size is 2.5mm X 1.4mm.

• Transactions on Electrical and Electronic Materials
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• 제13권4호
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• pp.181-184
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• 2012

$BaTiO_3$ based multilayer ceramic capacitors with Ni electrodes can be explained as 2-2 composites with different thermal expansion coefficient and sintering behaviors. To achieve the high capacitance and reliability of MLCCs, a homogenous Ni electrode configuration with high connectivity is required. We controlled the heating rates during sintering to achieve densification by suppressing grain growth. Experimental results revealed that a large heating rate gave high connectivity of Ni electrode, high capacitance, small dissipation factor, high breakdown voltage, and high reliability of MLCC chips.

• 공업화학
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• 제24권1호
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• pp.24-30
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• 2013

Quartz crystal microbalance with dissipation monitoring (QCM-D)을 활용하여 양이온성으로 치환된 전분 및 올리고당의 흡착특성을 연구하였다. 전 합성계열의 흡착량은 양이온 계면활성제($C_{12{\sim}16}$ trimethylammonium bromide) 대비 높은 흡착량을 보였으며, 치환비율 및 분자량에 따른 특별한 흡착량의 경향성은 관찰되지 않았다. 반면에, 점탄성(viscoelasticity) 측면에서는 분자량이 증가될수록 흡착층의 강도가 증가되는 경향이 관찰되었다. 흡착 및 탈착실험에서 단분자인 양이온성 계면활성제의 흡착량의 차이는 약 4~9배에 수준의 큰 차이가 발생되었으나 양성치환된 전분계열에서는 0~50% 수준의 작은 차이를 나타내었다. 또한, 탈착단계 이후 흡착단계에 비해 양이온 계면활성제에서는 흡착층의 강도 (rigidity)가 감소된 반면 양성치환된 전분계열에서는 강도가 증가되는 상반된 경향이 관찰되었다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 전력전자학술대회 논문집
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• pp.335-339
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• 2001

The recent advancements in power electronic switching devices have enabled high frequency switching operation and have improved the performance of pulse-width modulated (PWM) inverters for driving induction motors. But, the insulation failures of stator winding have attracted much concern due to high dv/dt of IGBT PWM inverter. In this paper, the test results for evaluation on the stator winding insulation of low-voltage induction motors for IGBT PWM inverter applications are presented. The insulation characteristics are analyzed with partial discharge and dissipation factor tests. Also, insulation breakdown tests by switching pulse voltage are performed. An effective insulation technique to enhance the insulation strength is suggested from the test results.