• 한국수소및신에너지학회논문집
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• 제26권2호
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• pp.96-104
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• 2015

Reactivity of commercial WGS catalyst and four new catalysts(RMC-3, PC-73, PC-67SU, PC-59) manufactured with various compositions by Korea Electric Power Research Institute(KEPCO RI) were compared to select suitable WGS catalyst for SEWGS system. Steam/CO ratio, gas velocity, flow rates of syngas, and temperature were considered as operating variables. As a result, commercial catalyst showed the highest CO conversion and RMC-3 catalyst showed also high CO conversion. Therefore, commercial and RMC-3 catalysts were selected as applicable catalysts. However, PC-73 catalyst showed low CO conversion at low temperature($200^{\circ}C$) but showed good reactivity at high temperature($225{\sim}250^{\circ}C$), and therefore, PC-73 catalyst was selected as applicable catalyst for high temperature operation. Continuous operations up to 24 hours for those three catalysts(commercial, RMC-3, PC-73) were conducted to check reactivity decay of catalysts. All three catalysts maintained their original reactivity.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 B
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• pp.635-636
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• 2006

A pulse with modulation(PWM) that keeps a constant angle of dwell and adjust duty ratio is a good method to control a speed of SRM. And a method of one pulse control is proper a operation on range of high speed in SRM for a good energy efficiency. Because PWM method is more safety than one pulse method, conversion of those is best choice according the speed range. So, some algorithm is need for smooth conversion of the mode of control. This paper presents a factor of conversion that proper the conversion of control mode between PWM and one pulse method This factor is from estimation of torque and proper at the variable range of conversion and show the better conversion characteristic than constant factor of conversion.

• 전자공학회논문지B
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• 제31B권7호
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• pp.42-48
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• 1994

In this paper, a low power and high speed flash Analog-to-Digital Converter using current-mode concept is proposed. Current-mode approach offers a number of advantages over conventional voltage-mode approach, such as lower power consumption small chip area improved accuracy etc. Rescently this concept was applied to algorithmic A/D Converter. But, its conversion speed is limited to medium speed. Consequently this converter is not applicable to the high speed signal processing system. This ADC is fabricated in 1.2um double metal CMOS standard process. This ADC's conversion time is measured to be 7MHz, and power consumption is 2.0mW, and differential nonlinearity is less than 1.14LSB and total harmonic distortion is -50dB. The active area of analog chip is about 350 x 550u$m^2$. The proposed ADC seems suitable for a single chip design of digital signal processing system required high conversion speed, high resolution small chip area and low power consumption.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.297.2-297.2
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• 2016

Photoacoustic generation of ultrasound is an effective approach for development of high-frequency and high-amplitude ultrasound transmitters. This requires an efficient energy converter from optical input to acoustic output. For such photoacoustic conversion, various light-absorbing materials have been used such as metallic coating, dye-doped polymer composite, and nanostructure composite. These transmitters absorb laser pulses with 5-10 ns widths for generation of tens-of-MHz frequency ultrasound. The short optical pulse leads to rapid heating of the irradiated region and therefore fast thermal expansion before significant heat diffusion occurs to the surrounding. In this purpose, nanocomposite thin films containing gold nanoparticles, carbon nanotubes (CNTs), or carbon nanofibers have been recently proposed for high optical absorption, efficient thermoacosutic transfer, and mechanical robustness. These properties are necessary to produce a high-amplitude ultrasonic output under a low-energy optical input. Here, we investigate carbon nanotube (CNT)-polydimethylsiloxane (PDMS) composite transmitters and their nanostructure-originated characteristics enabling extraordinary energy conversion. We explain a thermoelastic energy conversion mechanism within the nanocomposite and examine nanostructures by using a scanning electron microscopy. Then, we measure laser-induced damage threshold of the transmitters against pulsed laser ablation. Particularly, laser-induced damage threshold has been largely overlooked so far in the development of photoacoustic transmitters. Higher damage threshold means that transmitters can withstand optical irradiation with higher laser energy and produce higher pressure output proportional to such optical input. We discuss an optimal design of CNT-PDMS composite transmitter for high-amplitude pressure generation (e.g. focused ultrasound transmitter) useful for therapeutic applications. It is fabricated using a focal structure (spherically concave substrate) that is coated with a CNT-PDMS composite layer. We also introduce some application examples of the high-amplitude focused transmitter based on the CNT-PDMS composite film.

• 한국전자파학회논문지
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• 제27권9호
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• pp.825-833
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• 2016

본 논문에서는 $0.18{\mu}m$ CMOS 공정을 사용한 저 전력 고 이득 주파수 상향변환기를 이용하여 IEEE 802.15.4 규격을 만족하는 직접 변환 송신기를 제안 및 설계한다. 설계된 RF 직접 변환 송신기는 차동입력 디지털-아날로그 변환기, 수동 저역통과 필터, 가변이득 증폭기, Quadrature 주파수 상향 변환기 그리고 차동 출력 구동증폭기로 구성되어 있다. 제안하는 직접변환 송신기에서 핵심적인 부분은 2.4 GHz Zigbee 규격을 저 전력으로 구동하는데 있다. 특히 Quadrature 주파수 상향변환기는 이득 Boosting을 통하여 적은 전류 소모로도 충분한 이득과 선형성을 보이고 있다. 측정결과, 공급전압 1.2 V에서 송신기의 총 소모 전류는 7.8 mA이고, 최대 출력 전력은 0 dBm 이상 그리고 -30 dBc의 ACPR(Adjacent Channel Power Ratio)을 나타내고 있다.

• 농촌계획
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• 제20권4호
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• pp.55-66
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• 2014

This study analyzed the recognition of local residents surrounding farmland conversion area. The details of the survey on the residents included recognition of farmland conversion, the usage and reason of farmland conversion in the surrounding area, impacts of farmland conversion on the local region and agricultural production, and change in farmland prices. According to the analysis, the aging of the local residents progressed, and the ratio of farming population was high in the case study area. There were many warehouse facilities and small scale factories in terms of farmland conversion in the case study area, due to the surrounding area characteristics of industrial complex and relatively cheaper land prices. The farmland conversion affected the local area and residents both positively and negatively, and the surrounding area's land prices rose. The policy implications, based on the findings in this study, indicate the following need to be carried out: the consolidation of action on farmland pollution upon farmland conversion, review of planned collective conversion mode, and return of the land price hike profits to the affected local area and residents. Actually, farmland conversion should be conducted, after a comprehensive and systematic review, because it affects the local area and residents in a complex way.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 추계학술대회 초록집
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• pp.97.1-97.1
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• 2011

Dimethyl ether (DME) is an attractive fuel as a hydrogen carrier for mobile PEMFC applications. However, its reforming technologies are rarely studied especially by using autothermal reforming (ATR) method. This work explored the impact of operating conditions to the performance of DME ATR. Temperature, Steam to carbon ratio(SCR), Oxygen to carbon ratio(OCR) and Gas hourly space velocity(GHSV) were considered as the operating conditions. As results, conversion efficiency was increased as the temperature increased, but saturated around $700^{\circ}C$. There was no significant effect of SCR on conversion efficiency, but high SCR led reactions in endothermic manner. High OCR substantially suppressed conversion efficiency, but it helped to sustain the temperature by stimulating exothermic reactions. Conversion efficiency was decreased as GHSV increased. The optimized operating conditions was suggested: $700^{\circ}C$, SCR of 1.5, OCR of 0.45 and GHSV below 15000/h and conversion efficiency was ~85% at the conditions.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2004년도 춘계종합학술대회
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• pp.136-139
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• 2004

본 논문은 MPEG-2 동영상의 축소전환 시 IDCT기법을 이용한 임베디드 시스템 구현에 대한 연구이다 일반적으로 압축된 MPEG-2 동영상의 축소전환은 입력 비트열을 완전 복호화한 후, 저대역 필터링과 서브 샘플링을 수행하는 것이다. 그러나 이 방법은 큰 메모리와 많은 계산량을 요구하는 단점이 있다. 최근 이러한 문제점을 해결하기 위해 DCT 영역에 축소 전환하는 방법이 제안되었다. 이 방법은 고해상도 프레임 메모리의 1/4만을 요구한다. 이는 완전히 축소된 영상이 프레임 메모리에 저장되기 때문이다 그러나 이로 인한 필도 정보의 손실은 움직임 보상 단계에서 심각한 오차를 일으키며 영상 화질을 저하시킨다. 임베디드 시스템에서는 동영상의 화질을 유지하며 계산량이 적은 축소 변환 기법이 필요하다. 공간적인 영역에서 축소 변환 방법과 주파수 영역에서의 축소 변환 기법을 임베디드 시스템에 적용하였을 때 동영상의 프레임 속도에 대하여 비교하여 보았다. 주파수 영역에서 축소 변환을 수행하였을 때 평균 29 frame/sec로 주파수 영역에서의 변환 기법이 25% 우수하였다.

• Composites Research
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• 제36권3호
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• pp.180-185
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• 2023

본 논문에서는 스프레딩된 SiC 섬유를 적용해 SiC_f/SiC를 제조하였을 경우, 섬유의 분산도가 복합소재의 내부구조 및 기계적 강도에 어떠한 영향을 주는지를 연구하였다. Spread SiC 섬유를 적용한 시편의 섬유 체적비는 non-spread 시편 대비 9%p 감소하였으며, 수지 슬러리가 섬유 사이로 더 원활히 함침되어 기지내 기공도 거의 발견되지 않았다. 각 시편의 섬유 분산도를 비교하기 위해, 복합소재 내 섬유간 이격거리를 수치화하고 평가하는 방법을 제안하였다. 그 결과 spread 시편의 섬유간 중심거리는 non-spread 시편 대비 2.23 ㎛ 증가하였으며, 섬유 표면 사이 거리는 42.6%로 대폭 증가하였다. 3점 굽힘시험을 통해 spread 시편의 굽힘강도가 non-spread 시편 대비 49.3% 가량 높으며, 시험 데이터의 편차도 더 균일함을 확인하였다. 따라서 복합소재 기지내 SiC 섬유의 분산도 향상이 SiC_f/SiC의 균일한 기지상 치밀화와 기계적 강도 증가에 매우 큰 영향을 미친다는 점을 알 수 있다.

• Journal of Power Electronics
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• 제5권2호
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• pp.99-103
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• 2005

In this paper, a novel circuit topology of a three-winding coupling inductor-assisting a high-frequency PWM boost chopper type DC-DC power converter with a high boost voltage conversion ratio and low switch voltage stress is proposed for the new energy interfaced DC power conditioner in solar photovoltaic and fuel cell generation systems. The operating principle in a steady state is described by using its equivalent circuits under the practical condition of energy processing of a lossless capacitive snubber. The newly-proposed power MOSFET boost chopper type DC-DC power converter with the three-winding coupled inductor type transformer and a single lossless capacitor snubber is built and tested for an output power of 500W. Utilizing the lower voltage and internal resistance power MOSFET switch in the proposed PWM boost chopper type DC-DC power converter can reduce the conduction losses of the active power switch compared to the conventional model. Therefore, the total actual power conversion efficiency under a condition of the nominal rated output power is estimated to be 81.1 ％, which is 3.7％ higher than the conventional PWM boost chopper DC power conversion circuit topology.