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블루투스 4.0 통신을 이용한 모바일 휠체어 제어에 관한 연구
성민창(Minchang Sung),최영진(Youngjin Choi) 한국통신학회 2021 한국통신학회 학술대회논문집 Vol.2021 No.2
본 논문은 블루투스 4.0 통신으로 동작하는 모바일 휠체어 환경에서 휠체어의 운동학적 모델을 기술하고 위치제어를 수행한다. 하지만 해당 모바일 휠체어 환경은 두 가지의 제한 조건을 갖는다. 첫째, 블루투스 4.0 통신은 1Mbps 정도의 낮은 속도를 갖고 이는 제어성능에 영향을 끼친다. 둘째, 휠체어의 기어에서 발생하는 마찰력의 영향으로 속도는 0.5 ~ 5.5km/h의 좁은 범위를 갖게 된다. 두 가지의 제한 조건 하에서 MATLAB으로 모바일 휠체어의 운동모델을 구성하고 비선형 제어 테스트를 진행한다. 결과를 통해 실제 상황에서의 적용 가능성에 관하여 확인하였다.
시외통화 수요함수의 추정을 통한 시도간 시외통화와 이동통화의 대체관계에 관한 연구
成樂逸,金玟昌 한국국제경제학회 2002 국제경제연구 Vol.8 No.3
이동전화를 이용한 전화통화는 유선계 시외통화와 대체관계 또는 경쟁관계로 출발했으며, 이동전화의 급성장과 함께 그 대체관계는 더욱 강화되고 있다. 본 연구는 1993년~1997년 기간 중 수집된 시도별 패널자료를 사용해 시외통화 수요함수를 추정함으로써 이동전화의 성장추세가 시외통화시장에 어떤 영향을 미쳤는지를 분석하고 있다. 본 연구의 추정결과에 따르면, 가격, 소득, 가입자 수 등 다른 설명변수를 통제했을 때 실질 이동전화요금이 1% 하락하면 시외통화 분수는 약 1% 감소하였다. 이와 같은 결과는 종속변수로서 시외통화 호수를 사용했을 때 더욱 강화되며, 이동전화요금 대신에 이동전화 가입자 수를 사용해도 동일한 결론이 도출되었다. 이동통화와 시외통화가 대체관계라는 사실은 통신시장의 공공정책에 대해서 중요한 시사점을 가진다. Mobile telephone markets are expanding rapidly in Korea. One of the results of this expansion is that mobile calls are in direct competition with long-distance calls as close substitutes for each other. The aim of this paper is to present empirical evidence on fixed-mobile call substitution by using a point-to-point model of long-distance call demand. The paper shows that a 1% decrease in the real mobile price resulted in a 1% decrease in long-distance call minutes and a 1.5% decrease in the number of long-distance calls, respectively, with other variables being controlled. The empirical analysis is carried out with Korean inter-province long-distance call data for the period 1993∼1997. The empirical findings of the paper provide important public policy suggestions.
버블 병합 효과를 고려한 새로운 풀 핵비등 역학 모델 개발
김민창(Minchang Kim),김성진(Sung-Jin Kim) 대한기계학회 2020 대한기계학회 춘추학술대회 Vol.2020 No.12
A mechanistic model that includes the effect of bubble coalescence on nucleate pool boiling heat transfer is developed through experimental and theoretical investigations. Transient temperature and heat flux distributions on the boiling surface are obtained using a high-speed infrared imaging technique. According to the temperature and heat flux distributions, the boiling surface is classified into three regions: natural convection, quenching, and evaporation regions. By observing how the heat flux on each region and the corresponding area fraction change as the bubble coalescence occurs, the effect of the bubble coalescence on nucleate pool boiling is investigated. It is found that the bubble coalescence does not affect the heat fluxes on the three regions but affects the area fractions: As the bubble coalescence occurs, the rates of increase in evaporation and quenching area fractions decrease, and the natural convection area fraction remains the same. By accounting for the effect of the bubble coalescence on quenching and evaporation area fractions, a new correlation of the boiling heat flux is developed and presented. To validate the present model, the boiling curve for saturated water is reproduced and compared to experimental data.
An Ultra Low Power and Variation Tolerant GEN2 RFID Tag Front-End with Novel Clock-Free Decoder
KIM, Sung-Jin,CHO, Minchang,CHO, SeongHwan The Institute of Electronics, Information and Comm 2010 IEICE transactions on electronics Vol.93 No.6
<P>In this paper, an ultra low power analog front-end for EPCglobal Class 1 Generation 2 RFID tag is presented. The proposed RFID tag removes the need for high frequency clock and counters used in conventional tags, which are the most power hungry blocks. The proposed clock-free decoder employs an analog integrator with an adaptive current source that provides a uniform decoding margin regardless of the data rate and a link frequency extractor based on a relaxation oscillator that generates frequency used for backscattering. A dual supply voltage scheme is also employed to increase the power efficiency of the tag. In order to improve the tolerance of the proposed circuit to environmental variations, a self-calibration circuit is proposed. The proposed RFID analog front-end circuit is designed and simulated in 0.25µm CMOS, which shows that the power consumption is reduced by an order magnitude compared to the conventional RFID tags, without losing immunity to environmental variations.</P>
국소 열유속 및 온도 측정을 통한 물 풀비등에서의 임계열유속 메커니즘 연구
김민창(Minchang Kim),김성진(Sung Jin Kim) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12
In the present study, the critical heat flux (CHF) mechanism in pool boiling of water is experimentally investigated. The experiments are performed using an infrared (IR) camera to measure the temperature and heat flux distributions on the boiling surface. An IR-transparent boron-doped silicon wafer is used as the heater. Boiling takes place from an IRopaque titanium surface that is deposited on the silicon heater. The wetted area fraction (WF), the contact line length density (CLD) and the contribution of various heat transfer mechanism to overall heat transfer were measured throughout the boiling curve. Quantitative analysis of this data at high heat flux and transition through CHF revealed that the occurrence of the unquenchable dry spot triggers CHF.
국소 열유속 및 온도 측정을 통한 물 풀 핵비등에서의 열전달 메커니즘 연구
김민창(Minchang Kim),김성진(Sung Jin Kim) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11
The local heat flux and temperature on the boiling surface are measured to determine the heat transfer mechanism in nucleate pool boiling. Using infrared thermometry, the temperature distribution can be measured when mid-wave(3-5.5 ㎛) optical access to the surface is possible. The heat flux is calculated by the heat equation with this temperature information. The contact line length density(CLD) and the time-averaged wetted area fraction(WF) are also measured for an infrared opaque indium-tin-oxide surface over an electrically heated silicon substrate which is transparent to infrared. With this information, the dominant heat transfer mechanism during the nucleate pool boiling of water is evaluated. In conclusion, the convection heat transfer on the liquid area based on the micro-convection model is the predominant heat transfer mechanisms during the nucleate pool boiling of water.
Improved tensile strength of carbon nanotube-grafted carbon fiber reinforced composites
Lee, Geunsung,Sung, Minchang,Youk, Ji Ho,Lee, Jinyong,Yu, Woong-Ryeol Elsevier 2019 COMPOSITE STRUCTURES -BARKING THEN OXFORD- Vol.220 No.-
<P><B>Abstract</B></P> <P>Increased tensile strength of carbon nanotube (CNT)-grafted carbon fiber (CF) composites has been reported, but the mechanism of this increase is not yet clear. In this study, CNT-grafted CF unidirectional (UD) and woven composites were fabricated using a low-temperature chemical vapor deposition (CVD) and resin transfer molding. Two types of CNTs (short and thin, long and thick) were successfully grown and grafted to CFs without degrading the CFs in the preforms. The CNT-grafted CFs exhibited increased interfacial shear strength (IFSS) similarly regardless of the CNT type. Interestingly, however, long and thick CNT-grafted CF UD and woven composites exhibited significant increases in tensile strength (about 20% and 30%), suggesting other mechanisms besides increased IFSS. The splitting crack initiation under the mixed mode condition was quantitatively characterized for the CNT-grafted CF UD composites, demonstrating that long and thick CNTs delayed the splitting crack initiation. Delayed fiber splitting and increased IFSS were concluded to be the main sources of increased tensile strength of CNT-grafted CF composites.</P>
우리나라 기업의 e-비즈니스 시스템 도입현황과 성과 : 실증분석
성낙일(Nakil Sung),김민창(Minchang Kim),서성우(Seongwoo Seo) 한국데이타베이스학회 2011 Journal of information technology applications & m Vol.18 No.4
This study attempts to examine the factors affecting the introduction of e-Business systems and also, to assess the effects of various e-Business systems on firm performance. Empirical analysis is carried out with firm data of 2009, which is collected from Firm Activity Survey of Statistics Korea. Firm performance is measured by four indexes; operating income per employee, value added per employee, return on assets, and return on sales. Empirical results indicate that a firm is more likely to introduce any e-Business system as its size and its assets per employee are larger and as its ratio of labor compensations to operating costs is lower. Additionally, a firm with higher skill levels and more fruitful management experiences is more likely to have any e-Business system. In general, it appears that the presence of e-Business, especially enterprise resources planning, has positive effects on the firm performance.