• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권3호
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• pp.1492-1509
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• 2017

The wireless sensor network (WSN) is a key technology to support the Internet of things (IoT) paradigm. The efficiency of the MAC protocol in WSN is very important to take scalability with restricted wireless resources. The DESYNC-TDMA has an advantage of simple distributed slot allocation inspired by nature, but there is a critical disadvantage of split slots by firing message. The basic split slot model has less efficiency for continuous packet transmitting because of wasting of the slots less than the packet size. In this paper, we propose a firing offset adjustment scheme to improve the efficiency of slot utilizations, which can manage the slot assigned to each node as a single large block, called the single slot model. The performance analysis models for both the existing and the proposed schemes are also derived. Experimental results show that the proposed method provide better efficiency of slot utilization than the existing schemes without any loss of the nature of the desynchronization.

• Journal of Power Electronics
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• 제15권6호
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• pp.1468-1479
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• 2015

Renewable energy resources such as wind and photovoltaic power generation systems demand a high step-up DC-DC converters to convert the low voltage to commercial grid voltage. However, the high step-up converter using a transformer has limitations of high voltage stresses of switches and diodes when the transformer winding ratio increases. Accordingly, conventional studies have been applied to series-connect multioutput converters such as forward-flyback and switched-capacitor flyback to reduce the transformer winding ratio. This paper proposes new single-ended converter topologies of an isolation type and a non-isolation type to improve power efficiency, cost-effectiveness, and output ripple. The first proposal is an isolation-type charge-pump switched-capacitor flyback converter that includes an extreme-ratio isolation switched-capacitor cell with a chargepump circuit. It reduces the transformer winding number and the output ripple, and further improves power efficiency without any cost increase. The next proposal is a non-isolation charge-pump switched-capacitor-flyback tapped-inductor boost converter, which adds a charge-pump-connected flyback circuit to the conventional switched-capacitor boost converter to improve the power efficiency and to reduce the efficiency degradation from the input variation. In this paper, the operation principle of the proposed scheme is presented with the experimental results of the 100 W DC-DC converter for verification.

• 전력전자학회논문지
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• 제22권4호
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• pp.330-335
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• 2017

Increased fossil fuel consumption causes global warming, environmental pollution, and abnormal climate change. Wind-generated power installation is proposed to solve this problem. Recently, the wind power plant construction case encourages the installation of the energy storage system (ESS) to improve the intermittency of wind power. The maximized ESS operation profits connected to wind power are not generated in the simplest operation pattern of charging at night and discharging at day. The battery charging efficiency improvement should be considered to get more profits. Thus, there is a possibility of increasing ESS operation profits by analyzing the battery AC and DC charging/discharging efficiency and the yearly average sealed maintenance free (SMP) in hours. In this paper, the battery impedance characteristic, AC and DC charging/discharging efficiency, and the yearly average SMP are analyzed. The operation scenario to improve the ESS battery charging efficiency connected to wind power is proposed and verified via simulation.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 하계종합학술대회 논문집(2)
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• pp.48-51
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• 2000

플라즈마 디스플레이 패널의 발광효율을 개선하기 위하여 sustain 구간의 파형을 변화시킨 새로운 구동파 형을 제안하였다. 제안된 sustain 파형은 기존의 구형파에 기울기를 가진 ramp 형태의 파형을 덧붙여 줌으로써 Self-Erasing을 유도하는 파형이다. 기존에 제안된 Self-Erasing을 이용한 구동방식은 높은 구동주파수(>150kHz)에서만 발광효율이 개선되는 반면, 본 논문에서 제안하는 파형은 낮은 구동주파수(25kHz)에서도 30％정도의 발광효율이 개선되었다. 본 논문의 결과로부터 주파수, 듀티, 기울기 등의 다양한 구동조건에서의 연구가 진행된다면 더 큰 발광효율개선이 기대된다.

• 방송공학회논문지
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• 제22권1호
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• pp.136-139
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• 2017

최근 VR(virtual reality)의 관심이 급격하게 늘어감에 따라 HMD(Head Mounted Display), 360도 VR 카메라 등 많은 VR기기들이 출시되고 있다. 그럼에도 불구하고 현재 360도 VR 비디오의 경우 기존의 일반 2D 비디오의 코덱을 그대로 사용하고 있다. 기존의 코덱은 360도 VR 비디오의 특징을 고려하지 않고 비디오를 부/복호화하기 때문에 압축효율이 떨어지게 된다. 본 논문에서는 360도 VR 비디오의 특성 중 시점이 달라 생기는 왜곡을 보정한 참조프레임으로 사용함으로써 압축효율을 높이는 방법을 제안한다. 제안한 방법을 적용할 경우 시간적 예측 효율이 높아져 압축효율이 높아진다.

• Korean Chemical Engineering Research
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• 제55권4호
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• pp.530-534
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• 2017

Chitosan is a promising flocculant for microalgae harvesting, but its scale-up application is not economically supported yet. Low solubility of chitosan in microalgae suspension demands high dosage (as a flocculant) to destabilize the cells, and thus, increases the cost of microalgae harvesting. This study identifies efficient solvents for the chitosan, and optimizes the concentration of solvents and chitosan dose to improve the harvesting efficiency. Chitosan was dissolved in different acids, and subsequently used as a flocculant. The flocculant efficacy was measured in terms of harvesting efficiency and reduction in chemical oxygen demand (COD) of the microalgae suspension. It was found that chitosan dissolved in 0.05 M HCl showed the highest harvesting efficiency ($89{\pm}0.87%$) at only 30 mg/L of dosage. In comparison, 270 mg/L of $FeCl_3{\cdot}6H_2O$ was required to attain $86{\pm}0.083%$ of the harvesting efficiency. $H_2SO_4$ dissolved chitosan required high flocculant dose (150 mg/L) and resulted in relatively low harvesting efficiency ($77{\pm}0.11%$). It was concluded that the efficacy of chitosan is solvent dependent, and the selection of proper solvent can decrease the dosage requirement for microalgae harvesting.

• 한국산업경영시스템학회:학술대회논문집
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• 한국산업경영시스템학회 2002년도 춘계학술대회
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• pp.177-187
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• 2002

In this paper, we consider a multi-factor, multi-cause decision making problem of supply chain. And we show how to measure the operational efficiency of the components in supply chain and also how to improve the efficiency of each component and whole supply chain. As a methodology, the data envelopment analysis (DEA) is adopted to measure the efficiency by considering weight factors such as flexibility, information sharing, logistics level, etc. The proposed algorithm allows whole supply chain to have the improved efficiency rate.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2000년도 추계학술대회 논문집
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• pp.24-31
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• 2000

This paper evaluates the efficiency of Korea National Railroad on the basis of revenues from 1980 to 1999. There was a significant inefficiency in this organization due to operating at an decreasing return to scale area. Although Korean Railroad in 1990s has made a great effort, his performance is still low. Consequently, it is important to insure substantiality of operations than to expand business area in order to finally improve the efficiency, in particular the revenue efficiency, of the Korea Railroad.

• Journal of Information Display
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• 제9권2호
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• pp.14-17
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• 2008

A charge trapping host structure was developed to improve the light-emitting efficiency of green phosphorescent organic light-emitting diodes. N, N'-dicarbazolyl-3,5-benzene(mCP) and a spirobifluorene based triplet host(PHl) were co-deposited as hosts in the emitting layer and the device performance was examined according to the composition mCP and PH1. The results showed that the quantum efficiency could be improved by 30 % using a mixed host of mCP and PH1.

• 한국전자파학회논문지
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• 제26권6호
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• pp.593-596
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• 2015

본 논문은 무선전력전송 시스템에 활용할 수 있도록 낮은 드레인 전압에서 높은 효율을 가지는 class E 전력증폭기를 설계하였다. 붕괴전압이 40 V인 Si MOSFET을 이용하여 드레인 바이어스 전압이 12.5 V인 13.56 MHz 전력증폭기를 설계하였다. 출력 전력 및 효율을 개선하기 위하여 품질계수가 우수한 솔레노이드 인덕터를 제작하여 출력 정합회로에 사용하였다. 발진 방지와 간단한 회로 구성을 위하여 인덕터와 저항으로 입력 정합회로를 구성하였다. 측정 결과, 제작된 전력증폭기는 13.56 MHz에서 38.6 dBm의 출력전력과 16.6 dB의 전력이득, 그리고 89.3 %의 높은 전력부가효율을 보였다.