• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2008년도 춘계학술대회 논문집
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• pp.29-32
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• 2008

Testing was conducted to determine the performance of a residential fuel cell system when subjected to DSS and WSS operation, especially for start-up and shut-down characteristics. In terms of start-up time, it took about 70min to start output power generation and stably to reach 1kW at cold start. Measurement of the characteristics of heat and power generation were carried out at start-up and shut-down time. Fuel gas is used for heating both reformer and stack from start-up to the beginning of power generation. In terms of start-up and shut-down characteristics, it was important to control the reformer temperature precisely. The average output water temperature during the rated output operation(960W) was $63.2^{\circ}C$ constantly. The results of the investigation are being used to develop a new test protocols for residential fuel cell system.

• 정보통신설비학회논문지
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• 제4권1호
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• pp.7-13
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• 2005

In this paper, we propose the time synchronization module on fiber optic repeater to use optic line delay for obtaining time synchronization between up-link and down-link, in the 2.3 GHz WiBro network using TDD/OFDM (Time Division Duplex/Orthogonal Frequency Division Multiplexing) Generally, when we use fiber optic repeater to remove the shade area, it occurs transmission delay which is caused by optic transmission between RAS (Radio Access Station) and fiber optic repeater and inner delay of fiber optic repeater. Because the WiBro system is adopting a TOO method and there exists the difference of switching time which is caused by these delay between up-link and down-link, it occurs ISI (Inter Symbol Interference), ICI (Inter Carrier Interference). These interference results in the reduction of the coverage. And the inconsistency between Up-Link and Down-Link switching time maybe gives rise to the interruption of communication. In order to prevent these cases, we propose synchronization module using analog optic line delay as the one of synchronizing up-link and down-link. And we propose the consideration factor for the designing time synchronization module and the feature of optic line of analog method. The measurement result of optic line time synchronization module of structure proposed is as follows, the delay error of $0.5{\mu}g$ and the insertion loss value below maximum 4.5dB in range of $0{\sim}40{\mu}s$. These results fully meet the specification of WiBro System.

• 한국전기전자재료학회논문지
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• 제18권3호
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• pp.206-211
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• 2005

The device makers want to make higher density chips on the wafer through scale-down. The change of WSix/poly-Si gate film thickness is one of the key issues under 100 nm device structure. As a new device etching process is applied, end point detection(EPD) time delay was occurred in DPS+ poly chamber of Applied Materials. This is a barrier of device shrink because EPD time delay made physical damage on the surface of gate oxide. To investigate the EPD time delay, the experimental test combined with OES(Optical Emission Spectroscopy) and SEM(Scanning Electron Microscopy) was performed using patterned wafers. As a result, a EPD delay time is reduced by a new chamber seasoning and a new wavelength line through plasma scan. Applying a new wavelength of 252 nm makes it successful to call corrected EPD in WSix/poly-Si stack-down gate etching in the DPS+ poly chamber for the current and next generation devices.

• 한국자동차공학회논문집
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• 제11권6호
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• pp.141-146
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• 2003

This paper calculates the elapsed time to go down a straight as a function of the corner exit speed and considers air resistance, rolling resistance, and slope resistance to figure out the force for forward acceleration. In a car racing, the most critical comer in a course is the one before the longest straight. A driver can lose a quite amount of time by taking a bad line in a corner. Taking a bad line also causes poor comer exit speed which in turn costs more elapsed time to go down a straight. The results are not so dramatic as in the case of cornering but are showing why one should take the correct corner racing line to get the maximum exit speed. Also, for the case of drag race, the elapsed time to go 1/4 mile is calculated.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2006년도 춘계학술논문 발표대회 제6권1호
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• pp.133-136
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• 2006

The top-down construction method is an excavation and substructure construction method by excavating earth and building slabs from the ground level to the bottom of a building. The top-down method can be categorized into several types by its process and other technical details. Some of commonly used top-down methods in Korea today are S.O.G., N.S.T.D., and S.P.S. Among these, one method is chosen depending on construction field conditions, cost, construction time and so on. This study explores several factors that may affect the selection of a top-down method. This paper reports preliminary survey results with 54 top-down construction experts and comparison results of 5 top-down construction sites.

• 한국인터넷방송통신학회논문지
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• 제15권5호
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• pp.113-118
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• 2015

이동 무선망은 통신기반 설치가 필요 없는 빠르고 쉬운 망 구성 등의 장점으로 미래의 통신망으로 많은 주목을 받고 있다. 이동 무선망에서 임의의 두 노드간의 통신 경로는 노드의 이동성으로 인해 어떤 링크에서는 전송 범위($r_0$)를 벗어나 경로 붕괴가 일어나고 통신이 불가능하게 된다. 모든 노드 쌍의 경로 붕괴 시간의 모음인 총 경로붕괴 시간 집합(${\bigcup}T_i$)은 이동 무선망의 동적인 연결 상태를 측정하는 좋은 척도가 될 수 있다. 본 논문에서는 총 경로붕괴 시간의 확률 밀도함수는 지수함수로 근사화 될 수 있음을 보이고 실험 데이터를 통해서 확인하였다. 경로붕괴 시간에 대한 통계적 특성을 알면 이동 무선망에서의 노드 간 지연, 패킷 손실률 등에 대한 정량적 예측을 할 수 있고 시뮬레이션 결과에 대한 확신을 더해 주게 된다.

• 전기의세계
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• 제26권4호
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• pp.61-67
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• 1977

This paper treats the Ultrasonic effects on the break down characteristics of Liquid Dielectric Material 1) Relative Dielectric constant, Es of Liquid Dielectric Material at a constant temperature decreases in proportion to the irradiated time of Ultrasonic radiation and its intensity, and reaches to a certain saturated value. The saturated value varies with the intensity of Ultrasonic radiation. 2) Power factor of Liquid Dielectric Material at a constant temperature increases in proportion tothe irradiated time of Ultrasonic radiation and its intensity, and reaches to a certain saturated value. The saturated value varies with the intensity of Ultrasonic radiation. 3) Relative resistance of Liquid Dielectric Material at a constant temperature decrease with the irradiated time of Ultrasonic radiation, but the effect of its intensity is very irregular. 4) Break-down strength of Liquid Dielectric Material, at a constant temperature decreases with the irradiated time of Ultrasonic radiation and its intensity, and then reaches to a saturated value.

• 한국초전도ㆍ저온공학회논문지
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• 제24권4호
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• pp.65-70
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• 2022

A vacuum system is designed for thermal insulation of a 10 ton/day class air liquefaction cold box for liquid air energy storage. The vacuum system is composed of a turbomolecular pump, a backing pump and vacuum piping for the vacuum pumps. The turbomolecular pump is in combination with the backing pump for pumping capacity. The vacuum piping is designed with system installation conditions, such as distance from the cold box, connections to vacuum pumps and installation space. The capacity of the vacuum pump combination, namely pumping speed, is determined by analysis of the vacuum system, and pump-down time to 1×10^-5 mbar is estimated. Vacuum piping conductance, system pumping speed and outgassing rate are calculated for the pump-down time with the ultimate pumping speed range of the vacuum pump combination of 1400 - 2300 l/s. Although the pump-down time gets shorter by larger capacity vacuum pumps, it mainly depends on target vacuum degree and outgassing rate in the cold box. The pump-down time is estimated as 3 - 6 hours appropriate for cold box operation for the pumping speed range. Considering the outgassing rate has uncertainty, the vacuum pump combination with pumping speed of 1900 l/s is chosen for the vacuum system, which is middle value of the pumping speed range.

• Journal of Communications and Networks
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• 제12권3호
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• pp.209-215
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• 2010

In an asymmetrical speed channel environment like asymmetric digital subscriber line, the up-link bandwidth is normally smaller than the down-link bandwidth, which will lead to extremely low utilization of down-link bandwidth when current P2P video transmission is applied. To overcome this, a new fast P2P video transmission method applied in an asymmetrical speed channel environment is proposed in this paper. On the basis of the many-to-one concept, the proposed method uses a new multipeer aggregation technique to enhance the utilization of down-link bandwidth. In addition, an adaptive peer assignment algorithm is also introduced in order to minimize the overall transmission time. Experimental results show that by using our proposed method, the utilization of down-link bandwidth is significantly improved, and the overall transmission time is greatly reduced.

• Nuclear Engineering and Technology
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• 제50권6호
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• pp.854-859
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• 2018

Calculating minimal cut sets is a typical quantification method used to evaluate the top event probability for a fault tree. If minimal cut sets cannot be calculated or if the accuracy of the quantification result is in doubt, the Monte Carlo method can provide an alternative for fault tree quantification. The Monte Carlo method for fault tree quantification tends to take a long time because it repeats the calculation for a large number of samples. Herein, proposal is made to improve the quantification algorithm of a fault tree with circular logic. We developed a top-down iteration algorithm that combines the characteristics of the top-down approach and the iteration approach, thereby reducing the computation time of the Monte Carlo method.