• Journal of Advanced Marine Engineering and Technology
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• 제23권2호
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• pp.192-200
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• 1999

This paper describes experimental investigations of helium-air exchange flow through parti-tioned opening. Such exchange flow may occur following rupture accident of stand pipe in high temperature gas cooled reactor. A test vessel with a opening on top of test cylinder is used for experiments. An estimation method of mass increment is developed and applied to measure the exchange flow rate. A technique of flow visualization by Mach-Zehnder interferometer is provided to recognize the exchange flows. Flow measurements are made with partitioned opening for parti-tion rations $H_p/H_1$ in the range 0 to 1 where $H_p$ and $H_1$ are partition length and height of the open-ing respecticely. In the case of $H_p/H_1$ of 0 flow passages of upward flow of the helium and down-ward flow of the air within the opening are unseparated (bidirectional) and the two flows interact exchange flow rate is minimum through range of the partition ratios, Two flow zones i.e. separat-ed(unidirectional)flow zone and unseparated(bidirectional) flow zone exist with increasing the partition. length, The exchange flow rate increases with increasing the separated flow zone. It is found that a maximum exchange flow rate exists at $H_p/H_1$ of 1. As a result fo comparison of the exchange flow rates by changing the partition ration the fluids interaction in the unseparated zone is found to be an important factor on the helium-air exchange flow rate.

• Journal of Advanced Marine Engineering and Technology
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• 제27권6호
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• pp.797-805
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• 2003

This paper describes experimental investigations of helium-air exchange flow through single opening and partitioned opening. Such exchange flows may occur following rupture accident of stand pipe in high temperature gas cooled reactor. A test vessel with a small opening on top of test cylinder is used for experiments. An estimation method of mass increment is developed and applied to measure the exchange flow rate. A technique of flow visualization by Mach-Zehnder interferometer is provided to recognize the exchange flows. Flow measurements are made with the opening, for partition ratios H_p/H$_1$$ in the range 0 to 1. where H_p$ and H$_1$ are partition length and height of the opening. respectively. In the case of H_p/H$_1$$ of 0, flow passages of upward flow of the helium and downward flow of the air within the opening are unseparated (bidirectional), and the two flows interfere within the opening. The unseparated flow increases strength of flow resistance and therefore, the exchange flow rate is minimum through range of the partition ratios. Two flow zones, i.e., separated (unidirectional) flow zone and unseparated (bidirectional) flow zone, exist with increasing the partition length. The exchange flow rate increases with increasing the separated flow zone. It is found that a maximum exchange flow rate exists at H_p/H$_1$$ of 1. As a result of comparison of the exchange flow rates by changing the partition ratio, the fluids Interference in the unseparated zone is found to be an important factor on the helium-air exchange flow rate.

• 대한전자공학회논문지SD
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• 제40권1호
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• pp.36-44
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• 2003

본 논문에서는 비터비 디코더의 디코딩과정에서 trace-forward 과정이후. trace-back 동작 없이 decision bit를 결정 가능한 구조로 설계하여 사용 메모리 크기와 동작 cycle에서 이득을 가지는 변형된 레지스터 교환(modified register exchange) 방식을 제안하였다. 제안된 구조는 시뮬레이션에 의해 trace-back이 있는 기존의 방식과 동일한 결과를 나타냄을 확인하였으며, 변형된 레지스터 교환 방식과 기존의 레지스터 교환 방식, 그리고 trace-back 방식과 비교하였다. 제안한 방식은 다른 방식들에 비해 메모리를 1/(5 x constraint length)로 줄일 수 있고, trace-back 방식에 비해 throughput을 2배 향상시켰다. 변형된 레지스터 교환 방식을 적용한 비터비 디코더의 동작을 검증하기 위해 code rate 2/,3, constraint length, K가 3인 디코더를 radix-4 구조의 1 bit 디코딩 방식으로 설계하여 FPGA(field programmable gate away)를 이용하여 구현하고 측정을 통해 오류 정정 작용을 확인하였다. 또한 블록 디코딩 방식에도 적용할 수 있음을 보였다.

• 한국해양공학회지
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• 제18권6호
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• pp.22-28
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• 2004

A mathematical model has been developed to evaluate the capability of sea water exchanges under tidal and diffusive environments and has been verified through comparison with numerical experiments. From the mathematical analysis, this study presents the rates of sea water exchanges due to the tidal inflow and diffusion process. The port characteristic length $L_p$ is the most significant evaluation index.

• 한국자기학회지
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• 제6권1호
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• pp.1-6
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• 1996

MR/TbCo 박막 계면의 자기교환 결합의 특성을 시뮬레이션 하기 위해서 박막내에 존재 하는 자기 에너지를 최소화 하여 자화의 방향을 구하였다. 수치해석 방법으로는 Newton법과 Gauss-Seidel 방법이 이용되었다. TbCo의 이방성 상수에 비례적으로 자기 이력곡선의 폭이 변하고, TbCo 천이영역의 두께가 얇을수록 자기이력곡선이 벌어지지 않았다. 특히 TbCo 천이영역의 두께가 $400\;\AA$ 일때 단일 곡선(보자력 10 Oe 이하)을 보였다. 또한 계면 교환 결합상수가 작을수록 천이영역의 두께가 얇을 때와 비슷한 곡선을 보였고, 완전히 결합된 상태의 1/100 정도 일때, 단일 곡선을 보였다. 제작한 박막의 자기이력곡선과 비교하여 계면교환 결합상수를 추정할 수 있었다.

• 한국수소및신에너지학회논문집
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• 제33권3호
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• pp.209-218
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• 2022

Recently, research on the development of anion exchange membranes (AEMs) has received considerable attention from the scientific community around the world. Here, we fabricated a series of AEMs with branched structures with different alkyl spacers and conducted comparative evaluations. The introduction of these branched structures is an attempt to overcome the low ionic conductivity and stability problems that AEMs are currently facing. To this end, branched polymers with different spacer lengths were synthesized and properties of each membrane prepared according to the branched structure were compared. The chemical structure of the polymer was investigated by proton nuclear magnetic resonance, Fourier transform infrared, and gel permeation chromatography, and the thermal properties were investigated using thermogravimetric analysis. The branched anion exchange membrane with (CH₂)₃ and (CH₂)₆ spacers exhibited ionic conductivities of 8.9 mS cm^-1 and 22 mS cm^-1 at 90℃, respectively. This means that the length of the spacer affects the ionic conductivity. Therefore, this study showing the effect of the spacer length on the ionic conductivity of the membrane in the polymer structure constituting the ion exchange membrane is judged to be very useful for future application studies of AEM fuel cells.

• Journal of Magnetics
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• 제7권3호
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• pp.94-97
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• 2002

The dependence on nickel oxide thickness and a ferromagnetic layer thickness in unidirectional and isotropic exchange-coupled NiO/NiFe(Fe) bilayer films was investigated by magnetic force microscopy to better understand the relation between magnetic domain structure and exchange biasing at microscopic length scales. As the NiO thickness increased, the domain structure of unidirectional biased films formed smaller and more complex in-plane domains. By contrast, for the isotropically coupled films, large domains generally formed with increasing NiO thickness including a cross type domain with out-of plane magnetization orientation. The density of the cross domain is proportional to exchange biasing field, and the fact that the domain mainly originated from the strongest exchange coupled region was confirmed by imaging in an applied external field during a magnetization cycle.

• 한국통신학회논문지
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• 제21권10호
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• pp.2605-2619
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• 1996

In this paper, we evaluated performance of mobile exchange control part. Queueing network model is used for modeling of mobile exchange control part. We developed a call control processing and location registration scenartio which has a message exchange function between processors in mobile exchange control part. A network symbol are used the simulation models that are composed of the initialization module, message generation module, message routing module, message processing module, message generation module, HIPC network processing module, output analysis module. as a result of computer simulation, we obtain the processor utilization, the mean queue length, the mean waiting time of control part based on call processing and location registration capacity. The call processing and location registration capacity is referred by thenumber of call attempts in the mobile exchange and must be satisfied with the quality of service(delay time).

• Ocean and Polar Research
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• 제25권spc3호
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• pp.423-426
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• 2003

The seawater exchange breakwater equipped with an oscillating water channel and water transmitting pipes has a very spectacular function that seawater supply can be greatly increased due to the upsurge of the water surface inside the channel at resonance condition which can be reached when the incident wave period becomes close to the natural period of the channel. The variations of the water level and period inside the channel are very important factors in enhancing the efficiency of sea water exchange, especially when designing the breakwater cross-section in shallow water zone which requires longer resonance period with the elongated horizontal projection of the channel. In the present study, a hydraulic experiment was performed varying the length of the oscillating channel, and the resonance periods and water surface variations are analyzed in terms of water transmission through the pipes.

• 통상정보연구
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• 제7권3호
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• pp.269-286
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• 2005

The exchange rate volatility has been increased since the time when the floating exchange rate system was introduced in Korea. As a result, the increase of the exchange rate volatility raised the risk in international trades in Korea. The purpose of this study in to study the feature of exchange rate volatility and the main sources of its increase and to confirm whether the exchange rate volatility influence export volume and price of Korea. In the first place, I measured exchange rate volatility with two methods. The one is descriptive statistic method such as the width of daily exchange rate fluctuation and the rate of exchange rate devaluation. The other is the time varying conditional variance of exchange rate. Then, I studied the sources of exchange rate volatility. In the second place, I defined the exchange rate volatility as the time varying conditional variance and estimated it by using elastic a approach model which shows exchange rate is affected by itself and its conditional variance, I estimated its effects on export volumes and prices of electric home appliances, information & communication equal and semi-conductor. The result of this study is as follows. With presumed result EU and Korea because is not the goods which is to substantial competition relationship, The effect where the relative value change of presumed result expression anger and the dollar of import and export function goes mad to the import and export of Korea the income compared to is to export and it is appearing a lot. The EU goods is sold more expensively the Korean goods than from about length being caused by American market of the dollar and the balance of trade of Korea is visible like being visible the improvement of single breadth. Because the relationship of competition is weak but substantially there is to a short term and expression - the effect where the dollar rate fluctuation is big in Korean trade there is a possibility of saying that widely known it is not.