• International Journal of Automotive Technology
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• 제8권1호
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• pp.119-126
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• 2007

Because of the low temperature operation, proton exchange membrane (PEM) fuel cell has a water phase transition. Therefore, water management is an important operation issue in a PEM fuel cell because the liquid water in the fuel cell causes electrode flooding that can lower the cell performance under high current density conditions. In this study, in order to understand the reactant distributions in the cathode channels of the PEM fuel cell, an experimental technique that can measure the species concentrations of reactant gases by using gas chromatograph (GC) is applied for an operating PEM fuel cell. The oxygen distribution along the cathode flow channels of PEM fuel cell is mainly investigated with various operating conditions. Also, the relations between cathode flooding and oxygen concentrations and oxygen consumption pattern along the cathode channel configurations of the unit cell adopted for this study are discussed using GC measurement and visualization experiment of cathode flooding. It is found that the amount of oxygen consumption is very sensitive to various operating conditions of the fuel cell and was much affected by the flooding occurrence in cathode channels.

• 유통과학연구
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• 제21권7호
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• pp.83-90
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• 2023

Purpose: This study aims to set desirable directions for Korea's egg industry by comparing and analyzing the egg distribution structure and policies between Korea and other countries. Research design, data and methodology: We analyzed the current state of egg distribution in Korea, and based on this analysis, we derived problems. In addition, by comprehensively analyzing the egg distribution structure and policy issues in the US, EU, and Japan. Results: As a result of the analysis of the egg distribution status and policy in the country to be analyzed, it was found that for the development of the egg industry in Korea, it is necessary to unify the distribution system for transparent and stable management of the egg distribution process. It was found that detailed and clear information creation and management of egg production and distribution processes were required. Conclusions: We need to establish a regional egg distribution facility base and stipulate that eggs produced in Korea must be compulsorily traded through the regional facility base. Seemingly, scaling-up of the industry is the priority, but the government is promoting various policies to expand small and medium-sized egg joint markets, with limitations in improving the problems of the existing egg distribution structure.

• 한국유통학회지:유통연구
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• 제1권2호
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• pp.141-172
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• 1996

This study is to investigate global logistics strategies of Korean electronics companies. in terms of service parts. According to the survey, Korean electronics companies were pursuing multi-level global logistics network such as global, continental, national, regional and service center echelon for improving the efficiency of service parts global logistics. Especially there was a tendency of developing new continental distribution centers. And the companies were exploiting efficiency through inventory control by multi-level echelon, demand forecasting by the product life cycle and supply and service lead time management. But there were some insufficient factors for the efficiency of global logistics operation at the construction of worldwide real time logistics information system and pursuit of the efficiency on the whole network including subcontractors. For the future competitive advantage of the Korean electronics companies, the following are suggested: 1) the establishment of arranged logistics channel adjusting each company's global strategy, 2) the construction of worldwide real time logistics information system, 3) the reengineering of all logistics procedures such as order processing, shipping, inventory control, etc., 4) the enhancement of the ratio of the supply from the external companies and the internal manufacturing subsidiaries at each continent, 5) and the pursuit of operational internalization of external subcontractors.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 추계종합학술대회 논문집(1)
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• pp.73-76
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• 2000

We investigate the stepwise parallel processing of the serial search which can success the co]1 search at low Ec/Io. The single path Rayleigh fading channel which is worst-case channel model is considered. The typical 3-step cell search is used. The probabilities of detection, miss and false alarm for each step are used in closed forms based on the statistics of CDMA noncoherent demodulator output. The optimal power allocation to each channel and The optimal number of post-detection integrations for each step is obtained. Also, the cumulative probability distribution of the average eel] search time for serial search methods are compared.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2006년도 학술발표회 논문집
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• pp.1002-1006
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• 2006

Temperature monitoring techniques per depth have been recognized as important information in the reservoir environmental issues. However, old measurement method by single temperature sensor and cable type has demerits not only for its limited measuring location but for its inconvenience of users. In this study, multi-channel temperature monitoring system was introduced and executed experiment for actual application feasibility evaluation. Both type of new techniques such as multi-channel addressable built-in temperature sensor and fiber optic multi sensor were tested in Daechung and Imha reservoir. As a result, it was proved that these kinds of temperature monitoring skills had very good performance and availability for a output of spatial, simultaneous thermal distribution focused on the user's convenience. And these measuring method and thermal data will be useful for providing basic information in a water resources investigation like reservoir stratification and environmental problems.

• 물과 미래
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• 제23권2호
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• pp.213-225
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• 1990

본 연구는 불규칙한 단면을 가지면서 완곡을 이루는 일반하천에서 공장이나 가정으로부터 방류되는 오염물질의 횡확산현상을 예측하기 위한 수치모형을 제안하였다. 이 수치모형은 자연좌표계와 누적유량개념을 도입하였으며 여기에 필요한 여러가지 요소들을 직접측정하지 않고 컴퓨터 프로그래밍을 통하여 간단히 결과를 얻을수 있는 효율적인 방법을 개발하여 실험결과와 비교검토하므로서 본수치모형의 현지적용성을 검토하였다.

• 한국정보컨버전스학회논문지
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• 제6권2호
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• pp.89-96
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• 2013

본 연구는 도매안경테의 종사자를 중심으로 안경테 유통을 분석하여 유통의 개선점을 연구하였다. 다양한 연령층과 학력으로 유통업계에서 근무를 하고 있으며, 회사의 규모는 영세하였다. 안경테의 재고 관리를 위해서는 체계적인 관리가 이루어지지 않았고, 보다 나은 유통 시스템에 대한 기대도 크지 않았다. 안경소비자와 안경제조업체의 중간적인 역할에 있는 도매안경테 회사는 보다 나은 판매 확보를 위해 공동 판매장이나 internet판매의 활성화를 확보하여야 할 것으로 본다.

• Journal of Communications and Networks
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• 제13권4호
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• pp.319-326
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• 2011

Beamforming techniques have been successfully utilized for traffic channels in order to solve the interference problem. However, their use for control channels has not been sufficiently investigated. In this paper, a (semi-) centralized beamforming strategy that adaptively changes beam patterns and controls the total transmit power of cells is proposed for the performance enhancement of the common channel in hierarchical cell structure (HCS) networks. In addition, some examples of its practical implementation with low complexity are presented for two-tier HCS networks consisting of macro and pico cells. The performance of the proposed scheme has been evaluated through multi-cell system-level simulations under optimistic and pessimistic interference scenarios. The cumulative distribution function of user geometry or channel quality has been used as a performance metric since in the case of common control channel the number of outage users is more important than the sum rate. Simulation results confirm that the proposed scheme provides a significant gain compared to the random beamforming scheme as well as conventional systems that do not use the proposed algorithm. Finally, the proposed scheme can be applied simultaneously to several adjacent macro and pico cells even if it is designed primarily for the pico cell within macro cells.

• Journal of Communications and Networks
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• 제13권5호
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• pp.456-462
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• 2011

This paper investigates the outage behavior of peak interference power limited cognitive radio (CR) networks with multiple transmit antennas. In CR-multi-input single-output (MISO) channel, the total transmit power is distributed over the transmitantennas. First, we use the orthogonal space-time codes (STC) to achieve the transmit diversity at CR-receiver (rx) and investigate the effect of the power distribution on the interference power received at the primary-receiver (P-rx). Then, we investigate the transmit antenna selection (TAS) scheme in which the CR system selects the best transmit antenna and allocates all the power to the selected best antenna. Two transmit antenna selection strategies are proposed depending on if feedback channel is available or not. We derive the closed form expressions of outage probability and outage capacity of all schemes with arbitrary number of transmit-antennas. We show that the proposed schemes significantly improve the outage capacity over the single antenna systems in Rayleigh fading environment. We also show that TAS based scheme outperforms the STC based scheme when peak interference power constraint is imposed on the P-rx only if a feedback channel from CR-rx to CR-transmitter is available.

• International Journal of Fluid Machinery and Systems
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• 제3권1호
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• pp.11-19
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• 2010

The performance of the crossover system of a centrifugal compressor stage consisting of static components of $180^{\circ}$ U-bend, return channel vanes and exit ducting with a $90^{\circ}$ bend is investigated. This study is confined to the assessment of performance of the crossover system by varying the shape of the return channel vanes. For this purpose two different types of Return Channel Vanes (RCV1 and RCV2) were experimentally investigated. The performance of the crossover system is discussed in terms of total pressure loss coefficient, static pressure recovery coefficient and vane surface pressure distribution. The experimentation was carried out on a test setup in which static swirl vanes were used to simulate the flow at the exit of an actual centrifugal compressor impeller with a design flow coefficient of 0.053. The swirl vanes are connected to a mechanism with which the flow angle at the inlet of U-bend could be altered. The measurements were taken at five different operating conditions varying from 70% to 120% of design flow rate. On an overall assessment RCV1 is found to give better performance in comparison to RCV2 for different U-bend inlet flow angles. The performance of RCV2 was verified using numerical studies with the help of a CFD Code. Three dimensional sector models were used for simulating the flow through the crossover system. The turbulence was predicted with standard k-$\varepsilon$, 2-equation model. The iso-Mach contour plots on different planes and development of secondary flows were visualized through this study.