• Journal of Electrical Engineering and Technology
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• v.5 no.3
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• pp.353-362
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• 2010

This paper presents a centralized control algorithm for power system performance in the Korean power system using Flexible AC Transmission Systems (FACTS) devices. The algorithm is applied to the Korean power system throughout the metropolitan area in order to alleviate inherent stability problems, especially concerns with voltage stability. Generally, control strategies are divided into local and centralized control. This paper is concerned with a centralized control strategy in terms of the global system. In this research, input data of the proposed algorithm and network data are obtained from the SCADA/EMS system. Using the full system model, the centralized controller monitors the system condition and decides the operating point according to the control objectives that are, in turn, dependent on system conditions. To overcome voltage collapse problems, load-shedding is currently applied in the Korean power system. In this study, the application of the coordination between FACTS and switch capacitor (SC) can restore the solvability without load shedding or guarantee the FV margin when the margin is insufficient. Optimal Power Flow (OPF) algorithm, for which the objective function is loss minimization, is used in a stable case. The results illustrate examples of the proposed algorithm using SCADA/EMS data of the Korean power system in 2007.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.8
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• pp.1532-1541
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• 2015

D2D(Device-to-Device) communication is a promising technology to improve the system capacity and spectral efficiency. By sharing the same radio resources with cellular user equipments, D2D communications can significantly enhance the overall spectral efficiency. However, it may cause interference between D2D link and cellular link. So, careful resource allocation and interference coordination between them are very important and need to be properly handled. This paper proposes a radio resource allocation scheme that decreases interference through the use of area grouping and D2D pair grouping. Simulations results are provided to verify the performance improvement of the proposed scheme in terms of the number of assigned resource blocks and computational complexity.

• Journal of The Korean Society of Agricultural Engineers
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• v.62 no.5
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• pp.85-91
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• 2020

In order to calculate the Crop Water Stress Index (CWSI), it is necessary to collect weather data (air temperature, humidity, wind speed and solar radiation) and canopy temperature. However, it is not always available to have necessary data sets for CWSI calculation. Therefore, this study was aimed to develop an easy and simple CWSI equation (CWSI_EE) using only two data, air and canopy temperatures. Infrared sensors and weather sensors were installed on apple and peach trees and nearby a study area and every ten-minute data were collected from June to October in 2018 and 2019, respectively. A relationship between air-canopy temperature difference and CWSI was statistically analyzed and used to develop CWSI_EE using the three dimensional Gaussian model. The performance of CWSI_EE against original CWSI showed R² and NSE to 0.780 and 0.710 for apple trees and R² and NSE to 0.884 and 0.866 for peach trees. This study found that the level of crop water stress could be easily calculated using CWSI_EE with only air and canopy temperature data.

• Journal of the Korean Society of Clothing and Textiles
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• v.30 no.1 s.149
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• pp.20-30
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• 2006

The purposes of this study were to investigate demographic profiles between the consumer group under high time pressure(HTP) and the group under low time pressure(LTP) during the shopping, to examine the level of association between the fashion information sources and time pressure variable, to determine the difference in clothing benefits sought between HTP and LTP, and to determine the difference in purchase criteria. We distributed questionnaires to 600 women aged in 20-65. The reliable 562 questionnaires were used for a statistical analysis. Data analyses were conducted with SPSS program on t-test, cluster analysis, factor analysis, and Chi square test. We obtained the following results: There was a significant association between demographic variables such as age, occupation, education, residence area, & family cycle and time pressure variable. Fashion information sources were classified into 4 factors. HTP searched information on fashion products using more various sources than LTP did. There was also a significant difference between HTP and LTP in clothing benefit sought. Four clothing benefit factors such as trendy/social position, economic value, protection/comfort, and makeup of body shape were sought more by HTP than by LTP. In addition, HTP considered significantly more purchase criteria such as color/pattern, comfort, quality, suitability, material, sewing finishing, coordination, price, brand, easy care, and country of origin than LTP.

• Journal of Communications and Networks
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• v.11 no.5
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• pp.518-528
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• 2009

IEEE 802.11 wireless local area network (WLAN) has become the prevailing solution for wireless Internet access while transport control protocol (TCP) is the dominant transport-layer protocol in the Internet. It is known that, in an infrastructure-based WLAN with multiple stations carrying long-lived TCP flows, the number of TCP stations that are actively contending to access the wireless channel remains very small. Hence, the aggregate TCP throughput is basically independent of the total number of TCP stations. This phenomenon is due to the closed-loop nature of TCP flow control and the bottleneck downlink (i.e., access point-to-station) transmissions in infrastructure-based WLANs. In this paper, we develop a comprehensive analytical model to study TCP dynamics in infrastructure-based 802.11 WLANs. We calculate the average number of active TCP stations and the aggregate TCP throughput using our model for given total number of TCP stations and the maximum TCP receive window size. We find out that the default minimum contention window sizes specified in the standards (i.e., 31 and 15 for 802.11b and 802.11a, respectively) are not optimal in terms of TCP throughput maximization. Via ns-2 simulation, we verify the correctness of our analytical model and study the effects of some of the simplifying assumptions employed in the model. Simulation results show that our model is reasonably accurate, particularly when the wireline delay is small and/or the packet loss rate is low.

• Journal of The Korean Society of Agricultural Engineers
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• v.62 no.4
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• pp.63-73
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• 2020

The area of paddy fields for upland crop cultivation is gradually increasing. In this context, we developed a chain type mole drainer that can be attached to a tractor to prevent the wet injury of crops. To conduct a field test, we formed underdrains at 2 m intervals in a paddy field wherein soybeans are cultivated, and we investigated the status of the soil moisture, groundwater level, and soybean growth during the cultivation period. The soil moisture content decreased by 22.3~26.8% in the test plot and by 5.9~6.9% in the control plot during a period of 57~88 hour after a rainfall of 41.5~157.0 mm. The effect of underdrainage was clear as the hourly groundwater level decreased approximately 2.8 times faster in the test plot compared with the control plot. Moreover, the soybean yield was greater by 78.6 kg/10a in the test plot than in the control plot. Therefore, for soybean cultivation in paddy fields, the use of the developed mole drainer is expected to help in improving the drainage and increasing the soybean yield.

• Journal of the Korean Chemical Society
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• v.50 no.1
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• pp.53-59
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• 2006

.FAPO-5 molecular sieves were synthesized starting from the same reactant gel at 170 oC using microwave irradiation technique and conventional hydrothermal reaction. The FAPO-5 molecular sieves were characterized by several techniques such as SEM, FTIR, UV/Vis, and ESR. Moreover, the oxidation of styrene over FAPO-5s was carried out, and compared to check the oxidation and epoxidation ability of the two FAPO-5s. FAPO-5 can be obtained easily by microwave irradiation within 15 min at 170oC, whereas FAPO-5 synthesis is completed in 6 h by conventional electric heating, confirming the acceleration about 20 times by microwave technique. There are no appreciable differences between two FAPO-5s in surface area and coordination state of iron. The FAPO-5 synthesized by microwave irradiation shows higher epoxide selectivity in the styrene epoxidation, which may be explained by the higher hydrophobicity of the catalyst.

• Journal of Environmental Science International
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• v.4 no.4
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• pp.1-1
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• 1995

This paper evaluates the historical development of national park policy and administration in Japan from the perspective of achieving sustainable development in nationally important ecological areas. Contrary to the widely held belief, the national park system in Japan has been unsuccessful in balancing conservation and development. The fundamental reasons for its failure are as follows: the Japan's national park system has been largely founded and developed based on economic grounds and held sway by economic development policy; the policy and administrative coordination between government units concerning conservation and development has not been carried out; public participation and environmental groups' involvement in the decision making have been extremely limited; national parks have been perceived in the public image not as distinctive national heritage but as finest and popular tourist sites; and the dominant interest of tourism and recreational development has prevailed over conservation interest. Japan's unsuccessful experience and lessons imply that there is urgent need to drastically reform our national park system, largely founded on the Japanese model, in order to save our last national environmental heritage.

• Journal of Environmental Science International
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• v.4 no.4
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• pp.303-315
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• 1995

This paper evaluates the historical development of national park policy and administration in Japan from the perspective of achieving sustainable development in nationally important ecological areas. Contrary to the widely held belief, the national park system in Japan has been unsuccessful in balancing conservation and development. The fundamental reasons for its failure are as follows: the Japan's national park system has been largely founded and developed based on economic grounds and held sway by economic development policy; the policy and administrative coordination between government units concerning conservation and development has not been carried out; public participation and environmental groups' involvement in the decision making have been extremely limited; national parks have been perceived in the public image not as distinctive national heritage but as finest and popular tourist sites; and the dominant interest of tourism and recreational development has prevailed over conservation interest. Japan's unsuccessful experience and lessons imply that there is urgent need to drastically reform our national park system, largely founded on the Japanese model, in order to save our last national environmental heritage.

• Journal of the Korean Data and Information Science Society
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• v.21 no.6
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• pp.1211-1224
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• 2010

The study derives various anticipated benefits resulting from locating small and medium sized IT service firms in a specific industrial cluster area. The study also derives IT service agility factors to obtain competitive advantages vital to real-time global enterprises. The anticipated benefits were then used to analyze how they improve the firms' agility. Using questionnaire data, factor analyses were used to figure out eight anticipated benefit factors including coordination, information sharing, business costs, speciality, communication, trust improvement, mutual business understanding, and reciprocity. The eight empirically derived benefit factors were then used to examine how they affect the IT service agility including flexibility, speed, responsiveness, and lean efficiency. The results of regression analyses showed that each one of the anticipated benefit factors except communication influence one or more IT service agility factors.