• Proceedings of the KIEE Conference
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• 1998.07c
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• pp.926-928
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• 1998

A fast optimization algorithm has been evolved from a simple two stage optimal power flow(OPF) algorithm for constrained power economic dispatch. In the proposed algorithm, we consider various constraints such as power balance, generation capacity, transmission line capacity, transmission losses, security equality, and security inequality constraints. The proposed algorithm consists of four stages. At the first stage, we solve the aggregated problem that is the crude classical economic dispatch problem without considering transmission losses. An initial solution is obtained by the aggregation concept in which the solution satisfies the power balance equations and generation capacity constraints. Then, after load flow analysis, the transmission losses of an initial generation setting are matched by the slack bus generator that produces power with the cheapest cost. At the second stage we consider transmission losses. Formulation of the second stage becomes classical economic dispatch problem involving the transmission losses, which are distributed to all generators. Once a feasible solution is obtained from the second stage, transmission capacity and other violations are checked and corrected locally and quickly at the third stage. The fourth stage fine tunes the solution of the third stage to reach a real minimum. The proposed approach speeds up the coupled LP based OPF method to an average gain of 53.13 for IEEE 30, 57, and 118 bus systems and EPRI Scenario systems A through D testings.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.9
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• pp.33-41
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• 2015

To improve the power quality of distributed generation (DG) systems even in the presence of distorted grid condition, dual current control scheme of a grid-connected inverter is proposed. The proposed current control scheme is achieved by decomposing the inverter state equations into the fundamental and harmonic components. The derived models are employed to design dual current controllers. The conventional PI decoupling current controller is used in the fundamental model to control the main power flow in DG systems. At the same time, the predictive control is applied in the harmonic model to suppress undesired harmonic currents to zero quickly. To decompose the voltage inputs and state variables into the fundamental and harmonic components, the fourth order band pass filter (BPF) is designed in the discrete-time domain for a digital implementation. For experimental verification, 2kVA prototype of a grid-connected inverter has been constructed using digital signal processor (DSP) TMS320F28335. The effectiveness of the proposed strategy is demonstrated through comparative simulation and experimental results.

• Journal of the Korea Fashion and Costume Design Association
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• v.19 no.2
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• pp.145-157
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• 2017

This study aimed to investigate the relationship between values orientation and fashion image orientation with a focus on the new senior generation. The study conducted data analysis by using the SPSS 17.0 program for the final 397 copies excluding incomplete questionnaires. The results of this study are as follows. First, values orientation was drawn as the four factors of social orientation, dependent orientation, family-like orientation, and individual orientation. The fashion image orientation was compartmentalized as three factors: urban image, individual image, and feminine image. Second, social orientation had a significant effect on feminine image as shown in Photo 1, while only individual orientation exerted a significant influence on individual image (Photo 2). Social orientation and family-like orientation respectively exercised a significant influence on individual image and feminine image, and feminine image (Photo 3). Third, the four groups did not show a significant difference in the relationship with the sub-elements of fashion image orientation. It appeared that all four groups were felt as a complex image in which modern, feminine, and individual images were mixed. Fourth, the four groups showed a significant difference in the unusual, elegant, refined, youthful, feminine, and modern images among the factors of fashion image orientation.

• Journal of Communications and Networks
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• v.4 no.4
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• pp.336-343
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• 2002

A major challenge for next generation mobile communication is capturing the system architecture’s complexity with all its internal and external dependencies. Seamless integration of heterogeneous environments in all system parts is a key requirement. Moreover, future systems have to consider the different evolution cycles of individual system parts. Among those, services are expected to change the fastest. With respect to these considerations, we propose an overall architecture for next generation mobile communication systems. It covers all system parts from wireless transmission to applications including network and middleware platform. Our approach focuses on adaptability in terms of recon- figurability and programmability to support unanticipated system evolution. Therefore, we consider abstraction layers which consist of adaptable cooperating components grouped by open platforms rather than rigid system layers. In addition to that, we introduce cross-layer cooperation allowing an efficient use of the available resources. Specific scenarios illustrate the feasibility of our approach.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.873-878
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• 2008

Doosan Mecatec has developed alignment system for Organic Light-Emitting Diode (OLED) display production using large size substrate. In the present article, The alignment system between the substrate and the mask, which is a core technology for producing the OLED product using the fourth-generation substrate with $730{\times}920mm^2$ or more, will be described by dividing into a substrate loader, a magnet unit, a CCD camera, etc. The substrate loader is optimized through the simulation where the central portion of the substrate droops by about 1.5mm by clamping each of a long side (920mm direction) and a short side (730mm direction) thereof by 6 point and 4 point. A magnet unit using a sheet type of rubber magnet is constituted and a CCD camera model with the specifications capable of minimizing the errors between a clear image and the same image is selected. The system to which an upward evaporation technique of small molecular organic materials will be applied has been developed so that repeatability and position accuracy becomes ${\pm}1{\mu}m$ or less using an UVW type of stage. Also, the vision accuracy of the CCD camera becomes ${\pm}1{\mu}m$ or less and the align process TACT becomes 30sec. or less so that the final alignment accuracy between the substrate and the mask becomes ${\pm}3{\mu}m$ or less. In order to meet an extra-large glass substrate, an evaporation system using an extra-large AMOLED substrate has been developing through a vertical type of an alignment system.

• Education of Primary School Mathematics
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• v.24 no.1
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• pp.43-69
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• 2021

The purpose of this study is to confirm the influences of learner-centered instruction on learners' achievement and reason ability. In order to accomplish them, the fraction unit and the polygonal unit in the fourth grade were implemented with teaching methods and materials suitable for learner-centered mathematics instruction. Some conclusions could be drawn from the results as follows: First, learner-centered mathematics instruction has a more positive effect on learning of learned knowledge and generating unlearned knowledge in the experimental period than teacher-centered instructions. Second, learner-centered instruction makes an influence of low learning ability on getting achievement positively. Third, as the experimental treatment is repeated, learner-centered instruction has a positive effect on students' reasoning ability. The reasoning ability of students showed a difference in the comparison between the experimental group and the comparative group, and within the experimental group, there was a positive effect of the extension of the positive reasoning ability. Fourth, it can be estimated that the development of students' reasoning ability interchangeably affected their generation test results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.12B
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• pp.1623-1635
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• 2011

Fourth-generation (4G) cellular communication systems must provide different quality-of-service (QoS) to users according to the service type, membership class, and usage case of each user. For the purpose of user's QoS differentiation, we propose an enhanced uplink random access scheme for bandwidth request. More specifically, we divide a bandwidth request channel into two parts: One is a primary region and the other is a secondary region. Then, each region has a unique minimum access class that allows only specific users to perform random access through that region. By doing so, we can reduce collision probability and increase the success probability of bandwidth request. From the perspective of standardization, we presented this scheme in the IEEE 802.16m Session #66 held on March 2010. As a result, the concept of the proposed scheme and required messages were defined in the 802.16m standard.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2011.10a
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• pp.291-294
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• 2011

4G WiBro service in Korea, the world's fourth-generation communication is standardized. VoIP service has been activated one of the application in WiBro communications infrastructure. When using VoIP in the WiBro service, complementing the existing VoIP vulnerabilities in the encryption and authentication technology is a need for research. In this paper, fourth-generation WiBro, LTE, and the definition, 1G, 2G, 3G and 4G compares. And, WiBro service in the VoIP edaehan technical, administrative, physical, and hacker attacks and vulnerability analysis is the study of security measures. Enhanced security measures for the WiBro service to VoIP security through encryption and authentication technologies are studied.

• Journal of KIISE
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• v.43 no.5
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• pp.579-589
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• 2016

Currently, corporations have introduced the knowledge management system that utilizes knowledge effectively for practical purpose and development of core ability. However, existing knowledge systems have failed to share the knowledge content due to lack of elements that encourage the members to participate in the system. In this study, we designed a novel knowledge management system that employs the structure of social network service (SNS). More precisely, screen layout according to function and several algorithms to improve user friendliness and produce integrated knowledge content are recommended. The proposed SNS-based knowledge management system encourages the enterprise members to participate in the system to produce and share valuable knowledge contents.

• Journal of the Korea Society for Simulation
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• v.20 no.4
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• pp.91-96
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• 2011

As the user's demand for ultra high-speed wireless internet has increased, the standardization, research and development of future mobile communication systems have been done for several years. IMT-Advanced system which is called fourth generation mobile communication should support the data rate of 1 Gbps for nomadic users and 100 Mbps for mobile users. Also, the system should hold call connection at the mobile speed of 350 km/h. Meanwhile, since Doppler spread is linearly proportional to mobile speed, high mobility leads to the increase of interference between subcarriers and the deterioration of detection performance consequently. In this paper, we evaluate and analyze detection probability with respect to equalization methods in time-varying channels under system parameters complying with IMT-Advanced requirements. According to computer simulation conducted by varying mobile speed and code rate, MMSE based equalization can mitigate performance degradation of IMT-Advanced system considerably in time-varying channels.