• Journal of the Korean School Mathematics Society
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• v.13 no.1
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• pp.163-184
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• 2010

In this paper, we study the effects on mathematical communication and disposition for the writing mathematics letters in secondary mathematics education. For this purpose we construct a experimental class and then analyse the students' change in those aspects after applying writing mathematics letters made some significant changes on the students communication in mathematics and disposition. First. the results for this purpose on regarding the enhancement of mathematical communication are effective. Second, the results on regarding the improvement of disposition are effective.

• Archives of design research
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• v.13 no.4
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• pp.203-212
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• 2000

If researching popular culture is understanding a mechanism to make us the general public, then researching, design is discovering and developing a mechanism to qualitatively improve the life of the general public's life. Since this means that the relation of popular culture and design is correlated among social, cultural and historical ties, but this study isolated popular culture and design as a separate variable, and examined and analyzed cultural factors such as the constantly changing objective, role, contents and formativeness(Gestaltung) of design through already researched various(6) criteria of the concept of popular culture. Thus, this study strives to present the orientation of design with culture by including cultural thinking starting from the stage of design, design planning.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.91-92
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• 2011

Beat is a phenomenon, where the magnitudes and frequencies of the voltage and the current fluctuate. This paper describes a quantitative analysis of the beat phenomenon of a wind farm using the envelope of a current during intertie/grid fault conditions. In this paper, the ratio of the crest to the trough of the envelope curve and the time interval between adjacent troughs are defined and used to evaluate the beat phenomenon quantitatively. Beat phenomena under various fault and wind conditions are analyzed. The proposed quantitative analysis seems simple but effective in the more understanding of beat phenomenon of a wind farm, and thus can be used as a basis for operation and/or protection of an intertie.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.6
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• pp.1128-1133
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• 2011

In a wind farm, a large number of small wind turbine generators (WTGs) operate whilst a small number of a large generator do in a conventional power plant. To maintain high quality and reliability of electrical energy, a wind farm should have equal performance to a thermal power plant in the transient state as well as in the steady state. The wind farm shows similar performance to the conventional power plant in the steady state due to the advanced control technologies. However, it shows quite different characteristics during fault conditions in a grid, which gives significant effects on the operation of a wind farm and the power system stability. This paper presents an analysis of response of a wind farm during grid fault conditions. During fault conditions, each WTG might produce different frequency components in the voltage. The different frequency components result in the non-fundamental frequencies in the voltage and the current of a wind farm, which is called by "beats". This phenomenon requires considerable changes of control technologies of a WTG to improve the characteristics in the transient state such as a fault ride-through requirement of a wind farm. Moreover, it may cause difficulties in protection relays of a wind farm. This paper analyzes the response of a wind farm for various fault conditions using a PSCAD/EMTDC simulator.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.1484-1488
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• 2008

댐은 하천의 물을 조절하기 위해서 인공적으로 만들어진 하천구조물이다. 댐사용권은 공업화와 경제발전으로 통해 증가한 용수수요를 충족시키기 위하여 정부가 다목적댐을 건설함에 따라 추가적으로 확보되는 수량에 대한 소유권을 법적으로 인정하고 사고 팔수 있도록 하고 있다. 이는 최근 여러 가지 소모적인 물분쟁이 물분쟁의 원인이 되고 있다. 낙동강 권역의 댐들은 건설시기가 각기 다르며, 건설시의 댐계획량과 현재의 용수공급량은 기후변화와 수리환경 변화 및 용수수요의 증대로 인하여 차이를 나타내고 있다. 특히 상 하류에 건설된 댐과의 연계운영으로 이전 독립적으로 운영되었던 경우에 비해 용수공급능력이 변화할 수 있다. 그러나 이에 따른 댐의 용수공급능력을 재평가하기 위한 공식적인 방법이나 절차가 정립되어 있지 않아 댐 건설시의 계획량을 적용하고 있는 실정이다. 가용허가수량에 대한 재평가가 없이 수리권에 대한 갱신이 이루어질 경우 사용자 입장에서는 자신의 용수사용을 개선할 원인을 제공하지 못할 것이며, 임의적인 허가가 계속 부여될 경우, 갈수시 물공급의 안정성을 확보할 수 없게 될 것이다. 따라서 안정적인 용수의 공급을 위한 적절한 가용허가수량을 판단하는 것이 요구된다. 따라서 본 연구에서는 실제 낙동강권역 댐의 여러 가지 여건을 고려하여 21세기 프론티어연구개발사업 "유역통합물수지분석 및 수자원계획기술 개발"에서 활용된 통합수자원평가계획 모형 K-WEAP에 적용하였다. 이를 통하여 낙동강권역 댐의 가용허가수량을 분석하고, 현재 산정되어 있는 댐의 가용허가수량과 비교 분석하였다.

• Journal of the Korean Institute of Intelligent Systems
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• v.22 no.1
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• pp.75-80
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• 2012

Abnormal navigating ships affact the ships navigating normal routes seriously. So VTS centers and Korean Coast Guard co-work(cooperate) closely to trace the ships which break the regulations and make accidents. But it is evident that there is limitations to indetify the risk factors caused by men. Unfortunately there is very few of the researches on the identificaton of risk elements by men. This paper is to implement the intelligent system for identifying abnormal navigating ships by using fuzzy inference.

• Journal of The Korean Association of Information Education
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• v.15 no.4
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• pp.551-560
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• 2011

STEAM education is a topic-based curriculum to integrate the concepts into other subjects such as science, technology, engineering, art and mathematics in order to improve the students' interesting, understanding, integrated thinking and problem solving ability. In this paper, we designed STEAM curriculum in the form of Project-based Learning and developed the material for elementary students. We also developed the android-based application through searching for a utilization of IT simulation for enhancement the students' Project-based Learning effect.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2010.10a
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• pp.135-138
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• 2010

The goals of the Global Maritime Distress and Safety System (GMDSS) that initiated by the IMO and supported by IALA, IHO, ITU, IEC and manufacturers are to provide more effective and efficient emergency and safety communications and disseminate Maritime Safety Information (MSI) to all ships on the world's oceans regardless of location or atmospheric conditions. Much of the GMDSS is built on technologies more than 20 years old; some work well; others do not. While GMDSS requirements apply only to SOLAS vessels, there are many other vessels on the water. So some considerations are necessary for non-SOLAS vessels including fishing ships, leisure boats and small boats. This paper describes the analysis of IMO, ITU and IEC meeting results held on recently. Also it gives the trends of the international marine radio standards and its technologies.

• The Transactions of the Korean Institute of Power Electronics
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• v.14 no.2
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• pp.134-141
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• 2009

The new method is proposed to improve the dynamics of the phase angle detector during abrupt voltage dip caused by a grid fault. Usually, LPF(low pass filter) is used in the feedback loop of SRF(Synchronous Reference Frame) - PLL (Phase Locked Loop) system because the measured grid voltage contains harmonic distortions and sensor noises. A better transient response can be obtained with the proposed design method for SRF-PLL by the analysis of linearized model of the PLL system including LPF. Furthermore, in the proposed method, the controller gain and LPF cut-off frequency are changed from normal value to transient value when the voltage disturbance is detected. This paper shows the feasibility and the usefulness of the proposed methods through the computer simulation and the experiment.

• Proceedings of the KIEE Conference
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• 1999.07c
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• pp.1192-1194
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• 1999

Recently, there has been growing interest in utilizing cogeneration(COGN) system which has high energy efficiency due to the lacking of energy resource, but insertion of cogeneration system into existing power distribution system can cause several problems such as voltage variations, reenergizing of feeder isolated by fault, increasing fault current because of reverse power of COGN. Also these problems increase the complexity of control, protection, and maintenance of power distribution systems. Hence, some problems according to COGN interconnection operation to power distribution system must be taken into account so that operation and security of power distribution system is not disturbed. This paper deals with momentary voltage variations and fault analysis caused by interconnection operation of COGN.