• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.3
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• pp.214-220
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• 2022

This paper proposes a test device designed for developing a high-voltage multilayer ceramic capacitor (MLCC). The proposed topology consists of an energy recovery circuit for charging/discharging capacitor, a flyback converter, and a boost converter for supplying power and a bias voltage application to the energy recovery circuit. The energy recovery circuit designed with a half-bridge converter has auxiliary switches operating before the main switches to prevent excessive current from flowing to the main switches. A prototype has been designed to verify the reliability of target capacitors following the voltage fluctuation with a frequency range below 65 kHz. To conduct high root mean square (RMS) current to the capacitor as a load, the MLCC test was conducted after the topology verification was completed through the film capacitor as a load. Through the agreement between the RMS current formula proposed in this paper and the MLCC test results, the possibility of its use was demonstrated for high-voltage MLCC development in the future.

• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.2
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• pp.85-91
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• 2022

This study proposes a high efficiency bridgeless Power Factor Correction (PFC) converter with improved common mode noise characteristics. Conventional PFC has limitations due to low efficiency and enlarged heat sink from considerable conduction loss of bridge diode. By applying a Common Mode (CM) coupled inductor, the proposed bridgeless PFC converter generates less conduction loss as only a small magnetizing current of the CM coupled inductor flows through the input diode, thereby reducing or removing heat sink. The input diode is alternately conducted every half cycle of 60 Hz AC input voltage while a negative node of AC input voltage is always connected to the ground, thus improving common mode noise characteristics. With the aim to improve switching loss and reverse recovery of output diode, the proposed circuit employs Critical Conduction Mode (CrM) operation and it features a simple Zero Current Detection (ZCD) circuit for the CrM. In addition, the input current sensing is possible with the shunt resistor instead of the expensive current sensor. Experimental results through 480 W prototype are presented to verify the validity of the proposed circuit.

• Journal of The Geomorphological Association of Korea
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• v.27 no.3
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• pp.25-39
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• 2020

This study analyzed the management plan of Seomjin River Chimsil Wetland by identifying landscape changes through aerial photographs analysis and concentrations of sedimentation. Geophysical Landscape Change Analysis showed that vegetation accounts for more than half of the total area. The Barren land and water body was somewhere repeatedly increased and decreased and made an irregular form in the study area. The soil was acidic, and no eurtophication was shown, but it was potential to form wetland. In addition, the research area has been terrestrification of sand bar for a long period of time, forming a soil layer. Although the characteristics of river deposits were shown in the study area, the grain size was a particulate matter, and the sorting was 'very poorly sorted'. In some areas of Seomjin River Chimsil Wetland, sand bars were formed, but most areas were undergoing to terrestrification. Therefore, in order to preserve the riverine area and to serve by a bridge between the land ecosystem and the underwater ecosystem, it is very necessary to remove some vegetation, create a proper waterway, and restore the wetland.

• Journal of The Korean Association For Science Education
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• v.19 no.3
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• pp.409-427
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• 1999

The aim of this study was to illustrate how STS-related ideas in science education have been developed historically in the context of British education, particularly focused on the period of the 19th century and the first half of the 20th century. It has been hardly considered that the basic ideas of the STS education, one of the two paradigms of current science education together with constructivism, can be traced back to the beginning of the school science education itself. far beyond some of the programs which are largely regarded as the first-developed STS programs in Britain, such as Science in Society and SISCON. The movement of Mechanics' Institute during the first half of the 19th century would be the first systematic attempt to bridge the gap between the knowledge of pure science and its practical applications, although the main target was working-class adults rather than school pupils. At the end of the first half of the 19th century, this application-focused approach of science teaching was echoed in the elementary schools by Richard Dawes, one of the early experimenters of school science. The second half of the century was in large the period of the establishment of science as one of the core elements of school curriculum, mainly by emphasizing the aspect of pure science as a means for mental training. During this period, the elements of STS education-related appeared in the subject called 'Object Lesson' in elementary schools which was practically a separate subject from those of science. After the turn of the century, triggered by the experience of World War I, the growing appreciation of the impacts of science upon society and of the necessity of the teaching of science for wider audience gave a great impact towards two new main movements, i.e. for General Science and Citizen Science. The later illustrates a typical example of the STS movement in school science during the first half of the 20th century, particularly driven by the socialistic ideas towards the relation between science and society.

• Journal of the Korean Institute of Traditional Landscape Architecture
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• v.31 no.1
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• pp.71-86
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• 2013

This study was carried out to find the changed contents and details of the ponds at Jondeokjeong area in the Changdeok Palace, where was modified during the reign of King Gojong(高宗, 1863~1907), and considered the internal context through the diachronic views about royal garden building in the Joseon Dynasty. The results were as belows. First, this study found that the transformed time of the ponds at Jondeokjeong area was the 21th year of King Gojong(1884) based on the pictures taken in the last half of the 19th century and the records of "Gojongsilrok(高宗實錄: Annals of the King Gojong)". Second, this study also found that the remodeled ponds at Jondeokjeong area by King Gojong were followed the landscape of Geoncheong Palace(乾淸宮) and Hiangwon-pond(香遠池) in Gyeongbok Palace because the remodeled ponds of Jondeokjeong area had the spatial organization similar to Hiangwon-pond. Third, the bridge of remodeled ponds at Jondeokjeong area was utilized as the expedient to expand the function of rear garden, which combines the areas of Yungyungdang(演慶堂) and Jondeokjeong. This was the same method that Konchunggung(乾淸宮) in Gyeongbok Palace had occupied the whole area through the Chui-hiang bridge(醉香橋) which connects to the Hiangwonjeong(香遠亭). Fourth, ponds at Jondeokjeong area and Hiangwonjeong that were created during the year of King Gojong promised the use of Yungyungdang and Konchung Palace, and reflected the statuses of the two building-blocks. Lastly, this study concluded the remodeled Jondeokjeong ponds were not only to create the necessary spaces of the landscape for King Gojong, but also to build the space on the context of Huwonjeongdang(後苑政堂: political structure in rear garden), which has been passed down from their ancestors.

• Polymer(Korea)
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• v.31 no.6
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• pp.497-504
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• 2007

We have prepared the dinuclear half-sandwich CGC(constrained geometry catalyst) with polymethylene bridge $[Zr(({\eta}^5\;:\;{\eta}^1-C_9H_5SiMe_2NCMe_3)Me_2)_2\;[(CH_2)_n]$ [n=6(4), 9(5), 12(6)] by treating 2 equivalents of MeLi with the corresponding dichlorides compounds. To study the catalytic behavior of the dinuclear catalysts we conducted copolymerization of ethylene and 1-hexene in the presence of three kinds of boron cocatalysts, $Ph_3C^+[B(C_6F_5)_4]^-\;(B_1),\;B(C_6F_5)_3\;(B_3)$, and $Ph_3C^+[(C_6F_5)_3B-C_6F_4-B(C_6F_5)_3]^{2-}\;(B_2)$. It turned out that all active species formed by the combination of three dinuclear CGCs with three cocatalyst were very efficient catalysts for the polymerization of olefins. The activities increase as the bridge length of the dinuclear CGCs increases. At the same time the dinuclear cocatalyst exhibited the lowest activity among three cocatalysts. The prime observation is that the dinuclear cocatalyst gave rise to the formation of the copolymers with the least branches on the polyethylene backbone.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.3
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• pp.17-23
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• 2020

This paper proposes a simulation model using an equivalent circuit for the development of an MMC system. The MMC has been chosen as the most suitable topology for high voltage power transmission, such as a voltage-type HVDC, and it has dozens to hundreds of sub-modules in the form of a half-bridge or full-bridge connected in series. A simulation study is essential for the development of an MMC algorithm. On the other hand, it is virtually impossible to construct and implement MMC simulation models, including hundreds or thousands of switching devices. Therefore, this paper presents an MMC equivalent model, which is easily expandable and implemented by modeling the dynamic characteristics. The voltage and current equation of the equivalent circuit was calculated using the direction of the arm current and switching signal. The model was implemented on Matlab/Simulink. In this paper, to show the validity of the model developed using Matlab/Simulink, the simulation results of a five-level MMC using the real switching element and the proposed equivalent model are shown. The validity of the proposed model was verified by showing that the current and voltage waveform in the two models match each other.

• Journal of the Korean Institute of Landscape Architecture
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• v.38 no.2
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• pp.9-24
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• 2010

This study investigates how students perceive landscape design studio classes and provides basic data to set guidelines for future student-oriented pedagogical strategies in landscape architectural design education. This study is based on the premise that the current dominant educational method, which is based on positivism, should shift to a constructivist approach, which allows students to question objective and absolute truths and restructure knowledge based on their own experiences. Unlike lecture-oriented classes, studio education relies heavily on the perceptions, attitudes, and capabilities of individual students because the nature of the class asks each student to find solutions to given project problems in creative and visual ways. Therefore, it is important to understand the psychological state of students during these classes in order to set alternative criteria for design studio education. This study contains three parts. The first part reviews theoretical discourses to understand the demands for a student-oriented educational paradigm shift and the nature of the design studio at many levels. The second part analyzes how students perceive design studio classes in terms of their satisfaction and stress levels and how studio classes affect their decision making regarding future careers. The stress levels accompanying the design process are also investigated, based on a survey of undergraduate students who are enrolled in the landscape architecture programs of four universities in Korea. According to the findings, design studio classes play a specific role in students' decision making about their future careers. Almost half of students turn out to be dissatisfied with their design education, and half of students suffer from high stress levels caused by studio classes, especially in the early phases of the design process. The findings suggest that instructors should give more attention to discovering ways to help students initiate the design process and bridge ideas and forms, provide clear guidelines for evaluation of students' abilities, and develop a more holistic approach in design studio classes that is based on individual problem-solving processes.

• Journal of international Conference on Electrical Machines and Systems
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• v.1 no.4
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• pp.483-491
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• 2012

It is expected that, in the future, DC power service will be widely used for photovoltaic home power generation systems, since DC consuming devices are ever increasing. Instead of using multiple converters to convert DC to AC and then AC to DC, the power service could solely be based on DC. This would eliminate the need for converters, reducing the cost, complexity, and possibly increasing the efficiency. However, configuration of direct DC power service with mechanical contacts can cause spark voltage or an electric shock when the switch is turned on and off. To solve these problems, in this paper, a contactless power supply for a DC power service that can transfer electric power produced by photovoltaics to the home electric system using magnetic coupling instead of mechanical contacts has been proposed. The proposed system consists of a ZVS boost converter, a half-bridge LLC resonant converter, and a contactless transformer. This proposed contactless system eliminates the use of DC switches. To reduce the stress and loss of the boost converter switching devices, a lossless snubber with coupled inductor is applied. In this paper, a switching frequency control technique using the contactless voltage sensing circuit is also proposed and implemented for the output voltage control instead of using additional power regulators. Finally, a prototype consisted of 150W boost converter has been designed and built to demonstrate the feasibility of the proposed contactless photovoltaic DC power service. Experimental results show that 74~83% overall system efficiency is obtained for the 10W~80W load.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.7
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• pp.4878-4883
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• 2015

The IP Multimedia Subsystem(IMS) is a framework that provides access to the content of Internet and Telecom services anytime and anywhere with guaranteed Quality of Service(QoS) and manageability by separating control functions from bearer and services. The Service Delivery Platform(SDP) provides common interfaces and protocols to deploy existing or new services in an efficient way. Therefore SDP over IMS plays a role of bridge between established network and new IMS network by simplifying the interaction among application services. In order to enrich the multimedia network communication, we try to deploy the Push-to-talk over Cellular(PoC) service which is considered as the outstanding and distinguished half-duplex Voice over IP(VoIP) application service among deployable candidate services over mobile network. In this paper we investigate the advantages of PoC service and PoC architecture firstly, and then focus on the its practical implementation for the prototype to validate the feasibility of its deployment and realization.