• Journal of Power Electronics
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• v.5 no.1
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• pp.67-75
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• 2005

A high efficiency ZVS PWM asymmetrical half bridge converter for a plasma display panel (PDP) sustaining power modules is proposed in this paper. To achieve the ZVS of power switches for the wide load range, a small additional inductor L/sub 1kg/, which also acts as an output filter inductor, is serially inserted into the transformer's primary side. At that point, to solve the problem of ringing in the secondary rectifier caused by L/sub 1kg/, the proposed circuit employs a structure without the output filter inductor, which helps the voltages across rectifier diodes to be clamped at the output voltage. Therefore, no dissipative RC (resistor capacitor) snubber for rectifier diodes is needed and a high efficiency as well as low noise output voltage can be realized. In addition, since it has no large output inductor filter, the asymmetrical half bridge converter features a simpler structure, lower cost, less mass, and lighter weight. In addition, since all energy stored in L/sub 1kg/ is transferred to the output side, the circulating energy problem can be effectively solved. The operational principle, theoretical analysis, and design considerations are presented. To confirm the operation, validity, and features of the proposed circuit, experimental results from a 425W, 385Vdc/170Vdc prototype are presented.

• Journal of Electrical Engineering and Technology
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• v.1 no.3
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• pp.351-358
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• 2006

In this paper, the electrical characteristics of the contactless transformer is presented using the conventional coupled inductor theory. Compared with the conventional transformer, the contactless transformer has a large airgap, long primary wire and multi-secondary wire. As such, the contactless transformer has a large leakage inductance, small magnetizing inductance and poor coupling coefficient. Therefore, large magnetizing currents flow through the entire primary system due to small magnetizing inductance, resulting in low overall system efficiency. In high power applications, the contactless transformer is so bulky and heavy that it needs to be split by some light and small transformers. So, the contactless transformer needs several small transformer modules that are connected in series or parallel to transfer the primary power to the secondary one. This paper shows the analysis and measurement results of each contactless transformer module and comparison results between the series- and parallel-connection of the contactless transformer. The results are verified on the simulation based on the theoretical analysis and the 30kW experimental prototype.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.8 s.239
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• pp.1102-1108
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• 2005

The integrity of nuclear piping systems has to be maintained sufficiently all the times during operation. In order to maintain the integrity, reliable assessment procedures including fracture mechanics analysis, etc, are required. Up to now, the integrity assessment has been performed using conventional deterministic approach even though there are lots of uncertainties to hinder a rational evaluation. In this respect, probabilistic approach is considered as an appropriate method for piping system evaluation. The objectives of this paper are to develop a probabilistic assessment program using reliability index and simulation technique and to estimate the damage probability of wall-thinned pipes in secondary systems. The probabilistic assessment program consists of three evaluation modules which are first order reliability method, second order reliability method and Monte Carlo simulation method. The developed program has been applied to evaluate damage probabilities of wall-thinned pipes subjected to internal pressure, global bending moment and combined loading. The sensitivity analysis results as well as prototypal evaluation results showed a promising applicability of the probabilistic integrity assessment program.

• Journal of Korea Multimedia Society
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• v.10 no.9
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• pp.1153-1164
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• 2007

One of the most challenging technical issues in mobile communication for multimedia is Quality of Service (QoS) management of handover calls. This paper proposes a 2-level handover control system to copy with this problem. A 2-level handover control system consists of resource reservation and call admission control modules. The resource reservation module divides the network resource into Hard and Soft reserved resource. The Hard reserved resource is only for the handover calls while the Soft reserved resource is for both the handovers and the new calls. And also, the resource reservation module classifies handovers into primary and secondary handovers based on often they occur. The call admission control module deals with the primary and secondary handover calls in different ways. The new calls can use Soft reserved resource only if there is sufficient amount available in the Hard reserved resource. Proposed system is evaluated using an M/M/c/c queueing model. It is shown that proposed system allows more efficient utilization of network resource without degrading QoS comparing with the legacy handover control systems.

• Journal of The Korean Association For Science Education
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• v.24 no.3
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• pp.556-564
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• 2004

Two biology modules were developed previously for the purpose of improving creativity and scientific thinking of secondary school students. A hypothetical-deductive experimental procedure was reflected in the module when students themselves can perform a series of activities of making hypothesis and designing an experiment to solve the questions. They followed a series of scientific processes to determine some characteristics regarding plant pigments and the transport process of materials in living organisms. Four classes of 9th graders in'S' Science High School were divided into the experimental and the control group. The same contents of the modules were taught to the control group by the traditional experimental way. The students' creativity, scientific thinking, scientific inquiry skill and knowledge achievement were examined before and after the interventions. As results, the experimental groups showed more significant improvement on the areas of the students' creativity, scientific thinking, scientific inquiry skill and achievement than the control groups. Results indicated that the specially designed modules in terms of hypothetical-deductive experimental procedure were effective to improve science high school students' creativity and scientific thinking abilities.

• Proceedings of the KIPE Conference
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• 1999.07a
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• pp.319-322
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• 1999

This paper presents a novel single-stage Power Factor Corrected(PFC) AC/DC forward converter with semi-automatic current shaping in order to achieve the unity power factor and an isolated output. Since the proposed circuit is combined a boost converter used for PFCs with a forward converter used for DC to DC conversion, the over-all size of system could be reduced. And thanks to the zero voltage switching(ZVS) in both switches, the voltage stress can be reduced considerably. A simple auxiliary circuit adopted into the secondary of transformer is composed of lossless components for reducing surge voltage. A prototype which has tow IGBT(Insulated Gate Bypolar Transistor) modules as switching device is manufactured to evaluate the proposed topology. The characteristics of the proposed circuit are tested, and the validity is verified by experimental results.

• Proceedings of the KIPE Conference
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• 2007.07a
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• pp.350-352
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• 2007

Modularized charge equalization converter for HEV lithium-ion battery cells is proposed in this paper, in which intra-module and inter-module charge equalization can be achieved at the same time. For intra-module charge equalization, the conventional flyback DC/DC converters of low power and small size are employed, in which all of the primary sides are coupled in parallel for selective charge of the specific under charged cell within the module. For inter-module charge equalization, the flyback DC/DC converters are also added, in which all the secondary windings are electrically linked in parallel for automatic charge balancing among the modules. An engineering sample of forty cells hiring the proposed cell balancing scheme is implemented and its experimental result shows that the proposed modularized charge equalization circuit has good cell balancing performance.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1500-1502
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• 2005

In this paper, the electrical characteristics of the non-contact transformer is presented using conventional coupled inductor theory. Each non-contact transformer is analyzed through simulation and measurement. In high power applications, non-contact transformer is so bulky and heavy that it should be split by some light transformers. So non-contact transformer needs several small transformer modules which are connected series or parallel to transfer the primary power to the secondary one. This paper shows analytic result of the each non-contact transformer module and comparison result between series-connection and parallel-connection of the non-contact transformer. The results are verified on the simulation based on the theoretical analysis and the 30kW experimental prototype.

• Hwankyungkyoyuk
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• v.11 no.2
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• pp.1-13
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• 1998

The purpose of this study is to investigate thel present situation and to analyze the needs and problems of the $\ulcorner$Environment$\lrcorner$ subject in secondary school of the current 6th curriculum in Korea and to indicate the directions of improvement environmental education. The first step of this research was to review the related literature and the result indicated that the number of secondary schools that selected $\ulcorner$environment$\lrcorner$ subject and the teachers who have $\ulcorner$environment$\lrcorner$ certification of a second-major has increased yearly but it shows much difference by regions. The second step was questionnaire surveys on 60 $\ulcorner$Environment$\lrcorner$ teachers in secondary school. According to the survey, 65% of teachers are not certificated and 50% of teachers have no self-confidence of teaching. And most of teachers thought it was difficult to select the modules out of textbook and teachers had difficulties such as the lack of appropriate reference materials and instructive experience of their own instructive experience of active researches. The third step was the questionnaire survey on a students group(606) learning the $\ulcorner$environment$\lrcorner$ subject and a students group(621) without the $\ulcorner$environment$\lrcorner$ subject in secondary school. The group learning $\ulcorner$environment$\lrcorner$ subject showed significantly higher scores than those of the group without $\ulcorner$environment$\lrcorner$ subject in most items. And among the students having $\ulcorner$environment$\lrcorner$ subject, the first year students achieved the highest score, and it revealed that the teaching was most effective to them. The suggestions based on the results of this study are as follows. First, the uncertifiable teachers currently teaching $\ulcorner$environment$\lrcorner$ subject should be given priority to the second-major certificate training program ; which are diverse in contents according to differences of majors and levels. Second, specific and practical re-training programs for the certificated teachers teaching the subject are needed. Third, considerable and continual adjustment of the textbook yearly is required in addition to regular curriculum amendment. Fourth, the more efficient and actual teaching.learning methods of $\ulcorner$environment$\lrcorner$ subject education that can attract students' interest must be developed. Fifth, it is most desirable to have first year students select the subject.

• The Journal of the Korea Contents Association
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• v.9 no.5
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• pp.230-240
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• 2009

This study proposes a theory of consumer experiences based on a cognitive science framework that serves as an alternative to the mainstream marketing paradigm of information processing and choice. The theory consists of three key theoretical constructs: experiential modules, primary vs. secondary experiences, and the hierarchy of experiential modules. Based on this theory, this study investigates the effect of experiential attributes and functional attributes on consumer's product evaluations, and the moderating role of consumer's knowledge. The main research findings are (1) the subjects react faster to sensory and affective stimuli(ex: experiential attributes) than they do to intellectual stimuli (ex: functional attributes), (2) the interaction modularity of attributes(functional vs. experiential) $\times$ tempo(normal vs. fast) $\times$ product knowledge(novice vs. expert) appear significantly with product evaluation as the dependent measure.