• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.8
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• pp.843-850
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• 2012

To satisfy the operational requirements of surveillance radar and the operational concept of a ship combat system, an active-array-type antenna was designed using solid-state transmitters and receivers. The arrangement of the constituent electronic components of the antenna system, considerably large in size, and therefore, the antenna needs to be housed in a box. The rotational antenna system installed on a ship mast is installed in a sealed housing to protect the interior equipment from environmental conditions. The outer shape of the housing is that the antenna should be capable of rotating normally despite strong winds. Furthermore, in recent times, designs with low radar cross section (RCS) have attracted attention from the viewpoint of improving the stealth of the ship. In this light, four types of models are proposed for the outer shape design of the antenna system, and they are investigated from the viewpoint of low RCS design as well as wind load.

• Journal of Korean Society for Geospatial Information Science
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• v.6 no.2 s.12
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• pp.21-34
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• 1998

SAR is an active imaging sensor emitting its own energy source and can be operated in all weather conditions. Thus SAR provides data which can not be obtained by an optical sensor. In this study, the potentials and problems of the techniques for DEM extraction from the SAR imagery were evaluated through theoretical researches and practical experiments. And then the accuracy was tested by RMS error between the digitized map contour and the results from this experiment. Here, two types of DEM extraction method were evaluated. One was an analytical photogrammetric technique, and the other was a SAR interferometric processing. From the experiment, we found that the photogrammetric technique is currently the most suitable method considering topographic conditions of Korea. In the SAR interferometry technique, we also conclude that the problems caused by decorrelations due to the temporal reasons and due to the scattering effects from vegetation should be solved.

• The Journal of the Korea Contents Association
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• v.11 no.10
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• pp.128-136
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• 2011

This is a study on the subjectivity of audiences about preference of documentaries on TV. Accordingly, Q-methodology was used for this study. As a result, audiences' various characteristics by preference types were able to be found. The individual characteristics were classified into three styles: an entertainment-oriented style pursuing enjoyment, public and society interest-oriented style pursuing public purpose, and culture-oriented style pursuing artistic value of documentaries in order. It could be inferred from the classification of preference styles that unlike the past, the choice of TV broadcasting of audiences was shifting from the passive and media-dependent form to positive form. Therefore, the research and development of content delivery and production in the multi-media and multi-channel digital broadcasting era should be focused on not only the content itself but also an audience-centered service development model reflecting audiences' desire and hope.

• Journal of KIISE:Computer Systems and Theory
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• v.27 no.8
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• pp.730-740
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• 2000

The software rejuvenation method for highly available multiplex systems uses a pro-active fault-tolerant approach to handle system failures. The software rejuvenation prevents failures from occurring, while the previous methods recover from failures after happening. Especially, since the software aging proceeds fast in the software used for the multimedia mobile computing due to the loss of communications or data, the preventive method from failures using software rejuvenation can be used for the multimedia mobile computing. In this paper, according to the operational parameters such as rejuvenation period, rejuvenation time, failure rate and repair rate of the servers, number of running servers, duration of running time, and type of running modes, we calculate steady-state probabilities, downtime, availability, and cost of the multiplex systems using software rejuvenation method. We validate the closed-form solutions of the mathematical model by experiments based on various operational parameters and find that the software rejuvenation method can be adopted as preventive fault-tolerant technique. The failure rate and unstable rate of the servers are essential factors for the decision making of the rejuvenation policies.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.6B
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• pp.559-567
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• 2009

Distributed Content Delivering Network (DCDN) will make use of the existing resources of the common Internet users in terms of storage space, bandwidth and Internet connectivity to create it. However DCDN has some limitations that are inefficient using of storage space, reliability and having special load balancing (LB) algorithm. So, this paper proposes Re-distribution based CDN (RDCDN) that overcomes the limitations of DCDN. RDCDN has the content re-distribution algorithm and separates surrogates to main surrogate and sub surrogates. Main surrogate can help service reliability be improved by storing all contents as back-up system. And content re-distribution algorithm also can help storage space be saved because all contents are not stored in every surrogate. Especially, when RDCwDN uses content re-distribution algorithm, it can work active load balancing function without extra LB algorithm like as DCDN. Results of simulation show that the proposed architecture can improve reliability and efficiency of storage space, and it also can offer the same performance as that of commercial CDN and DCDN.

• Proceedings of the Korea Society of Elementary Mathematics Education
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• 2010.08a
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• pp.143-156
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• 2010

사회가 변화함에 따라 수학교육과정도 변화를 거듭하고 있으며, 이러한 변화에 잘 대처하기 위해서 교사는 수학교육의 방향에 대한 깊이 있는 성찰과 함께 수학, 교육학, 심리학 등 수학교육과 관련된 학문에 대한 이해가 필요하다. 이러한 교사에 대한 시대적인 요구에 능동적으로 대처하는 방안으로 Wittmann(1984)은 수학교과의 특성상 변하지 않는 요소들을 교수단위(Teaching Units)라 하고, 수학교육을 통합시키는 개념으로 교수단위이론으로 제시하였다. 교수단위는 수학에서 가르쳐야 할 내용들을 목적, 자료, 활동, 배경 등의 4요소에 따라 작은 단위로 조직화한 것으로, 이를 통해 수학연구자나 교사는 가르쳐야 할 내용에 대한 구조적인 이해와 체계적인 조직화를 도모할 수 있게 되어 나아가 사회의 변화에 대응할 수 있게 된다. 본 연구에서는 2007년 개정 수학과 교육과정 도형영역의 교수단위를 학년별로 추출하고, 추출된 교수단위의 특징과 제목을 분석하였다. 이를 통해 교수단위가 수학교육과정연구에 어떻게 활용될 수 있는지 그 방안을 모색해 보았다. 도형영역의 교수단위(TU)는 특징과 제목에 따라 '개념알기형', '개념적용형', '관계알기형'의 세 유형으로 분류할 수 있다. 현재의 도형영역 교육과정은 대체로 개념알기형, 개념적용형, 관계알기형의 순으로 구성되어 있으며, 개념적용형이 개념알기형보다 조금 더 많다. 이는 도형영역 교육과정이 학습한 개념을 다양한 방법을 통해 여러 활동에 적용시켜 봄으로써 도형의 개념을 좀 더 명확하게 알게 되는 초등학생의 발달단계를 고려하여 구성되었음을 알 수 있다. 이러한 교수단위(TU)는 수업자가 도형학습주제에 맞게 수업을 재구성하거나 학생들의 수준에 맞는 수준별 맞춤자료를 제작할 때 유용하게 활용될 수 있으며, 더 나아가 수학연구자들이 새로운 교육과정을 수립하고자 할 때 기초자료로 활용될 수도 있을 것이다. 교수단위는 고정불변의 것이 아니고 계속 보완되고 진화될 수 있는 모델이다. 따라서 앞으로도 많은 수학연구자나 현장교사의 참여로 교수단위가 보다 더 체계적이고 조직적으로 연구되어야 한다. 또한 추출된 교수단위를 교사나 학생들이 보다 편리하게 활용할 수 있도록 컴퓨터용 소프트웨어로 개발하려는 후속 연구가 필요하다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.4C
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• pp.451-457
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• 2006

A peer-to-peer(P2P) network is inherently vulnerable to malicious attacks from participating peers because of its open, flat, and autonomous nature. This paper addresses the problem of effectively defending from active attacks of malicious peers at bootstrapping phase and at online phase, respectively. We propose a secure membership handling protocol to protect the assignment of ID related things to a newly joining peer with the aid of a trusted entity in the network. The trusted entities are only consulted when new peers are joining and are otherwise uninvolved in the actions of the P2P networks. For the attacks in online phase, we present a novel message structure applied to each message transmitted on the P2P overlay. It facilitates the detection of message alteration, replay attack and a message with wrong information. Taken together, the proposed techniques deter malicious peers from cheating and encourage good peers to obey the protocol of the network. The techniques assume a basic P2P overlay network model, which is generic enough to encompass a large class of well-known P2P networks, either unstructured or not.

• Archives of design research
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• v.16 no.1
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• pp.15-24
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• 2003

In the latest date, vehicles are offered to the drivers, not only the skill for shifting but the pleasure for driving vehicles that are existing today can be a social problem because the amount of vehicles that are increasing give difficulty for the traffic facilities and parking expansion. these day 80% of four wheeled vehicle carriers single or double person the reducing car scale is an important thing about the financial good use resources of energy and the storage of environment. A solution for these problem is a new general idea vehicle development for one or two person to ride. For the sake of these reasons, first, the information is collected and analyzed about existing foreign countries production. Car external design is intended by mathematical modeling, simulation and model testing about frame system of new concept specially we would like to show three wheeled vehicle that has active tilt control(ATC) system. This car tilts actively by the center rotation wheel and frame when the vehicle turns.

• Archives of design research
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• v.15 no.1
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• pp.113-122
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• 2002

This thesis is focused on online education and proposes a guideline for selecting teaming theories and multimedia representation without difficulty. On the first, consideration of learning theories and analysis of multimedia properties are made, and from these results guidelines are formed. Then they are applied to each 6 types of CAI. Objectivism and constructivism could be used for the basic framework of CAI. The former is suitable for reed, sequential, structural, and passive learning style and the latter is suitable for selectable, unstructural, active, self-controled, learning style. And the quideline for selecting multimedia representation is made out of the properties of media, learners(cognitive model, proficiency, acceptance), and teaming contents. On the basis of guideline obtaining from the previous process, I suggest mosts suitable conditions for each 6 types of CAI available today. Those conditions are consist of learning theories, media selection, levels of learners, and categories and properties of teaming contents.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.1
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• pp.72-78
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• 2015

Recently, the usage of the satellite is increased more and more in the areas that are communication, weather, marine, optical, radar etc. The functions of the Satellite are evolving from passive transponder to active transponder by the developing of a technology. Advanced countries in satellites install the DCAMP for increase of bandwidth efficiency, improvement of QoS by interference rejection. DCAMP includes many digital components in order to implement functions. Thus, these kinds of active transponders consume much more power compared to passive transponder and then increase the heat. In this paper, we discuss the TVAC test result of DCAMP in EQM(Engineering Qualification Model) level. The paper shows the test results of digital gain control in order to verify DCAMP status under the TVAC test. In addition, the temperature and heat condition of main components from viewpoint of derating will be treated through the official environment test for qualification.