• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.2
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• pp.141-148
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• 2015

This paper presents a sun-synchronous orbit design which effectuvely includes the requirements derived from spacecraft to ground station contact and spacecraft to target image accessibility. For this purpose, operation parameters of multiple spacecraft are defined as Contact Overlap, Contact Overlap Gap, Access Overlap, Access Overlap Gap. These parameters are used to form a Figure of Merit that reflects the operational requirements. The Figure of Merit is optimized to increase the efficiency of operating multiple spacecraft in constellation and is used to determine the operational orbit of each spacecraft that constitutes the constellation.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.387-387
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• 2011

탄소 나노튜브(Carbon nanotubes, CNTs)는 육각형 모양의 구조로서 오직 탄소만으로 이루어진 소재이다. CNT는 열전도율이 다이아몬드보다 약 2배 우수하고, 전기 전도는 구리에 비해 1,000배 높으며, 강도는 강철보다 100배나 뛰어나다. CNT의 이러한 특성을 이용한 트랜지스터, 태양전지, 가스 검출을 위한 고감도 센서, 나노 섬유, 고분자-탄소나노튜브 고기능 복합체 등 많은 분야에서 연구가 활발히 진행되고 있다. 또한 수직으로 성장된 탄소 나노튜브는 일반적인 재료에서는 보기 드물게 힘들게 직경이 나노 크기인 반면 길이는 수 mm까지 합성 되기 때문에 앞서 언급한 분야로의 활용이 더욱 유리하며, 그 중에서도 나노 섬유, 나노 복합체로서의 활용에 극히 유용하다. 이러한 이유로 수직 배열된 CNT 합성에 많은 연구가 집중 되고 있다. 여러 합성 방법 중 성장 변수를 비교적 용이하게 조절 가능한 열 화학 기상 증착법(Thermal chemical vapor deposition, TCVD)을 이용하여 수직 배열된 수 mm의 CNT를 합성한 연구 결과들이 보고된 바 있다. 그러나 앞선 연구결과들은 CNT의 성장속도가 느릴 뿐만 아니라 합성 시간이 길어질수록 성장 속도가 감소하는 경향을 보였다. 반면, 마이크로웨이브 플라즈마 화학 기상 증착법(Microwave plasma CVD, MPCVD)은 기존의 다른 TCVD에 비해 낮은 온도에서 CNT를 합성할 수 있는 장점을 가지며, 고출력(~600 W 이상)의 플라즈마를 사용하기 때문에 성장률이 높고 고밀도의 CNT 합성이 가능하다. 본 연구에서는 철을 촉매금속으로 사용하고 MPCVD을 이용하여 얇은 다중벽 CNT를 합성하였다. 철은 직류 마그네트론 스퍼터(D.C magnetron sputter)를 사용하여 증착하였다. 합성시 가스는 탄소 공급원인 메탄($CH_4$)과 함께 플라즈마 공급원인 수소($H_2$)를 사용하였다. 또한 산소($O_2$)의 주입 여부에 따른 CNT의 성장 속도와 성장 길이를 비교하였다. 산소를 주입하였을 때, CNT의 성장 속도와 길이 모두 크게 향상됨을 확인 할 수 있었다. 이는 촉매금속 표면의 비정질 탄소의 흡착으로 인해 활성화된 촉매금속의 반응시간을 증가시키기 때문이다. 성장된 CNT는 주사전자 현미경(Scanning Electron Microscopy, SEM)과 라만 분광법(Raman spectroscopy)을 통해 표면형상과 결정성을 분석하였다.

• Journal of KIISE
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• v.43 no.2
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• pp.237-245
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• 2016

In this paper we introduce a novel database research area called science of databases (SoDB) and carry out a comprehensive analysis of its case studies. SoDB aims to better understand interesting phenomena observed across multiple database management systems (DBMSes). While mathematical and engineering work in the database field has been dominant, less attention has been given to scientific approaches through which DBMSes can be better understood. Scientific investigations can lead to better engineered designs through deeper understanding of query optimizers and transaction processing. The SoDB research has investigated several interesting phenomena observed across different DBMSes and provided several engineering implications based on our uncovered results. In this paper we introduce a novel scientific, empirical methodology and describe the research infrastructure to enable the methodology. We then review each of a selected group of phenomena studied and present an identified structural causal model associated with each phenomenon. We also conduct a comprehensive analysis on the case studies. Finally, we suggest future directions to expand the SoDB research.

• Journal of Digital Convergence
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• v.14 no.1
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• pp.479-489
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• 2016

This study examines how disability pride of people having acquired visual impairment can be constructed. The theme is explored with the Japanese TV drama "Challenged". The paradigms regarding construction of disability pride and acceptance of disability are fundamentally different. In this context it can be said that a criticism of disability acceptance theory has something with a criticism of medical model of disability. It is main character Hanawa and chairman of teachers, and principal who were noticeable specifically at the point of forming disability pride, and these characters show a common feature that social idealism is embodied in their awareness. Other characters of the drama show a change of their consciousness to social idealism. As a conclusion this study suggests importances of humanistic and social scientific analysis as well as of educational effects achieved by means of drama.

• Physical Therapy Korea
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• v.9 no.4
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• pp.1-11
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• 2002

본 연구의 목적은 이중과업 방법론(dual task methology)을 사용해서 젊은 사람과 노인을 대상으로 독립된 두 사건(two separate concurrent events)을 동시에 수행하는데 요구되는 주의력에 대한 분석과 노인에서의 특징적 차이를 찾는 것이다. 본 실험은 대상자가 힘판(force plate) 위에서 장애물(10cm) 보행시에 경피자극(cutaneous stimulation)에 대하여 마이크로 스위치(micro-switch)를 사용하여 반응하면서 시행되었다. 힘판과 시간(temporal events) 그리고 반응시간(reaction time)에 관한 자료들은 1000 Hz의 주파수로 수집되었다. 반응시간은 대상자들이 서 있는 상태(baseline) 장애물 보행시(dual task)에서 수집되었다. 반응시간은 아중과업 조건에서 대상자 모두에게서 긴 것으로 나타났으며 특히 노인에서 정상 성인보다 반응시간이 긴 것으로 나타났다. 이중과업 조건 하에서 노인 대상자가 정상 성인에 비해 발가락이 장애물에 닫지 않고 통과할 수 있는 공간, 즉 토우 클리어런스( toe-clearance)와 슬관전 굴곡(knee flexion) 각도가 훨씬 큰 것으로 나타났다. 이중과업 조건하에서 모든 대상자가 족관절 배측굴곡(ankle dorsiflexion) 각도를 감소시키는 것으로 나타났다. 노인들은 젊은 대상자들보다 훨씬 더 긴(124 ms) 유각시간을 보여 주었으며 정상 장애물 보행시 유각 시간은 이중과업보다 50 ms 긴 것으로 나타났다. 이러한 보행 특성의 차이는 노인대상자들이 젊은 대상자들보다 장애물 보행시에 이중과업의 영향을 더 받았기 때문인 것으로 판단된다. 이중 과업 시행시 이러한 토우 클리어런스의 감소와 장애물 통과시에 보행 속도의 증가는 아마도 낙상의 가능성을 증가시키는 요인이 될 수 있는 것으로 보여진다. 본 연구의 결과는 다중과업(multitasks)을 필요로 하는 보행 훈련 프로그램(gait training program)의 개발과 시행에 있어서 기초적인 자료를 제공할 수 있는 것으로 보여진다.

• Journal of the Korean Geographical Society
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• v.44 no.3
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• pp.395-409
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• 2009

The objective of this paper is to illustrate that kriging can provide an effective framework both for integrating remote sensing data and for uncertainty modeling through a case study of sediment grain size mapping with remote sensing data. Landsat TM data which show reasonable relationships with grain size values are used as secondary information for sediment grain size mapping near the eastern part of Anmyeondo and Cheonsuman bay. The case study results showed that uncertainty attached to prediction at unsampled locations was significantly reduced by integrating remote sensing data through the analysis of conditional variance from conditional cumulative distribution functions. It is expected that the kriging-based approach presented in this paper would be efficient integration and analysis methodologies for any environmental thematic mapping using secondary information as well as sediment grain size mapping.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.7C
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• pp.712-722
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• 2002

We have investigated a novel optical decoder for a fiber-optic code division multiple access(CDMA) communication systems. The conventional optical encoder and decoder have the advantage of simple structure. However the number of users in the system is limited by the auto- and cross-correlation properties generated in decoding process. In previous studies, to improve the system performance, although they used an optical code that minimize the sidelobe and cross-correlation, could not yet find a novel methods for performance improvement in fiber-optic CDMA system. Thus, it is necessary to investigate the novel optical decode in order to improve the performance of system. In this paper, we schematize the AND gate logic element(AGLE) composed with 1$\times$2 or 1$\times$3 coupler and the optical thyristor and propose the novel optical decoder using K(weight) AGLE. The optical thyristor only passes the overlapped signal and clips other signals. Such a novel concept means that the optical thyristor can operate as a hard-limiter. We analyze the fiber-optic CDMA system using the novel optical decoder with simulation and is found that the novel optical decoder using the AGLE and optical thyristor excludes the sidelobe and cross-correlation intensity between any two sequences.

• KIPS Transactions on Software and Data Engineering
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• v.8 no.4
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• pp.171-178
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• 2019

The use of anti-scatter grids in radiographic imaging has the advantage of preventing the image distortion caused by scattered radiation. However, it carries the side effect of leaving artifacts in the X-ray image. In this paper, we propose a grid line suppression technique using discrete cosine transform(DCT). In X-ray images, the grid lines have different characteristics depending on the shape of the object and the area of the image. To solve this problem, we adopt the DCT transform based on a dynamic segmentation, and propose a filter transfer function for each individual segment. An algorithm for detecting the band of grid lines in frequency domain and a band stop filter(BSF) with a filter transfer function of a combination of Kaiser window and Butterworth filter have been proposed. To solve the blocking effects, we present a method to determine the pixel values using multiple structured images. The validity of the proposed theory has been evaluated from the experimental results using 140 X-ray images.

• Knowledge Management Research
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• v.23 no.1
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• pp.1-26
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• 2022

With the spread of social networks, platform-based social commerce has grown rapidly with the use of multiple smart devices. Given the rapid growth of social commerce sites such as Coupang and Ticket Monster, it is very important to understand the user's purchase decision-making process in a social commerce environment. The purpose of this study is to develop a richer understanding of the goals of users using social commerce. Second, a methodological alternative for analyzing the user's goals is introduced. In this study, laddering interview and means-end chain analysis were used. As a result of interview conducted on 40 users who have more than 6 months of purchasing experience using social commerce, a hierarchical goal map showing the user's goal structure was derived. This map contains 22 ultimate goals of social commerce, including warm relationships with others, fun and enjoyment of shopping, accomplishment, satisfaction, financial saving, and convenience. In addition, there are various paths from activities to ultimate goals, so investigating the goals pursued by users can give us insight into understanding user.

• Journal of Korea Society of Industrial Information Systems
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• v.27 no.4
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• pp.1-10
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• 2022

Attempts to interpret human perspectives using computer vision have been developed in various fields. In this paper, we propose a method for evaluating the walking environment through semantic segmentation results of images from road images. First, the Kakao Map API was used to collect road images, and four-way images were collected from about 50,000 points in JeonJu. 20% of the collected images build datasets through crowdsourcing-based paired comparisons, and train various regression models using paired comparison data. In order to derive the walkability score of the image data, the ranking score is calculated using the Trueskill algorithm, which is a ranking algorithm, and the walkability and analysis using various regression models are performed using the constructed data. Through this study, it is shown that the walkability of Jeonju can be evaluated and scores can be derived through the correlation between pixel distribution classification information rather than human vision.