• Smart Structures and Systems
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• 제22권2호
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• pp.185-192
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• 2018

Participants in the Asia Pacific Conference of the Prognostics and Health Management Society 2017 (PHMAP 2017) Data Challenge were given measured vibration signals from motor-driven gearboxes used in pulverizers. Using this information, participants were requested to predict failure dates and the faulty components. The measured signals were affected by significant noise and disturbance, as the pulverizers in the provided data worked under actual operating conditions. This paper thus presents a fault prediction method for a motor-driven gearbox in a pulverizer system that can perform under external noise and disturbance conditions. First, two fault features, an RMS value in the higher frequency zones (HRMS) and an amplitude of a period for high-speed shaft in the quefrency domain ($QA_{HSS}$), were extracted based on frequency analysis using the higher and lower sampling rate data. The two features were then applied to each pulverizer based on results of frequency responses to impact loadings. Then, a regression analysis was used to predict the failure date using the two extracted features. A weighted regression analysis was used to compensate for the imbalance of the features in the given period. In addition, the faulty components in the motor-driven gearboxes were predicted based on the modulated frequency components. The score predicted by the proposed approach was ranked first in the PHMAP 2017 Data Challenge.

• 조명전기설비학회논문지
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• 제21권5호
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• pp.126-132
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• 2007

본 논문에서는 일반적으로 사용되어지는 배전압 단상 정류회로에 LC 공진회로를 첨가하여, 고조파의 성분을 저감시키는 고역률 단상 정류회로를 제안하였다. 제안한 회로는 다이오드 브리지에 병렬로 커패시터를 접속하고, 입력에 인덕터L을 추가하여 접속시키므로써 상용주파수에서 LC 공진현상을 이용하여, 수동소자만으로 입력전류를 정현파화한다. 그리고 고조파 제어 규제값의 여유도 만족시킨다. 이 모든 사항에 대해 실험과 시뮬레이션 결과를 비교, 분석을 통하여 그 타당성을 확인하였다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 제13회 신호처리 합동 학술대회 논문집
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• pp.959-962
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• 2000

A heart sound algorithm, which separates the heart sound signal into four parts; the first heart sound, the systolic period, the second heart sound, and the diastolic period has been developed. The algorithm uses discrete intensity envelopes of approximations of the wavelet transform analysis method to the phonocard-iogram(PCG)signal. Heart sound a highly nonstation-ary signal, so in the analysis of heart sound, it is important to study the frequency and time information. Further more, Wavelet Transform provides more features and characteristics of the PCG signal that will help physician to obtain qualitative and quantitative measurements of the heart sound.

• 한국음향학회지
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• 제5권4호
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• pp.22-26
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• 1986

The following methods have been proposed for implementing R2 multi-frequency receiver digitally: using digital filters, period-counting algorithm, discrete Fourier transform or Goertzel algorithm, and fast Fourier transform.

• 정보교육학회논문지
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• 제21권1호
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• pp.57-66
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• 2017

최근 빅데이터 분석과 함께 사회연결망에 대한 관심이 증대되고 있다. 이러한 사회연결망분석을 이용한 연구가 사회과학 영역뿐 아니라 자연과학 영역 등 여러 분야에서 다양하게 이루어지고 있다. 이에 본 논문에서는 정보교육 관련 석 박사 학위논문을 수집하여 텍스트분석과 사회연결망분석을 실시하였다. 그 결과, 모든 기간에서 출현빈도수가 높게 나오거나 지속적으로 나오는 단어가 있었으며, 기간별로 출현빈도가 갑자기 높아진 단어들도 있었다. 또한, 출현빈도수가 큰 단어가 대체적으로 매개중심성도 컸으며, 기간별 연구흐름의 특징이 있음도 알 수 있었다. 그러므로 IT 기술발전과 초 중 고등학교 정보교육과정 변화에 민감하게 정보교육 석 박사학위 논문 주제가 변화되었음을 알 수 있었다. 앞으로 기간4에서 출현빈도가 높아진 스마트, 모바일, 스마트폰, SNS, 어플리케이션, 스토리텔링, 다문화, STEAM과 관련된 연구가 지속될 것으로 예측하며, 로봇, 프로그래밍, 코딩, 알고리즘, 창의성, 상호작용, 개인정보보호와 관련된 주제도 꾸준히 연구될 것으로 예측된다.

• Nuclear Engineering and Technology
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• 제54권6호
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• pp.2067-2076
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• 2022

The importance of safety culture has been emphasized to achieve a high level of safety. In this light, a systematic method to more properly deal with safety culture is necessary. Here, a decision-making tool that can apply a graded approach to the analysis of safety culture is proposed, called the F-D matrix, which determines the frequency and the difficulty of safety culture attributes recently defined by the IAEA. A hierarchical model of difficulty contributors was developed as a scoring standard, and its elements were weighted via expert evaluation using the analytic hierarchy process. The frequency of the attributes was derived by analyzing reported events from nuclear power plants in the Republic of Korea. Period-by-period comparisons with the F-D matrix can show trends in the change of the maturity level of an organization's safety culture and help to evaluate the effectiveness of previously implemented measures. In the evaluating the difficulty of the attributes in the recently developed harmonized safety culture model, the difficulties of Trending, Benchmarking, Resilience, and Documentation and Procedures were found to be relatively high, while the difficulties of Conflicts are Resolved, Ownership, Collaboration, and Respect is Evident were found to be relatively low. A case study was conducted with an analysis period of 10 years to attempt to reflect the many changes in safety culture that have been made following the Fukushima accident in March 2011. As a result of comparing two periods following the Fukushima accident, the overall frequency decreased by about 40%, providing evidence for the effects of the various improvements and measures taken following the increased emphasis on safety culture. The proposed F-D matrix provides a new analytical perspective and enables an in-depth analysis of safety culture.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2007년도 정기총회 및 학술발표대회
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• pp.319-322
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• 2007

This study aims to find the characteristics of damage and states of natural disasters at the Korean Peninsula from 1985 to 2004. Using the data of Statistical yearbook of calamities issued by the National Emergency Management Agency and Annual Climatological Report issued by the Korea Meteorological Administration. we have analyzed the cause, elements, and vulnerable regions for natural disasters. Major causes of natural disaster at Korean Peninsula are four, such as a heavy rain, heavy rain typhoon, typhoon, storm snow, and storm. The frequency of natural disaster is the highest from June to September. The period from December to March also shows high frequency. The total amount of damage is high during the summer season(Jul.-Sept). The period from January to March shows relatively high amount of damage due to storm and storm snow The areas of Gangwon-do, Gyeongsangnam-do and Gyeongsangbuk-do are classified the vulnerable region for the natural disasters. By establishing mitigation plans which fit the type and characteristics of disaster for each region, damage from disaster can be reduced with efficient prevention activities.

• International Journal of Computer Science & Network Security
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• 제21권2호
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• pp.40-43
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• 2021

In the article of instability on the peak power level, duration and repetition period of a multifrequency space-time signal, we calculated the maximum values of the errors of the parameters of the laws of spatial-phase-frequency control. Requirements for the accuracy of the location of the phase centers of the emitters in a cylindrical phased array antenna with pyramidal horns; it is advisable to calculate the radiation field using single-stage and multi-stage distribution laws. The phase centers of individual radiation sources of a cylindrical phased array antenna have been studied; they have almost no effect on the duration and period of recurrence.

• East Asian Economic Review
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• 제19권2호
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• pp.189-220
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• 2015

Multi-scale representations are effective in characterising the time-frequency characteristics of financial return series. They have the capability to reveal the properties not evident with typical time domain analysis. Given the aforesaid, this study derives crucial insights from multi scale analysis to investigate the co-movements between Indian and emerging Asian equity markets using wavelet correlation and wavelet coherence measures. It is reported that the Indian equity market is strongly integrated with Asian equity markets at lower frequency scales and relatively less blended at higher frequencies. On the other hand the results from cross correlations suggest that the lead-lag relationship becomes substantial as we turn to lower frequency scales and finally, wavelet coherence demonstrates that this correlation eventually grows strong in the interim of the crises period at lower frequency scales. Overall the findings are relevant and have strong policy and practical implications.

• 한국콘텐츠학회논문지
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• 제20권12호
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• pp.23-35
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• 2020

본 연구는 산업과 사회 전반에 걸쳐서 많은 영향을 미칠 사물인터넷에 관한 국내 논문들을 수집하고 분석하여 사물인터넷 분야의 동향을 살펴보고자 한다. 본 연구를 위한 조사 기간은 2015년에서 2019년까지로 하였으며 네이버의 학술정보를 이용하여 사물인터넷에 관한 국내 논문들을 수집하였다. 기간별로 수집된 국내 논문으로부터 빈도가 높은 키워드들을 추출하였으며 빈도가 높은 키워드 중에서 중심적인 키워드를 파악하기 위해서 중심성 분석을 하였다. 키워드 빈도에서는 2015년부터 2017년까지는 '센서', '보안' 그리고 2017년부터는 '차', '지능'이 빈도가 높은 상위 키워드로 나타났다. 키워드 중심성에서는 2015년부터 2016년까지 '보안', '센서' 그리고 2017년부터는 '지능', '차', '산업혁명'이 중심성이 높은 키워드로 나타났다.