• 한국산학기술학회논문지
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• 제18권11호
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• pp.817-825
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• 2017

AC 방식 마이크로그리드는 다양한 DC/AC 인버터를 AC 네트워크에 연결하여, DC 방식 마이크로그리드의 약점을 극복 하고 있다. 그러나 소규모 마이크로그리드에서 일반적으로 발생하는 심각한 부하 불평형 현상에 의하여, AC 마이크로그리드 시스템의 성능을 약화시킬 수 있다. 이것은 마이크로그리드 내의 불평형 부하로 인하여 상별 에너지 흐름과 전압조정기능이 제한되기 때문이다. 이러한 불평형 전압문제를 해결하기 위하여, 3상 4-Leg 방식의 인버터가 제안되고 있지만, 이를 안정적으로 운용할 수 있는 제어알고리즘이 미비한 실정이다. 따라서, 본 논문에서는 부하 불평형에 의해서 발생하는 인버터의 전압 불평형 문제를 해결하고 안정적으로 제어하기 위하여 d-q제어를 기반으로 3상4선식 인버터의 각상 개별제어 알고리즘을 제안하였다. 또한, 이 알고리즘을 바탕으로 Matlab/Simulink를 이용하여 4-Leg 방식의 전압제어기 모델링을 수행하였다. 이 모델링과 250KW급 시험장치를 바탕으로 인버터의 출력전압 제어특성을 분석한 결과, 정상상태에서는 기존의 방식과 비슷한 특성을 보이지만, 과도상태에서는 제안한 각상 개별제어 방식이 기존의 방식보다 안정적으로 동작하여 제안한 방식의 유용성을 확인할 수 있었다.

• 한국산학기술학회논문지
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• 제10권4호
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• pp.811-817
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• 2009

IT 시스템 기반의 네트워크 환경의 급속한 발전은 지속적인 연구방향의 중요한 이슈의 결과이다. 침입시도 탐지는 관심분야의 하나인 것이다. 최근에 다양한 기술을 기반으로 하는 침입시도탐지들이 제안되고 있으나 이러한 기술은 여러 형태의 침입시도의 패턴 중에 한가지 형태 및 시스템에 적용이 가능한 것이다. 또한 새로운 형태 침입시도를 탐지하지 못하고 있다. 그러므로 새로운 형태를 인식하는 침입탐지 관련 기술이 요구되어 지고 있다. 본 연구에서는 퍼지인식도와 비정상 트래픽 분석을 이용한 네트워크 기반의 침입탐지기법(NePID)을 제안한다. 이 제안은 패킷 분석을 통하여 서비스거부공격과 유사한 침입시도를 탐지하는 것이다. 서비스거부공격은 침입시도의 형태를 나타내며 대표적인 공격으로는 syn flooding 공격이 있다 제안한 기법은 syn flooding을 탐지하기 위하여 패킷정보를 수집 및 분석한다. 또한 피지인식도와 비정상 트래픽 분석을 적용하여 판단모듈의 분석 결과를 토대로 기존의 서비스 거부 공격의 탐지 툴과의 비교분석을 하였으며 실험데이터로는 MIT Lincoln 연구실의 IDS 평가데이터 (KDD'99)를 이용하였다. 시뮬레이션 결과 최대평균 positive rate는 97.094% 탐지율과 negative rate는 2.936%을 얻었으며 이 결과치는 KDD'99의 우승자인 Bernard의 결과치와 유사한 수준의 값을 나타내었다.

• 해양환경안전학회지
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• 제23권4호
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• pp.393-399
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• 2017

왕복동식 압축기에서 피스톤과 커넥팅로드는 중요한 부분이다. 이러한 주요부에 기계적 부하가 과도하게 가해지면 해당 기부속이 손상될 수 있으며, 교체하기도 쉽지 않고 비용도 많이 든다. 따라서 내구성과 수명에 영향을 미치는 요인을 분석할 필요가 있다. 본 연구의 주요 목적은 피스톤과 커넥팅로드의 최대 응력 집중 위치를 확인하는 것이다. 이를 위해 설계된 공기압축기의 작업 공정의 동적계산을 기반으로 피스톤 및 커넥팅로드의 응력 분석을 수행하였다. 공기압축기의 피스톤과 커넥팅로드의 3 차원 모델을 따로 설계하고, 이러한 부품들의 유한요소 해석은 수치해석적인 근사해법을 사용하였다. 피스톤은 열 경계 조건 없이 크랭크 샤프트의 각도에 따라 압력 부하를 받는다. 시뮬레이션 결과는 피스톤과 커넥팅로드의 응력 집중 위치와 그 값을 예측하고 추정할 수 있다. 그 결과 크랭크 각도 $135^{\circ}$와 $225^{\circ}$에서 피스톤은 190MPa, 커넥팅로드는 123MPa 이상의 최대 등가응력이 나타났으며 이는 인장 항복강도 이하의 값이다. 또한, 커넥팅로드와 피스톤에 계산 된 안전 계수는 1보다 높게 나타났다. 더욱이, 이러한 결과는 왕복동 공기압축기 제작사에 피스톤 및 커넥팅로드를 설계함에 있어서 최적화를 위한 참고 자료로 활용 될 수 있다.

• 한국터널지하공간학회 논문집
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• 제18권2호
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• pp.119-128
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• 2016

성능기반 설계에서 구조물의 안정성은 손상 상태와 이를 수치화한 손상 지수에 의해 평가한다. 지상 구조물에 대해서는 이들이 비교적 명확하게 정의되어 있으나 지중 구조물에 대한 연구 수행 사례는 매우 제한적이다. 본 연구에서는 국내 지하철 시스템에 널리 사용되는 박스형 개착식 터널에 작용하는 지진하중에 의한 손상 상태와 손상 지수를 일련의 비탄성 프레임 해석을 통하여 규명하였다. 터널의 3 단계 손상 상태는 구조물에 발생한 소성 힌지의 수에 의해 정의하였다. 손상 지수는 터널 구조 부재의 탄성 모멘트와 항복 모멘트의 비로 정의하여 탄성 해석만으로도 비탄성 거동과 파괴 메커니즘의 모사가 가능하도록 하였다. 또한 손상 지수를 자유장 전단 변형률의 함수로도 제시하였다. 전단 변형률은 1 차원 지반응답해석으로 쉽게 계산할 수 있으므로 이를 이용하여 간편하게 박스형 터널의 초기 내진 안정성 평가가 가능할 것으로 판단된다. 보다 일반적이고 보편적인 적용성 확보를 위해서는 추후 포괄적인 해석을 수행하여 다양한 형태의 터널과 지반에서의 전단 변형률 분포와 불확실성에 대한 연구가 진행되어야 할 것이다. 본 연구에서 제시된 터널 내진설계를 위한 손상 상태, 손상 지수, 그리고 전단파 속도 및 전단변형률 간의 상호관계 플래트폼은 새로운 아이디어를 담고 있으며 추후 설계에 널리 활용될 수 있을 것으로 판단된다.

• Journal of Pharmaceutical Investigation
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• 제37권4호
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• pp.255-261
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• 2007

A bioequivalence study of $Nimegen^{TM}$ soft capsule (Medica Korea Pharma. Co., Ltd.) to $RoAccutane^{(R)}$ soft capsule (Roche Korea Ind. Co., Ltd.) was conducted according to the guidelines of Korea Food and Drug Administration (KFDA). Thirty healthy male Korean volunteers received each medicine at the isotretinoin dose of 60 mg in a $2{\times}2$ crossover study. There was one week wash-out period between the doses. Plasma concentrations of isotretinoin were monitored by a high performance liquid chromatography (HPLC) for over a period of 48 hours after drug administration. $AUC_t$ (the area under the plasma concentration-time curve from time zero to 48 hr) was calculated by the linear trapezoidal rule method. $C_{MAX}$ (maximum plasma drug concentration) and $T_{MAX}$ (time to reach $C_{MAX}$) were compiled from the plasma concentration-time data. Analysis of variance was carried out using logarithmically transformed $AUC_t\;and\;C_{MAX}$. No significant sequence effect was found for all of the bioavailability parameters indicating that the crossover design was properly performed. The 90% confidence intervals of the $AUC_t$ ratio and the $C_{MAX}$ ratio for $Nimegen^{TM}/RoAccutane^{(R)}$ were $log0.860{\sim}log0.98\;and\;log0.85{\sim}log1.00$, respectively. These values were within the acceptable bioequivalence intervals of $log0.80{\sim}log1.25$. Thus, our study demonstrated the bioequivalence of $Nimegen^{TM}\;and\;RoAccutane^{(R)}$ with respect to the rate and extent of absorption.

• 유통과학연구
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• 제12권11호
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• pp.77-83
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• 2014

Purpose - The National Agricultural Cooperative Federation of Korea and National Fisheries Cooperative Federation of Korea have prosecuted both financial and retail businesses. As cooperatives are public institutions and receive government support, their sound management is required by the Financial Supervisory Service in Korea. This is mainly managed by CAEL, which is changed by CAMEL. However, NFFC's business section, managing the finance and retail businesses, is unified and evaluated; the CAEL model has an insufficient classification to evaluate the retail industry. First, there is discrimination power as regards CAEL. Although the retail business sector union can receive a higher rating on a CAEL model, defaults have often been reported. Therefore, a default prediction model is needed to support a CAEL model. As we have the default prediction model using a subdivision of indexes and statistical methods, it can be useful to have a prevention function through the estimation of the retail sector's default probability. Second, separating the difference between the finance and retail business sectors is necessary. Their businesses have different characteristics. Based on various management indexes that have been systematically managed by the National Fisheries Cooperative Federation of Korea, our model predicts retail default, and is better than the CAEL model in its failure prediction because it has various discriminative financial ratios reflecting the retail industry situation. Research design, data, and methodology - The model to predict retail default was presented using logistic analysis. To develop the predictive model, we use the retail financial statements of the NFCF. We consider 93 unions each year from 2006 to 2012 to select confident management indexes. We also adapted the statistical power analysis that is a t-test, logit analysis, AR (accuracy ratio), and AUROC (Area Under Receiver Operating Characteristic) analysis. Finally, through the multivariate logistic model, we show that it is excellent in its discrimination power and higher in its hit ratio for default prediction. We also evaluate its usefulness. Results - The statistical power analysis using the AR (AUROC) method on the short term model shows that the logistic model has excellent discrimination power, with 84.6%. Further, it is higher in its hit ratio for failure (prediction) of total model, at 94%, indicating that it is temporally stable and useful for evaluating the management status of retail institutions. Conclusions - This model is useful for evaluating the management status of retail union institutions. First, subdividing CAEL evaluation is required. The existing CAEL evaluation is underdeveloped, and discrimination power falls. Second, efforts to develop a varied and rational management index are continuously required. An index reflecting retail industry characteristics needs to be developed. However, extending this study will need the following. First, it will require a complementary default model reflecting size differences. Second, in the case of small and medium retail, it will need non-financial information. Therefore, it will be a hybrid default model reflecting financial and non-financial information.

• 유통과학연구
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• 제11권2호
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• pp.71-81
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• 2013

Purpose - The TOEIC test has been leading the change in the quality and the globalization of companies for about last 30 years. The TOEIC test is taken by about two million people each year and is used as a criterion to select new employees in companies or government offices, for performance ratings, and for overseas posting selections. Universities also use TOEIC test in various ways. Since the TOEIC test is used for the selection of new students for admission, transferring extra credits, scholarships, graduation certification, and admission of international students studying abroad, many universities all over the country provide students with TOEIC study lectures through their own language institutes. Despite the fact, there has been no research on the service quality or even the current situation of these institutes. Thus, this study aims to evaluate the factors that impact TOEIC lecture service quality and analyzes the effect of the expectation related to the education service quality and the result of education on intentional behavior. Research design, data, methodology - Data was collected by administering a survey to current TOEIC students from different university language institutes. The survey questionnaire comprised of a five-point Likert scale. The demographic analysis was conducted using the frequency analysis method and the factor analysis was conducted to verify the validity of questionnaire over any variable. The reliability analysis was conducted to verify the reliability of the results. Besides, multiple regression analysis, regression analysis, and mediated effect verification were also conducted. For education service quality, four different independent variables such as reliability, response, conviction, and sympathy were considered using the SERVQUAL survey model. Based on the research models, the study hypotheses below were formulated in order to recognize an effect relationship between the variables. The four hypotheses are, "the hypothesis on education service quality and TOEIC study result expectation," "the hypothesis on education service quality and behavioral intention," "the hypothesis on study result expectation and behavioral intention," and "the hypothesis on study result expectation and mediated effect." Results - The results are as follows. First, the factors like response, conviction, and sympathy have a positive influence on TOEIC study result expectations. Second, the TOEIC study result expectation has a positive influence on the factors of behavioral intention such as re-sign up, positive word-of-mouth, "loyalty towards school." Third, it was verified that the mediated effect on behavioral intention was influenced by education service quality at university foreign language institute, while the study result expectation has only a partial mediated effect. Conclusions - The implications of this study are summarized as follows: First, it suggests a new research model for the effect of the expectation related to the education service quality and the result of education in the university language institutes on the behavioral intention. Second, it has established a relationship between the education service quality and study result expectation by verifying the mediated effect on them.

• 산경연구논집
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• 제9권9호
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• pp.63-74
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• 2018

Purpose - The current study is to compare the cognition of stakeholders on hosting a mega sports event between Korea and the United States. In particular, to understand their cognition and perceptual conflict towards hosting a mega sports event, the study employed conflict theory. Furthermore, the study reviewed the role of social capital in the process of managing the mega sports events. Research Design, Data, and Methodology - Of homogeneous sampling, purposeful sampling method and criterion-based selection approach were used to collect interview data from key stakeholders who have been involved in hosting a mega sports events in Korea and the United States. In-depth interview transcripts were reviewed multiple tiems after transcription to extract concepts and meanings that were pertinenet to the experience involving hosting a mega sports event. Further member checks was conducted to increase the credibility of the results. Results - Results can be summarized as followed: First, stakeholders of Korea have a strong desire for positive economic effects of a mega sports event, compared to those in the United States who are more concerned in enhancing the public interests and concerns. Second, in Korea, various socio-political issues emerged at the same time and conflicts among multiple stakeholders have aggravated the situations to coordinate the issues. This was because legal system supporting socio-trust has not been established. On the other hand, major stakeholders of the United States consisted of community members who have socio-trust and networks. Thereby these social resources have been found playing a key role in building social capital that assists the stakeholders to coordinate the current issues and to solve them. Conclusions - The current study analyzed the cognition and perceptual conflict of stakehoders in a mega sports event. Social capital has beend found as a key catalyst to increase a network and cooperation among stakeholders. In order to enhance social capital in managing a mega sports event hosted in Korea, legal systems that establish networks and relationships among the related stakeholders need to be developed. Furthermore, the systematic guideline needs to be developed, organizing the sub-committees according to the types of stakeholders and the categorized common needs.

• 산경연구논집
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• 제10권8호
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• pp.45-53
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• 2019

Purpose - The purpose of this study was to clarify the factors to make an exclusive importation contract between foreign fashion brands and local retailers for successful business in Korea. Even though imported fashion brand market shows stead increasing in terms of sales amount, the number of store related study was very rare in fact. Meanwhile, as long as this business is glowing a lot of brands are suffering from bad business performance or getting in ruins thus these problems result in foreign currency loss. The local marketers therefore, strongly expect to know the solution for this matter. Research design, data, and methodology - For the qualitative research, 10 experts who are operating foreign brands with an exclusive contract at a department store or at duty free shop now and who had at least over 10 years of related working experience were included. The factors for the exclusive importation contract with foreign brands were drawn up through the one-to-one in-depth interview method from September 3, 2017 to January 15, 2018. The expert group for the validity analysis includes 2 professors and 5 postgraduate students. Results - As a result of qualitative study on the factors for imported fashion brand's launching with the exclusive importation contract, it turned out that there were 5 factors - safety, profitability, reliability, speed and global retailing. Safety, profitability, and reliability have been mentioned in most related surveys but some details are added and speed and global retailing have been newly highlighted and many unknown legal issues that it was not easy to get form common academic research are included. Speed simply means quick lead time and global retailing means stores where located in other countries. Conclusions - The reason that qualitative research should be done before the quantitative research is due to the scant theoretical background for this matter. Because the market of an imported fashion brand is steadily increasing, determining the factors to make exclusive importation contract is very meaningful from the point of academic and business. After this study, many marketers may get basic conditions to apply for real business and I hope the following quantitative research will give more effective results. The next study also will have extended range concerning industry area, product and distribution channel.

• 한국위성정보통신학회논문지
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• 제2권2호
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• pp.48-52
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• 2007

최근들어 하드웨어방식의 GPS 수신기를 소프트웨어 방식의 Software-Defined Radio(SDR)기법으로 구성하는 연구가 활발히 진행되고 있다. 이러한 소프트웨어 기반의 GPS 수신기는 기존의 하드웨어 방식으로 처리하는 신호획득부와 추적부를 마이크로 프로세서를 통해 소프트웨어 기법으로 처리하는 것을 말한다. 본 논문에서는 이러한 소프트웨어 기법을 이용하여 GPS 수신기를 설계하며 PC 기반에서 시뮬레이션을 통해 신호획득부, 추적부, 메시지 복조부를 설계하고 검증한다. 또한 의사거리 오차를 도출하기 위하여 신호 획득부와 추적부에 대해 효율적인 알고리즘을 제안하고 최종적으로L1 주파수대역의 여러 위성을 통해 수신된 채널간의 상대적 지연을 통해 의사거리를 계산한다. 본 논문에서 제시된 수신기기법은 향후 개발목표인 GPS/Galileo 복합시스템의 개발요소에 포함될 것이며 규격 및 성능을 검증할 방법을 제시할 뿐만 아니라 다양한 디버깅 환경을 제공함으로써 개발단계에 매우 유용하게 적용될 것이다.