• Journal of Power Electronics
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• 제19권5호
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• pp.1142-1152
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• 2019

This paper presents a control method for reducing the current distortion in an indirect matrix converter (IMC) operating in boost mode under unbalanced input conditions. IMCs operating in boost mode are useful in distributed generation (DG) systems. They are connected with renewable energy systems (RESs) and the grid to transmit the power generated by the RES. However, under unbalanced voltage conditions of the RES, which is connected with the input stage of the IMC operating in boost mode, the input-output currents are distorted. In particular, the output current distortions cause a ripple of the power, which is transferred to the grid. This aggravates the reliability and stability of the DG system. Therefore, in this paper, a control method using positive/negative sequence voltages and currents is proposed for reducing the current distortion of both side in IMCs operating in boost mode. Simulation and experimental results have been presented to validate effectiveness of the proposed control method.

• 한국지반공학회논문집
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• 제31권8호
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• pp.5-15
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• 2015

불포화 지반에서 선행강우에 의한 강우침투특성을 분석하기 위하여 국내 편마암 풍화토에 대한 일차원 실내강우 침투실험을 수행하였다. 춘천 및 충주지역 시료에 대한 실내모형실험에서 불포화토의 음의 간극수압은 강우 재하시 급격히 감소하고, 강우 종료후 점차 회복되었다. 강우강도가 증가함에 따라 침투속도가 증가하였으며, 선행강우시보다 본강우에서 침투속도가 빠른 것으로 나타났다. 이는 선행강우에 의하여 증가된 지반의 높은 포화도가 본강우시 강우침투속도를 증가시킨 것으로 사료된다. 특히 점토함유량이 많은 충주시료에서 음의 간극수압의 회복 속도와 침투속도가 느리게 나타났다. 유한요소 사면안정에 대한 수치해석 결과는 강우 침투에 의한 음의 간극수압의 감소에 따른 사면 안전율을 감소와 강우 종료후 간극수압의 확산에 의한 추가적인 사면 안정성 저감을 보여주고 있다. 사면의 안전율은 선행강우시 보다 본강우에서 더욱 감소하였다. 선행강우는 불포화지반의 초기 간극수압의 크기와 깊이별 패턴에 지대한 영향을 미치며, 이는 강우 사면의 안정성 해석에 고려해야 할 중요한 요소이다.

• 벤처창업연구
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• 제18권6호
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• pp.11-26
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• 2023

본 연구는 한국기업의 해외직접투자가 재무성과에 미치는 영향을 수익성, 안정성, 성장성, 활동성 부문으로 구분하여 실증 분석하였고, 기업 속성이 다른 중소기업과 대기업에서 각각 특징적 재무성과가 있는지 비교하였다. 해외직접투자 기업은'한국무역투자진흥공사'해외진출기업 Directory에서 선정하였고,'Fn Guide'를 활용하여 1990년부터 2021년까지의 재무자료 중 최초 투자 후 5년간의 재무자료가 완벽한 총 409개 기업(중소기업 136개, 대기업 273개)의 재무자료를 사용하였다. 분석 결과, 수익성부문에서 중소기업은 총자산영업이익률(ROA), 총매출액영업이익률(ROS)에 각각 정(+), 대기업은 각각 부(-)의 영향이 나타나 결과가 달랐다. 안정성부문에서 중소기업은 통계적 유의성이 없었으나 대기업은 부채비율(LEV)에 유의한 부(-)의 영향을 보였다. 성장성부문에서 중소기업은 총자산증가율(AGR)에 유의한 부(-)의 영향이 나타났고, 대기업은 유의한 결과가 없었다. 활동성부문에서 중소기업은 통계적 유의성이 없었으나 대기업은 총자산회전율(ATR), 고정자산회전율(FATR)에 정(+)의 영향이 있었다. 결론적으로 중소기업과 대기업의 해외직접투자는 수익성과 안정성, 성장성, 활동성의 재무성과가 서로 다르게 나타났다.

• Journal of applied mathematics & informatics
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• 제30권3_4호
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• pp.365-380
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• 2012

Non-negative matrix factorization (NMF) is a very efficient method to explain the relationship between functions for finding basis information of multivariate nonnegative data. The multiplicative update (MU) algorithm is a popular approach to solve the NMF problem, but it fails to approach a stationary point and has inner iteration and zero divisor. So the elementwisely alternating projected gradient (eAPG) algorithm was proposed to overcome the defects. In this paper, we use the fact that the equilibrium point is stable to prove the convergence of the eAPG algorithm. By using a classic model, the equilibrium point is obtained and the invariant sets are constructed to guarantee the integrity of the stability. Finally, the convergence conditions of the eAPG algorithm are obtained, which can accelerate the convergence. In addition, the conditions, which satisfy that the non-zero equilibrium point exists and is stable, can cause that the algorithm converges to different values. Both of them are confirmed in the experiments. And we give the mathematical proof that the eAPG algorithm can reach the appointed precision at the least iterations compared to the MU algorithm. Thus, we theoretically illustrate the advantages of the eAPG algorithm.

• Journal of the Korean Statistical Society
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• 제30권1호
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• pp.41-61
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• 2001

The minimum negative exponential disparity estimator(MNEDE), introduced by Lindsay(1994), is an excellenet competitor to the minimum Hellinger distance estimator(Beran 1977) as a robust and yet efficient alternative to the maximum likelihood estimator in parametric models. In this paper we define the negative exponential deviance test(NEDT) as an analog of the likelihood ratio test(LRT), and show that the NEDT is asymptotically equivalent to he LRT at the model and under a sequence of contiguous alternatives. We establish that the asymptotic strong breakdown point for a class of minimum disparity estimators, containing the MNEDE, is at least 1/2 in continuous models. This result leads us to anticipate robustness of the NEDT under data contamination, and we demonstrate it empirically. In fact, in the simulation settings considered here the empirical level of the NEDT show more stability than the Hellinger deviance test(Simpson 1989). The NEDT is illustrated through an example data set. We also define a goodness-of-fit statistic to assess adequacy of a specified parametric model, and establish its asymptotic normality under the null hypothesis.

• Wind and Structures
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• 제19권6호
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• pp.623-647
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• 2014

In this paper, a probability distribution which is consistent with the observed phenomenon at the roof corner and, also on other portions of the roof, of a low-rise building is proposed. The model is consistent with the choice of probability density function suggested by the statistical thermodynamics of open systems and turbulence modelling in fluid mechanics. After presenting the justification based on physical phenomenon and based on statistical arguments, the fit of alpha-stable distribution for prediction of extreme negative wind pressure coefficients is explored. The predictions are compared with those actually observed during wind tunnel experiments (using wind tunnel experimental data obtained from the aerodynamic database of Tokyo Polytechnic University), and those predicted by using Gumbel minimum and Hermite polynomial model. The predictions are also compared with those estimated using a recently proposed non-parametric model in regions where stability criterion (in skewness-kurtosis space) is satisfied. From the comparisons, it is noted that the proposed model can be used to estimate the extreme peak negative wind pressure coefficients. The model has an advantage that it is consistent with the physical processes proposed in the literature for explaining large fluctuations at the roof corners.

• 대한전자공학회논문지SD
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• 제49권1호
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• pp.1-7
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• 2012

산화물 박막트랜지스터를 이용하여 액정 디스플레이 패널에 내장할 수 있는 새로운 게이트 드라이버 회로를 설계하고 제작하였다. 산화물 박막트랜지스터는 문턱전압이 음의 값을 갖는 경우가 많기 때문에 본 회로에서는 음의 게이트 전압을 인가하여 트랜지스터를 끄는 방법을 적용하였다. 또한 세 개의 풀다운 트랜지스터를 병렬로 배치하고 번갈아 사용하므로 안정적인 동작이 가능하다. 제안한 회로는 트랜지스터의 문턱전압이 -3 V ~ +6 V인 범위에서 정상적으로 동작하는 것을 시뮬레이션을 통해서 확인하였으며, 실제로 유리 기판 상에 제작하여 안정적으로 동작하는 것을 검증하였다.

• 한국의류산업학회지
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• 제13권5호
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• pp.705-716
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• 2011

The purpose of this study was to investigate salesperson's perception of fashion company in the middle management system of department store. This study was conducted by a qualitative research method. An in-depth interview was managed to 14 fashion shop managers and salesperson who have three or more years of work experience at the department store. Interview details were classified three categories: relations with fashion company and others, concern with products supply, concern with products sales. First, the positive factors on relations with fashion company are mutual trust, stability of fashion company, coordination and consideration for shop, communication with fashion company, methodical IT system, methodical education, and social gathering support. The negative factors are unilateral breach of contract from fashion company, communication problem, gap between sales status in shop and product design in fashion company, lack of professional education, difficulty of participating in education, and inadequate employee benefits. Second, the positive factor on products supply is priority of products supply. The negative factors are lack of main items, product procurement lacking rapidity, and problem of securing a supply. Third, the positive factors on products sales are brand pride, display and information support about products, and free gift support. The negative factors are unfair selling commission policy, sales pressure, and excessive responsibility.

• Nutrition Research and Practice
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• 제8권4호
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• pp.476-481
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• 2014

BACKGROUND: A higher frequency of family meals is associated with good dietary habits in young people. This study focused on the relationships of family meal frequency with food neophobia and personality traits in adolescents. SUBJECTS/METHOD: For this purpose, we administered a survey to 495 middle school students in Seoul metropolitan city, after which the data were analyzed using the SPSS (18.0) program. Pearson correlation was used to determine the relationships among dietary habits, personality traits, and food neophobia according to frequency of family meals. RESULTS: Dietary habits, personality traits, and food neophobia all showed significant differences according to the frequency of family meals. Further, eating regular family meals was associated with good dietary habits (P < 0.001) and was linked with improved extraversion, agreeableness, conscientiousness, emotional stability, and openness/intellect (P < 0.001). On the other hand, it showed a negative relationship with food neophobia (P < 0.001). The relationship between dietary habits and food neophobia showed a negative correlation (P < 0.01). The relationship between dietary habits and personality traits showed a positive correlation (P < 0.01). Lastly, the relationship between personality traits and food neophobia showed a negative correlation (P < 0.01). Conclusion: Based on the results of the study, the frequency of family meals affects dietary habits, personality traits, and food neophobia in adolescents.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2014년도 제49회 KOSCO SYMPOSIUM 초록집
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• pp.175-178
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• 2014

The flame cell dynamics in 2-D opposed nonpremixed tubular configuration was investigated using high-fidelity numerical simulations. The diffusive-thermal instability occurs as the $Damk{\ddot{o}}hler$ number, Da, approaches the 1-D extinction limit of the tubular flames and several flame cells are generated depending on Da, and flame radius. In general, the number of flame cells are found close to the largest wave number from the linear stability analysis. It was also found from the displacement speed analysis that during the local flame extinction and cell formation, negative edge flame speed is observed due to small gain from reaction compared to large loss from diffusion.