• 한국정밀공학회지
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• 제26권3호
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• pp.40-46
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• 2009

Toroidally-wound brushless direct-current (BLOC) machines are compact, highly efficient, and can work across a large magnetic gap. For these reasons, they have been used in pumps, flywheel energy storage systems and left ventricular assist devices among others. The common feature of these systems is a spinning rotor supported by a set of (either mechanical or magnetic) bearings. From the view point of dynamics, it is desirable to increase the first critical speed of the rotor so that it can run at a higher operating speed. The first critical speed of the rotor is determined by the radial stiffnesses of the bearings and the rotor mass. The motor also affects the first critical speed if the rotor is displaced from the rotating center. In this paper, we analytically derive the flux density distribution in a toroidally-wound BLOC machine and also derive the negative stiffness of the motor, based on the assumption that the rotor displacement perturbs the flux density distribution linearly. The estimated negative stiffness is validated by finite element analyses.

• Journal of Power Electronics
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• 제16권4호
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• pp.1551-1564
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• 2016

The high penetration level of inverter-based distributed generation (DG) power plants is challenging the low-voltage ride-through requirements, especially under unbalanced voltage sags. Recently, a flexible injection of both positive- (PS) and negative-sequence (NS) reactive currents has been suggested for the next generation of grid codes. This can enhance the ancillary services for voltage support at the point of common coupling (PCC). In light of this, considering distant grid faults that occur in a mainly inductive grid, this paper proposes a complete voltage support control scheme for the interface inverters of medium or high-rated DG power plants. The first contribution is the development of a reactive current reference generator combining PS and NS, with a feature to increase the PS voltage and simultaneously decrease the NS voltage, to mitigate voltage imbalance. The second contribution is the design of a voltage support control loop with two flexible PCC voltage set points, which can ensure continuous operation within the limits required in grid codes. In addition, a current saturation strategy is also considered for deep voltage sags to avoid overcurrent protection. Finally, simulation and experimental results are presented to validate the effectiveness of the proposed control scheme.

• 한국생활과학회지
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• 제17권4호
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• pp.639-648
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• 2008

This study is to examine the meaning of death, the level of death anxiety, and the aspect of death anxiety that the aged have. For this, a quantitative research subjecting 532 of the aged living in local area, Jeollabuk-do was carried out. And among those 532 questionnaires, 10 were subjected for depth interview. The following is a summary of the result from this study. First, the meaning of death for the aged is classified into three classes as positive, neutral and negative meaning. Among these, there were far greater numbers of the aged who put neutral or negative meanings on their death than the positive one. Second, death anxiety of the aged are divided into three factors: 'annihilation anxiety', 'process anxiety', and 'afterdeath anxiety'. The factor that involves death anxiety the most was process anxiety, then afterdeath anxiety, and annihilation anxiety, in the order. Third, as a result of classifying the feature of death anxiety in the aged into the symptoms of death anxiety and the motive of recognizing death anxiety. Death anxiety is classified into the people with symptoms and those without symptoms, and those with certain symptoms are classified into the physical symptoms and the mental symptoms. The motive of recognizing death anxiety appeared when the individual is aged, experiences the death of other people, suffers physical pains, and when there is a mental loneliness.

• 대한전자공학회논문지SP
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• 제41권6호
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• pp.175-186
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• 2004

본 논문은 복잡한 컬러 영상에서의 문자 추출을 위한 텍스춰와 연결성분 방법의 결합된 방법을 제안한다. 자동 학습 방법으로 구축된 다층 신경망(multilayer perceptron)은 부트스트랩 학습 방법을 사용함으로써 별도의 특징값 추출 단계 없이 다양한 환경의 입력 영상에 대한 검출률(recall rate)을 향상시키며, 검출률을 향상함으로써 발생되는 정확도(precision rate) 저하 문제는, NMF(Non-negative matrix factorization)를 이용한 연결 성분 방법을 사용함으로써 극복한다. 문자의 존재 비율이 낮은 입력영상에 대하여 CAMShift 알고리즘을 이용한 영역 마킹 방법을 사용함으로써, 두 방법을 결합함으로써 야기되는 속도 저하 문제의 해결을 시도하였다. 이와 같이 텍스춰와 연결성분 방법을 결합함으로써 강건하고 효율적인 시스템을 구성할 수 있었다.

• 한국인터넷방송통신학회논문지
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• 제12권4호
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• pp.95-102
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• 2012

대화식 드라마는 사용자의 자유로운 선택과 참여가 요구되는 상호작용성을 가진 이야기를 말한다. 본 논문에서는 이러한 대화식 드라마의 특성을 이용하여 훈련 데이터를 만들어 사용자의 선호도를 파악한다. 그 후 파악된 선호도 특성에 맞게 새로운 사용자들에게 스토리의 경로를 추천하는 시스템 구현 과정을 기술한다. 선호도 특성을 추출하기 위하여 Principal Component Analysis(이하 PCA)와 Non-negative Matrix Factorization(이하 NMF)를 사용하였다. PCA를 이용하여 추천한 결과 성공률은 75%, NMF을 이용하여 추천한 결과 성공률은 62.5%를 나타냈다.

• 한국정보과학회논문지:소프트웨어및응용
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• 제31권10호
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• pp.1412-1417
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• 2004

전체관적인 표현방법인 희소 코딩 또는 독릴 성분 분해(ICA)는 이전의 청각의 처리와 소리 분류의 작업을 해명하는데 성공적으로 적용되었다. 반대로 부분 기반 표현법은 뇌에서 물체를 인식하는 방법을 이해하는 또 다른 방법이다. 이 논문에서, 우리는 소리 분류의 작업에 부분기반 표현법을 학습시키는 비음수화 행렬 분해(NMF)(1) 방법을 적용하였다. 잡음이 존재할 때와 존재하지 않을 때 두 가지 상황에서, NMF를 이용하여 주파수-시간영역의 소리로부터 특징을 추출하는 방법을 설명한다. 실험결과에서는 NMF에 기반을 둔 특징이 ICA에 기반을 두어 추출한 특징보다 소리 분류의 성능을 향상시킴을 보여준다.

• 한국분말재료학회지
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• 제25권6호
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• pp.507-513
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• 2018

This study investigates the viability of using a Na-ion battery with a tin(Sn) anode to mitigate the vulnerability caused by volume changes during discharge and charge cycling. In general, the volume changes of carbon material do not cause any instability during intercalation into its layer structure. Sn has a high theoretical capacity of $847mAh\;g^{-1}$. However, it expands dramatically in the discharge process by alloying Na-Sn, placing the electrode under massive internal stress, and particularly straining the binder over the elastic limit. The repeating strain results in loss of active material and its electric contact, as well as capacity decrease. This paper expands the scope of fabrication of Na-ion batteries with Sn by fabricating the binder as an auxetic structure with a unique feature: a negative Poisson ratio (NPR), which increases the resistance to internal stress in the Na-Sn alloying/de-alloying processes. Electrochemical tests and micrograph images of auxetic and common binders are used to compare dimensional and structural differences. Results show that the capacity of an auxetic-structured Sn electrode is much larger than that of a Sn electrode with a common-structured binder. Furthermore, using an auxetic structured Sn electrode, stability in discharge and charge cycling is obtained.

• The Journal of Asian Finance, Economics and Business
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• 제8권8호
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• pp.647-658
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• 2021

Analysts' forecasts are important for providing useful guidance to investors, especially individual or small investors, and therefore it becomes critical to identify the elements which can potentially increase errors in analysts' forecasts. This study investigates potential factors which can lead to errors in forecasting by analysts, specifically in terms of the level and attributes of corporate earnings. Utilizing a sample of firms listed on the Korean stock markets, this study provides evidence that firms with more volatile and unpredictable earnings feature less accurate analyst forecasts. This study fills a void in the literature by conducting empirical tests for earnings attributes in terms of volatility and unpredictability that could potentially undermine the forecast accuracy. The negative association between the quality of earnings and forecast accuracy is more pronounced for firms with negative net income values. Additional analysis demonstrates that forecast accuracy is significantly lower for the fourth quarter than for other fiscal quarters and that fourth quarter earnings tend to be more volatile and unpredictable. This study contributes to the literature by providing new empirical evidence regarding the comprehensive effects of earnings quality and level on analysts' forecasting accuracy and further suggests potential factors contributing to the fourth quarter anomaly in analyst forecasts in terms of earnings attributes.

• 산경연구논집
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• 제9권2호
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• pp.47-55
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• 2018

Purpose - To meet the needs of various customers in an uncertain market environment, many companies use product modularization strategies. Modularization of a product means that one product consists of several components and that the type of product can be changed according to the combination of components. The greatest feature of modularity is that changes in one component do not significantly affect the physical changes in the other component to which they are connected. Modularization of products is recognized as a very important strategy to reflect increasingly complicated customer requirements to products and respond to the needs of various markets. Many studies have been made in connection with the concept of mass customer satisfaction. There are many prior studies that modularization of such products positively affects the operational performance (manufacturing cost, fast delivery, etc.) and innovation of the product. However, excessive modularization has been found to have a negative effect on this performance. However, there are very few studies on the nonlinear relationship between product modularization and customer satisfaction. Supplementing these academically insufficient parts is very necessary when considering the current market environment. Research design, data, and methodology - In order to make up for the shortcomings of academic research in Korea, this study collects data through questionnaires in electronic, auto, and defense industry. This is because these industries are using modularity of products. based on lots of previous studies and information overload theory, we made two hypothesis and verify with empirical analysis. All 108 data were used. We used the R program and SPSS program for statistical verification. Results - As a result of the study, modularization of products showed positive relationship with customer satisfaction to a certain level. However, it has been found that when the modularization is over and beyond a certain level, there is a negative relationship with customer satisfaction. Conclusions - Excessive modularization of products can have a negative impact on customer satisfaction. This result can be understood as a result of human limited rationality due to information overload. Therefore, it is important for companies to apply appropriate modularity to product design.

• 한국산학기술학회논문지
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• 제14권8호
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• pp.3925-3932
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• 2013

감성은 인간의 삶과 밀접한 관련을 가지고 있으며 이는 집중력, 학습능력 등 많은 부분에 영향을 주어 다양한 행동 패턴을 가지게 한다. 따라서 본 논문의 목적은 부정감성을 구분하기 위하여 생체신호를 기반으로 주요한 특징들을 추출하는 것이다. 이를 위해 본 논문에서는 심전도, 뇌파, 피부 온도와 피부전도도를 기반으로 생체신호를 측정한 후, 선형분류기와 유전 알고리즘의 조합으로 정확하고 신속한 알고리즘 개발하고, 주요 특징을 추출하였다. 그 결과, 알고리즘은 최대 96.4%의 정확도를 가짐을 확인할 수 있었고, 추출된 파라미터는 심박변이도의 Mean, RMSSD, NN50과 뇌파의 전두엽 영역에서의 ${\sigma}$파와 ${\alpha}$파의 주파수 파워, 두정엽 영역에서 ${\alpha}$파, ${\beta}$파, ${\gamma}$파와 의 주파수 파워, 그리고 피부온도의 평균과 표준편차 값이었다. 이에 따라 각 각의 생체신호를 기반으로 한 추출 된 특징들은 부정감성의 분류에 있어 중요한 역할을 함을 확인할 수 있었다.