• 응용통계연구
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• 제34권6호
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• pp.905-922
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• 2021

라벨 없이 진행되는 비지도 학습 중 하나인 군집분석은 자료에 어떤 그룹이 내포되어 있는지 사전 지식이 없을 경우에 군집을 발굴하고, 군집 간의 특성 차이와 군집 안에서의 유사성을 분석하고자 할 때 유용한 방법이다. 기본적인 군집분석 중 하나인 K-means 방법은 변수의 개수가 많아질 때 잘 동작하지 않을 수 있으며, 군집에 대한 해석도 쉽지 않은 문제가 있다. 따라서 고차원 자료의 경우 주성분 분석과 같은 차원 축소 방법을 사용하여 변수의 개수를 줄인 후에 K-means 군집분석을 행하는 Tandem 군집분석이 제안되었다. 하지만 차원 축소 방법을 이용해서 찾아낸 축소 차원이 반드시 군집에 대한 구조를 잘 반영할 것이라는 보장은 없다. 특히 군집의 구조와는 상관없는 변수들의 분산 또는 공분산이 클 때, 주성분 분석을 통한 차원 축소는 오히려 군집의 구조를 가릴 수 있다. 이에 따라 군집분석과 차원 축소를 동시에 진행하는 방법들이 제안되어 왔다. 그 중에서도 본 연구에서는 De Soete와 Carroll (1994)이 제안한 방법론을 확률적인 모형으로 바꿔 군집분석을 진행하는 확률적 reduced K-means를 제안한다. 모의실험 결과 차원 축소를 배제한 군집분석과 Tandem 군집분석보다 더 좋은 군집을 형성함을 알 수 있었고 군집 당 표본 크기에 비해 변수의 개수가 많은 자료에서 기존의 비 확률적 reduced K-means 군집분석에 비해 우수한 성능을 확인했다. 보스턴 자료에서는 다른 군집분석 방법론보다 명확한 군집이 형성됨을 확인했다.

• 한국응용과학기술학회지
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• 제35권4호
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• pp.1088-1095
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• 2018

본 연구에서는 탄소 나노재료 중 환원된 그래핀 옥사이드와 전도성 고분자중 폴리아닐린을 복합화 하여 슈퍼커패시터용 전극을 제조하였으며, 각각의 전극 재료가 가지는 단점을 서로 보완하고 장점을 극대화시킴으로써 전극의 전기화학적 특성을 크게 향상 시킬 수 있었다. 전극 물질에 사용된 폴리아닐린은 아닐린 단량체를 화학 중합법으로 제조하였고, 환원된 그래핀 옥사이드는 별도의 전 처리 과정 없이 사용하였으며, DMF(N,N-dimethyl formamide)를 용매로 도입하여 분산용액을 제조하였다. 분산용액은 금이 코팅된PET(Polyethylene terephthalate) 기판위에 산업적 스케일로 적용이 가능한 스프레이 코팅 방법을 이용하여 전극으로 제조하였다. 환원된 그래핀 옥사이드/폴리아닐린 복합재료를 기반으로 제조된 전극의 전기화학적 특성을 비교하기 위하여 환원된 그래핀 옥사이드와 폴리아닐린 단일 전극을 제조하였으며, 동일한 조건하에서 순환전압전류법, 임피던스 분광법, 정전류 충 방전법을 통하여 각각의 전극이 나타내는 전기화학적 특성을 비교 분석 하였다. 그 결과로, 환원된 그래핀 옥사이드/폴리아닐린 복합재료를 기반으로 제조된 전극은 폴리아닐린, 환원된 그래핀 옥사 단일 전극에 비하여 전기 용량 값이 높게 나타났으며, 전해질 계면과의 내부 저항은 폴리아닐린, 환원된 그래핀 옥사이드 단일 전극에 비하여 각각 24 %, 58 % 감소하는 결과를 나타내었다. 이러한 결과로 미루어보아 본 연구를 통하여 제조된 환원된 그래핀 옥사이드/폴리아닐린 복합재료 기반의 전극은 유연성 에너지 저장 매체나 웨어러블 전자기기에 적용이 가능할 것으로 판단된다.

• Archives of Pharmacal Research
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• 제4권1호
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• pp.33-41
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• 1981

The prepared dextran sulfates were characterized by measuring the reduced viscosisty at five different concentrations to obtain an intrinsic viscosity in both phosphate and tris buffers, pH 7.4, ionic strength of 0.1 Dextran sulfates having 0.81, 1.06 sulfate groups per hexose unit have reduced viscosity value below 40 ml/g whereas dextran sulfates having 1.21, 1.43, 1.69 sulfate groups per hexose unit have reduced viscosity value over 40 ml/g. Dextran sulfate having 1.21 sulfate groups per hexose unit had highest value of reduced viscosity. The reduced viscosity of dextran sulfate in tris buffer was always higher than that in phosphate buffer regardless of the sulfate content of dextran sulfate. The influence of the sulfation of the dextran sulfate. The influence of the sulfation of the dextran sulfate molecule on the dextran sulfate-LDL interaction was studied with three different dextran sulfate molecules. Dextran sulfate molecules having more than one sulfate group per hexose unit. The dextran sulfate having 0.81 sulfate groups per hexose unit showed considerably different precipitation curves in phosphate and tris buffers. This peculiar behavior of dextran sulfate having 0.81 sulfate groups per hexose unit in the two buffer systems was not noticed with dextran sulfate having more than one noticed with dextran sulfate having more than one sulfate group per hexose unit.

• 대한기계학회논문집B
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• 제32권2호
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• pp.133-140
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• 2008

A reduced chemical kinetic mechanism is developed in order to predict the flame phenomena in premixed $CO/H_2/Air$ flames at atmospheric pressure, aimed at studying the coal gas combustion for the IGCC applications. The reduced mechanism is systematically derived from a full chemical kinetic mechanism involving 11 reacting species and 66 elementary reactions. This mechanism consists of four global steps, and is capable of explicitly calculating the concentration of 7 non-steady species and implicitly predicting the concentration of 3 steady state species. The fuel blend contains two fuels with distinct thermochemical properties, whose contribution to the radical pool in the flame is different. The flame speeds predicted by the reduced mechanism are in good agreement with those by the full mechanism and experimental results. In addition, the concentration profiles of species and temperature are also in good agreement with those by the full mechanism.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1586-1591
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• 2004

Flow visualization experiments have been performed to investigate the effects of phase lag, reduced frequency qualitatively by examining wake pattern on a dragonfly type wing. The model was built with a scaled-up, flapping wings, composed of paired wings with fore- and hindwing in tandem, that mimicked the wing form of a dragonfly. The present study was conducted by using the smoke-wire technique, and an electronic device was mounted to find the exact positional angle of wing below the tandem wings, which amplitude is ranged from $-16.5^{\circ}$ to $+22.8^{\circ}$. Phase lag applied on the wings is $0^{\circ}$, $90^{\circ}$, $180^{\circ}$ and $270^{\circ}$. The reduced frequency is 0.15, 0.3 and 0.45 to investigate the effect of reduced frequency. It is inferred through observed wake pattern that the phase lag clearly plays an important role in the wake structures and in the flight efficiency as changing the interaction of wings. The reduced frequency also is closely related to wake pattern and determines flight efficiency.

• 전력전자학회논문지
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• 제17권4호
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• pp.322-329
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• 2012

This paper proposes a non-isolated bidirectional soft-switching converter with high voltage for high step-up/down and high power applications. Compared to the conventional boost converter the proposed converter can achieve approximately doubled voltage gain using the same duty cycle. The voltage ratings of the switch and diode are reduced to half, which result in the use of devices with lower $R_{DS(ON)}$ and on drop leading to reduced conduction losses. Also, voltage ratings of the passive components are reduced, and therefore the total energy volume is reduced to half. Further, the switch is turned on with ZVS in the CCM operation which results in negligible surge caused leading to reduced switching losses. The validity of the proposed converter is proved through a 10kW prototype.

• 한국대기환경학회지
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• 제17권4호
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• pp.347-354
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• 2001

SCR (Selective Catalytic Reduction) process is presently considered as one of the most effective techniques for removing nitric oxides from exhaust gases. In this study, based on the conceptually designed SCR reactor of 500 MW coal fired power plant. a reduced scale (1/20) SCR reactor model was made to analyze the flow pattern in front of catalyst layer according to the guide vane's design factors such as the number, interval, and angle of vanes. The results of the test were compared to those numerical simulation in order to assure the reliability of two methods. On the basis of our study. the critical Reynolds number (2.0$\times$ 10$^{5}$ ) was proposed for ensuring the similarity between the reduced scale model and the prototype of SCR reactor. Optimum design parameters of guide vanes were determined as follows, 4 vanes, the first vane angle of 93$^{\circ}$, and the vane intervals of 0.85 S/n, 1.05 S/n, 1.1 S/n, 1.0S/n, 1.0S/n (S: the distance of duct, n: the number of guide vanes). The excellent agreement between the results of the numerical simulation and the reduced scale model provides the validation of two methods for prediction of flow through SCR reactor.

• 대한한의학회지
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• 제27권2호
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• pp.70-85
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• 2006

Objectives; This study examined the neuroprotective effect of Hyulbuchookautang (血府逐瘀湯, HBCAT)against neural damage following focal cerebral infarction. Methods : Sprague-Dawley Rats were induced with focal cerebral infarction by temporal middle cerebral artery occlusion (MCAO). The rats were divided into 2 groups. We treated extract of HBCAT to one group after operation (sample group), and the other group wasn't treated after operation (control group). We observed neurological scores and TIC-stained infarct area, total infarct volume in brain sections and Bax-positive neurons, HSP70- positive neurons in brain regions. Results : HBCAT treatment at 3 days after MCAO reduced neurological scores induced by MCAO. HBCAT treatment at 5 days after MCAO reduced TTC-stained infarct area in brain sections induced by MCAO. HBCAT treatment at 5 days after MCAO reduced total infarct volume in brain sections induced by MCAO. HBCAT treatment after MCAO reduced Bax-positive neurons in cortex infarct core and cortex infarct penumbra and caudo-putamen of brain regions induced by MCAO. HBCAT treatment after MCAO reduced HSP70- positive neurons in cortex infarct penumbra of brain regions induced by MCAO. Conclusions : These results suggest that HBCAT has a neuroprotective effect against focal cerebral ischemia.

• Structural Engineering and Mechanics
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• 제21권5호
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• pp.539-551
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• 2005

Finite elements based on isoparametric formulation are known to suffer spurious stiffness properties and corresponding stress oscillations, even when care is taken to ensure that completeness and continuity requirements are enforced. This occurs frequently when the physics of the problem requires multiple strain components to be defined. This kind of error, commonly known as locking, can be circumvented by using reduced integration techniques to evaluate the element stiffness matrices instead of the full integration that is mathematically prescribed. However, the reduced integration technique itself can have a further drawback - rank deficiency, which physically implies that spurious energy modes (e.g., hourglass modes) are introduced because of reduced integration. Such instability in an existing stiffness matrix is generally detected by means of an eigenvalue test. In this paper we show that a knowledge of the dimension of the solution space spanned by the column vectors of the strain-displacement matrix can be used to identify the instabilities arising in an element due to reduced/selective integration techniques a priori, without having to complete the element stiffness matrix formulation and then test for zero eigenvalues.

• 한국군사과학기술학회지
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• 제9권4호
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• pp.128-136
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• 2006

The purpose of this paper is to examine the dynamic stall characteristics of an elliptic airfoil when subject to constant pitch motions. In this study, which was motivated by the pressing need for a greater understanding of the reduced frequency$({\kappa})$ effects on flow patterns of elliptic airfoil, the various reduced frequencies were considered. The result confirms that the reduced frequency has a profound effects on the flow patterns. The increase of ${\kappa}$ accelerate the separation bubble bursting process up to ${\kappa}=0.10$, then diminish with further increase in ${\kappa}$. Compared with static condition, the dynamic pitching airfoil delays stall angle approximate $4{\circ}{\sim}5{\circ}$ during pitch-up stroke for ${\kappa}=0.10$. Results from this qualitative analysis provided valuable insight Into the control of dynamics stall.