• International Journal of Fuzzy Logic and Intelligent Systems
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• 제9권1호
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• pp.36-41
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• 2009

Self organizing map(SOM) is one of the unsupervised methods based on the competitive learning. Many clustering works have been performed using SOM. It has offered the data visualization according to its result. The visualized result has been used for decision process of descriptive data mining as exploratory data analysis. In this paper we propose improvement of SOM using stratified sampling of statistics. The stratification leads to improve the performance of SOM. To verify improvement of our study, we make comparative experiments using the data sets form UCI machine learning repository and simulation data.

• 지질공학
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• 제8권2호
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• pp.153-161
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• 1998

경상계 퇴적암은 층리가 잘 발달하고 있어 강도 및 변위 특성은 이방성을 띄기 때문에 터널 등 지반 특성과 밀접하게 관계되는 건설공사 시에 지반의 이방성 특성을 고려한 설계가 필요하다. 경상계 퇴적암을 기반암으로 하여 건설 중인 대구 지하철 2호선은 운영 중에 지하철 노선 상부에 건설되는 것으로 계획된 동서고가도로의 하중을 추가로 받게 된다. 교각 기초에 작용하는 76.2 MN의 고가도로 하중이 하부의 지하철 터널에 미치는 영향을 수치해석으로 검토하였다. 검토결과 지하철 터널 주변 지반은 추가 하중으로 인하여 5∼6 MPa의 응력을 받게되며 콘크리트 라이닝은 8∼10mm의 추가 변위를 받게되어 라이닝의 손상 가능성이 큰 것으로 나타났다. 따라서, 지하철 운영시의 안전을 위하여 고가도로 교각 기초 부근의 터널은 지하철 공사 시에 적절히 보강되어야 할 것으로 판단된다.

• 대한기계학회논문집B
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• 제22권9호
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• pp.1317-1324
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• 1998

In general, DI gasoline engine has the advantages of higher power output, higher thermal efficiency, higher EGR tolerance and lower emissions due to the operation characteristics of increased volumetric efficiency, compression ratio and ultra-lean combustion scheme. In order to apply the concept of stratified charge into direct injection gasoline engine, some kinds of methodologies have been adapted in various papers. In this study, a reflector was adapted around the injector nozzle to apply the concept of stratified charge combustion which leads the air-fuel mixture to be rich near spark plug. Therefore, the mixture near the spark plug is locally rich to ignite while the lean mixture is wholly introduced into the combustion chamber. The characteristics of combustion is analyzed with the variations of fuel injection pressure and load in a stratified -charge direct injection single cylinder gasoline engine. The obtained results are summarized as follows ; 1. The MBT spark timing approached to TDC with the increase of load on account of the increase of evaporation energy, but has little relation with fuel injection pressure. 2. The stratification effects are apparent with the increase of injection pressure. It is considered by the development of secondary diffusive combustion and the increase of heat release of same region, but proceed rapidly than diesel engine. Especially, in the case of high pressure injection (l70bar) and high load (3.0kgf m), the diffusive combustion parts are developed excessively and results in the decrease of peak pressure than in the case of middle load. 3. The index of engine stability, COVimep value, is drastically decreased with the increase of load. 4. To get better performance of DI gasoline engine development, staged optimizaion must be needed such as injection pressure, reflector, intake swirl, injection timing, chamber shape, ignition system and so on. In this study, the I50bar injection pressure is appeared as the optimum.

• 한국시뮬레이션학회논문지
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• 제19권1호
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• pp.133-141
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• 2010

본 연구는 층화추출법과 통제변수기법을 시뮬레이션 실험설계에서 동시에 사용하여 파라미터의 추정 효율성을 개선하는 방법을 제안하였다. 시뮬레이션을 수행하는 도중에 수집한 표준화 부가변수를 통제변수기법에 활용하여 파라미터 추정을 위한 반응변수의 오차를 줄이도록 하였으며 통제변수 구성에 사용되지 않은 부가변수를 층화변수로 활용하는 층화추출기법을 적용하여 통제반응변수의 변이성을 추가로 감소하였다. 반응변수와 통제변수 사이의 공분산 관계가 알려진 경우에 두 방법을 동시에 활용하여 파라미터를 추정하는 기법의 시뮬레이션 효율성을 이론적으로 도출하였다. 반응변수와 통제변수 사이의 상관관계 구조가 알려지지 않은 경우 선택된 모형의 시뮬레이션 결과는 제안된 층화 통제 추정기법이 층화추출법이나 통제변수기법을 개별적으로 적용하여 파라미터를 추정하는 것보다 우수한 것으로 나타나고 있다.

• 대한토목학회논문집
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• 제33권6호
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• pp.2411-2425
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• 2013

퇴적층과 암반층이 층상구조로 되어있는 지반의 층상암반층 위에 말뚝기초를 설계할 경우, 연직하중에 대한 지지암반의 파괴모드(휨파괴, 펀칭전단파괴 혹은 선단지지파괴)를 검토하고 지지력을 계산하기 위해서는 층상지지암반층의 구조해석이 필요하다. 그러나 ACI committee 436과 우리나라 구조물기초설계기준에서 제안하고 있는 기존의 이용 가능한 탄성평판해석법(Elastic Plate Analysis Method)은 매우 복잡하여 기술자가 이용하는데 어려움이 많다. 따라서 본 연구에서는 복잡한 탄성평판해석법 대신 비교적 간단한 원형기초해석법(Circular Foundation Analysis Method)을 이용할 수 있도록 등가유효폭(반경)의 개념과 식을 제시하였고, 이를 통하여 탄성평판해석에 의한 모멘트와 전단력이 원형평판해석의 결과와 같도록 관계식을 제안하였다. 그 결과 등가유효폭을 이용한 원형기초해석의 방법은 매우 단순하고 편리하였고, 제안된 방법에 의한 결과를 탄성평판해석과 유한요소해석 결과와 비교한 결과 매우 잘 일치하였다.

• Asian Pacific Journal of Cancer Prevention
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• 제15권23호
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• pp.10293-10298
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• 2015

Background: Previous epidemiologic studies on the association between energy intake and endometrial cancer risk have only generated contradictory results. The role of energy intake in endometrial carcinogenesis thus remains unclear. To quantitatively assess the potential association between energy intake and endometrial cancer, a meta-analysis of case-control and cohort studies was here conducted. Materials and Methods: Eligible studies were retrieved via both computerized searches and review of references. Fixed-or random-effect models were used to summarize the estimates of OR with 95%CIs. Stratified analyses on study design, region and macronutrients' calorie were performed. Results: Sixteen studies met the inclusion criteria of the meta-analysis. No association between total energy intake and endometrial cancer was observed in either overall group (OR=1.11, 95%CI 0.92-1.30) or subgroups stratified by study design and region. In the specific macronutrients' calorie analysis, higher fat energy intake was found to be associated with increased endometrial risk (OR=1.72, 95%CI 1.12-2.32) while energy from carbohydrate and protein was not related to endometrial cancer risk. Conclusions: Our analysis did not support that total energy intake is related to endometrial cancer risk, in contrast to fat energy.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1998년도 추계학술발표회요약집
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• pp.133-133
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• 1998

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1999년도 춘계학술발표회요약집
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• pp.151-151
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• 1999

• 한국자동차공학회논문집
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• 제12권5호
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• pp.58-65
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• 2004

A cylindrical constant volume combustion chamber was used to investigate the combustion characteristics of stratified methane-air mixture under several initial charge conditions in the author's previous reports. The results showed that the improvement of thermal efficiency and reduction of heat loss was realized simultaneously by using 2-stage injection method. This paper deals with the reason why the stratified combustion has showed better combustion rate through the measurement and analysis of chemiluminescence of C $H^{*}$ and $C_{2}$$^{*}$ radicals. An optic fiber bundle is used to measure the local emission of C $H^{*}$ and $C_{2}$$^{*}$ radicals to map the relationship between the excess air ratio and local radical intensity ratio in the combustion vessel at 5 mm apart form the geometric center. The results show that there exist a relationship between the intensity ratio and the air-fuel ratio. It is revealed that the improvement of combustion rate in a lean-stratified mixture is realized through the 2-stage injection method. method.

• 한국자동차공학회논문집
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• 제16권5호
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• pp.157-163
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• 2008

The HCCI combustion mode poses its own set of narrow engine operating by knocking. In order to solve this, inhomogeneity method of mixture and temperature is suggested. The purpose of this research is to get fundamental knowledge about the effect of thermal stratification on HCCI combustion of PRF -Air mixture. The temperature stratification is made by buoyancy effect in combustion chamber of RCM. The analysis items are pressure, temperature of in-cylinder gas and combustion duration. In addition, the structure of flames using the two dimensional chemiluminescence's images by a framing camera are analyzed. Under stratification, the LTR starting time and the HTR starting time are advanced than that of homogeneous. Further, the LTR period of homogeneous conditions became shorter than that of the stratified conditions. With the case of homogeneous condition, the luminosity duration becomes shorter than the case of stratified condition. Additionally, under stratified condition, the brightest luminosity intensity is delayed longer than at homogeneous condition.