• Korean Journal of Cognitive Science
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• v.12 no.4
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• pp.41-47
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• 2001

Palmer and Rock (1994) proposed that a connected region of uniform visual properties (uniform connectedness) strongly tends to be organized as a single perceptual unit To test this hypothesis using briefly presented forms three experiments were executed. In Experiment 1 and 2 participants were asked to report the identity of a post-cued target. and there was no difference between connected and disconnected displays. In Experiment 3 participants were asked to report the predesignated name of each whole display and the accuracy rate was higher in the connected displays than in the disconnected ones. However negative repetition effects were observed consistently in all the experiments. This indicates uniform connectedness does not have a strong effect in perceiving briefly presented forms.

• Korean Journal of Cognitive Science
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• v.15 no.2
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• pp.17-22
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• 2004

Two experiments were executed to investigate the effect of uniform connectedness systematically using the identification task of briefly exposed forms. Previous study observed negative repetition effected (i.e., NRE) in the identification task of two parentheses either connected or disconnected vertically, which was interpreted as an evidence against the hypothesis of uniform connectedness. Experiment I tested the hypothesis that NRE resulted from the Perceptual set or anticipating disconnected displays. Experiment 2 tested the hypothesis that NRE resulted from relatively shorter exposure time. Using partial report task asking participants to report only the cued target and whole report task asking them to report the whole pattern with only connected displays, experiment 1 observed NRE respectively. Experiment 2, with longer exposure time equivalent to 83% accuracy and response bias controlled by use of catch trials, obtained the same NRE. Those results seems to indicate that uniformly connected forms were processed analytically by perceivers without task demand and futhermore, the hypothesis of uniform connectedness as a principle of perceptual organization is not plausible.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.47-50
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• 2009

본 논문에서는 불균질 재료의 균열진전을 해석하기 위한 방법으로 변절점 유한요소를 이용한 멀티스케일 기법을 제시하였다. 효율적인 해석을 위하여 서로 다른 스케일의 요소망을 적용하여 전체 모델의 자유도를 감소시킨다. 균열선단과 비교적 멀리 떨어져 있는 영역은 균질화 기법을 도입하여 불균질 재료에 대한 등가물성을 갖는 성긴 요소망으로 대체하고, 균열선단 주변의 요소망은 재료의 기하학적 특성과 불균질성을 반영하도록 조밀하게 구성한다. 한편 균열선단에 존재하는 응력 특이성을 표현하기 위하여 균열선단을 포함한 요소를 더욱 조밀한 요소망으로 분할하여 구성한다. 여기에서 서로 다른 스케일의 요소망 경계에는 변절점 유한요소를 적용함으로써 경계에서의 절점 연결조건과 적합성을 만족시킬 수 있다. 제시한 멀티스케일 기법을 수치예제에 적용함으로써 정확성과 효율성을 검증하였으며, 특히 불균질 성분이 균열진전에 미치는 영향을 경계조건과 T-응력의 관점에서 분석하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.8
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• pp.1-7
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• 2005

This paper proposes a local improvement method that combines extended topological clean up and optimization-based smoothing for homogenizing triangular grid system. First extended topological clean up procedures are applied to improve the connectivities of grid elements. Then, local optimization-based smoothing is performed for maximizing the distortion metric that measures grid quality. Using the local improvement strategy, we implement the grid homogenizations for two triangular grid examples. It is shown that the suggested algorithm improves the quality of the triangular grids to a great degree in an efficient manner and also can be easily applied to the remeshing algorithm in adaptive mesh refinement technique.

• Journal of Soil and Groundwater Environment
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• v.11 no.5
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• pp.1-8
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• 2006

The objective of this study is to assess impacts of sorption heterogeneity on the transport of leachate leaked from unlined landfill sites and is accomplished by examining the results from a series of Monte-Carlo simulations. For random distribution coefficient ($K_{d}$) fields with four different levels of heterogeneity ranging from homogeneous to highly heterogeneous, the transport of leachate was investigated by linking a saturated flow model with a contaminant transport model. Impacts of a chemical heterogeneity were evaluated using point statistics values such as mean, standard deviation, and coefficient of variation of the concentration obtained at monitoring wells from 100 Monte-Carlo trials. Inspection of point statistics shows that the distribution of distribution coefficient in the landfill site proves to be an important parameter in controlling leachate concentrations. In comparison to homogeneous sorption, heterogeneous $K_{d^-}$ fields produce the variability in the leachate concentration for different realizations. The variability increases significantly as the variance in the $K_{d^-}$ field and the travel time between source and monitoring well increase. These outcomes indicate that use of a constant homogeneous $K_{d}$ value for predicting the transport of leachate can result in significant error, especially when variability in $K_{d}$ is high.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.136.1-136.1
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• 2010

고체산화물 연료전지(SOFC)에서 사용되는 연결재의 주 기능은 각 단위 셀의 연료극과 다음 셀의 공기극을 전기적으로 연결하여, 공기와 사용연료의 분리역할을 하기위해 사용된다. SOFC용 연결재는 다른 구성요소 소재보다 높은 전기전도성, 낮은 이온전도성이 요구되며 SOFC는 고온에서 작동되기 때문에 다른 구성 소재들과 유사한 열팽창계수와 물리, 화학적인 안정성이 요구된다. 현재 연결재 제조기술은 plasma coating, sputtering, screen printing, 전사법등 다양한 연구가 진행되고 있다. 본 연구에서는 저렴한 비용으로 대량생산이 용이한 고상반응법을 적용하여 세라믹연결재를 제조하고, 그 특성을 연구하였다. 세라믹 연결재로서 선정한 합성조성은 $(La_{0.7}Ca_{0.3})(Cr_{0.9}Co_{0.1})O_3$로 SOFC 작동온도에서 높은 전기전도도를 나타낸다. LCCO 연결재를 1300, 1400 및 $1500^{\circ}C$에서 합성을 진행하였을 때 출발원료로 $CaCO_3$를 $CaF_2$로 대체하였을 때의 소결특성을 평가하였고, SEM과 XRD분석을 통하여 균질하고 결정성이 우수한 분말이 합성된 것을 확인하였고 DC impedance analyzer를 사용하여 전기전도도를 측정하였다. TMA를 사용하여 열팽창계수를 측정한 결과 YSZ(${\sim}10.8{\times}10^{-6}/^{\circ}C$)와 동일한 값을 나타내었다.

• Proceedings of the Acoustical Society of Korea Conference
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• 1993.06a
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• pp.195-198
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• 1993

해수의 물리적 성질 변화에 의한 수중음속 변화는 수중음파 전파에 커다란 영향을 미친다. 매질변동에 의한 음파 전파경로 변동특성, 즉 음파 도달시간 변동에 의한 매질변위량 추정으로 해양을 탐사하는“해양음향 토모그라피”를 운용하기 위하여 비균질 매질에서의 음파 전파경로 파악이 우선이다. 수심이 일정한 비균질한 매질에서의 음파 전파경로를 파악하기 위해 파동방정식의 해를 Ray theory에 의거 ray path를 구하고 송,수신기 사이를 연결하는 eigenray 정보를 얻었다. 음원의 주파수가 400Hz($\pm$25Hz), pulse length가 20ms인 LFM pulse를 사용하였다. 이 음원을 동해의 최소음속층에서 송,수신하였을 경우 음원에서 150Km 떨어진 수신기에 도달한 신호는 평균음속분포 일 때 보다 약 66ms 정도 빨리 도착한다. 또한 Eigenray 정보에 의거 모의된 수신신호는 토모그라피 운용을 위한 필수 조건인 ray path의 식별, 안정성, 그리고 분해능을 만족한다. 또한 모의 수신신호 음파 도달시간 변동 분석으로 송,수신기 사이의 매질 변동을 파악 할 수 있다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.1
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• pp.1-8
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• 2003

Topology optimization has been evolved into a very efficient conceptual design tool and has been utilized into design engineering processes. Traditional topology optimization has been using homogenization method and optimality criteria method. homogenization method provides relationship equation between structure which includes many holes and stiffness matrix in FEM. Optimality criteria method is used to update design variables while maintaining that volume fraction is uniform. Traditional topology optimization has advantage of good convergence but has disadvantage of too much convergency time. In one way to solve this problem, element removal method using the criterion of an average stress is presented. As the result of examples, it is certified that convergency time is very reduced.

• The Journal of Engineering Geology
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• v.14 no.1
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• pp.93-104
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• 2004

This paper intended to assess the hydro-structure characteristics of volcanic rocks based on the hydrogeological data obtained from the underground storage cavern during construction. The variation of groundwater levels was periodically measured from the 28 surface monitoring holes(NX size) and the hydraulic pressures and injection rates were daily monitored from the water curtain holes(95 horizontal holes and 63 vertical holes). The hydraulic interference tests were performed in whole water curtain holes. The distribution patterns of hydraulic pressure are closely related to the dip angles of fracture intersected to the water curtain holes. Three domains can be grouped by the distribution of hydraulic pressures in the horizontal water curtain holes. The initial hydraulic pressures measured immediately after drilling of water crutain holes are high in ascending order of the cavern C-2, C-1, and C-3. The priliminary hydrochemical data also indicate that the portions of the deep groundwater composition is relatively great in the cavern C-3 area. Some of the horizontal water curtain holes in the cavern C-3 show a steady higher groundwater pressure with the composition of shallow groundwater indicating the outer boundary as constant hydraulic boundary. The water curtain holes in the cavern C-2 is characterized as low initial hydraulic pressure and less injection rates, suggesting poor hydraulic connectivity to a shallow groundwater system. The results of the study can help to understand a hydraulic compartment concept in a fracture hydro-geology and be utilized during the surface investigation for a groundwater system.

• Economic and Environmental Geology
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• v.39 no.5 s.180
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• pp.525-535
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• 2006

A study on stream-groundwater exchange was performed using head and temperature data of stream water, streambed, and groundwater. Groundwater level and temperature were obtained from multi-depth monitoring wells in small-scale watershed. During the summer and winter season, time series of temperature data at streambed and groundwater were monitored for six months. In the winter time, we measured the temperature gradient between stream water and streambed. The observed data showed three typical types of temperature characteristics. First, the temperature of streambed was lower than that of stream water; second, the temperature of streambed and stream water was similar; and the last, the temperature of streambed was higher than that of stream water. The interconnections between the stream and the streambed were not homogeneously distributed due to weakly developed sediments and heterogeneous bedrock exposed as bed of the stream. The temperature data may be used in formal solutions of the inverse problems to estimate groundwater flow and hydraulic conductivity.