• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.1
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• pp.131-140
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• 1993

The major objective of this study is to develop practical methods for estimating sediment yield rates of medium size watersheds of which areas range from 200 to $2,000km^2$ In the first phase of the study that were presented in the companion paper followed by this paper, a methodology for estimating sediment yield rate was introduced and a total of 13 data points including eight sampled river-sediment data and five reservoir deposit data were collected. In this study, a three-parameter empirical model and a six-parameter rating model, both of which are based on empiricism, have been developed. By limited comparisons, the models developed in this study appear to be more reliable and applicable than the existing ones. According to the sediment yield data collected and the estimations by the models, meanwhile, the lowest value for the sediment yield rate of medium size watersheds in Korea is estimated to be about $100tons/km^2/yr$, and the maximum to be about $1,000tons/km^2/yr$.

• The Journal of Korean Association of Computer Education
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• v.18 no.4
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• pp.55-62
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• 2015

Recommender systems through collaborative filtering has been utilized successfully in various areas by providing with convenience in searching information. Measuring similarity is critical in determining performance of these systems, because it is the criteria for the range of recommenders. This study analyzes distributions of similarity from traditional measures and investigates relations between similarities and the number of co-rated items. With this, this study suggests a method for selecting reliable recommenders by restricting similarities, which compensates for the drawbacks of previous measures. Experimental results showed that restricting similarities of neighbors by upper and lower thresholds yield superior performance than previous methods, especially when consulting fewer nearest neighbors. Maximum improvement of 0.047 for cosine similarity and that of 0.03 for Pearson was achieved. This result tells that a collaborative filtering system using Pearson or cosine similarities should not consult neighbors with very high or low similarities.

• The Korean Journal of Applied Statistics
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• v.20 no.1
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• pp.1-9
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• 2007

This investigation on the change of the daily maxima temperature in Seoul, Daegu, Chunchen, Youngchen was triggered by news items such as the earth is getting warmer and a recent news item that said that Korea is getting warmer due to this climatic change. A statistical analysis on the daily maxima for June over this period in Seoul revealed a positive trend of 1.1190 centigrade over the 45 years, a change of 0.0249 degrees annually. Due to the large variation on these maximum temperatures, one can raise the question on the significance of this increase. To check the goodness of fit of the proposed extreme value model, we shown a Q-Q plot of the observed quantiles against the simulated quantiles and a probability plot. And we calculated statistics each month and a tolerance limit. This is tested through simulating a large number of similar datasets from an Extreme Value distribution which described the observed data very well. Only 0.02% of the simulated datasets showed an increase of this degrees or larger, meaning that the probability is very low for such an event to occur.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.4
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• pp.243-250
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• 2001

This paper presents the structure of a $\mu$Spring package, its fabrication process and an analysis of its electrical characteristics compared to that of a $\mu$BGA. It was found that both $\mu$BGA and $\mu$Spring packages provide with outstanding high speed signal transmission characteristics due to their lower inductance of package interconnection lines, smaller than half of inductance of TSOP package lines. Even the worst case substrate trace of a Rambus DRAM $\mu$Spring package yields the line inductance of 2.9nH, which provides with 25% margin compared to the Rambus DRAM specification of 4nH. The fabrication cost of $\mu$Spring package is lower than that of $\mu$BGA by 50%, passes 1000 thermal cycles, meets JEDEC Level 1 specification whereas $\mu$BGA does not, and thereby yields high reliability and strong competing power.

• The Journal of Korean Academic Society of Nursing Education
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• v.13 no.1
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• pp.95-104
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• 2007

연구목적: 고혈압환자의 효과적인 자가관리 간호중재를 개발하는데 필요한 기초자료로 혈압자가측정(self-monitoring of blood pressure)에 대한 특성, 장점, 범위 및 제한점을 파악한다. 연구방법: 1996년부터 2005년까지 PubMed에 수록된 고혈압환자의 자가관리 방법중 혈압자가측정방법이 포함된 외국의 연구를 중심으로 체계적인 고찰을 실시하였다. 전체 69개 자가관리방법을 적용한 논문 중에서 혈압자가측정이나 가정에서의 혈압측정(home monitoring)에 대한 45개 논문을 선정하여 분석하였다. 연구결과 전반적으로 혈압자가측정 방법은 고혈압환자의 혈압조절을 향상시키는 효과가 유의한 것으로 나타났다. 환자가 혈압을 자가측정한 방법에서 평균 혈압, 수축기 혈압, 맥압이 유의하게 감소한 것으로 보고되었다. 장기적 프로그램에서 혈압조절율이 향상되거나, 이완기혈압의 감소효과도 보고되었다. 혈압자가측정의 기준치는 연구마다 일치하지는 않았지만 135/85mmHg 수준이 정상혈압의 상한수준으로 제시되었다. 일부 연구에서는 가정 내 혈압측정이 24시간혈압측정을 대체하는 방법으로 추천되었다. 보다 정확한 혈압자가측정을 위해서 신뢰성 있는 혈압측정기구의 사용과 정확한 측정방법이 환자들에게 교육될 필요가 있다. 결론: 혈압자가측정은 고혈압환자의 혈압조절에 유용한 방법으로 고찰되었다. 또한 고혈압의 진단, 혈압치료와 고혈압 약물복용 행위를 향상시키는 교육적 효과도 긍정적으로 나타났다. 따라서 고혈압환자를 위한 효과적인 자기조절프로그램에 혈압자가측정법을 포함하는 것이 추천되며, 추후 한국에서 시도된 관련 연구에 관한 문헌고찰의 비교연구가 필요하다.

• Journal of the Korean Institute of Intelligent Systems
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• v.18 no.4
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• pp.445-450
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• 2008

In order to analyze the reliabilities of the fuzzy systems, the reliabilities of the components in the fuzzy systems are represented by real values between zero and one, fuzzy numbers, intervals of confidence, vague sets, interval valued fuzzy sets, etc in the conventional researches. In this paper, we propose a method to represent and analyze the reliabilities of the fuzzy systems based on the interval valued vague sets defined in the universe of discourse [0, 1]. In the interval valued vague sets, the upper bounds and the lower bounds of the conventional vague sets[12, 14] are represented as the intervals. Therefore, it can allow the reliabilities of a fuzzy system to represent and analyze in a more flexible manner. Because the proposed method uses the simplified arithmetic operations of the fuzzy triangular numbers rather than the complicated of the fuzzy trapezoidal numbers mentioned by Kumar[14], the execution of the proposed method is faster than the one.

• Proceedings of the Korea Information Processing Society Conference
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• 2021.05a
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• pp.293-296
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• 2021

K-water에서는 다목적댐의 관리를 위해 실시간으로 댐수위, 하천 수위 및 강우량 등을 계측하고 있으며, 계측된 값들은 댐을 효과적으로 운영하는데 필요한 데이터로 활용되고 있다. 특히 댐수위 이상 데이터를 탐지하지 못한 채 그대로 사용할 경우 댐의 방류 시기와 방류량 등을 결정하는 중요한 의사결정을 그르칠 수 있으므로 이를 신속히 탐지하는 것이 매우 중요하다. 현재의 자동화된 이상 데이터 탐지방법 중 하나는 현재 데이터가 최댓값과 최솟값을 초과할 때, 다른 하나는 현재 데이터와 일정 시간 동안의 평균값 간의 차이가 관리자가 정한 특정 값을 벗어났을 때를 기준으로 삼고 있다. 전자는 상한과 하한의 초과 여부만 판단하므로 탐지가 쉬우나 정상범위 내에서 발생한 이상 데이터는 탐지가 불가하다. 후자는 관리자의 경험을 통해 판단 조건을 정하기 때문에 객관성이 결여되는 문제가 있다. 특히 방류와 강우가 복합적으로 댐수위에 영향을 미치는 홍수기에 관리자의 경험에 기초한 이상 데이터 판별은 신뢰성의 문제가 있을 수 있다. 따라서 본 연구에서는 기계학습을 최초로 적용하여 이상 데이터를 탐지하고자 하였다. 댐수위, 누적강우량 및 누적방류량 데이터와 댐수위데이터를 가공하여 생성한 댐수위차, 댐수위차평균, 댐수위평균 등 자질들의 다양한 조합을 만든 후 이를 Random Forest, SVM, AdaptiveBoost 및 다층퍼셉트론(MLP) 등과 같은 여러 가지 기계학습모델 등을 통해 이상 데이터를 판별하는 실험(분류)을 하였다. 실험결과 댐수위, 댐수위차, 댐수위-댐수위평균, 누적강우량, 누적방류량 및 댐수위차평균을 사용하였을 때 MLP에서 가장 우수한 성능을 보였다. 이 연구를 통해서 댐수위 이상 데이터를 기계학습의 분류기능을 통해 효과적으로 탐지할 수 있다는 것과 모델의 성능은 실험에 사용한 자질의 수뿐 아니라 자질의 종류에도 큰 영향을 받는다는 것을 알 수 있었다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.2
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• pp.101-108
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• 2016

In designing of the wind power facilities, the highest and lowest astronomical tides (HAT and LAT) are needed in terms of an international design tidal water levels. The AHHW and ALLW, however, have been used as the design tidal levels in Korea. The HAT and LAT in the Wido coastal sea should be estimated to satisfy the standard because the pilot wind power facilities will be located in the adjacent Wido coastal sea. In this study, the HAT and LAT are estimated using the 31-years hourly tidal elevation data of the Wido tidal gauging station and the nodal variation patterns of the major lunar components, such as $M_2$, $O_1$, and $K_1$, are analysed to check the expected long-term lunar cycle, i.e., 18.61-year's nodal variation patterns. The temporal amplitude variations of the $M_2$, $O_1$, and $K_1$ clearly show the 18.61-years periodic patterns in case of the no-nodal correction condition. In addition, the suggested HAT and LAT elevations, estimated as the upper and lower confidence limits of the yearly HAT and LAT elevations, show 40 cm greater than AHHW and 35 cm lower than ALLW, respectively.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.2
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• pp.127-140
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• 2015

A fault is one of the critical factors that may lead to a possible ground collapse occurring in construction site. A fault core, however, possibly acting as a failure plane in whole fault zone, is composed of fractured rock and gouge nonuniformly distributed and thus can be characterized by its wide range of shear strength which is generally acquired by experimental method for stability analysis. In this study, we performed direct shear test and grain size distribution analysis for 62 fault core samples cropped from 12 different spots located in the vicinity of Kyongju and Ulsan, Korea. As a result, the range of shear strength representing the characteristics of fault cores in the study regions is determined with regard to vertical stress using a regression analysis for experiment data. The weight ratio of gravels in the samples is proportional to the shear strength and that of silt and clay is in inverse proportion to the shear strength. For most samples, the coefficient of determination is over 0.7 despite of inhomogeneity of them and consequently we determined the lower limit and upper limit of the shear strength with regard to the weight ratio by setting the confidence interval of 95%.

• Journal of Korea Water Resources Association
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• v.41 no.9
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• pp.943-958
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• 2008

This study employs Bayesian regression analysis for fitting discharge rating curves. The parameter estimates using the Bayesian regression analysis were compared to ordinary least square method using the t-distribution. In these comparisons, the mean values from the t-distribution and the Bayesian regression are not significantly different. However, the difference between upper and lower limits are remarkably reduced with the Bayesian regression. Therefore, from the point of view of uncertainty analysis, the Bayesian regression is more attractive than the conventional method based on a t-distribution because the data size at the site of interest is typically insufficient to estimate the parameters in rating curve. The merits and demerits of the two types of estimation methods are analyzed through the statistical simulation considering heteroscedasticity. The validation of the Bayesian regression is also performed using real stage-discharge data which were observed at 5 gauges on the Anyangcheon basin. Because the true parameters at 5 gauges are unknown, the quantitative accuracy of the Bayesian regression can not be assessed. However, it can be suggested that the uncertainty in rating curves at 5 gauges be reduced by Bayesian regression.