• Journal of Korea Port Economic Association
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• v.23 no.2
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• pp.109-120
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• 2007

The purpose of this paper is to verify the two problems(normalization for the different inputs and outputs data, translation invariant for the negative data) which will be occurred in measuring the seaport DEA(data envelopment analysis) efficiency. The main result is as follow: Normalization and translation invariant in the BCC model for measuring the seaport efficiency by using 26 Korean seaport data in 1995 with two inputs(berthing capacity, cargo handling capacity) and three outputs(import cargo throughput, export cargo throughput, number of ship calls) was verified. The main policy implication of this paper is that the port management authority should collect the more specific data and publish these data on the inputs and outputs in the seaports with consideration of negative(ex. accident numbers in each seaport) and positive value for analyzing the efficiency by the scholars, because normalization and translation invariant in the data was verified.

• Journal of Korea Water Resources Association
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• v.56 no.12
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• pp.871-881
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• 2023

This study investigates the geomorphic changes and Bed Relief Index of the river downstream of the Yeongju Dam by Nays2DH, a two-dimensional numerical model, in order to grasp the dynamics of the downstream river while applying various flow patterns such as pulse discharge. It shows that the geomorphic and the bed elevations changes are the largest under the condition of the normalized pulse discharge. The total change in the riverbed is 29.88 m for uniform flow, 27.46 m for normalized hydrograph, 29.63 m for pulse flow and 31.87 m for pulse flow with normalized hydrograph which result in the largest variation in scour and deposition. The Bed Relief Index (BRI) increases with time under conditions of uniform flow, pulse flow and pulse flow with normalized hydrograph. However, BRI increased rapidly until 30 hrs after the peak flow (14 hrs), but decreased from 56 hrs under the condition of normalized hydrograph. Therefore, the condition of normalized hydrograph gives greater dynamics than the condition of a single flood or constant flow, and the dynamics increase downstream than upstream, resulting in an effect on improving the environment of the river downstream of the dam.

• The Korean Journal of Financial Management
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• v.7 no.1
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• pp.1-20
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• 1990

In most of studies on market efficiency, the stability of risk measures and the normality of residuals unexplained by the pricing model are presumed. This paper re-examines stock splits, taking the possible violation of two assumptions into accounts. The results does not change the previous studies. But, the size of excess returns during the 2-week period before announcements decreases by 43%. The results also support that betas change around announcements and the serial autocorrelation of residuals is caused by events. Based on the results, the existing excess returns are most likely explained as a compensation to old shareholders for unwanted risk increases in their portfolio, or by uses of incorrect betas in testing models. In addition, the model suggested in the paper provides a measure for the speed of adjustment of the market to the new information arrival and the intensity of information contents.

• Journal of Gifted/Talented Education
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• v.24 no.4
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• pp.657-677
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• 2014

Considering the expansion of gifted education and the quantitative increase the Gifted Science Academy, it is important to seek the appropriate methods of mathematics teaching for gifted high school students. In particular, to reflect current trends in mathematics education that the mathematical creativity is being presented as an important educational goal, Now is the time we need student-centered discussion model for regular mathematics classes, not teacher-centered instruction in the way of knowledge transfer. In this study, class model of preparation-based discussion was designed and applied to the regular mathematics classes for the Science Academy. Students participating in this research had a lot of pressure in preparation activities for discussion, but they said that the discussion compared to traditional lecture was mathematically meaningful experience. These findings suggest the implication that class model of preparation-based discussion can be meaningfully applied to the regular mathematics class.

• The Korean Journal of Applied Statistics
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• v.33 no.4
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• pp.379-393
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• 2020

A terminal event such as death may censor an intermediate event such as relapse, but not vice versa in semi-competing risks data, which is often seen in medicine, public health, and epidemiology. We propose a Weibull regression model with a normal frailty to analyze semi-competing risks data when all three transition times of the illness-death model are possibly interval-censored. We construct the conditional likelihood separately depending on the types of subjects: still alive with or without the intermediate event, dead with or without the intermediate event, and dead with the intermediate event missing. Optimal parameter estimates are obtained from the iterative quasi-Newton algorithm after the marginalization of the full likelihood using the adaptive importance sampling. We illustrate the proposed method with extensive simulation studies and PAQUID (Personnes Agées Quid) data.

• The Korean Journal of Applied Statistics
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• v.16 no.1
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• pp.101-115
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• 2003

Lately there has been much theoretical and applied interest in linear models with non-normal heavy tailed error distributions. Starting Zellner(1976)'s study, many authors have explored the consequences of non-normality and heavy-tailed error distributions. We consider hierarchical models including selection models under a skewed heavy-tailed e..o. distribution proposed originally by Chen, Dey and Shao(1999) and Branco and Dey(2001) with Dirichlet process prior(Ferguson, 1973) in order to use a meta-analysis. A general calss of skewed elliptical distribution is reviewed and developed. Also, we consider the detail computational scheme under skew normal and skew t distribution using MCMC method. Finally, we introduce one example from Johnson(1993)'s real data and apply our proposed methodology.

• Journal of the Korean Data and Information Science Society
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• v.21 no.6
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• pp.1031-1039
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• 2010

The decathlon is an athletic event consisting of ten track and field events. Events are held over two consecutive days and the winners are determined by the combined performance in all. Performance is judged in meters, centimeters, minutes, and seconds. However, how to convert results into points is a difficult and controversial issue. We explored the distribution of decathlon results from the 1991 to 2009 using top 200 decathlons in the Olympic games and word championships. The conclusion is that the results from top level decathlon competition are normally distributed, and the current scoring system does not have the property that the performance with same difficulty should get same points. A new model for evaluating the decathlon score has been applied that display uniform characteristics over all events in order to meet the notion of allroundness. The proposed model is uniform over the events and support self-stabilization.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.264-264
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• 2019

개수로 흐름 해석을 위해 수치모형을 적용할 때 반드시 거쳐야 하는 과정이 격자망을 구성하는 일이다. 불규칙한 형상의 자연수로를 모의할 때 격자망 생성은 쉬운 일이 아니며, 따라서 가시적으로 격자망 생성을 돕고, 격자망의 수정도 용이한 도구가 요구된다. 따라서 본 연구에서는 수심적분된 흐름방정식을 지배방정식으로 하여 개수로 흐름 해석을 용이하게 하고자 그래픽 사용자 인터페이스(GUI)를 개발하였으며, 이를 소개하고자 한다. 격자망은 기본적으로 사각형과 삼각형 요소로 구성될 수 있으며, 유한차분모형 등에서는 정형사각형 격자망을, 유한요소모형에서는 비정형 사각형 및 삼각형 격자망 또는 혼합망을 생성시킬 수 있다. 이산점(scatter points)이나 절점(node points)을 생성하거나 기존의 자료를 불러들여 삼각망 또는 사각망을 형성시킬 수 있으며, 연속선(polylines)을 작성하여 형성된 폐다각형(polygones)을 이용하여 정규 또는 비정규의 삼각망 또는 사각망을 형성시킬 수 있다. 또한 두 점사이를 선형 또는 반원 형태로 편향 정도(biased value)를 설정하여 원하는 개수만큼 나눌 수 있도록 하여, 보다 효율적인 격자형성이 가능토록 하였다. 기존 상용 프로그램에서 작성된 격자를 불러들여 활용 가능하며, 백그라운드 이미지로 지형도나 위성사진을 띄어놓고 이미지 상에서 격자를 형성할 수도 있다. 기본적으로 마우스를 이용하여 화면의 이동, 확대 및 축소와 점, 선, 요소의 생성 및 선택이 가능하다. 본 프로그램은 Qt와 modern OpenGL을 바탕으로 제작되었으며, 마이크로소프트사의 windows 뿐만 아니라 Mac OS, Linux 버전의 설치 파일 작성이 가능하다.

• The Korean Journal of Applied Statistics
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• v.15 no.1
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• pp.73-84
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• 2002

Linear regression models with inequality constraints on the coefficients are frequently used in economic models due to sign or order constraints on the coefficients. In this paper, we propose a Bayesian approach to selecting significant explanatory variables in linear regression models with inequality constraints on the coefficients. Bayesian variable selection requires computation of posterior probability of each candidate model. We propose a method which computes all the necessary posterior model probabilities simultaneously. In specific, we obtain posterior samples form the most general model via Gibbs sampling algorithm (Gelfand and Smith, 1990) and compute the posterior probabilities by using the samples. A real example is given to illustrate the method.

• Journal of the Korean Data and Information Science Society
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• v.5 no.2
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• pp.45-57
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• 1994

이 연구에서는 Hjort(1991)에의해 제안된 누적위험률함수의 비모수적 추정량을 이용하여 무한인 구간까지 정의된 평균잔여수명함수의 추정량을 제안하고 제안된 추정량의 일치성과 점근적 정규성을 밝히고, 모의실험을 통하여 다른 추정량들과 비교하고자 한다.