• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.310-310
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• 2019

본 연구에서는 기상청 ASOS(종관기상관측장비) 자료와 통계적 기반의 다중회귀분석모형을 이용하여 경안천 유역에 대한 봄철 강수량(3~5월 누적강수량)의 예측성을 평가하였다. 예측대상기간은 2006~2018년이며 예측인자로서 전국 96개 지점의 ASOS 자료 중 35개 기상요소에 대한 월 자료를 활용하였다. 전망기간(1~12개월)에 따라 강수량 기준 최소 1개월에서 최대 24개월까지의 지체시간을 고려하여 1~24개월 선행 ASOS 기상자료와 강수량 사이의 상관성을 분석하였다. 예측대상년도를 기준으로 과거 40년간의 자료를 이용하여 상관성 분석을 수행하였으며, 상관성이 높은 상위 30개 기상인자를 조합하여 다중회귀분석모형의 예측인자(독립변수)로 활용하였다. 예측대상년도와 전망기간에 따라 최적의 예측인자를 조합하고, 교차검증을 통하여 각각 4,000개의 다중회귀모형을 도출하여 예측범위를 산출하였다. 다중회귀모형에 의한 예측범위를 분석한 결과, 2013년 자료까지는 예측범위가 관측값을 잘 포함하고 예측값의 평균이나 중간값이 관측값과 유사하게 나타난 반면, 2014년부터는 전망기간에 따라 관측값과 예측범위의 차이가 크게 나타나는 경우도 있었다. 예측치의 중간값을 기준으로 3분위(평년 이상, 평년 수준, 평년 이하) 적중률을 분석하면, 2006~2013년에 대해서는 58.3%인 반면, 2014~2018년에 대해서는 11.2% 수준으로 나타났다.

• Proceedings of the Korean Association of Geographic Inforamtion Studies Conference
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• 2010.09a
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• pp.134-141
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• 2010

임분 단위의 재적 및 생체량은 LiDAR 자료의 높이 분포변수들로부터 추정될 수 있다. LiDAR 자료의 높이 분포변수들은 재적을 측정하는 임분고(stand height)와 임분평균 지하고(mean crown base height), 그리고 수관형태에 따른 평균수관장(mean crown depth) 등의 변수와 직 간접적인 연관성이 있다. 그러므로, 본 연구에서는 잣나무림의 샘플지역에서 반사된 LiDAR 자료의 높이분포변수를 이용하여 임분단위의 수간재적을 추정한 다음, 앞 세부연구에서 수행한 방법을 이용하여 임분의 생체량을 추정하였다. 변수는 임분 내에서 반사되는 LiDAR 자료의 평균높이, 최대 최소높이, 높이값들의 표준편차, 변이계수, 첨도, 왜도, 식생반사비율, 10분위 높이자료와 강도데이터의 기술통계량 등을 사용하였다. 그리고, 최종적인 임분수간재적은 다중회귀분석을 통하여 수행되었다. 다중회귀분석을 통하여 각 변수들은 임분수간재적과 가장 관련있는 2~3개의 변수들로 추려졌으며, 추정된 회귀식의 결정계수는 0.66으로 분석되었다. 또한 유보표본을 이용하여 검증한 결과의 결정계수는 0.59로 분석되어 LiDAR 자료의 높이분포변수들은 임분의 재적을 비교적 잘 설명할 수 있음이 밝혀졌다.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.232-232
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• 2022

1차원 관망해석모형과 2차원 지표면범람 해석모형을 이용한 도시지역의 실시간 홍수예·경보시스템 구축은 모형의 모의에 많은 시간이 소요되므로 한계가 있다. 또한, 연구유역에서 시나리오 강우에 대해 침수를 유발시키는 한계강우량을 1-2차원 모형의 시행착오법을 적용한 반복적인 수행을 통해 산정하는 것은 비효율적인 방법이다. 따라서, 본 연구에서는 이에 대한 해결책으로 로지스틱 회귀를 이용하여 배수분구별 침수 발생기준 강우량을 산정하고자 한다. 침수 발생 한계강우량 산정을 배수분구 단위로 제시하기 위하여 로지스틱 회귀분석을 이용하였다. 풍수해저감종합계획(2015)과 침수흔적도를 이용하여 배수분구 별 침수이력에 대한 데이터베이스를 구축하고, 이를 1-2차원 수리해석을 통한 침수심과 함께 로지스틱 회귀모형에 학습하였다. 지속시간 1시간, 10mm 강우부터 500년 빈도의 Huff 3분위 시나리오 17개를 사용하여 확률강우량을 산정하였고, 이를 1-2차원 수리해석을 위한 입력자료로 사용하였다. EPA-SWMM을 통한 1차원 도시유출해석과 FLO-2D를 통한 2차원 침수해석에서 20cm 이상의 침수심이 발생하거나 지상관측자료, 침수흔적도 및 풍수해저감종합계획에서 실제 침수가 발생했을 경우를 1, 그렇지 않은 경우를 0으로 하여 데이터베이스를 구축하여 로지스틱 회귀모형에 학습시켜 침수 발생 한계강우량을 산정하였다. 로지스틱 회귀분석을 통해 서울시 지역의 배수분구별 한계강우량을 산정할 수 있으며, 지속적으로 관측되는 강우 및 침수 발생 유무 자료를 추가함으로써 산정된 침수 한계강우량을 상회하는 강우 사상이 나타났을 시에 침수 발생 유무를 확인하여 본 연구에서 제안한 방법에 대해 검증이 가능할 것으로 보인다.

• Journal of Cadastre & Land InformatiX
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• v.50 no.2
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• pp.133-153
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• 2020

Officially assessed land price has been the index of South Korea since 1989 throughout different sectors of tax and welfare. Officially assessed land price is used as a tax valuation for the tax on property holdings, and the equity of such is the most important factor in the fair taxation for the people of South Korea. On this wise, this research analyzed and verified the horizontal and vertical inequity of officially assessed land price in Seoul by using the real transaction data between 2016 and 2018. In fact, Seoul's assessment ratio for the entire three-year period was 60.64% and it showed to increase each year. Horizontal equity was found to be most favorable in 2017, and the horizontal equity of each borough of Seoul appeared to improve each year. Vertical inequity was found to have reverse inequality in most boroughs of Seoul, however, some parts of Gangnam districts such as Gangnam-gu, Seocho-gu, and Gangdong-gu presented progressive inequality. Such example showed the need for improvement in terms of balance by each borough. The use of quantile regression demonstrated reverse inequality in most quantile, but, the differences in the value of the coefficient by each quantile showed the need for improvement of officially assessed land price with the equity of each quantile. Through the equity verification of officially assessed land price, it was analyzed that the lack of equity was found by year, by borough, and by use district. In order to redeem the lack of equity, the government must systematically supplement the real-estate disclosure system by initiating ratio studies to verify horizontal and vertical equity.

• Journal of the Korea Institute of Building Construction
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• v.9 no.6
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• pp.141-149
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• 2009

The objective of this study was to propose a development length equation for bottom and top GFRP bars. Including the bottom and top GRPP bars, a total of 104 modified pullout tests were completed. The test variables were embedment length (15, 30, 45db), net cover thickness (0.5~2.0db), different GFRP bar types, and bar diameters (10, 13, 16mm). The average bond stresses were determined based on the modified pullout test results. Two variable linear regression analyses were performed on the results of the average bond stresses. Utilizing the 5% fractile concept, a conservative development length design equation was derived. The design equation of the development length for bottom and top GFRP bars was proposed and the design equation derived in this study was compared to the ACI 440.1R-06 committee equation.

• Journal of vocational education research
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• v.37 no.4
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• pp.45-66
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• 2018

The purpose of this study is to explore the factors affecting the social capital of youth and to draw implications for the policies related to development of the social capital of them. To this end, we utilized the OLS regression model and the quantile regression model exploiting the 12th year dataset of the Korean Education & Employment Panel(KEEP). First, this study shows that the effect on trust is higher than that of the counterpart when the case is a) unmarried, b) with the high level of education, c) with a large asset, d) with high self-respect and the satisfaction for financial situation, and e) social media user. On the other hand, the higher the monthly average income, the lower the trust level. In addition, when the cases are grouped into 25 quantile, 50 quantile, and 75 quantile according to the level of trust, it is revealed empirically that the factors affecting social capital formation are somewhat different. Second, this study also shows that the effect is higher in a specific condition. The effect is higher compared to the counterpart when the case is a) male, b) with children, c) metropolitan city resident, d) non-employee, e) with a large asset, f) with high level of happiness, g) with high expense of purchasing books, and h) social media user. As a result, it is found that there are no personal characteristics that have statistically significant influence on students belonging to the 25th quantile of social capital. This study suggests that, in order to support the formation of social capital of Korean youths, it is necessary to enhance their psychological satisfaction and to provide cultural support or policies. In addition, it suggests that a tailored social capital accumulation program is needed according to the level of social capital, and the support for this need to be changed according to the amount of social capital of young people.

• The Korean Journal of Applied Statistics
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• v.29 no.5
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• pp.773-786
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• 2016

Multiple quantile regression that simultaneously estimate several conditional quantiles of response given covariates can provide a comprehensive information about the relationship between the response and covariates. Some quantile estimates can cross if conditional quantiles are separately estimated; however, this violates the definition of the quantile. To tackle this issue, multiple quantile regression with non-crossing constraints have been developed. In this paper, we carry out a comparison study on several popular methods for non-crossing multiple linear quantile regression to provide practical guidance on its application.

• Journal of Korea Technology Innovation Society
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• v.21 no.3
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• pp.1077-1100
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• 2018

The present study analyzed the effect of firms' external research and development (R&D) on corporate productivity, while investigating the moderating effect of firm size on the external R&D-productivity nexus. In the empirical analysis, we estimated South Korean manufacturing firms' total factor productivity (TFP) using the firm level data drawn from the Survey of Business Activities (Korea National Statistical Office) for the years 2006-2015. Thereafter, focusing on the role of external R&D and its interaction with the firm size in determining firms' TFP, the productivity function was estimated as well. To this end, we used ordinary least squares (OLS) and quantile regression to highlight the heterogeneous impacts of external R&D by companies' productivity level. Empirical results confirmed that firms' external R&D significantly enhanced corporate productivity in all manufacturing industries, from high-tech to low-tech. The moderating effect of firm size in determining the productivity effect of external R&D was not as prominent as in the case for internal R&D, which exhibited some degree of the size premium in the productivity-enhancing effect. These results suggest that regardless of the firm size, external R&D can be an important channel for corporate productivity improvement, and can be a particularly effective strategy for SMEs with relatively limited internal R&D capacities.

• Journal of Korea Water Resources Association
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• v.54 no.5
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• pp.311-320
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• 2021

The agricultural water, which occupy about 61% of total water usage in the South Korea, is significantly objective to archieve effecitive water resources management. The objective of the study is to suggest a simple method in actual practice that could be used to estimate agricultural water usage in river considering hydrological condition. Historical record of agricultural water usage and runoff, which take account for hydrological condition of the basin, were obtained for totally 27 river basins. As the result, the high threshold value of the agricultural water usage rates compared to maximum usage amount has a particular correlations to the percent of normal year runoff for last 2 month, and threshold line of agricultural water usage rates was derived using the quantile regressions. Finally, two dimensionless threshold line and empirical formulas that described the correlation between the percent of normal year runoff for last 2 month and the agricultural water usage rate compared to maximum usage amount were derived. Also, the simple criteria to select which line and formula based on the characteristics of the basins was suggested but it need further studies. The result of the study could be used as an elemantary data in actual practice for water resoureces management.

• Journal of Labour Economics
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• v.33 no.1
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• pp.1-30
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• 2010

Using the College Scholastic Ability Test of year 1995, the paper investigates effects of classroom peers on a student's test scores. It exploits exogenous assignment of students across different classrooms within a school under the leveling policy in 1990s. The empirical results reveal strong impacts of peers on individual students. Negative effects of low-performing peers exceed positive effects of high-performing peers. Such a structure of peer interactions has important implications for ability grouping vs. mixing debates in Korea.