• Journal of Korean Society of Environmental Engineers
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• v.33 no.7
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• pp.501-510
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• 2011

In this study, water pollution sources of 14 major tributaries of Han river and characteristics of water quality for each target streams were evaluated based on water quality data in 2007.1-2009.12 (14 data sets) using a statistical package, SPSS-17.0. Cluster analysis over time and space for each stream resulted in 4 groups for the spatial variations in which type and density of pollution sources in the basins showed the greatest impact on grouping. Moreover, cluster analysis for the time variation in which rainfall, temperature and eutrophication were shown to contribute to the clustering, produced 2 groups, from summer to fall (July-Oct.) and from winter to early summer (Nov.-June). Four factors were found as responsible for the data structure explaining 71-90% of the total variance of the data set depending on the streams and they were organic matter, nutrients, bacterial contamination. Factor analysis showed main factors (water pollutants) changed according to the season with different pattern for each stream. This study demonstrated that water quality of each stream could produce useful outcomes when factor and pollution source of basin were evaluated together.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.11 no.2
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• pp.10-20
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• 2012

This study shows how to estimate AADT(Annual Average Daily Traffic) on temporary count data using new grouping method. This study deals with clustering permanent traffic counts using monthly adjustment factor, daily adjustment factor and a percentage of hourly volume. This study uses a percentage of hourly volume comparing with other studies. Cluster analysis is used and 5 groups is suitable. First, make average of monthly adjustment factor, average of daily adjustment factor, a percentage of hourly volume for each group. Next estimate AADT using 24 hour volume(not holiday) and two adjustment factors. Goodness of fit test is used to find what groups are applicable. MAPE(Mean Absolute Percentage Error) is 8.7% in this method. It is under 1.5% comparing with other method(using adjustment factors in same section). This method is better than other studies because it can apply all temporary counts data.

• The Korean Journal of Applied Statistics
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• v.29 no.6
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• pp.1025-1039
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• 2016

We introduce various methods to investigate the relations between innovation of technology and social changes by analyzing more than 4 millions of patents registered at United States Patent and Trademark Office(USPTO) from year 1985 to 2015. First, we review the history of patent law and its relation with the quantitative changes of registered patents. Second, we investigate the differences of technical innovations of several countries by use of cluster analysis based on the numbers of registered patents at several technical sectors. Third, we introduce the PageRank algorithm to define important nodes in network type data and apply the PageRank algorithm to find important technical sectors based on citation information between registered patents. Finally, we explain how to use the canonical correlation analysis to study relationship between technical innovation and social changes.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.547-547
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• 2015

본 연구에서는 달천구간 (괴산댐~송동보)에서 어류 군집 (Fish Community)을 고려한 생태학적 최적유량 (Ecological Optimum Discharge)을 산정하였다. 이를 위해 유량증진방법론(IFIM: Instream Flow Incremental Methodology)을 기반으로 한 2차원 모형인 River-2D를 적용하여 수리해석 및 대상어종 (Target Fishes)에 대한 가중가용면적 (WUA: Weighted Usable Area)을 산정하였다. 모형 검증을 위해 김원 등 (2007)에 의해 수행된 과업구간 내 수위 및 유량 모니터링 자료를 활용하였으며, 하류경계조건은 김지성 등 (2007)에 의한 수위-유량 관계곡선식을 활용하였다. 또한 평저류량 조건에서의 조도높이 (Roughness Height) 산정을 위해 유량 및 하상재료의 영향을 고려할 수 있는 멱함수 및 반대수함수 형태의 조도계수 공식을 적용하였다. 모형검증 결과 River-2D에 의해 계산된 수위값이 모니터링값과 비교적 잘 일치함을 알 수 있었다. 대상유역에 대한 어류 모니터링 (에코리버21사업단, 2007~2010) 결과를 바탕으로, 과업지역내 우점종 (피라미), 아우점종 (쉬리 등 3개 어종), 멸종위기어종 (묵납자루)을 대상어종으로 선정하였으며, 대상어종에 대한 서식도적합도지수 (HSI, Habitat Suitability Index) 산정을 위해 IFASG (Instream Flow and Aquatic Systems Group) 방법 및 WDWF (Washington Department of Fish and Wildlife) 방법을 적용하였다. 수심, 유속, 하상재료 및 하상형상에 대한 서식도적합도지수가 5가지 대상어종에 대해 각각 산정되었으며, 복합적합도지수 (CSI : Combined Suitability Index)를 고려한 과업대상 위치별 어류의 발생확률이 모의되었다. 어류 군집에 대한 가중가용면적 (WUA)이 최대로 되는 생태학적 최적유량 산정 결과, Type I~III의 경우 모두 $10m^3/s$ 이하의 유량조건에 대해서 WUA가 최대값을 갖는 것을 확인할 수 있었으며, 납자루속의 어류 (Type III)의 WUA가 000 및 000속 (Type II)의 어류에 비해서 작은 유량에서 더 큰 값을 갖으며, $10m^3/$s 초과 유량에 대해서는 반대의 경향이 나타나는 것을 확인할 수 있었다.

• The Journal of the Korea Contents Association
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• v.21 no.7
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• pp.558-566
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• 2021

This study was conducted to classify college students using games based on the stress, satisfaction and balance of basic psychological needs and to identify how gaming behaviors differ according to the divided clusters. This study used data of 447 college students who used games with the support of JangHoon Scholarship Foundation. As a result, the college students using games were divided into four groups with different characteristics according to stress, satisfaction and balance of basic psychological needs. Also, the level of gaming behavior was different according to the degree of satisfaction of basic psychological needs. The lower the stress and the higher the balance when the level of satisfaction was similar, the lower the level of gaming behaviors was. This study confirmed the importance of satisfactory balance of basic psychological needs as well as satisfaction, and supported the biopsychological perspective by suggesting that there are significant differences in gaming behavior according to clusters.

• The Korean Journal of Applied Statistics
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• v.32 no.3
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• pp.331-348
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• 2019

Understanding the tumor heterogeneity due to differences in the growth pattern of metastatic tumors and rate of change is important for understanding the sensitivity of tumor cells to drugs and finding appropriate therapies. It is often possible to test for differences in population means using t-test or ANOVA when the group of N samples is distinct. However, these statistical methods can not be used unless the groups are distinguished as the data covered in this paper. Statistical methods have been studied to test heterogeneity between samples. The minimum combination t-test method is one of them. In this paper, we propose a maximum combinatorial t-test method that takes into account combinations that bisect data at different ratios. Also we propose a method based on the idea that examining the heterogeneity of a sample is equivalent to testing whether the number of optimal clusters is one in the cluster analysis. We verified that the proposed methods, maximum combination t-test method and gap statistic, have better type-I error and power than the previously proposed method based on simulation study and obtained the results through real data analysis.

• Journal of the Korean Society for Library and Information Science
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• v.55 no.2
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• pp.147-178
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• 2021

In this study, co-word analysis was conducted to investigate the intellectual structure of the domestic open access area. Through KCI and RISS, 124 research articles related to open access in Korea were selected for analysis, and a total of 1,157 keywords were extracted from the title and abstract. Network analysis was performed on the selected keywords. As a result, 3 domains and 20 clusters were extracted, and intellectual relations among keywords from open access area were visualized through PFnet. The centrality analysis of weighted networks was used to identify the core keywords in this area. Finally, 5 clusters from cluster analysis were displayed on a multidimensional scaling map, and the intellectual structure was proposed based on the correlation between keywords. The results of this study can visually identify and can be used as basic data for predicting the future direction of open access research in Korea.

• Korean Journal of Ecology and Environment
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• v.55 no.4
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• pp.259-273
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• 2022

Interactions between species in a community are very complex, and they are visualized and analyzed through a food web in simple way. Food web is a network of species connected by trophic links showing energy flow from prey to predator. Various models were developed to characterize the food web in ecosystems. In this study, we classified food web models to static models such as Ecopath and dynamic models such as AQUATOX. We presented characteristics of several different types of food web models in each category, and reviewed their applications used in aquatic ecosystems. Finally, we presented issues to be considered to develop food web models.

• The Journal of Society for e-Business Studies
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• v.27 no.2
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• pp.21-36
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• 2022

Recently, as COVID-19 has made the e-commerce market expand widely, customers who have different consumption patterns appear in the market. Because companies can obtain opinions and information of customers from reviews, they increasingly face the requirements of managing customer reviews on online platform. In this study, we analyze customers and carry out market segmentation for classifying and defining type of customers in e-commerce. Specifically, K-means clustering was conducted on customer review data collected from Wemakeprice online shopping platform, which leads to the result that six clusters were derived. Finally, we define the characteristics of each cluster and propose a customer management plan. This paper is possible to be used as materials which identify types of customers and it can reduce the cost of customer management and make a profit for online platforms.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.32-32
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• 2020

하나의 수계 또는 용수구역 내에서 작물생육기간 동안 지하수자원 수요량의 집중적인 증가로 인해 지역적 지하수 고갈이 발생하여 농작물 피해가 발생하고 있으며 과잉양수로 인한 지하수위 하강으로 사용자간 갈등도 빈번하다. 또한, 기후변화로 인해 극한기후인 가뭄의 잦은 발생은 이러한 현상을 가속화 한다. 지하수 산출성이 좋은 대수층의 공간적 분포는 복잡한 지질구조로 인해 균일하지 않으며 같은 대수층 내에서도 양수 위치에 따라 산출성은 다르게 나타난다. 이러한 지하수 수요와 공급 및 대수층 분포로 인한 지하수자원 불균형의 해소를 위해 지하수가 풍부한 지역에서 부족한 지역으로 지하수를 공급하는 방법을 적용할 수 있다. 이때 기술적용 지역의 지하수 사용 상황 및 공급 가능량을 정량적으로 평가하고 이를 기반으로 지하수 공급을 제어하는 것이 매우 중요하다. 지하수자원의 수요-공급 불균형이 발생할 때 즉각적으로 대응하기 위해서는 실시간으로 지하수 현황을 감시하고 이를 기반으로 공급 가능량을 산정할 필요가 있으며 이는 정보통신기술(Information and Communication Technology, ICT)에 기반한 관정연계관리체계(Well Network System, WNS)를 구성하는 기술 중 하나인 관정군집제어 기술로 구현될 수 있다. 수계 내에 설치된 기존의 양수정과 새롭게 추가된 관측정들을 4G LTE 네트워크를 통해 하나의 관정군으로 묶고 중앙 서버를 통한 자료 분석 및 양수 펌프 제어를 통해 대수층의 공급 능력과 사용자의 수요 현황에 따른 지하수자원의 체계적 분배를 구현하고자 하였다. 관정군집제어는 관정별 지하수위 및 양수정 양수량을 실시간으로 관측하고 이를 분석서버에 전송하여 해당 지하수계의 공급 가능량 및 인접관정 간섭 등을 분석하여 양수정의 펌프를 실시간으로 제어하고 양수된 지하수를 수요 지역으로 이송한다. 본 연구를 통해 관정군집제어 기술의 구현에 필요한 구성요소를 정의하고 이에 대한 구현 방법을 기술하여 WNS를 구성하는 하나의 요소기술 모델로 제시하고자 하였다.