• Journal of Korean Society on Water Environment
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• v.26 no.1
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• pp.61-70
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• 2010

The increase of impervious cover (IC) in a watershed is known as an important factor causing alteration of water cycle, deterioration of water quality and biological communities of urban streams. The study objective was to assess the impact of IC changes on the surface runoff characteristics of Kap Stream basin located in Geum river basin (Korea) using the Storm Water Management Model (SWMM). SWMM was calibrated and verified using the flow data observed at outlet of the watershed with 8 days interval in 2007 and 2008. According to the analysis of Landsat satellite imagery data every 5 years from 1975 to 2000, the IC of the watershed has linearly increased from 4.9% to 10.5% during last 25 years. The validated model was applied to simulate the runoff flow rates from the watershed with different IC rates every five years using the climate forcing data of 2007 and 2008. The simulation results indicated that the increase of IC area in the watershed has resulted in the increase of peak runoff and reduction of travel time during flood events. The flood flow ($Q_{95}$) and normal flow ($Q_{180}$) rates of Kap Stream increased with the IC rate. However, the low flow ($Q_{275}$) and drought flow ($Q_{355}$) rates showed no significant difference. Thus the subsurface flow simulation algorithm of the model needs to be revisited for better assessment of the impact of impervious cover on the long-term runoff process.

• Journal of Environmental Impact Assessment
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• v.19 no.1
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• pp.99-106
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• 2010

The project of Cheonggyecheon revived the 5.8 kilometer stream and it removed the cover of stream and Cheonggye elevated road. It was begin October of 2003 and completed October of 2005. The purpose of this study is to analyze the air pollution change of Cheonggyecheon area and neighboring area from before and after the project. The change of concentration is compared with an air monitoring station data and measurement data. The analyzed pollutants are $NO_2$, $PM_{10}$, heavy metal, VOC which are measured at Cheonggyecheon and neighboring area. As the results, $NO_2$ concentration shows 10 % decreases in Cheonggyecheon area and neighboring area shows 16 % decreases by Chenoggyecheon restoration, and $PM_{10}$ concentration shows 15 % decreases in Cheonggyecheon area and neighboring area shows 16 % increases. One of VOC, benzene is increased in Cheonggyecheon area compared with neighboring area but Toluene, Ethylbenzene, m+p Xylene increased in neighboring area. After the Cheonggyecheon restoration, The heavy metals are not shows the improvement, but $PM_{10}$ and $NO_2$ concentration improved more than the changes of neighboring area. These improvements of pollution due to reduction of transportation and clearing of elevated road by Cheonggyecheon restoration project.

• Proceedings of the Korean Information Science Society Conference
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• 2006.10c
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• pp.28-32
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• 2006

유비쿼터스(Ubiquitous)환경과 같이 외부로부터 입력되는 데이터가 stream의 형식으로 실시간으로 들어오고, 입력의 끝을 알 수 없는 환경에서는 기존의 join방식으로는 문제를 해결 할 수 없다. 또한 이러한 환경 하에서는 데이터의 크기나 특성이 모두 다르고 네트워크 상태에 따라 입력이 많은 영향을 받게 된다. 이런 stream환경의 join연산을 위하여 double pipelined hash join, Xjoin, Pjoin등 많은 알고리즘이 기존의 연구를 대표하여 왔다. 그 중 Xjoin은 symmetric hash join과 hybrid hash join의 특징들을 이용해서 들어오는 data의 흐름에 따라서 reactive하게 join과정을 조절함으로써 streaming data에 대한 join을 수행한다. 그러나 여러 단계의 수행에 따른 연산의 중복결과를 체크하기 위한 overhead로 인해 성능이 떨어진다. 이 논문에서는 이러한 점을 개선하기 위해서 Xjoin의 수행과정을 수정한 방법을 제시할 것이다. 각 partition마다 구분자만을 추가함으로써 간단하게 중복을 만들어내지 않는 방법을 제안하고 불필요한 연산과 I/O를 줄일 수 있도록 partition선택방법을 추가할 것이다. 이를 통해서 중복된 연산인지 체크하는 과정을 상당히 단순화함으로써 좀 더 좋은 성능을 가지게 될 것이고 또한 timestamp를 저장해야 하는 overhead를 줄여서 전체 연산에 필요한 저장 공간을 절약할 수 있다.

• Journal of The Korean Society of Agricultural Engineers
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• v.56 no.5
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• pp.21-27
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• 2014

Sediment-laden water is problematic in aquatic ecosystem and for hydraulic structures in a watershed, and agriculture area in a watershed is one of source areas of nonpoint source (NPS), since soil surface typically exposures due to agricultural activities. Especially, severe sediment might flow into stream when agricultural area is located near stream like the Imha-dam watershed. Soil erosion is affected by precipitation, therefore there is a need to consider precipitation characteristics in soil erosion and best management practices (BMPs) simulation. The Web-based Spreadsheet Tool for the Estimation of Pollutant Load (STEPL WEB) allows estimating long-term sediment loads and the impact of best management practices to reduce sediment loads. STEPL WEB and predicted precipitation data by MIROC-ESM model was used to estimate sediment loads and its reduction by filter strip and conversion of agricultural area to forest in the future 30 years. The result indicates that approximately 70 % of agricultural area requires filter strip installation or that approximately 50 % of agricultural area needs to be converted to forest, for 41 % of sediment load reduction.

• Journal of Korea Water Resources Association
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• v.42 no.11
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• pp.921-931
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• 2009

For the assessment of climate change impacts for the Byeongseong stream, CGCM 3.1 T63 is selected as future climate information. The projections come from CGCM used to simulate the GHG emission scenario known as A2. Air temperature and precipitation information from the GCM simulations are converted to regional scale data using the statistical downscaling method known as MSPG. Downscaled climate data from GCM are then used as the input data for the SWAT model to generate regional runoff and water quality estimates in the Byeongseong stream. As a result of simple sensitivity analysis, the increase of CO2 concentration leads to increase water yield through reduction of evapotranspiration and increase of soil water. Hydrologic responses to climate change are in phase with precipitation change. Climate change is expected to reduce water yields in the period of 2021-2030. In the period of 2051-2060, stream flow is expected to be reduced in spring season and increased in summer season. While soil losses are also in phase with water yields, nutrient discharges (i.e., total nitrogen) are not always in phase with precipitation change. However, it should be noted that there are a lot of uncertainties in such multiple-step analysis used to convert climate information from GCM-based future climate projections into hydrologic information.

• Journal of Korean Society for Geospatial Information Science
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• v.6 no.1 s.11
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• pp.75-90
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• 1998

In this study, as a method for management of waterquality in stream, we build a database on a environmental information such as a pollution source, a waterquality. And especially, we simulate the BOD concentration which is a index indicate the status of organic pollution in stream. Also This study purposes not only building a database on all sorts of envirnomental data, but also searching, statistic and analysis of the database. The result of this study enables us to see and understand contamination state in stream esaily, so it can help to enhance the attention. Also, we can quickly know study area and the degree of effects when water contamination occurs abruptly. And also, we can compare and know pollution source state and the pollutant load among districts. It is expected to use it as an auxiliary basis when we make a policy about pollutant load reduction, because we can know the extent of the pollution in strean by each a pollution source.

• Journal of Korea Water Resources Association
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• v.30 no.6
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• pp.621-628
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• 1997

Excavation works on stream beds have been done for various reasons including aggregate collection, sediment dredging, bridge constructions, or laying pipes under the ground. These activities may cause significant loadings of SS (suspended solids) resulting in water pollution and other detrimental effects to the surrounding environment. This research investigates application potential of a fickian diffustion model, derived from two dimensional advection-diffusion equation through some simplifying assumptions, as a planning tool for the estimation of SS loadings from excavation works and evaluation fo pollution prevention measures in case that sophisticated numerical simulation models are not applicable due to various practical reasons. Through a case study of the Juncheon stream in the Donghae City on the Kangwondo Province, this study demonstrates applicability of the fickian diffustion model as a practical method for the preliminary estimation of Ss loadings from excavation works and evaluation of performance of fabrics made of synthetic fiber for the reduction of downstream SS concentration with deficient field data.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.2
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• pp.304-309
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• 2004

Recently, the needs for multimedia stream such as digital audio and video in the Internet has increased tremendously. Unlike TCP, the UDP protocol, which has been used to transmit streaming traffic thorough the Internet, does not apply any congestion control mechanism to regulate the data flow thorough the shared network And it leads to congestion collapse of the Internet and results in long-term transmission delay. To avoid any adverse effect on the current Internet functionality, a now protocol of modification or addition of some functionality to perform congestion control and to reduce huge transmission delay in transmitting of multimedia stream are in study. TCP-friendly congestion control mechanism is classified into two : one is window-based congestion control scheme using general window management functionalities, the other is rate-based congestion control scheme using TCP modeling equation. In this paper, we propose an algorithm for improving the transmitting rate on a hybrid TCP-friendly congestion control scheme combined with widow-based and late-based congestion control for multimedia stream. And we also simulate the performance of improved TEAR implementation using NS. With He simulation results, we show that the improved TEAR can provide better fairness and lower rate fluctuations than TCP.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.51-56
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• 2006

Biases embedded in numerical weather precipitation forecasts by the RDAPS model was determined, quantified and corrected. The ultimate objective is to eventually enhance the reliability of reservoir operation by Korean Water Resources Corporation (KOWACO), which is based on precipitation-driven forecasts of stream flow. Statistical post-processing, so called MOS (Model Output Statistics) was applied to RDAPS to improve their performance. The Artificial Neural Nwetwork (ANN) model was applied for 4 cases of 'Probability of Precipitation (PoP) for wet and dry season' and 'Quantitative Precipitation Forecasts (QPF) for wet and dry season'. The reduction on the large systematic bias was especially remarkable. The performance of both networks may be improved by retraining, probably every month. In addition, it is expected that performance of the networks will improve once atmospheric profile data are incorporated in the analysis. The key to the optimal performance of ANN is to have a large data set relevant to the predictand variable. The more complex the process to be modeled by the ANN, the larger the data set needs to be.

• 대한공업교육학회지
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• v.32 no.2
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• pp.199-216
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• 2007

Stream Control Transmission Protocol(SCTP) is a transport layer protocol to support the data transmission. SCTP is similar to Transmission Control Protocol(TCP) in a variety of aspects. However, several features of SCTP including multi-homing and multi-streaming incur the performance difference from TCP. This paper highlights the data transfer during the initial slow start phase in SCTP congestion control composed of slow start phase and congestion avoidance phase. In order to compare the mean transfer time between SCTP and TCP, we experiment with different performance parameters including bandwidth, round trip time, and data length. By varying data length, we also measure the corresponding initial window size, which is one of factors affecting the mean transfer time. For the experiment, we have written server and client applications by C language using SCTP socket API and have measured the transfer time by ethereal program. We transferred data between client and server using round-robin method. Analysis of these experimental results from the testbed implementation shows that larger initial window size of SCTP than that of TCP brings the reduction in the mean transfer time of SCTP compared with TCP by 15 % on average during the initial slow start phase.