• Journal of Wetlands Research
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• v.21 no.spc
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• pp.61-68
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• 2019

Recently, climate indices represented by quantifying atmospheric-ocean circulation patterns have been widely used to predict hydrologic variables for considering long-term climate variability. Hydrologic forecasting models based on artificial neural networks have been developed to provide accurate and stable forecasting performance. Forecasts of hydrologic variables considering climate variability can be effectively used for long-term management of water resources and environmental preservation. Therefore, identifying significant indicators for hydrologic variables and applying forecasting models still remains as a challenge. In this study, we selected representative climate indices that have significant relationships with dam inflow time series in the Han-River basin, South Korea for applying the dam inflow forecasting model. For this purpose, the ensemble empirical mode decomposition(EEMD) method was used to identify a significance between dam inflow and climate indices and an artificial neural network(ANN) ensemble model was applied to overcome the limitation of a single ANN model. As a result, the forecasting performances showed that the mean correlation coefficient of the five dams in the training period is 0.88, and the test period is 0.68. It can be expected to come out various applications using the relationship between hydrologic variables and climate variability in South Korea.

• Journal of Chest Surgery
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• v.31 no.12
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• pp.1165-1171
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• 1998

Background: All currently available mechanical and bioprosthetic valves are associated with various types of deterioration leading to dysfunction and/or valvular complications. Reoperation on prosthetic heart valves is increasingly under consideration for both clinical and prophylactic indications. This review was conducted to determine the factors affecting the risk of reoperation for prosthetic valve replacement. Material and method: From January 1985 to July 1996, 124 patients underwent reoperation on prosthetic heart valves, and 3 patients had a second valve reoperation. The causes of reoperation were prosthetic valve failure(96 cases, 77.4%), prosthetic valve thrombosis(16 cases, 12.9%), prosthetic valve endocarditis(7 cases, 5.6%) and paravalvular leak(5 cases, 4.1%). This article is based on the analysis of the experience with particular emphasis on the preoperative risks affecting the outcome of the reoperation. Result: Overall hospital mortality rate was 8.9%(11/124). Low cardiac output was the most common cause of death(70.6%). Left ventricular systolic dimension(p=0.001), New York Heart Association functional class IV(p=0.003) and serum creatinine level(p=0.007) were the independent risk factors, but age, sex and cardiothoracic ratio did not have any influence on the operative mortality. Follow-up period was ranged from 3 to 141 months (mean, 50.6 months). A late mortality rate was 1.8%. Conclusion: The surgical risk of reoperation on heart valve prostheses in the advanced NYHA class patients is higher, therefore reoperation is recommended before the hemodynamic impairment become severe.

• Journal of Korea Water Resources Association
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• v.51 no.3
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• pp.273-280
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• 2018

Accurate estimation of evapotranspiration is mightily important for understanding and analyzing the hydrological cycle. There are various methods for estimating evapotranspiration and each method has its own advantages and limitations. Therefore, it is necessary to develop an optimal evapotranspiration product by combing different evapotranspiration products. In this study, we developed an optimal evapotranspiration by fusing two satellite- and model-based evapotranspiration estimates, including revised remote sensing-based Penman-Monteith (RS-PM) and Modified Satellite-Based Priestley-Taylor (MS-PT) methods, Global Land Data Assimilation System (GLDAS), and Global Land Evaporation Amsterdam Model (GLEAM). The statistical analysis (i.e., correlation coefficients, index of agreement, MAE, and RMSE) of combined evapotranspiration product showed to be improved compared to the individual model results. After confirming the overall results, in future studies, advanced data fusion techniques will be used to obtained improved results.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.212-216
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• 2011

현재 하천 건천화에 따른 수생태계 교란 및 수질악화 등의 근본적인 문제가 발생하고 있으며, 최근 정부의 저탄소 녹색성장기조에 따라 조성되고 있는 신도시, 소규모 및 대규모 택지개발사업의 경우는 환경 친화적인 단지조성 요구에 부응하기 위해 기존 도심하천의 복원 및 인공하천의 녹색성장을 고려한 친환경적 생태하천으로 조성하고자 하는 다양한 노력이 시도되고 있으나 안정적인 생태복원의 수원확보 방안을 마련하지 못해 실제 설계가 반영되지 못하고 있다. 또한, 조성하고자 하는 소하천 혹은 실개울 등의 수질보전 및 생태계 보호 등 하천이 본래의 기능을 유지할 수 있도록 생태하천유량을 확보하는 다양한 기술들이 개발되어 있지만, 공사 유형과 주변 환경에 적합한 생태하천유량 확보 방안을 선정할 수 있는 비구조적 대책마련이 부족한 실정이다. 이러한 실정과 문제점을 고려해 볼 때, 조성하고자 하는 도시 내 자연하천 및 인공하천 조성 등 수변환경을 고려한 단지조성에 맞는 생태하천유량 확보 방안 및 평가에 대한 연구가 단계적으로 이루어져야 할 것이다. 따라서 본 연구에서는 생태하천유량 확보와 하천수질 개선이 필요한 특정 지역 또는 다양한 유형의 공사 지구 내 하천이 정상적인 기능을 수행할 수 있도록 적용 가능한 생태하천유량 확보 방안들과 수리해석 모델인 HEC-RAS(River Analysis System), 생태하천유량 산정 모델인 PHABSIM(Physical HABitat SIMulation)을 연계한 물리서식처 평가 모듈을 개발하고, 이를 기초로 가중치부여매트릭스 평가(국토해양부, 2006) 기법을 적용한 최적의 생태하천유량 확보 방안과 수질개선 방안을 제시해 줄 수 있는 의사결정지원 시스템을 구축 하고자 한다. 본 연구에서 개발된 최적의 생태하천유량 확보 방안 도출을 위한 의사결정지원 시스템의 활용으로 필요유량은 물론, 기준을 만족하는 수질의 확보가 절실히 요구되는 중 소규모 하천에 실질적으로 적정수질의 생태하천유량을 확보함으로서 하천으로서의 역할을 위한 본 기능의 회복과 동시에 소하천, 도심하천 및 인공하천 등 중 소규모 수계의 수문순환을 정상화하여 하천의 지속 가능한 개발과 관리가 효율적으로 이루어지도록 하는데 이용될 수 있을 것으로 예상되어진다.

• Journal of Biomedical Engineering Research
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• v.19 no.3
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• pp.297-303
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• 1998

The sinus distal to the prosthetic heart valve influences the valve closure behavior and velocity field near the valve, therefore affects the hydrodynamic performance of the prosthetic heart valve. In order to study the effects of valve distal geometry on the hydrodynamic performance of the prosthetic valves, mechanical bileaflet valve(SJMV), monoleaflet polymer valve(MLPV) and trileaflet polymer valve(FTPV) are inserted in the test sections which have the straight and the sinus shape distal to the valve. Leakage volumes and systolic mean pressure drops are measured in the pulsatile mock circulation flow loop. Leakage volumes are slightly less and systolic mean pressure drops are higher in the sinus test section comparing to those in the straight test section, but the differences are statistically insignificant. Flow waveforms are analyzed in order to predict the valve closure behavior. The distal sinus does not affect the closure of the MLPV, but early valve closure of SJMV is observed in the sinus test section. This effect is more significant in FTPV, and the reverse flow peak of FTPV is reduced in the sinus test section. Therefore the sinus distal to the valve can reduce the reverse flow jet caused by sudden valve closure.

• Journal of Biomedical Engineering Research
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• v.10 no.2
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• pp.139-150
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• 1989

A new motor-driven blood pump for artificial heart was developed. In this blood pump, a small size, high torque brushless DC motor was used as an energy converter and the motor rolls back and forth on a circular track. This movement of the "rolling-cyliner" causes blood ejection by alternately pushing left or right polyurethane blood sacs. This moving-actuator mechanism could be eliminate two potential problems of other motor-driven artificial hearts such as large size and poor anastomosis for the implantation. Theoretical analyses on the pump efficiency, the temperature rise, and the inflow mechanism were also performed. In a series of mock circulation tests, the theoretical analyses were compared to the measured hemodynamic and mechanical values. The pump system was shown to have sufficient cardiac output (upto 9 L/min), sensitivity to preload, and mechanical stability to be tested as an implantable total artificial heart.ial heart.

• Journal of the Korea Convergence Society
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• v.6 no.2
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• pp.25-30
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• 2015

The purpose of this study was to analyze the factors that affects the participating in a smoking cessation program. Data were from the A Study on the Seoul Welfare Panel Study 2010. Subjects were 1,326 smokers aged 19 and older living in the community. Dependent variable was defined as experience of smoking cessation. Explanatory variables were included as age, gender, level of education, employment status, household income, marital status, drinking, self-reported health status, depression, disease, and physical activity. A prediction model was developed by the use of a Decision Tree and Neural Network Algorithm. In the Prediction model, self reported health status, disease, income, household income were significantly associated with participating in a smoking cessation program. Based this study, systematic education and development of programs are required.

• International Journal of Highway Engineering
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• v.9 no.4
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• pp.45-54
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• 2007

This study was carried out for developing artificial short-term aging(SA) and long-term aging(LA) methods of asphalt mixtures in which the aging level is properly matched with those of RTFO and PAV aged binders, respectively. The specimens were made of the short-term aged loose asphalt mixture which was kept in a convection oven at $154^{\circ}C$ for 2 hours and were aged at $110^{\circ}C$ for 24, 48, 72 and 96 hours for SA. Large molecular size(LMS) were measured using GPC after SA and LA to evaluate aging extents of each mixture with aging time. It is shown that the LMS was increased with aging time increment and that from the LMS(%) change ratio, it was possible to suggest an appropriate artificial aging time which is corresponding level of aging with RTFO and PAV. It was found that SA was somewhat strong and LA for 48 hours at $110^{\circ}C$ would be appropriate if sort-term aging is properly controlled.

• Journal of Biomedical Engineering Research
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• v.24 no.4
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• pp.301-307
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• 2003

In this study, we Presented computational results on the blood flow in the sac of the Korean artificial heart. Two dimensional unsteady flow was assumed and we utilized a finite element commercial code ADINA to simulate the blood flow. Rigid body-solid contact were considered between the actuator and the blood sac and fluid-structure interaction between the blood and the sac. The three geometric models proposed in the design process were simulated to assess the hemodynamic characteristics of the models According to the computational results, a strong flow to the outlet and a stagnated flow region near the inlet were observed during systole. The sac was filled with blood and recirculating flow was generated near the outlet during diastole. Shear stress during systole had its extreme values near the outlet edge whereas the magnitude of shear stress values were relative)v high near the inlet edge and the contacting surface with the actuator.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.494-494
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• 2017

국내의 호소는 대부분이 농업용수 공급을 목적으로 설치된 인공 호소이다. 최근 이상기후 및 유역 오염원 증가로 호소의 수질오염도가 증가 추이에 있으며, 특히 하절기 외기온도 상승과 함께 녹조 대량발생, 어류 집단폐사 등 수질오염사고가 야기되고 있다. 이러한 수질오염사고는 호소의 지역적 특성으로 인한 여러 가지 원인이 있겠지만 직접적인 원인으로는 호소의 산소 고갈에 기인된다. 본 연구에서는 농업용 호소의 수온, DO, EC 등에 대한 일주기 및 계절적 동적변화를 규명하여 호소의 수질개선대책수립에 활용하고자 하였다. 연구대상 지구는 경기도 시흥시에 소재하고 있는 M 농업용 저수지이며, 2015년 6월 4일부터 9월 22일까지 수온, DO, EC을 측정할 수 있는 연속 자동측정장치를 설치하였고, 측정지점은 저수지 수심을 상(바닥층에서 1.5m 상부), 중(바닥층에서 1.0m 상부), 하(바닥층에서 0.5m 상부)로 구분하여 각각 측정하였다. 호소의 수온은 일주기로 수온성층 형성과 대류혼합이 반복되었으며, 상 하층간의 수온 차이가 평균 $1.4^{\circ}C$, 최대 $5.0^{\circ}C$의 차이를 보였다. 또한 강우가 발생한 이후에는 일시적으로 저수지 상 하 층간 수온 차이가 거의 없는 것으로 나타났는데, 이는 강우에 의한 수체의 수직혼합으로 저수지 전체의 물질순환에 영향을 미친 것으로 판단된다. 호내 DO 농도는 일(day) 주기 동안 농도변화가 크게 나타났으며, 여름철 무강우 기간에는 저수지 바닥층의 평균 DO 농도가 약 0.5mg/L로 거의 무산소 상태가 지속되는 것으로 관측되었다. DO는 기온이 낮아지거나 강수가 발생할 때 대류에 의한 수직혼합에 의해 간헐적으로 회복되다가 다시 고갈되는 현상이 반복되는 것으로 나타났다.