• 통합자연과학논문집
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• 제13권1호
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• pp.27-33
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• 2020

The unsustainable human activities like increased use of automobiles, heavy industrialization and the use of large volumes of fertilizers, chemicals and pesticides in the agricultural land cause climate change problems in one way or another. Under normal circumstances, the heat radiations from the sun will be reflected back. An excessive volume of GHGs in the atmosphere would prevent these radiations from reflecting back. East Asia is facing severe climate change issues in recent times. A lot of climate change problems such as hurricanes and floods have been reported from this region in the last couple of decades. The study aimed at investigating the climate change in East Asia with changing Sea Surface Temperature (SST). The study adopted a quantitative research method with a case study research design where a deliberate focus was made on the East Asia Region. Secondary data was gathered and analyzed to yield both descriptive and inferential statistics. The study concluded that the impact of East Asia Climate variability was significant mainly for some extreme events. Also, the study concluded that there was a significant link between the change of the East Asia climate variability and that of the sea surface temperature. Further, the study concluded that a linear relationship existed between the sea surface temperature and the climate of East Asia. Hence, a linear regression was a significant predictor of the East Asia Climate (EAC) based on changing sea surface temperature. The model revealed that 37.4% of the variations in the climate change index were explained by the changes in the sea surface temperature. The climate was expected to change with a value of 49.48 for a unit change in the sea surface temperature.

• 한국산림과학회지
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• 제90권6호
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• pp.683-691
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• 2001

산림의 수원함양기능 지표로서 표층토양에서의 조공극률(組孔隙率)(pF2.7)에 영향하는 인자를 밝히기 위해 1995년 3월부터 10월까지 전국의 활엽수림 표본조사구를 대상으로 입지, 토양, 임분환경인자 등 총 24종에 대하여 spss/pc+를 이용하여 상관 분석하였다. 표층토양에서의 조공극률에 영향을 미치는 인자는 B층 토양에서의 조공극률, 하층식생 피복도, 표층 토양의 유기물함량비, F층 두께 등 4개 인자가 유의한 정(正)의 상관관계를, 표층토양의 견밀도, 10cm 깊이의 토양견밀도가 각각 5%, 1% 수준에서 유의한 부(負)의 상관관계를 나타내었다. Stepwise를 이용한 다중회귀분석결과 산림의 수원함양기능 증대에 영향하는 표층토양에서의 조공극률에 영향하는 인자는 B층 토양에서의 조공극률, 유기물함량비 등 2개 인자이었다.

• 한국수자원학회논문집
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• 제57권2호
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• pp.139-150
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• 2024

본 연구에서는 물리 기반 증발량 경험식인 Penman 혼합식(Penman combination equation, PCE)과 경험적인 바람 함수(Penman wind function, PWF)를 이용한 저수지 증발량 추정 방법을 제시하였다. 용담댐 시험유역에서 2016-2018년 기간의 실측 증발량 자료를 이용하여 두 가지 경험식에 매개변수를 추정하고 적용성을 검토하였다. 용담댐 시험유역 중 덕유산 플럭스 타워에서 PWF와 PCE에 대해 증발량을 평가한 결과, PWF 방법이 상관성 측면에서 더욱 개선된 결과를 보여주었지만, 두 가지 방법 모두 과대 추정 현상을 나타내었다. 용담호 수면 위에서 관측된 기상자료를 활용하여 PWF 방법을 통한 증발량을 평가하였으며, 관측 수면증발량과 통계적 지표 및 시각적 평가에서 우수한 성능을 확인하였다. 향후 본 연구를 통해 산정된 매개변수를 이용하여 저수지 수면 증발량을 간접적으로 추정할 수 있을 것으로 판단되나, 정확한 저수지 수면증발량 추정을 위해서는 타 댐들에 수면 증발량을 종합적으로 연계한 지역화 연구도 필요할 것으로 판단된다.

• Korean Chemical Engineering Research
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• 제52권5호
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• pp.564-573
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• 2014

이 연구는 벤젠과 프로필렌의 기상반응을 통해 쿠멘을 생산하는 쿠멘 생산 공정의 경제성 최적화에 대한 것이다. 최적화의 목적함수는 제품 판매 이득에서 자본비용, 유틸리티 비용, 원료 비용을 뺀 연간 조업이득이고, 설계변수는 6개이다. 설계변수의 변화에 따른 조업이득의 계산을 위해 Unisim Design과 Matlab을 연동하였다. 최적화는 3단계로 수행되었다. 설계변수를 샘플링한 후 조업이득 데이터를 얻고, 이 데이터로부터 설계변수와 조업이득의 관계를 추정 모델로 표현하고, 이 모델을 이용하여 최적화하였다. 추정모델로는 반응표면법에서 사용되는 2차 회귀 다항식과 비선형 모델인 support vector regression을 비교하였다. 설계변수의 샘플링 방법으로는 중심합성계획과 Hammersley 순차 추출법을 비교하였다. 각각 얻어진 모델을 이용한 최적화 결과, 추정방법으로는 SVR이, 샘플링 방법은 Hammersley 순차추출법이 더 정확하였다. 최적화된 조업이득은 연간 17.96 MM$로, 기준 조건에서의 연간 16.04 MM$에 비해 12% 증가하였다.

• 한국측량학회지
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• 제35권4호
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• pp.221-230
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• 2017

Demographic change was considered to be the most major driver of land use change although there were several interacting factors involved, especially in the developing countries. This paper presents an approach to predict the future land use change using a hybrid model. A hybrid model consisting of logistic regression model, Markov chain (MC), and cellular automata (CA) was designed to improve the performance of the standard logistic regression model. Experiment was conducted in Giao Thuy district, Nam Dinh Province, Vietnam. Demography and socio-economic variables dealing with urban sprawl were used to create a probability surface of spatio-temporal states of built-up land use for the years 2009, 2019, and 2029. The predicted land use maps for the years 2019 and 2029 show substantial urban development in the area, much of which are located in areas sensitive to source protections. It also showed that aquacultural land changes substantially in areas where are in the vicinity of estuary or near the sea dike. There was considerable variation between the communes; notably, communes with higher household density and higher proportion of people in working age have larger increases in aquacultural areas. The results of the analysis can provide valuable information for local planners and policy makers, assisting their efforts in constructing alternative sustainable urban development schemes and environmental management strategies.

• 한국도로학회논문집
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• 제16권5호
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• pp.59-66
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• 2014

PURPOSES : This study is to predict the Sound Pressure Level(SPL) obtained from the Noble Close ProXimity(NCPX) method by using the Extended Kalman Filter Algorithm employing the taylor series and Linear Regression Analysis based on the least square method. The objective of utilizing EKF Algorithm is to consider stochastically the effect of error because the Regression analysis is not the method for the statical approach. METHODS : For measuring the friction noise between the surface and vehicle's tire, NCPX method was used. With NCPX method, SPL can be obtained using the frequency analysis such as Discrete Fourier Transform(DFT), Fast Fourier Transform(FFT) and Constant Percentage Bandwidth(CPB) Analysis. In this research, CPB analysis was only conducted for deriving A-weighted SPL from the sound power level in terms of frequencies. EKF Algorithm and Regression analysis were performed for estimating the SPL regarding the vehicle velocities. RESULTS : The study has shown that the results related to the coefficient of determination and RMSE from EKF Algorithm have been improved by comparing to Regression analysis. CONCLUSIONS : The more the vehicle is fast, the more the SPL must be high. But in the results of EKF Algorithm, SPLs are irregular. The reason of that is the EKF algorithm can be reflected by the error covariance from the measurements.

• 한국항공우주학회지
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• 제34권5호
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• pp.30-38
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• 2006

기존의 전통적인 회귀분석 기반 교정방법에 비해 높은 교정정밀도를 얻을 수 있는 5-hole pressure probe의 교정방안을 연구하였다. 이 새로운 교정기법은 교정시험으로부터 획득한 데이터와 곡선적합 결과간의 차이를 이용하여 산정한 단일 영역에 대한 오차보간 반응곡면을 사용한다. 끝단의 직경이 4.0 mm인 5-hole probe를 자체 제작하고, 레이놀즈수$4.11{\times}10^6$/m와 흐름각 ${\pm}48$에서 교정시험을 수행하였다. 최소자승 회귀분석모델과 단일영역 오차보간 모델을 적용하여 자료처리를 수행하고 이들 두 교정방안에 대한 비교평가와 분석을 수행하였으며, 아울러 교정 정밀도에 대한 평가도 수행하였다.

• Structural Engineering and Mechanics
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• 제66권6호
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• pp.677-691
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• 2018

Reliability assessment of complex structures using simulation methods is time-consuming. Thus, surrogate models are usually employed to reduce computational cost. AK-MCS is a surrogate-based Active learning method combining Kriging and Monte-Carlo Simulation for structural reliability analysis. This paper proposes three modifications of the AK-MCS method to reduce the number of calls to the performance function. The first modification is related to the definition of an initial Design of Experiments (DoE). In the original AK-MCS method, an initial DoE is created by a random selection of samples among the Monte Carlo population. Therefore, samples in the failure region have fewer chances to be selected, because a small number of samples are usually located in the failure region compared to the safe region. The proposed method in this paper is based on a uniform selection of samples in the predefined domain, so more samples may be selected from the failure region. Another important parameter in the AK-MCS method is the size of the initial DoE. The algorithm may not predict the exact limit state surface with an insufficient number of initial samples. Thus, the second modification of the AK-MCS method is proposed to overcome this problem. The third modification is relevant to the type of regression trend in the AK-MCS method. The original AK-MCS method uses an ordinary Kriging model, so the regression part of Kriging model is an unknown constant value. In this paper, the effect of regression trend in the AK-MCS method is investigated for a benchmark problem, and it is shown that the appropriate choice of regression type could reduce the number of calls to the performance function. A stepwise approach is also presented to select a suitable trend of the Kriging model. The numerical results show the effectiveness of the proposed modifications.

• 한국수자원학회논문집
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• 제53권2호
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• pp.121-129
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• 2020

도시화로 인한 불투수층 증가와 하천 주변 개발은 홍수 시 위험에 노출되는 재해요인의 증가뿐 아니라 피해의 파급을 발생시켜 홍수 관리 측면에서 어려움을 낳는다. 홍수 방재대책을 위해서는 도시지역에 분포하는 다양한 지표면 공간특성을 반영하여 침수가 예상되는 지역에 대한 파악이 우선시되어야 한다. 본 연구에서는 도시하천의 홍수 위험지역을 대상으로 확률적 홍수위험 평가가 수행되었다. 홍수와 관련된 지형적 영향요인인 고도, 경사, 유출곡선지수, 하천까지 거리를 예측변수로 하여 하천 주변 침수 예상지역을 설명하기 위해 모형의 학습데이터로 100년 빈도 홍수위험 지도가 사용되었다. 연구 대상 지역은 격자로 변환하여 Bayesian Logistic 회귀분석을 수행하여 각 격자별로 홍수영향요인이 침수 여부를 설명하는 모형을 구축하였다. 최종적으로 모형을 통해 대상 지역 전체에 대하여 침수위험도를 확률적으로 제시하였다.

• Carbon letters
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• 제28권
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• pp.72-80
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• 2018

In this study, an empirical relationship between the energy band gap of multi-walled carbon nanotubes (MWCNTs) and synthesis parameters in a chemical vapor deposition (CVD) reactor using factorial design of experiment was established. A bimetallic (Fe-Ni) catalyst supported on $CaCO_3$ was synthesized via wet impregnation technique and used for MWCNT growth. The effects of synthesis parameters such as temperature, time, acetylene flow rate, and argon carrier gas flow rate on the MWCNTs energy gap, yield, and aspect ratio were investigated. The as-prepared supported bimetallic catalyst and the MWCNTs were characterized for their morphologies, microstructures, elemental composition, thermal profiles and surface areas by high-resolution scanning electron microscope, high resolution transmission electron microscope, energy dispersive X-ray spectroscopy, thermal gravimetry analysis and Brunauer-Emmett-Teller. A regression model was developed to establish the relationship between band gap energy, MWCNTs yield and aspect ratio. The results revealed that the optimum conditions to obtain high yield and quality MWCNTs of 159.9% were: temperature ($700^{\circ}C$), time (55 min), argon flow rate ($230.37mL\;min^{-1}$) and acetylene flow rate ($150mL\;min^{-1}$) respectively. The developed regression models demonstrated that the estimated values for the three response variables; energy gap, yield and aspect ratio, were 0.246 eV, 557.64 and 0.82. The regression models showed that the energy band gap, yield, and aspect ratio of the MWCNTs were largely influenced by the synthesis parameters and can be controlled in a CVD reactor.