• Biotechnology and Bioprocess Engineering:BBE
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• 제8권1호
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• pp.23-31
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• 2003

A mathematical model was formulated to simulate the long-term performance of an anaerobic bioreactor designed to digest Korean food wastes. The system variables of various decomposition steps were built into the model, which predicts the temporal characters of Solid waste, and volatile fatty acid (VFA) in the reactor, and gas production in response to various input loadings and temperatures. The predicted values of VFA and gas production were found to be in good agreement with experimental observations in batch and repeated-input systems. Finally, long-term reactor performance was simulated with respect to the seasonal temperature changes from 5C in winter to 25C in Summer at different food waste input loadings. The simulation results provided us with information concerning the success or failure of a process during long-term operation .

• Journal of Forest and Environmental Science
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• 제33권4호
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• pp.330-341
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• 2017

Tropical forests play a key role for functioning of the planet and maintenance of life. These forests support more than half of the world's species, serve as regulators of global and regional climate, act as carbon sinks and provide valuable ecosystem services. Forest floor biomass and litterfall dynamics was measured in different sites influenced by fire in a seasonally dry tropical forest of Bhoramdeo wildlife sanctuary of Chhattisgarh, India. The forest floor biomass was collected randomly placed quadrats while the litterfall measured by placing stone-block lined denuded quadrat technique. The seasonal mean total forest floor biomass across the fire regimes varied from $2.00-3.65t\;ha^{-1}$. The total litterfall of the study sites varied from $4.75-7.56t\;ha^{-1}\;yr^{-1}$. Annual turnover of litter varied from 70-74% and the turnover time between 1.35-1.43 years. Monthly pattern of forest floor biomass indicated that partially decayed litter, wood litter and total forest floor were differed significantly. The seasonal variation showed that leaf fall differed significantly in winter season only among the fire regimes while the wood litter was found non significant in all the season. This study shows that significant variation among the site due to the forest fire. Decomposition is one of the ecological processes critical to the functioning of forest ecosystems. The decomposing wood serves as a saving account of nutrients and organic materials in the forest floor. Across the site, high fire zone was facing much of the deleterious effects on forest floor biomass and litter production. Control on such type of wildfire and anthropogenic ignition could allow the natural recovery processes to enhance biological diversity. Chronic disturbances do not provide time for ecosystem recovery; it needs to be reduced for ecosystem health and maintaining of the high floral and faunal biodiversity.

• Ocean and Polar Research
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• 제44권1호
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• pp.1-11
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• 2022

Hypoxia can affect water-atmosphere methane flux by controlling the production and consumption processes of methane in coastal areas. Seasonal methane concentration and fluxes were quantified to evaluate the effects of seasonal hypoxia in Dangdong Bay (Gyeongsangnamdo, Jinhae Bay, South Korea). Sediment-water methane flux increased more than 300 times during hypoxia (normoxia and hypoxia each 6, 1900 µmol m^-2 d^-1), and water-atmospheric methane flux and bottom methane concentration increased about 2, 10 times (normoxia and hypoxia each 190, 420 µmol m^-2 d^-1; normoxia and hypoxia each 22, 230 nM). Shoaling of anaerobic decomposition of organic matter in the sediments during the hypoxia (August) was confirmed by the change of the depth at which the maximum hydrogen sulfide concentration was detected. Shoaling shortens the distance between the water column and methanogenesis section to facilitate the inflow of organic matter, which can lead to an increase in methane production. In addition, since the transport distance of the generated methane to the water column is shortened, consumption of methane will be reduced. The combination of increased production and reduced consumption could increase sediment-aqueous methane flux and dissolved methane, which is thought to result in an increase in water-atmospheric methane flux. We could not observe the emission of methane accumulated during the hypoxia due to stratification, so it is possible that the estimated methane flux to the atmosphere was underestimated. In this study, the increase in methane flux in the coastal area due to hypoxia was confirmed, and the necessity of future methane production studies according to oxygen conditions in various coastal areas was demonstratedshown in the future.

• 한국산업보건학회지
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• 제32권4호
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• pp.425-434
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• 2022

Objectives: This study analyzes TVOC concentrations in root industry workplaces in order to prevent probable occupational disease among workers. Root industry includes all the infrastructure of manufacturing, such as casting and molding. Methods: Real-time TVOC sensors were deployed in three root industry workplaces. We measured TVOC concentrations with these sensors and analyzed the results using a data-analysis tool developed with Python 3.9. Results: During the study period, the mean of the TVOC concentrations remained in an acceptable range, 0.30, 2.15, and 1.63 ppm across three workplaces. However, TVOC concentrations increased significantly at specific times, with respective maximum values of 4.98, 28.35, and 26.65 ppm for the three workplaces. Moreover, the analysis of hourly TVOC concentrations showed that during working hours or night shifts TVOC concentrations increased significantly to higher than twice the daily mean values. These results were scrutinized through classical decomposition results and autocorrelation indices, where seasonal graphs of the corresponding classical decomposition results showed that TVOC concentrations increased at a specific time. Trend graphs showed that TVOC concentrations vary by day. Conclusions: Deploying a real-time TVOC sensor should be considered to reflect irregularly high TVOC concentrations in workplaces in the root industry. It is expected that the real-time TVOC sensor with the presented data analysis methodology can eradicate probable occupational diseases caused by detrimental gases.

• 한국수자원학회논문집
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• 제52권12호
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• pp.1075-1086
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• 2019

최근 기후 온난화의 발생과 이상기후의 발생빈도가 증가함에 따라 강수량, 하천유량과 같은 수문학적 요소의 예측이 복잡해지고 있으며 물부족 발생 위험도 증가하고 있다. 따라서 본 연구에서는 중단기 하천 취수량을 예측하기 위한 모델을 개발하고자 하였다. 입력인자를 선정하기 위해 취수량과 기상인자들 간의 상관성분석을 수행한 결과 온도가 가장 영향이 큰 것으로 나타났다. 또한 취수량은 시계열에 따른 증가 경향과 계절적 특성이 뚜렷하게 나타나므로 시계열분해기법을 이용하여 전처리를 수행하고 잔차에 대해 서포트 벡터 머신(SVM)을 적용하여 취수량 예측 모델을 개발하였다. 이 모델은 평균적으로 4.1%의 오차율을 나타내며, 전처리를 하지 않은 SVM 모델에 비해 높은 정확도를 나타냈다. 특히, 1~2달에 대해 중단기 예측을 수행하였을 때 더 유리한 결과를 나타냈다. 본 연구에서 개발된 취수량 예측모델은 수자원의 지속가능하고 효율적인 관리를 위해 하천수 사용허가, 수질관리, 가뭄 대책 마련에 활용이 가능할 것으로 예상된다.

• Ocean and Polar Research
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• 제28권2호
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• pp.119-127
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• 2006

We measured oxygen microprofiles using an oxygen microelectrode in Ganghwa intertidal flat in April and September. Oxygen consumption rate was calculated by using three different methods based on the oxygen microprofiles. The method using the PROFILE software was thought to be the most reliable among the three methods. The oxygen consumption rates calculated at station D1 by using the PROFILE software were 10.5 and 6.27mmol $m^{-2}d^{-1}$ in April and September, respectively. At station D2, they were 10.9mmol $m^{-2}d^{-1}$ in April and 5.39 mmol $m^{-2}d^{-1}$ in September. There was little spatial variation, but large seasonal variation, with almost two times larger values in April than in September. The higher rate in April is ascribed to higher oxygen concentration in the seawater and higher organic carbon content in the surface sediments, which probably accelerate oxygen consumption for organic matter decomposition in the sediments. Aerobic remineralization rates estimated from the oxygen consumption rates ranged from 4.14 to 8.07 mmol C $m^{-2}d^{-1}$ in Ganghwa intertidal flat, which were much lower than the anaerobic remineralization rate.

• International Journal of Computer Science & Network Security
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• 제22권1호
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• pp.225-233
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• 2022

The recent outbreak of corona virus (COVID-19) infectious disease had made its forecasting critical cornerstones in most scientific studies. This study adopts a machine learning based time series model - Auto Regressive Integrated Moving Average (ARIMA) model to forecast COVID-19 confirmed cases in Botswana over 60 days period. Findings of the study show that COVID-19 confirmed cases in Botswana are steadily rising in a steep upward trend with random fluctuations. This trend can also be described effectively using an additive model when scrutinized in Seasonal Trend Decomposition method by Loess. In selecting the best fit ARIMA model, a Grid Search Algorithm was developed with python language and was used to optimize an Akaike Information Criterion (AIC) metric. The best fit ARIMA model was determined at ARIMA (5, 1, 1), which depicted the least AIC score of 3885.091. Results of the study proved that ARIMA model can be useful in generating reliable and volatile forecasts that can used to guide on understanding of the future spread of infectious diseases or pandemics. Most significantly, findings of the study are expected to raise social awareness to disease monitoring institutions and government regulatory bodies where it can be used to support strategic health decisions and initiate policy improvement for better management of the COVID-19 pandemic.

• 대한환경공학회지
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• 제39권9호
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• pp.534-541
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• 2017

바이오리액터형 매립지는 매립지 내부로 침출수나 폐수 같은 수분의 공급을 통하여 폐기물의 분해를 촉진하기 위하여 운영하며, 이러한 수분 공급은 매립가스를 증산하고 결국 매립지 조기안정화에 기여한다. 최근 바이오리액터형 매립지 운영을 위한 환경법이 제정되었으며 이에 따라 국내 최초로 수도권매립지에 도입하였다. 바이오리액터형 매립지의 안정적인 적용을 위하여는 매립지 내부의 수분분포 파악이 필수적이며 이를 통해 해당 구역에 적정하게 수분이 유지되도록 한다. 이를 위하여 매립지내부 수분분포 파악을 위하여 전기비저항탐사를 실시하였다. 본 연구에서는 수도권매립지 제2매립장 내에 침출수 재순환과 함께 장기간 전기비저항탐사를 수행하였다. 그 결과, 전기비저항값이 계절적 온도 변화에 큰 영향을 받고 있는 것을 확인할 수 있었다. 이에 따라 본 연구를 통해 조사된 온도와 전기비저항값의 상관관계를 통한 보정방법을 이용하여 바이오리액터형 매립지를 안정적으로 운영할 수 있도록 하였다.

• 한국물환경학회지
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• 제28권5호
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• pp.704-716
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• 2012

본 논문은 California의 South Lake Tahoe, 서울 뚝섬정수장 그리고 성남 복정정수장에서 2010년 2월에서 2012년 2월까지 수행된 파일럿 실험에 대한 분석결과를 기초로 작성되었다. 본 실험의 목적은 첫째, 한강을 원수로 하는 모래여과 처리수에 대한 오존 및 과산화수소(Peroxone)의 반응특성을 파악하고, 둘째는 AOP(고도산화공정)을 통해 맛 냄새 유발물질인 2-methylisoborneol(MIB)를 제거하기위한 경험적인 오존 및 과산화수소의 투입량을 결정하고자 하였다. 또한 셋째로, 처리공정이후 인체에 안전한 잔류오존농도로 감소시키기 위한 최적 투입량을 결정하고자 하였다. 본 실험은 계절의 기온변화에 따라 저수온 및 고수온의 조건하에서 실시간으로 수행되었다. 본 실험을 통해 오존의 분해속도는 온도와 pH에 영향을 받는 것으로 나타났으며, 이는 다른 연구결과와 일치한다. 원수로 모래여과수에 MIB를 40~50ng/L의 농도로 투입하였으며, 모든 경우에서 7ng/L 이하로 처리되었으며 대부분의 경우에서 검출(ND)되지 않았다. Peroxone은 MIB을 제거할 뿐아니라 오존을 단독으로 사용한 경우보다 오존+과산화수소 동시에 투입한 경우에 잔류오존농도가 더 낮았다. 저수온에서 상당량의 오존이 반응 및 분해를 통해 감소된다. 본 실험을 통해 "Pre-Conditioned" 과산화수소를 적용함으로써 초기 반응율을 향상시키고 잔류오존농도를 낮출 수 있었으며, 약품의 과투입 및 효율저하를 방지하는 과산화수소의 투입 위치 및 구성 그리고 투입방법을 제시하였다.

• 한국산학기술학회논문지
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• 제16권11호
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• pp.7820-7830
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• 2015

우리나라 도시근로자의 가계소득과 외식비는 함께 증가하고 있으나, 시간이 경과와 더불어 가계소득에 비해 외식비 증가율이 크게 둔화되고 있을 뿐만 아니라 가계소득에서 외식비가 차지하는 비율도 감소하고 있다. 이러한 외식비 지출패턴의 변화는 소득계층에 따라서도 달라 외식비가 가계소득에서 차지하는 비중은 2005년 이후 감소하나 10분위의 외식비 비중이 가장 낮고 1분위의 비중이 가장 높다는 것과, 외식비 비중의 표준편차도 소득계층이 높을수록 작고 소득계층이 낮을수록 크다는 것을 보인다. 외식비모형에 회귀분석을 적용하여 소득계수가 모두 유의하며 소득분위가 높을수록 계수의 크기가 작다는 것과 외환위기는 1분위와 10분위를 제외하고 음의 부호로 유의하다는 것을 밝힌다. 1분위와 2분위에서는 계절에 따른 외식비 변화가 없으며, 소득계층이 높을수록 계절에 따른 외식이 분명해진다는 것도 제시한다. 시간이 흐름에 따른 외식비 패턴의 변화를 살펴보기 위하여 전향적 이동회귀를 실시하여 단순 추정에 따른 것보다 훨씬 빠른 속도로 외식비의 소득탄력성 감소가 이루어지고 있다는 것을 밝힌다. 외식비를 분산분해하여 소득수준이 낮은 계층에서는 소득이 중요한 변수이나 소득수준이 높은 계층에서는 소득 이외의 요인들이 외식비에 많은 영향을 미친다는 것을 보인다.