Experimenting biochemical oxygen demand decay rates of Malaysian river water in a laboratory flume

Nuruzzaman,Abdullah Al-Mamun,Noor Bin Salleh 대한환경공학회 2018 Environmental Engineering Research Vol.23 No.1

Lack of information on the Biochemical Oxygen Demand (BOD) decay rates of river water under the tropical environment has triggered this study with an aim to fill the gap. Raw sewage, treated sewage, river water and tap water were mixed in different proportions to represent river water receiving varying amounts and types of wastewater and fed in a laboratory flume in batch mode. Water samples were recirculated in the flume for 30 h and BOD and Carbonaceous BOD (CBOD) concentrations were measured at least six times. Decay rates were obtained by fitting the measured data in the first order kinetic equation. After conducting 12 experiments, the range of BOD and CBOD decay rates were found to be 0.191 to 0.92 per day and 0.107 to 0.875 per day, respectively. Median decay rates were 0.344 and 0.258 per day for BOD and CBOD, respectively, which are slightly higher than the reported values in literatures. A relationship between CBOD decay rate and BOD decay rate is proposed as kCBOD = 0.8642kBOD - 0.0349 where, kCBOD is CBOD decay rate and kBOD is BOD decay rate. The equation can be useful to extrapolate either of the decay rates when any of the rates is unknown.

Survey on Dental Caries Experience of Students in Vientiane Province, Laos

Sun-Gil Park,Ja-Won Cho,Hyun-Jun Yoo,Phommavongsa Nitthasack,Ji-Hyeon Park 대한예방치과학회 2023 International Journal of Clinical Preventive Denti Vol.19 No.4

Objective: The purpose of this study is to assess the prevalence of dental caries among students in the Vientiane area of Laos. Methods: We conducted an analysis of the oral examination outcomes for a cohort of 344 children in Vientiane, including 121 in primary school, 138 in middle school, and 85 in high school, to evaluate the prevalence of dental caries in this group. Results: For 12-year-olds, equivalent to the first year of middle school, the index of experienced decay in permanent teeth was 3.30, with a decayed permanent tooth surface index of 6.01. The rate of caries experience in permanent teeth was 86.13%, the decay rate in permanent teeth was 92.09%, the treatment rate for permanent teeth was 1.98%, and the caries fatality rate was determined to be 12.09%. Conclusion: The prevalence of dental caries experience among most age groups was significantly higher compared to other regions, with a permanent tooth decay rate ranging from approximately 88% to 91%. Notably, the primary tooth decay rate was found to be around 99%, indicating an exceptionally high level. The dental caries fatality rate was also estimated to be in the range of 5% to 12%, underscoring the need for simultaneous preventive measures and treatment programs in Laos to halt the progression of dental caries and reduce the dental caries fatality rate.

저신장율 대향류확산화염에서 진동불안정성을 갖는 에지화염의 동적거동

박준성(June Sung Park),김현표(Hyun Pyo Kim),박정(Jeong Park),김정수(Jeong Soo Kim),길상인(Sang In Keel) 한국연소학회 2006 KOSCOSYMPOSIUM논문집 Vol.- No.-

Experiments in methane-air low strain rate counterflow diffusion flames diluted with nitrogen have been conducted to study the behavior of flame extinction and edge flame oscillation in which flame length is less than the burner diameter and thus lateral conduction heat loss in addition to radiative heat loss could be remarkable at low global strain rates. Critical mole fraction at flame extinction is examined with velocity ratio and global strain rate. Onset conditions of edge flame oscillation and flame oscillation modes are also provided with global strain rate and added nitrogen mole fraction to fuel stream (fuel Lewis number). It is seen that flame length is closely relevant to lateral heat loss, and this affects flame extinction and edge flame oscillation considerably. Edge flame oscillations in low strain rate flames are experimentally described well and are categorized into three: a growing oscillation mode, a decaying oscillation mode, and a harmonic oscillation mode. The regime of flame oscillation is also provided at low strain rate flames. Important contribution of lateral heat loss even to edge flame oscillation is clarified.

실간환기량 측정을 위한 추적가스 실험방법론에 관한 연구

한화택(Hwataik Han),조석효(Seok Hyo Cho) 대한설비공학회 2009 설비공학 논문집 Vol.21 No.11

Interzonal air movements are important to characterize overall ventilation performance of complicated multi-zone buildings. Tracer gas techniques are widely used to measure ventilation rates, ventilation effectiveness, and interzonal air movements. Depending on the number of gases used, they are divided into single and multi tracer gas methods. This paper deals with the comparison of the tracer gas methods in measuring air exchange rate between rooms. Experiments have been conducted in a simple two-room model with known airflow rates. In multi-gas procedure, the concentration decays of two tracer gases, i.e SF6 and R134a are measured after simultaneous injections in each room. The single tracer gas method is also applied by injecting SF6 gas with a time lag between two rooms. The data reduction procedures are developed to obtain the interzonal airflow rate using the matrix inversion, and various data manipulation methods are tested, such as data shift, interpolation, and smoothing. Uncertainty for each airflow rate is investigated depending on the parameters based on the setting values.

Numerical study on mixing characteristics of symmetrical and asymmetrical twin jets

Ch. Narendra Kumar,K. P. Sinhamahapatra 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.6

This paper aims to examine the effects of orientation and asymmetry on the mixing characteristics of circular and elliptical twin jets produced from sharp orifices. The twin jets that emerged from two similar orifices are termed as symmetrical twin jets, and the twin jets issued from two different orifices are referred to as asymmetrical twin jets. The twin jets are separated by the spacing ratio of 2, and numerical simulations are performed at a Mach number of 0.8 and a Reynolds number based on an equivalent exit diameter of 3.46×10 5 . RANSbased two-equation turbulence model, namely SST k-ω model was used to carry out the simulations. It was observed that the core length is not affected by the orifice orientation. However, the spread rates and velocity decay are sensitive to orifice orientation, and among the tested twin jet configurations, the circular-elliptical major asymmetrical jet experienced the highest decay and spread rates. In addition, the turbulent intensity peak values of asymmetrical twin jets decreased by 8 % compared to symmetrical twin jets.

Nutrient dynamics in decomposing litter from four selected tree species in Makurdi, Benue State, Nigeria

Thomas Okoh,Esther Edu 한국생태학회 2019 Journal of Ecology and Environment Vol.43 No.4

Background: Nutrient release during litter decomposition was investigated in Vitex doniana, Terminalia avecinioides, Sarcocephallus latifolius, and Parinari curatellifolius in Makurdi, Benue State Nigeria (January 10 to March 10 and from June 10 to August 10, 2016). Leaf decomposition was measured as loss in mass of litter over time using the decay model Wt/W0 = e−kd t, while Kd ¼ −1t InðWt W0Þ was used to evaluate decomposition rate. Time taken for half of litter to decompose was measured using T50 = ln 2/k; while nutrient accumulation index was evaluated as NAI = ðωt Xt ωoXoÞ: Results: Average mass of litter remaining after exposure ranged from 96.15 g, (V. doniana) to 78.11 g, (S.lafolius) in dry (November to March) and wet (April to October) seasons. Decomposition rate was averagely faster in the wet season (0.0030) than in the dry season (0.0022) with P. curatellifolius (0.0028) and T.avecinioides (0.0039) having the fastest decomposition rates in dry and wet seasons. Mean residence time (days) ranged from 929 to 356, while the time (days) for half the original mass to decompose ranged from 622 to 201 (dry and wet seasons). ANOVA revealed highly significant differences (p < 0.01) in decomposition rates and exposure time (days) and a significant interaction (p < 0.05) between species and exposure time in both seasons. Conclusion: Slow decomposition in the plant leaves implied carbon retention in the ecosystem and slow release of CO2 back to the atmosphere, while nitrogen was mineralized in both seasons. The plants therefore showed effectiveness in nutrient cycling and support productivity in the ecosystem.

Forecasting KOSPI Return Using a Modified Stochastic AdaBoosting

Sangil Bae,정민수 대외경제정책연구원 2021 East Asian Economic Review Vol.25 No.4

AdaBoost tweaks the sample weight for each training set used in the iterative process, however, it is demonstrated that it provides more correlated errors as the boosting iteration proceeds if models’ accuracy is high enough. Therefore, in this study, we propose a novel way to improve the performance of the existing AdaBoost algorithm by employing heterogeneous models and a stochastic twist. By employing the heterogeneous ensemble, it ensures different models that have a different initial assumption about the data are used to improve on diversity. Also, by using a stochastic algorithm with a decaying convergence rate, the model is designed to balance out the trade-off between model prediction performance and model convergence. The result showed that the stochastic algorithm with decaying convergence rate’s did have a improving effect and outperformed other existing boosting techniques.

Nutrient dynamics in decomposing litter from four selected tree species in Makurdi, Benue State, Nigeria

Okoh, Thomas,Edu, Esther The Ecological Society of Korea 2019 Journal of Ecology and Environment Vol.43 No.4

Background: Nutrient release during litter decomposition was investigated in Vitex doniana, Terminalia avecinioides, Sarcocephallus latifolius, and Parinari curatellifolius in Makurdi, Benue State Nigeria (January 10 to March 10 and from June 10 to August 10, 2016). Leaf decomposition was measured as loss in mass of litter over time using the decay model W_t/W₀ = e-^{kd t}, while $Kd=-{\frac{1}{t}}In({\frac{Wt}{W0}})$ was used to evaluate decomposition rate. Time taken for half of litter to decompose was measured using T₅₀ = ln ²/k; while nutrient accumulation index was evaluated as $NAI=(\frac{{\omega}t\;Xt}{{\omega}oXo})$. Results: Average mass of litter remaining after exposure ranged from 96.15 g, (V. doniana) to 78.11 g, (S. lafolius) in dry (November to March) and wet (April to October) seasons. Decomposition rate was averagely faster in the wet season (0.0030) than in the dry season (0.0022) with P. curatellifolius (0.0028) and T. avecinioides (0.0039) having the fastest decomposition rates in dry and wet seasons. Mean residence time (days) ranged from 929 to 356, while the time (days) for half the original mass to decompose ranged from 622 to 201 (dry and wet seasons). ANOVA revealed highly significant differences (p < 0.01) in decomposition rates and exposure time (days) and a significant interaction (p < 0.05) between species and exposure time in both seasons. Conclusion: Slow decomposition in the plant leaves implied carbon retention in the ecosystem and slow release of CO₂ back to the atmosphere, while nitrogen was mineralized in both seasons. The plants therefore showed effectiveness in nutrient cycling and support productivity in the ecosystem.

행정동별 접근도가 교통수단별 분담률에 미치는 영향 분석

장성만(Jang Seong-Man),안영수(An Young-Soo),이승일(Lee Seung-Il) 대한국토·도시계획학회 2011 國土計劃 Vol.46 No.4

To deal with urban environmental issues, efforts to shift car-oriented transportation system to transit-oriented one have been being made in modern cities. The City of Seoul also has aimed to reduce car user by providing lots of transit facilities. However, the modal share rate of transit has not been increased. Based on that, the purpose of this paper is to explore the accessibility values to transportation facilities and compare them with the rates of each mode traffic. This study set up a method to calculate the accessibility values of three modes: subway, bus and car. They were converted to Dong’s accessibility values to analyze their impacts on Dong’s modal share rates. For considering urban characteristics of each Dong, the density of population and building, the rate of job and residence, and the land price were included in the independent variables of the multiple linear regression model for the modal share rate analysis. This study found an apparent correlation between the accessibility values to the transportation facilities and the modal share rates, especially by subway. Additionally, the price of land fairly influenced the modal share rate of subway and car in a contrary way. The analysis method and results from this study would affect the urban transportation policy positively and be used to invigorate transit use.

Analysis of Blood Flow-dependent Blood Nitric Oxide Level and Half-life of Nitric Oxide in Vivo

Kim Cuk-Seong,Kim Hyo-Shin,Lee Young-Jun,Park Jin Bory,Ryoo Sung-Woo,Chang Seok-Jang,Jeon Byeong-Hwa Biomedical Engineering Society for Circulation 2003 International Journal of Vascular Biomedical Engin Vol.1 No.2

Endothelial release of nitric oxide (NO) contributes to the regulation of vascular tone by inducing vascular relaxation. To estimate the blood flow-dependent nitric oxide level and half-life (T1/2) of nitric oxide in vivo state, we investigated the change of aortic NO currents during the change of aortic blood flow rate using NO-selective electrode system and electromagnetic flowmeter in the aorta of anesthetized rats. Resting mean aortic blood flow rate was $49.6{\pm}5.6ml/min$ in the anesthetized rats. NO currents in the aorta were increased by the elevation of blood pressure and/or blood flow rate. When the aortic blood flow was occluded by the clamping, aortic NO currents were decreased. The difference of NO concentration between resting state and occluded state was $1.34{\pm}0.26{\mu}M$ (n=7). This NO concentration was estimated as blood flow-dependent nitric oxide concentration in the rats. Also, while the aortic blood flow was occluded, NO currents were decreased with exponential pattern with $12.84{\pm}2.15$ seconds of time constant and $7.70{\pm}1.07$ seconds of half-life. To summarize, this study suggested that blood flow-dependent NO concentration and half-life of nitric oxide were about $1.3{\mu}M$ and 7.7 seconds, respectively, in the aorta of anesthetized rats. The nitric oxide-selective electrode system is useful for the direct and continuous measurement of NO in vivo state.