• Journal of Korean Society of Water and Wastewater
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• v.34 no.2
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• pp.105-114
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• 2020

In this study, based on the System Dynamics (SD) methodology, the interrelationship between the factors inherent in the operation of the New Technology Certification System (NTCS) in Korea was identified by a causal map containing a feedback loop mechanism in connection with 'new technology development investment', 'commercialization of new technology', and 'sales by new technology'. This conceptualized causal map was applied to the simulation of the operations of the New Excellent Technology and Environmental Technology Verification System (NET&ETV) run by the Ministry of Environment among various NTCSs in Korea. A SD computer simulation model was developed to analyze and predict the operational performance of the NET&ETV in terms of key performance indices such as 'sales by new technology'. Using this model, we predicted the future operational status the NET&ETV and found a policy leverage that greatly influences the operation of the NET&ETV. Also the sensitivity of the key indicators to changes in the external variables in the model was analyzed to find policy leverage.

• Korean Journal of Environmental Biology
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• v.39 no.3
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• pp.298-310
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• 2021

Prediction of the behavior of heavy metals over time is important to evaluate the heavy metal toxicity in algae species. Various modeling studies have been well established, but there is a need for an improved model for predicting the chronic effects of metals on algae species to combine the metal kinetics and biological response of algal cells. In this study, a kinetic dynamics model was developed to predict the copper behavior(5 ㎍ L^-1, 10 ㎍ L^-1, and 15 ㎍ L^-1) for two freshwater algae (Pseudokirchneriella subcapitata and Chlorella vulgaris) in the chronic exposure experiments (8 d and 21 d). In the experimental observations, the rapid change in copper mass between the solutions, extracellular and intracellular sites occurred within initial exposure periods, and then it was slower although the algal density changed with time. Our model showed a good agreement with the measured copper mass in each part for all tested conditions with an elapsed time (R² for P. subcapitata: 0.928, R² for C. vulgaris: 0.943). This study provides a novel kinetic dynamics model that is compromised between practical simplicity and realistic complexity, and it can be used to investigate the chronic effects of heavy metals on the algal population.

• Korean System Dynamics Review
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• v.13 no.3
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• pp.5-22
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• 2012

Although many system dynamists point out the close relationship between institutional economics and system dynamics, the relationship between institutional political theory and system dynamics approach is not explicitly appreciated yet. We developed a system dynamics model to investigate theoretical propositions of institutional politics. Our system dynamics model showed how the endogenous mechanism can explain the political changes as well as orders. Although simple in the causal structure, our model could show a complex behavior of political competition. Several simulation results imply that some unexpected changes in election and power competition may come from the endogenous system rather than from exogenous factors such as economic and environmental shocks.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 1996.10a
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• pp.65-65
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• 1996

• Journal of Korean Society of Water and Wastewater
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• v.30 no.5
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• pp.561-569
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• 2016

In this paper a concept of the paradigm shift in the operations of Water and Wastewater systems regarding the production and usage of water was introduced. Based on this concept the interrelationships between the water quality in the upper basin of NakDong River relative to Busan and the degree of satisfaction of the customers on the water supply service in Busan were modeled using the System Dynamics modeling methodology. SamRangJin basin area was determined as the upper basin of Busan after analyzing the relationships between the water quality of MoolGeum water intake point and water quality data of various mid- and upper water intake points along NakDong River. The amount of contaminants generated in SamRangJin basin was modeled using the Gross Regional Domestic Product in the area and the treated amount was calculated using the efficiency of wastewater treatment and the degree of improvement of environmental condition per investment. The water quality at MoolGeum water intake point was modeled to take the effects of the remaining amount of contaminants after treatment and the non-point source contaminants in SamRangJin basin. Using the developed System Dynamics model the effects of the investment for the improvement of environmental condition in SamRangJin basin were compared to the case of alternate water source development for Busan in terms of the degree of satisfaction of the customers on the water supply service in Busan.

• Korean Journal of Ecology and Environment
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• v.37 no.3 s.108
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• pp.304-312
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• 2004

The transient dynamics of three-trophic populations (prey, predator, and super predator) using ratio-dependent models responding to environmental impacts is analyzed. Environmental factors were divided into two parts: periodic factor (e.g., temperature) and general noise. Periodic factor was addressed as a frequency and bias, while general noise was expressed as a Gaussian distribution. Temperature bias ${\varepsilon}$, temperature frequency ${\Omega}$, and Gaussian noise amplitude ${\`{O}}$ accordingly revealed diverse status of population dynamics in three-trophic food chain, including extinction of species. The model showed stable limit cycles and strange attractors in the long-time behavior depending upon various values of the parameters. The dynamic behavior of the system appeared to be sensitive to changes in environmental input. The parameters of environmental input play an important role in determining extinction time of super predator and predator populations.

• 한국생물공학회:학술대회논문집
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• 2003.10a
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• pp.174-174
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• 2003

• Journal of Environmental Science International
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• v.25 no.7
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• pp.927-935
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• 2016

Dissolved oxygen is necessary for many biological processes as well as many industrial practices. Dissolved oxygen released from water in dissolved air flotation (DAF) systems can be have many different applications. However, DAF systems are very costly to operate. To develop more efficient DAF systems, a deeper understanding of the process of oxygen being released from water is required. In this study, molecular dynamics (MD) simulations were used to simulate 100 oxygen molecules surrounded by 31002 water molecules at temperatures ranging from $0^{\circ}C$ to $100^{\circ}C$. Simulations were carried out for 10 ns, during which, in most cases, all the oxygen molecules were released from the water droplet. With MD simulations, visualization of the molecules escaping the water droplet was possible, which aided the understanding of the interactions between molecules at the nano-scale. The results showed that as the oxygen molecules moved near the edge of the water droplet that the oxygen molecules hesitated before escaping the water droplet or returned to the interior of the water droplet. This was because of the attractive forces between the water and oxygen molecules. Moreover, after most of the oxygen molecules were released from the droplet, some were found to return to the droplet's edge or even the interior of the droplet. It was also confirmed that oxygen molecules were released at a faster rate at higher temperatures.

• Structural Engineering and Mechanics
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• v.30 no.2
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• pp.177-190
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• 2008

Material failure behavior is generally dependent on loading rate. Especially in brittle and quasi-brittle materials, rate dependent material behavior can be significant. Empirical formulations are often used to predict the rate dependency, but such methods depend on extensive experimental works and are limited by practical constraints of physical testing. Numerical simulation can be an effective means for extracting knowledge about rate dependent behavior and for complementing the results obtained by testing. In this paper, the failure behavior of a brittle material under different loading rates is simulated by molecular dynamics analysis. A notched specimen is modeled by sub-million particles with a normalization scheme. Lennard-Jones potential is used to describe the interparticle force. Numerical simulations are performed with six different loading rates in a direct tensile test, where the loading velocity is normalized to the ratio of the pseudo-sonic speed. As a consequence, dynamic features are achieved from the numerical experiments. Remarkable failure characteristics, such as crack surface interaction/crack arrest, branching, and void nucleation, vary in case of the six loading cases. These characteristics are interpreted by the energy concept approach. This study provides insight into the change in dynamic failure mechanism under different loading rates.

• Proceedings of the Korea Society of Environmental Biology Conference
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• 2001.12a
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• pp.134-134
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• 2001