• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.4
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• pp.191-197
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• 2021

To calculate the induced charge of atoms in molecular dynamics, linear equations for the induced charges need to be solved. As induced charges are determined at each time step, the process involves considerable computational costs. Hence, an efficient method for calculating the induced charge distribution is required when analyzing large systems. This paper introduces the Uzawa method for solving saddle point problems, which occur in linear systems, for the solution of the Lagrange equation with constraints. We apply the accelerated Uzawa algorithm, which reduces computational costs noticeably using the Schur complement and preconditioned conjugate gradient methods, in order to overcome the drawback of the Uzawa parameter, which affects the convergence speed, and increase the efficiency of the matrix operation. Numerical models of molecular dynamics in which two gold nanoparticles are placed under external electric fields reveal that the proposed method provides improved results in terms of both convergence and efficiency. The computational cost was reduced by approximately 1/10 compared to that for the Gaussian elimination method, and fast convergence of the conjugate gradient, as compared to the basic Uzawa method, was verified.

• Geophysics and Geophysical Exploration
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• v.5 no.3
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• pp.206-216
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• 2002

The finite element method (FEM), a powerful numerical modeling tool for solving various engineering problems, is frequently applied to three-dimensional (3-D) modeling thanks to its capability of discretizing and simulating the shape of model with finite number of elements. Considering the accuracy of the solution and computing time in modeling of engineering problems, it is preferable to construct physical continuity and simplify mesh system. Although there exist systematic mesh generation systems for arbitrary shaped model, it is hard to model a simple cylinder in terms of 3-D coordinate system especially in the vicinity of the central axis. In this study I adopt cylindrical coordinate system for modeling the 3-D model space and define the origin of the coordinates with mathematically clear coordinate transformation. Since we can simulate the whole space with hexahedral elements, the cylindrical coordinate system is effective in handling the 3-D model structure. The 3-D do resistivity modeling scheme developed in this study provides basie principle for borehole-to-surface resistivity survey, which can be a useful tool for the application to environmental problem.

• Pediatric Infection and Vaccine
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• v.28 no.2
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• pp.57-65
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• 2021

School closures during the coronavirus disease 2019 (COVID-19) pandemic have been outlined in studies from different disciplines, including economics, sociology, mathematical modeling, epidemiology, and public health. In this review, we discuss the implications of school closures in the context of the current COVID-19 pandemic. Modeling studies of the effects of school closures, largely derived from the pandemic influenza model, on severe acute respiratory syndrome coronavirus 2 produced conflicting results. Earlier studies assessed the risk of school reopening by modeling transmission across schools and communities; however, it remains unclear whether the risk is due to increased transmission in adults or children. The empirical findings of the impact of school closures on COVID-19 outbreaks suggest no clear effect, likely because of heterogeneity in community infection pressure, differences in school closure strategies, or the use of multiple interventions. The benefits of school closings are unclear and not readily quantifiable; however, they must be weighed against the potential high social costs, which can also negatively affect the health of this generation.

• Journal of Elementary Mathematics Education in Korea
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• v.14 no.3
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• pp.907-935
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• 2010

The purpose of this study was to investigate the effects of using open-ended problems in ability-level activities in mathematics instruction and to draw some informative conclusions in order to improve the practice of teaching and learning mathematics in the elementary school. To fulfill the purpose, the research questions were established as follows: 1. Is there any difference between the academic achievements of the experimental group(doing ability-level activities using open-ended problems) and the control group(doing general ability-level activities)? 2. Which sub-group(grouped by achievement score in pretest) get affected most by ability-level activities using open-ended problem in the experimental group? 3. What kinds of responses do students show in their ability-level activities using open-ended problems? By applying t-test and analysing the response, the conclusions were drawn as follows: First, using open-ended problems in ability-level activities has positive effects on the academic achievement of the experiment group. The mean of posttest scores of the experiment group was statistically meaningfully higher(p<.05). Second, using open-ended problems in ability-level activities affect most to the achievement of lower sub-group in the experiment group. The mean of posttest scores of lower sub-group in the experiment group was statistically meaningfully higher than that of control group(p<.05). Third, students showed various and creative response in their ability-level activities using open-ended problems.

• Journal of Korean Society of Transportation
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• v.17 no.2
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• pp.83-90
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• 1999

A computer algorithm is presented that evaluate the performance of coordinated signal timing plans for the signalized arterials. The procedures calculating delay and stops are based on Michalopoulos's analytical model derived from shock wave theory. The delay-offset relationship predicted from the algorithm produced consistent results with the delays venerated by TRANSYT-7F. From performance test, the delays estimated using the proposed a1gorithm are shown to be sensitive to the quality of progression as well as to traffic demand, link length, and turning flow ratio from upstream signal.

• Proceedings of the Korea Information Processing Society Conference
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• 2007.11a
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• pp.1158-1161
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• 2007

IPv6는 IETF가 IPv4를 대체하기 위해 제안한 프로토콜이다. 하지만 현재 모든 네트워크를 IPv4에서 IPv6로 전환하는 것은 비용과 시간적인 측면에서 힘들기 때문에 상당 기간 IPv4와 IPv6가 공존하는 IPv4/IPv6 혼재 네트워크가 유지될 것이다. IPv4/IPv6 혼재 네트워크에서 통신을 위해 다양한 메커니즘들이 개발되었다. Teredo는 이러한 메커니즘들 중에 하나로 NAT 내에 위치한 IPv4 호스트가 IPv6를 이용할 수 있게 하고, 향후 다수의 사용자에 의해 사용이 예상되는 윈도우 비스타에서 기본적으로 이용할 수 있기 때문에 혼재 네트워크에서 상당히 오랜 기간 동안 사용될 것이다. 하지만 Teredo 메커니즘은 NAT 내의 보안 장비 우회, Teredo 구성 요소의 신뢰성 등 보안 취약점을 가지고 있다. 본 논문에서는 Teredo를 이용하는 네트워크에서 발생 가능한 보안 취약점들에 대해서 기술하고, 그 중에서 캐쉬 오버플로우 공격에 대한 실험 결과를 기술한다.

• Journal of The Korean Association of Information Education
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• v.19 no.2
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• pp.159-166
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• 2015

STEAM is a multidisciplinary education program which intended to promote creative thinking by combining studies in the arts and STEM(Science, Technology, Engineer, Mathematics) fields. STEAM education can bring out creativities in students through educational activities of integrating and combining diverse studies. In this research, we integrated the educational elements of science, technology, engineering, mathematics, and arts using robots and then developed an educational program that raises the creative and character (focused on collaboration and communication) of students in a more fun and effective way. Using our developed educational program, we taught 6th grade students of an elementary school located in Seoul. As the result, most of students were found to be enhanced in their creativity and character after participating in the STEAM-based programming education course.

• Korea journal of population studies
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• v.29 no.2
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• pp.27-51
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• 2006

In this paper, I have tested various kinds of methods for mortality projection and chose Lee-Carter method for projection of Korean mortality by age and sex. I reviewed the trends of life tables and life expectancies by age and sex from 2005 to 2050 projected by Lee-Carter method and found that the method was very applicable for Korean mortality projection. The differences between reported and estimated data for the period of 1971-2003 were small enough for both sexes and for all of the age groups. The projected life expectancies in 2051 were 82.73 years for males and 89.41 for females, and the differences decreased from 7.06 years in 2005 to 6.68 years. Because of the limitation of Korean infant mortality rate, I adopted the Japanese estimated IMR in 2050 as Korean object level in 2051. When the time series of IMR become long enough, we can use Korean IMR directly for the mortality projection. In addition, if we can estimate the changes of the main cause of death correctly in future, the mortality projection will be more correct and reliable. This will be available when we can produce a long series of life tables by cause of deaths.

• Journal of the Korean Society of Marine Environment & Safety
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• v.30 no.2
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• pp.200-208
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• 2024

The occurrence a fire on a training ship with a large number of people on board can lead to severe casualties. Hence the Seafarers' Act and Safety Life At Sea(SOLAS) emphasizes the importance of the abandon ship drill. Therefore, in this study, the training ship of Mokpo National Maritime University, Segero, which has a large number of people on board, was selected as the target ship and the likelihood and severity of fire accidents on each deck were predicted through the preliminary hazard analysis(PHA) qualitative risk assessment. Additionally, assuming a fire in a high-risk area, a simulation of evacuation time and population density was performed to quantitatively predict the risk. The the total evacuation time was predicted to be the longest at 501s in the meal time scenario, in which the population distribution was concentrated in one area. Depending on the scenario, some decks had relatively high population densities of over 1.4pers/m², preventing stagnation in the number of evacuees. The results of this study are expected to be used as basic data to develop training scenarios for training ships by quantifying evacuation time and population density according to various evacuation scenarios, and the research can be expanded in the future through comparison of mathematical models and experimental values.

• Journal of the Korea Society for Simulation
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• v.27 no.4
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• pp.9-18
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• 2018

This paper proposes new algorithms of accessibility indices to analyze the connectivity of the Korean highway network. First of all, we find a transportation network that presents Korea's highway network in graphs in 2011 and 2017. And we analyze and compare the nation's highway network in 2011 and 2017 using concepts such as associated number, the relative distance, the accessibility, the degree of connectivity, the index of dispersion, the diameter of graph theory. To do this, an algorithm is presented which can easily obtain various accessibility indices from a given transportation network. Using the simulation results of this study, we can find city that is the center of traffic in the highway transportation network. In addition, cities that are included in the network but are relatively underdeveloped can be found and used as basic data for enhancing the connectivity of the nationwide traffic in the future. Moreover, the proposed algorithms of accessibility indices, which are modeled on highway transport networks, can help identify the accessibility space structure of each city and provide criteria for efficient and reasonable selection of alternatives in various regional planning processes, including transportation.