• Journal of Astronomy and Space Sciences
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• v.15 no.2
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• pp.307-320
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• 1998

We investigate the propagation of Coronal Mass Ejections(CMEs) near the earth with multi-satellite observations. Among the CMEs observed in the near-earth between Nov. 1994 and Nov. 1997, we select two events of Jan. 6-11,1997 and Nov. 4-7, 1997 which were observed by more than 3 satellites when these satellites were located apart with a sufficient distance from each other. We determine the speed and propagation of the two CMEs by calculating the position of each satellite in various coordinates and the onset time of each event. The results show that the speed of CMEs becomes significantly reduced when the perturbation arrives in the magnetosphere. It is also suggested that the propagation of the CMEs is approximated as the -x direction in GSE coordinates in the near-earth space.

• Journal of the Korean Institute of Gas
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• v.11 no.3
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• pp.13-18
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• 2007

The multivariate statistical analysis, using the multiple linear regression(MLR), have been applied to analyze and predict the flash points of binary systems. Prediction for the flash points of flammable substances is important for the examination of the fire and explosion hazards in the chemical process design. In this paper, the flash points are predicted by MLR based on the physical properties of pure substances and the experimental flash points data. The results of regression and prediction by MLR are compared with the values calculated by Raoult's law and Van Laar equation.

• Journal of Korea Soil Environment Society
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• v.1 no.1
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• pp.89-102
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• 1996

An integrated model is presented to describe underground flow and mass transport, using a multicomponent multiphase approach. The comprehensive governing equation is derived considering mass and force balances of chemical species over four phases(water, oil, air, and soil) in a schematic elementary volume. Compact and systemati notations of relevant variables and equations are introduced to facilitate the inclusion of complex migration and transformation processes, and variable spatial dimensions. The resulting nonlinear system is solved by a multidimensional finite element code. The developed code with dynamic array allocation, is sufficiently flexible to work across a wide spectrum of computers, including an IBM ES 9000/900 vector facility, SP2 cluster machine, Unix workstations and PCs, for one-, two and three-dimensional problems. To reduce the computation time and storage requirements, the system equations are decoupled and solved using a banded global matrix solver, with the vector and parallel processing on the IBM 9000. To avoide the numerical oscillations of the nonlinear problems in the case of convective dominant transport, the techniques of upstream weighting, mass lumping, and elementary-wise parameter evaluation are applied. The instability and convergence criteria of the nonlinear problems are studied for the one-dimensional analogue of FEM and FDM. Modeling capacity is presented in the simulation of three dimensional composite multiphase TCE migration. Comprehesive simulation feature of the code is presented in a companion paper of this issue for the specific groundwater or flow and contamination problems.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.6
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• pp.442-448
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• 2013

There are two approaches in measuring colors (or chromaticity) in water, i.e., visual comparison method and spectrophotometric method. The color of sample was determined by comparing with that of platinum-cobalt standard solution in the visual comparison method. Single or multiple wavelengths are used for the spectrophotometric method. As the accuracy and precision of visual comparison method depend on the eye sight of the analyzer, the results are not so reliable and representative. In addition, it is hard to measure chromaticity less than 5 TCU. Single wavelength approach in spectrophotometric method, can be applied for groundwater or surface water with natural organic matter (i.e., humic substances) while it's hard to measure the color of wastewater which includes anthropogenic chemical compounds. The measurements with multiple wavelengths approach resulted in reliable data regardless of the source of sample water, i.e., surface water and wastewater. As dozens of measurements and complicated calculations for one sample were required for the multiple wavelengths approach, the approach could not be applied for field measurement. In the present study, the authors tested efficient method which could measure the color of water sample accurately and precisely regardless of the source of water. With the colorimeter with multiple wavelengths and calculation program, the colors of water samples could be measured within 3~4 seconds with accuracy and precision.

• Clean Technology
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• v.26 no.4
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• pp.293-303
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• 2020

According to the World Health Organization (WHO), air pollution is a typical health hazard, resulting in about 7 million premature deaths each year. Sulfur dioxide (SO2) is one of the major air pollutants, and the combustion process with sulfur-containing fuels generates it. Measuring SO2 generation in large combustion environments in real time and optimizing reduction facilities based on measured values are necessary to reduce the compound's presence. This paper describes the concentration measurement for SO2, a particulate matter precursor, using a wavelength modulation spectroscopy (WMS) of tunable diode laser absorption spectroscopy (TDLAS). This study employed a quantum cascade laser operating at 7.6 ㎛ as a light source. It demonstrated concentration measurement possibility using 64 multi-absorption lines between 7623.7 and 7626.0 nm. The experiments were conducted in a multi-pass cell with a total path length of 28 and 76 m at 1 atm, 296 K. The SO2 concentration was tested in two types: high concentration (1000 to 5000 ppm) and low concentration (10 ppm or less). Additionally, the effect of H2O interference in the atmosphere on the measurement of SO2 was confirmed by N2 purging the laser's path. The detection limit for SO2 was 3 ppm, and results were compared with the electronic chemical sensor and nondispersive infrared (NDIR) sensor.

• 한국노년학
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• v.37 no.4
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• pp.835-852
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• 2017

The purpose of this study was to examine the moderating effects of social support on material hardship of low-income elderly people that have been excluded from the National Basic Livelihood Security System. For this research, data of 255 persons aged 65 and over were collected using a survey conducted in 2014 by the National Human Rights Commission of Korea on the minimum living cost of low-income household. Data analysis was performed through descriptive analysis, correlation analysis, and multiple regression analysis with STATA13. According to the results, the average level of material hardship in low-income elderly people was 1.45 out of 6, with the most hardship shown in heating and health care. The results of multiple regression analysis showed that when low-income elderly people became excluded from the system, they suffered more than the recipients. They also showed that the social support system of low-income elderly people brought a negative impact on their material hardship when they were connected by the strong social support system. In other words, social support system reduced their material hardship caused by exclusion. Based on the results, this study suggests some practical and political means to reduce material hardship of low-income elderly people.

• Journal of Energy Engineering
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• v.20 no.2
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• pp.103-108
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• 2011

$Li_2MnSiO_4$/C was synthesized by solid state reaction and solution synthesis with sucrose for carbon source. The X-ray diffraction patterns of solid state reaction indicates small amount of impurities. By FE-SEM and HR-TEM, solution synthesis comprised several tens of nanometer comparing to 500~600 nm of $Li_2MnSiO_4$/C prepared by solid state reaction. The $Li_2MnSiO_4$/C prepared by solution synthesis show better electrochemical performance than solid state reaction. The first charge-discharge capacity are 236, 189 mAh/g respectively by solution synthesis. But its cycle performance was poor as yet and its capacity retention was 62% after 10 cycles.

• Journal of Korean Elementary Science Education
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• v.41 no.2
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• pp.418-431
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• 2022

In this study, we analyzed the form, presentation, and interactivity of external representations presented in the matter units of elementary school science digital textbooks developed under the 2015 Revised National Curriculum. The analytic framework of the previous study was modified and supplemented. The matter units in the 3rd-6th grade science digital textbooks were analyzed by dividing them into "body texts" and "inquiries" area. The results revealed that visual-verbal and visual-nonverbal representations were presented the most. Conversely, audial-nonverbal representations were presented at a high frequency only in the body texts, and audial-verbal representations were presented at a low frequency in both the body texts and the inquiries. Regarding the presentation, when verbal and visual-nonverbal representations appeared together, visual-verbal and visual-nonverbal representations were primarily presented together. In some cases where visual-verbal, audial-verbal, and visual-nonverbal representations were presented together, information on visual-verbal and audial-verbal representations was presented redundantly. Audial-nonverbal representations unrelated to contents were presented along with other external representations, and the frequency was particularly high in the body texts. Regarding the contiguity, no visual-verbal and visual-nonverbal representations were presented on different pages, and no audial-verbal representations were presented asynchronously with visual-nonverbal representations. Regarding the interactivity, explanatory feedback and low-level manipulations were mainly presented. Based on the results, implications to improve digital textbooks are discussed from the perspective of multiple representation-based learning.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.42 no.6
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• pp.787-792
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• 2022

In winter, the excessive use of deicing salt deteriorates concrete pavement durability. To reduce the amount of deicing salt used, phase-change materials (PCMs) potentially offer an alternative way to melt snow through their latent heat storage characteristics. In this research, thermal energy storage concrete was developed by using PCM-impregnated expanded clay as 50 % replacement to normal aggregate by volume. In addition, to improve the thermal efficiency of PCM lightweight aggregate (PCM-LWA)-incorporated concrete, multi-walled carbon nanotubes (MWCNTs) were incorporated in proportions of 0.10 %, 0.15 %, and 0.20 % by binder weight. Compressive strength testing and programmed thermal cycling were performed to evaluate the mechanical and thermal responses of the PCM-LWA concrete. Results showed a significant strength reduction of 54 % due to the PCM-LWA; however, the thermal performance of the PCM-LWA concrete was greatly improved with the addition of MWCNTs. Thermal test results showed that 0.10 % MWCNT-incorporated concrete had high thermal fatigue resistance as well as uniform heat flow, whereas specimens with 0.15 % and 0.20 % MWCNT content had a reduced thermal response due to supercooling when the ambient temperature was varied between -5℃ and 10℃.

• Korean Chemical Engineering Research
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• v.52 no.6
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• pp.713-719
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• 2014

When multiple reactions of quaternary mixtures take place in a reactive distillation column, the behavior of composition trajectory is analyzed by a visual-aided method. By adding additional vectors of multiple reactions and visualizing them in composition space, the composition of each component and extent of each reaction on an arbitrary stage can be easily estimated in terms of the composition trajectory and reaction cascade difference points. Moreover, for a given operating conditions, the number of total stages and position of optimum reaction zone can be determined by the visual-aided method. In this study, ethylene glycol synthesis with a side reaction is taken as an example and analyzed by the proposed graphical method. Through this method, the quaternary reactive distillation with multiple reactions can be analyzed without numerous experiments and simulations.