• Journal of dental hygiene science
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• v.15 no.4
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• pp.509-517
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• 2015

This study attempted to identify the entrance exam stress levels in high school students and analyze the relationship this entrance exam stress and perceived oral health status. Self-administered survey was conducted in total 304 students attending in academic high schools in Bucheon. For analysis, SPSS was used to perform t-test and one-way ANOVA. As a result of the study, the entrance exam stress level of academic high school students was 2.71. The level of sub-factors were that tension for exam/poor result was highest by 3.08 and the next were future uncertainty (2.81), parents pressure (2.56), and insufficient free time (2.52). The group with high entrance exam stress showed significantly high perceived degrees of temporomandibular disorder, oral mucosal disease and xerostama. Among sub-factors of stress, the group with high tension for exam/poor result stress had significantly high perceived degrees of dental caries, teporomandibular disorder, oral mucosal disease and xerostama. Because perception on oral health issues increased with high entrance exam stress in high school students, it is necessary to seek some ways to decrease oral health problems even though entrance exam stress is intensified. To do so, it is inferred that it will be very important to promote oral health education to develop ability of high school students to practice correct oral management method.

• Journal of the Korean Ceramic Society
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• v.41 no.3
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• pp.235-242
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• 2004

Si, NH$_4$Cl, NaN$_3$, NaCl, $N_2$ were used as raw materials for preparation of $\alpha$-Si$_3$N$_4$ powder. NH$_4$Cl and NaN$_3$ were used as additives, and NaCl was used as a diluent. Initial $N_2$ gas pressure in the SHS reactor was 60 atm. In preparation of $\alpha$-Si$_3$N$_4$, the reactivity and the properties of the products were examined with the various kinds of additives and the content of diluent. At first, the optimum reaction system for the preparation of $\alpha$-Si$_3$N$_4$ is examined and then the optimum composition was examined in the optimum reaction system. The optimum reaction system was Si-$N_2$-additive(NH$_4$Cl+NaN$_3$)-diluent(NaCl) and the optimum composition was 38 wt%Si+50 wt%(NH$_4$Cl+NaN$_3$)+12 wt%NaCl. The maximum fraction of $\alpha$-phase of Si$_3$N$_4$ produced in this condition was 96.5 wt% and the shape of the $\alpha$-Si$_3$N$_4$ produced in this condition was an irregular fiber with a length of 10 ${\mu}{\textrm}{m}$ and a diameter of 1 ${\mu}{\textrm}{m}$.

• Journal of Wetlands Research
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• v.20 no.2
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• pp.181-189
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• 2018

This study was performed to analyze the dynamics and distributional condition of biological community and to support the basic information about the estuarine ecosystem management by using the intensively surveyed results by each taxon experts around Tamjin river. We analyzed the biological diversity, abundance, correlation among species, and ecological characteristics about 11 taxa groups including vegetation, fish, birds, mammals, etc. in the Tamjin river estuarine ecosystem. We classified vegetation types into 7 physiognomic types and 18 communities according to habitat conditions with the physical environments and salinity. In total, 1125 species including 9 species of endangered species were identified in research area. The species composition and distributional characteristics of each taxon were corresponded to the environmental characteristics of the estuarine ecosystem. Especially, the species diversity and distribution were clearly distinguished in the river according to the difference of the environmental factors such as flow rate, salinity, and soil. Despite the disturbance factors such as barrage and levees, the biodiversity and its distribution were evaluated to be high level under the current environmental conditions. However, loss or reduction of wildlife habitat due to reclamation, embankment, barrage installation and expansion of farmland has been identified as a major threat to the diversity and health of the local ecosystem. The results of this study can be used as a basic data to cope with various development pressure and damage crisis of the whole estuaries including Tamjin river.

• Clean Technology
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• v.14 no.2
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• pp.110-116
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• 2008

The radioactive wastes generated from the nuclear industry can be divided into the forms of solid, liquid, or gas. Radioactive methyl iodide, a gaseous radioactive waste, is absorbed by activated carbon with 5 wt% of Trietylenediamine (1,4-diazania-bicycle[2.2.2]octane, TEDA) impregnated on the surface. Methyl Iodide ($CH_3I$) is combined chemically with TEDA (the final product : I-TEDA). To recycle radioactive activated carbon, removal of I-TEDA from activated carbon is needed. A wet method for recycling impregnated active carbon was developed to remove radioactive I-TEDA using an acetonitrile solution, which produces lots of secondary wastes. We suggest the removal of I-TEDA by supercritical carbon dioxide with co-solvents. In this experiment, we used a quartz crystal microbalance (QCM) for measuring the removal rate of the I-TEDA. From the experimental results, methanol was found to be the optimum co-solvent, and the optimum conditions such as temperature, pressure, and co-solvent flow rate were obtained. Possibility of using supercritical fluid in the removal of I-TEDA from radioactive activated carbon was also discussed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.1
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• pp.698-704
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• 2020

Although various biological extracts derived from the resources from Jeju are currently being developed for cosmetic materials, few studies using Brown algae from Jeju have been conducted. This study identified materials with high antioxidant levels and examined their whitening effects to assess their feasibility as potential cosmetic resources. Brown algae from Jeju (Undaria pinnatifida (Harvey) Suringar, Laminaria japonica, Ecklonia cava, Hizikia fusiforme (Harvey) Okamura (HF), and Sargassum fulvellum (Turner) C. Agardh (SF) were processed using a supercritical fluid system at 50℃ and 400 bar, and their total phenol content, antioxidant activity, tyrosinase inhibition, and primary skin irritation were measured. Of all the samples, only SF using the supercritical fluid system (SFS) displayed concentration-dependent behavior for the total phenol content (p<0.05). Among the samples, the antioxidant activity of SFS was significantly higher (p<0.05) and the one increased at higher concentrations (p<0.05). On the other hand, tyrosinase was inhibited to a greater extent with HF than the others. The primary skin irritation tests showed that none of the samples were skin irritants. This study confirmed the feasibility of using Phaeophyceae from Jeju as potential cosmetic materials, where the samples can be selected and utilized based on the required physicochemical properties.

• Membrane Journal
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• v.11 no.4
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• pp.190-203
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• 2001

In this study the discharged wastewater from a paper plant was filtrated by 4 kinds of tubular carbon ceramic ultrafiltration membranes with periodic water-back-flushing. We could investigate effects of watch-back-flushing period, transmembrane pressure (TMP) and flow rate, and find optimal operating conditions. The back-f1ushing time (BT) was fixed at 3 sec, and fi1tration times (FT) werc changed in 15~60 scc, TMP in 1.00~2.50$kg_{f}$/$cm^2$, and the flow rates in 0.27~1.75 L/min. The optimal conditions were discussed in 7he viewpoints of dimensionless permeate flux (J/J$_{0}$), total permeate volume ($V^T$) and resistance of membrane fouling ($R^f$). Optima1 back-flushing period was BT/FT=0.20, suggesting that the frequent back-flushing should decrease membrane fouling. Optimal TMP in the viewpoint of $V^T$ was 1.00~1.55$kg_{f}$/$cm^2$, suggesting that rising TMP should increase membrane fouling and decrease permeate flux. But, rising f1ow rate should decrease membrane fouling and increase permeate flux. Then, average rejection rates of pollutants filtratedby carbon ceramic membranes were 88~98 % for turbidity, 48~72% fort $COD_{cr}$ and 37~76% for TDS.

• Journal of the Korean Institute of Gas
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• v.26 no.4
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• pp.9-17
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• 2022

This paper is the continuation of our previous paper, which we refer to as numerical analysis of phase behavior and flow properties in an injection tubing during gas phase CO₂ injection. Our study in this paper show the results during supercritcal CO₂ injection under the same project. Geological CO₂ storage technology is one of the most effective method to decrease climate change due to high injectivity and storage capacity and economics. A demonstration-scale CO₂ storage project was performed in a deep aquifer in the Pohang basin, Korea for a technological development in a large-scale CO₂ storage project. A problem to consider in the early stage design of the project was to analyze CO₂ phase change and flow characteristics during CO₂ injection. To solve this problem, injection conditions were decided by calculating injection rate, pressure, temperature, and thermodynamic properties. For this research, we simulated and numerically analyzed CO₂ phase change from liquid to supercritical phase and flow characteristics in injection tubing using OLGA program. Our results provide discharge pressure and temperature conditions of CO₂ injection combined with a pressure of an aquifer.

• Journal of Korea Entertainment Industry Association
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• v.13 no.8
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• pp.551-561
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• 2019

The purpose of this study was to investigate the relationship between entrance exam stress and oral care self-efficacy in girls high school. From June to July 2018, A self-reported questionnaire was administered to 192 high school students in the G area. The data were analyzed for independent t-test, one-way ANOVA and Pearson's correlation coefficient by using SPSS/WIN 21.0 program. Among the sub-sectors of entrance exam stress, exam tension/poor was the highest with 3.07 points, followed by Insufficient spare time stress 2.83 points, future uncertainty stress 2.57 points, and parent pressure stress 2.44 points. the variables related to exam tension/poor stress were academic performance (p<.01), family income level (p<.05), Subjective oral health status(p<.05), and daily brushing frequency(p<.01). The highest level of oral care self-efficacy was 3.13 points for brushing self-efficacy, followed by dental visits 2.80 points and interdental hygiene 2.64 points. As a result of analyzing the general characteristics and oral care self-efficacy, subjects related to brushing self-efficacy were subjective oral health status, caries snacking(daily), and caries drinks(daily)(p<.01). There were negative correlations between entrance exam stress and oral care self-efficacy. The higher the entrance stress, the lower the oral care self-efficacy. To prevent oral disease and increase oral care self-efficacy of students with high entrance stress, it is necessary to provide school oral health education programs that can facilitate oral health behaviors.

• Journal of Korea Foundry Society
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• v.43 no.6
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• pp.302-309
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• 2023

In general, castings often have complex shapes and significant variations in thickness within a single product, making grid generation for simulations challenging. Casting flows involve multiphase flows, requiring the tracking of the boundary between air and molten metal. Additionally, considerable time is spent calculating pressure fields due to density differences in a numerical analysis. For these reasons, the Cartesian grid system has traditionally been used in mold filling simulations. However, orthogonal grids fail to represent shapes accurately, leading to a momentum loss caused by the stair-like grid patterns on curved and sloped surfaces. This can alter the flow of molten metals and result in incorrect casting process designs. To address this issue, simulations in the Cartesian grid system involve creating a large number of grids to represent shapes more accurately. Alternatively, the Cut Cell method can be applied to address the problems arising from the Cartesian grid system. In this study, analysis results based on the number of grid in the Cartesian grid system for a casting flow analysis were compared with results obtained using the Cut Cell method. Casting flow simulations of actual products during various casting processes were also conducted, and these results were analyzed with and without applying the Cut Cell method.

• Analytical Science and Technology
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• v.29 no.3
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• pp.142-153
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• 2016

In crime scene investigation, fingerprint identification is regarded to be one of the most important techniques for personal identification. However, objective and unbiased evaluation methods that would compare the fingerprints with diverse available and developing methods are currently lacking. To develop an objective and quantitative method to improve fingerprint evaluation, a preliminary study was performed to extract useful research information from the analysis with densitometric image analysis (CP Atlas 2.0) and the Automated Fingerprint Identification System (AFIS) for the developed fingerprints on porous surfaces. First, inked fingerprints obtained by varying pressure (kg.f) and pressing time (sec.) to find optimal conditions for obtaining fingerprint samples were analyzed, because they could provide fingerprints of a relatively uniform quality. The extracted number of minutiae from the analysis with AFIS was compared with the calculated areas of friction ridge peaks from the image analysis. Inked fingerprints with a pressing pressure of 1.0 kg.f for 5 seconds provided the most visually clear fingerprints, the highest number of minutiae points, and the largest average area of the peaks of the friction ridge. In addition, the images of the developed latent fingerprints on thermal paper with the iodine fuming method were analyzed. Fingerprinting condition of 1.0 kg.f/5 sec was also found to be optimal when generating highest minutiae number and the largest average area of peaks of ridges. Additionally, when the concentration of ninhydrin solution (0.5 % vs. 5 %) was used to compare the developed latent fingerprints on print paper, the best fingerprinting condition was 2.0 kg.f/5 sec and 5 % of ninhydrin concentration. It was confirmed that the larger the average area of the peaks generated by the image analysis, the higher the number of minutiae points was found. With additional tests for fingerprint evaluation using the densitometric image analysis, this method can prove to be a new quantitative and objective assessment method for fingerprint development.