• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.2
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• pp.1469-1476
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• 2015

The bridges take a significant part of entire route in Korea railway, because 70% of Korean territory is covered with mountains. For this reason, span enlargement of railway bridges is more advantageous to increase economic efficiency on the bridge design. However there are many limitations such as additional axial force of the rail, excessive displacement due to track-bridge interaction. In this study, track-bridge interaction analysis was conducted considering the sliding layer which was installed between the track and girder. From the numerical analysis results, the behavior of track-bridge interaction was investigated according to the installation method of sliding layer. Finally, a guideline for development of track-bridge structure system to reduce the track-bridge interaction was proposed.

• Journal of Korean Society of Steel Construction
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• v.19 no.5
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• pp.527-537
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• 2007

The main girders and cross-beams of an H-beam bridge consisted of factory-made H-beams, providing better conditions for quality control. Also, on-site fabrication works can be minimized and most of the stiffeners can be omitted, enabling simple and economic construction. In this study, the effect of the Multi-Stepwise TPSM (M-TPSM) on improving the maximum span length and section efficiency is analyzed. Compared to a 30-m-long, five-girder conventional plate girder bridge, structural analysis results showed that 50.7~55.1% of the girder height and 24.1~26.2% of the self-weight may be reduced by the application of M-TPSM to a five-girder H-beam bridge constructed with H-$900{\times}300$beams. In case of conventional H-beam bridges without M-TPSM, it was found that seven girders are required for a similar level of load-carrying capacity. Therefore, it is concluded that by the application of the M-TPSM, the H-beam bridge would become one of most cost-competitive options for short- and medium-span bridges.

• Journal of Korean Society of Transportation
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• v.26 no.4
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• pp.87-97
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• 2008

The traditional trip-based modeling approach has assumed that a trip is generated for a purpose. However, the approach has not considered trips as a set of connected trips nor has it considered trip chaining. The purpose of this study is to identify general characteristics of trip chaining, and to explore relationships between trip purposes and trip chains using multivariate regression models. The data for this study come from the 2006 Seoul household travel diary survey. It is found that simple trip chains are dominant phenomena, and socio-economic characteristics such as occupation, income, age, and gender are closely related to types of trip chains. People aged less than 20, females, or high-income people are more likely to have a higher number of home-based trip chains. In addition, commute and school trips for workers and students respectively tend to be strongly associated with simple trip chains, while shopping and leisure trips for housewives tend to be related to simple trip chains.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.277.2-277.2
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• 2013

Petri dishes and glass slides have been widely used as general substrates for in vitro mammalian cell cultures due to their culture viability, optical transparency, experimental convenience, and relatively low cost. Despite the aforementioned benefit, however, the flat two-dimensional substrates exhibit limited capability in terms of realistically mimicking cellular polarization, intercellular interaction, and differentiation in the non-physiological culture environment. Here, we report a protocol of culturing embryonic rat hippocampal neurons on the electro-spun polymeric network and the results from examination of neuronal cell behavior and network formation on this culture platform. A combinatorial method of laser-scanning confocal fluorescence microscopy and live-cell imaging technique was employed to track axonal outgrowth and synaptic connectivity of the neuronal cells deposited on this model culture environment. The present microfiber-based scaffold supports the prolonged viability of three-dimensionally-formed neuronal networks and their microscopic geometric parameters (i.e., microfiber diameter) strongly influence the axonal outgrowth and synaptic connection pattern. These results implies that electro-spun fiber scaffolds with fine control over surface chemistry and nano/microscopic geometry may be used as an economic and general platform for three-dimensional mammalian culture systems, particularly, neuronal lineage and other network forming cell lines.

• Journal of the Korean Society of Food Science and Nutrition
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• v.44 no.1
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• pp.29-34
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• 2015

The objective of this study was to obtain data on the safety-in-use of nano calcium as a dietary supplement by assessing its acute and subacute oral toxicities in female and male Sprague-Dawley rats. A single oral dose of 5,000 mg/kg of nano calcium did not result in mortality or significant changes in the general behavior and gross appearance of the internal organs of rats. For subacute toxicity study, nano calcium was administered orally at a dose of 1,000 mg/kg daily for 14 days. There were no significant differences in organ weights between control and treated groups of both sexes. Hematological analysis and blood chemistry revealed no toxic effects of nano calcium. Pathologically, neither gross abnormalities nor histopathological changes were observed. These results show that nano calcium possesses very low toxicity as indicated in a rat model.

• Steel and Composite Structures
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• v.36 no.1
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• pp.75-86
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• 2020

The grid structures with welded hollow spherical joint (WHSJ) have gained increasing popularity for use in industrial buildings with suspended cranes, and usually welded with steel tube (ST). The fatigue performance of steel tube-welded hollow spherical joint (ST-WHSJ) is however not yet well characterized, and there is little research on fatigue life prediction methods of ST-WHSJ. In this study, based on previous fatigue tests, three series of specimen fatigue data with different design parameters and stress ratios were compared, and two fatigue failure modes were revealed: failure at the weld toe of the ST and the WHSJ respectively. Then, S-N curves of nominal stress were uniformed. Furthermore, a finite element model (FEM) was validated by static test, and was introduced to assess fatigue behavior with the hot spot stress method (HSSM) and the effective notch stress method (ENSM). Both methods could provide conservative predictions, and these two methods had similar results. However, ENSM, especially when using von Mises stress, had a better fit for the series with a non- positive stress ratio. After including the welding residual stress and mean stress, analyses with the local stress method (LSM) and the critical distance method (CDM, including point method and line method) were carried out. It could be seen that the point method of CDM led to more accurate predictions than LSM, and was recommended for series with positive stress ratios.

• Parasites, Hosts and Diseases
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• v.57 no.5
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• pp.499-504
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• 2019

Head-lice infestation, pediculosis capitis, remains a public-health burden in many countries. The widely used first-line pediculicides and alternative treatments are often too costly for use in poor socio-economic settings. Ivermectin has been considered an alternate treatment for field practice. This study was composed of 2 parts, a cross-sectional survey and an intervention study. The main objectives were to determine the prevalence and potential factors associated with head-lice infestation, and to evaluate the effectiveness and safety of oral ivermectin administration. A community-based cross-sectional survey was conducted among 890 villagers in rural areas along Thai-Myanmar border. Females with infestations were eligible for the intervention study, and 181 participated in the intervention study. A post-treatment survey was conducted to assess acceptance of ivermectin as a treatment choice. Data analysis used descriptive statistics and a generalized-estimation-equation model adjusted for cluster effect. The study revealed the prevalence of head-lice infestation was 50% among females and only 3% among males. Age stratification showed a high prevalence among females aged <20 years, and among 50% of female school-children. The prevalence was persistent among those with a history of infestation. The major risk factors were residing in a setting with other infected cases, and sharing a hair comb. The study also confirmed that ivermectin was safe and effective for field-based practice. It was considered a preferable treatment option. In conclusion, behavior-change communication should be implemented to reduce the observed high prevalence of head-lice infestation. Ivermectin may be an alternative choice for head-lice treatment, especially in remote areas.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.5
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• pp.279-286
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• 2019

In this study, a numerical investigation is conducted for the shock deceleration prediction of a conical impactor in gas-gun tests. With the development of weapon systems, gas-gun tests are required to validate the survivability and structural reliability of devices under test (DUT) in high-G shock environments, such as those over ten thousand Gs or more. As shock endurance is highly influenced by various bird parameters, such as mass, velocity, and pressure, it is important to determine the appropriate test conditions to generate a high-G shock environment. However, experimental repetitive studies are inefficient to validate test conditions in terms of economic aspects. Therefore, a numerical technique is required to replace experimental gas-gun tests. Here, a numerical investigation is conducted with ANSYS AUTODYN using explicit code. Through this investigation, the dynamic behavior of DUT is presented. In addition, the results of numerical studies are verified through a comparison with the experimental results of a gas-gun test.

• Journal of the Korean Society of School Health
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• v.30 no.3
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• pp.317-324
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• 2017

Purpose: Breakfast is the most important meal to provide energy for the day. Breakfast is especially important to give enough nutritional support to children and adolescents for their physical growth and sexual development. Sleep-related factors like average sleep duration and wake up time would mostly be associated with regular breakfast. This study aimed to investigate the effect of sleep on regular breakfast consumption in Korean adolescents. Methods: The study used the data from the 12th Korea Youth Risk Behavior Web-based Survey (KYRBS-XII) conducted in 2016 by the Korea Centers for Disease Control and Prevention. The data of 62,820 subjects (middle/high school students) were included in the final analysis. The study examined the factors related to regular breakfast, focusing on weekday average sleep duration and wake up time of middle school students and high school students, respectively. Results: Regular breakfast consumption was shown to have a statistically significant association with high economic status, nutritional education, weekday average sleep duration, wake up time, and subjective sleep satisfaction in the multivariate logistic regression. Regardless of the school level, regular breakfast consumption was significantly associated with early wake up time. As to the effect of weekday average sleep duration on regular breakfast consumption, it showed some different results depending on the school level. Conclusion: Regular breakfast consumption of Korean adolescents was related to weekday average sleep duration and wake up time. Having breakfast regularly was affected by both adequate weekday average sleep duration and early wake up time.

• Journal of dental hygiene science
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• v.21 no.3
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• pp.133-139
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• 2021

Background: Smoking in adolescence leads to an intensified addiction to nicotine when physical and mental growth has not yet been completed. With the advent of e-cigarettes, the rate of e-cigarette use among Korean adolescents has been steadily increasing. To date, studies on e-cigarettes and oral health, especially on the relationship between smoking styles and oral health in adolescents, are limited. Therefore, this study aimed to identify the risk factors for oral health problems caused by the repeated use of conventional cigarettes and e-cigarettes. Methods: This explanatory research study compared the adolescents' experiences of periodontal disease symptoms according to smoking type through a secondary analysis of the original data from the 15th Adolescent Health Behavior Survey (2019). Cross-analysis was performed to compare the smoking patterns according to the adolescents' general characteristics. Finally, a binary logistic regression analysis was performed to determine how smoking characteristics affect the adolescents' experience of periodontal disease symptoms. Results: In terms of patients' general characteristics, significant differences were observed in sex, school level, grades, household economic status, type of residence, and father's education level between adolescents who smoked conventional cigarettes alone and those who smoked both conventional cigarettes and e-cigarettes (p<0.05). After checking the factors affecting the smoking pattern and the experience of periodontal disease symptoms in adolescents, it was found that the duplicate smoking group was more likely to experience periodontal disease symptoms (odds ratio, 1.20) than the group that smoked conventional cigarettes alone (p<0.05). Conclusion: Duplicate smokers experienced more symptoms of periodontal disease than those who smoked cigarettes alone. Based on the findings of this study, smoking cessation counseling according to the smoking type and differentiated education for oral health promotion should be provided.