• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.409-416
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• 2005

Design analysis for underground spaces requires evaluating stability related to tunnel collapses. A failure mode is one of the critical factors in the conventional methods of stability analysis. Therefore identification of failure modes is essential in securing safe construction in the phase of design analysis, instrumentation planning and implementation of reinforcing measures. In this study failure modes at the tunnel heading in granular soils are investigated using physical model tests and numerical simulation for various tunnel depths and ground surface inclinations. Test results indicated that the effect of depth and inclination of ground surface on a failure mode are significant. It is identified that, with an incase in depth, failure modes become localized in a region close to the tunnel. It is also known that an increase in the inclination of ground surface results in inclined and wide failure modes.

• Korean Journal of Health Education and Promotion
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• v.20 no.3
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• pp.207-219
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• 2003

This study was conducted to identify the effects of the comprehensive nursing aided self-help program for hypertensives. The program educates hypertensives in community areas about blood pressure, self-care, health promoting behaviors, and life satisfaction. For this purpose a one group time series design was used. Sixteen subjects were evaluated from S Community Health center of B city. Self-help programs developed by the author were given to the subjects. The program consisted of group education on hypertension and self-care including blood pressure self-monitoring, recording of self-care activities, and encouraging and reinforcing self-help. The whole program was carried out from October to December in 2002. Data was analyzed by repeated measure ANOVA, and post-hoc Turkey. The results were as follows： There were significant relationships between changes in systolic pressure(F＝10.638. P=.000), diastolic pressure(F＝6.783. p＝.013), self-care(F＝13.506. p＝.000), and health promoting behavior(F＝9.067. p＝.001) at the 6th week and the 9th week. There were no significant relationships between changes in life satisfaction at the 6th week or 9th week. From these results, it can be concluded that the self-help program is an effective nursing strategy to promote self-care of hypertensives in community areas.

• Korean Journal of Health Education and Promotion
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• v.20 no.3
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• pp.171-188
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• 2003

This study, based on stages of behavioral change, was aimed at suggesting strategies for the adoption of moderate drinking habits for community-based health education designed to help rural people. An interview survey was conducted during the period from March 4 to April 5, 2002 by sampling 467 rural people living in 6 villages covered by a public healthcare clinic. The results of this study can be summarized as follows； 1. The perceived non-moderate drinkers were less prepared for behavioral change. 2. The heavier drinking habits were ‘drinking alone’, ‘meals accompanied by drinking’ and ‘drinking twice or more at a time’. The agricultural off-season and the custom of brewing liquor at home were negative environmental factors for moderate drinking. 3. The predisposing factors affecting moderate drinking were recognition of health, expectation of the drinking effect, etiquette encouraging overdrinking and control of drinking. The reinforcing factors were stress from ordinary life and perception of being loved. The enabling factor was accessibility to the public healthcare clinic. 4. Rural residents are less motivated to participate in health education for moderate drinking. Based on the above findings, health education strategies for each stage can be suggested as follows： 1) Pre-contemplation stage： improvement of perception, motivation, sharing of experiences, and reawakening. 2) Contemplation/preparation stag e： measurement of value, departure from the inertia against a change, formation of a habit, and reinforcement of the behavior. 3) Action/maintenance stage： creation of a social atmosphere, encouragement of participation, change of life style, and improvement of environment.

• International Journal of Concrete Structures and Materials
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• v.10 no.3
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• pp.325-335
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• 2016

This paper studies the effects of steel fibre geometry and architecture on the cracking behaviour of steel fibre reinforced concrete (SFRC), with the reinforcements being four types, namely 5DH ($Dramix^{(R)}$ hooked-end), 4DH, 3DH-60 and 3DH-35, of various hooked-end steel fibres at the fibre dosage of 40 and $80kg/m^3$. The test results show that the addition of steel fibres have little effect on the workability and compressive strength of SFRC, but the ultimate tensile loads, post-cracking behaviour, residual strength and the fracture energy of SFRC are closely related to the shapes of fibres which all increased with increasing fibre content. Results also revealed that the residual tensile strength is significantly influenced by the anchorage strength rather than the number of the fibres counted on the fracture surface. The 5DH steel fibre reinforced concretes have behaved in a manner of multiple crackings and more ductile compared to 3DH and 4DH ones, and the end-hooks of 4DH and 5DH fibres partially deformed in steel fibre reinforced self-compacting concrete (SFR-SCC). In practice, 5DH fibres should be used for reinforcing high or ultra-high performance matrixes to fully utilize their high mechanical anchorage.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.11a
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• pp.125-128
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• 2005

The dispersion of carbon nanofiber (CNF) was carried out by solution blending, mechanical mixing, and sonication. CNFs at levels of 5-50% fiber weight content were mixed with polypropylene (PP) powder, and then were melt-mixed using a twin-screw extruder. For the further alignment of fibers, extruded rods were stacked uni-directionally in the mold cavity for the compression molding. For the evaluation of mechanical properties of nanocomposites, tension, in-plane shear, and flexural tests were conducted. CNF/PP composites clearly showed reinforcing effect in the longitudinal direction. The tensile modulus and strength have improved by 100% and 40%, respectively for 50 % fiber weight content, and the flexural modulus and strength have increased by 120% and 25%, respectively for the same fiber weight content. The shear modulus showed 65% increase, but the strength dropped sharply by 40%. However, the property enhancement was not significant due to the poor adhesion between fiber and matrix. In the transverse direction, the tensile, flexural, and shear strength decreased as more fibers were added.

• Journal of Korea Foundry Society
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• v.16 no.6
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• pp.537-549
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• 1996

This study aims at investigating the correlation of microstructure and mechanical properties of the AZ91 Mg/Al borate whisker composites fabricated by squeeze csting technique with a variation of applied pressure. Microstructure observation and in-situ fracture tests were conducted on the composites to identify the microfracture process. Detailed microstructural analyses indicated that the grain refinement could be achieved with applied pressure and the little change in volume fraction on reinforcing whiskers could be carried out. It was also found clearly from in-situ observation of crack initiation and propagation that in the composite processed by the lower applied pressure, microcracks were initiated earily at whisker/matrix interfaces, thereby resulting in the drop in strength. In the composite processed by the higher applied pressure, on the other hand, planar slip lines were well developed in the matrix, and then propagated through whiskers without whisker/matrix decohesion. Thus, the effect of the applied pressure on microstructure and mechanical properties can be explained by grain refinement, increased amounts of reinforcements, and improvement of whisker/matrix interfacial strength as the applied pressure in increased.

• Composites Research
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• v.32 no.6
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• pp.375-381
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• 2019

Multiwalled carbon nanotubes (MWCNTs) are covalently functionalized with isocyanates by directly reacting commercial hydroxyl functionalized MWCNTs with excess 4,4'-methylenebis (phenyl isocyanate) (MDI) and hexamethylene diiosocyanate (HDI). HDI-modified MWCNTs results in a higher surface isocyanate density than MDI-modified MWCNTs. Anionic ring-opening polymerization of ε-caprolactam is conducted using a sodium caprolactam initiator in combination with a di-functional hexamethylene-1,6-dicarbamoylcaprolactam activator in the presence of isocyanate functionalized MWCNTs. This polymerization proceeds in a highly efficient manner at relatively low reaction temperature (150℃) and short reaction times (10 min). During the polymerization, the isocyanate functionalized MWCNTs act not only as reinforcing fillers but also as second activators. Nanocomposites with HDI modified MWCNTs exhibit higher reinforcement and faster isothermal crystallization than MDI modified MWCNTs. The results show that PA6 chains grow more effectively from HDI modified MWCNT surface than from MDI modified MWCNT surface, resulting in stronger interaction between PA6 and MWCNTs.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.20 no.1
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• pp.7-15
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• 2014

Agar-based composite films were prepared with variety of food processing and agricultural processing waste materials in order to screen natural lingo-cellulosic resources for the value-added utilization of the under-utilized materials. The effect of these waste materials (10 wt% based on agar) on mechanical properties, moisture content (MC), water vapor permeability (WVP), water absorption behavior of biocomposite films were investigated. Biocomposite films prepared with various fibers resulted in significant increase or decrease in color and percent transmittance. The MC, WVP, and surface hydrophobicity of biocomposite films increased significantly by incorporation of fibers, while the water uptake ratio and solubility of the film decreased. SEM images of biocomposite film showed better adhesion between the fiber and agar polymer. Among the tested cellulosic waste materials, rice wine waste, onion and garlic fibers were promising for the value-added utilization as a reinforcing material for the preparation of biocomposite food packaging films.

• Earthquakes and Structures
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• v.3 no.6
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• pp.889-910
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• 2012

Because of the heavy demand of confining steel to restore the column ductility in seismic regions, it is more efficient to confine these columns by hollow steel tube to form concrete-filled-steel-tube (CFST) column. Compared with transverse reinforcing steel, steel tube provides a stronger and more uniform confining pressure to the concrete core, and reduces the steel congestion problem for better concrete placing quality. However, a major shortcoming of CFST columns is the imperfect steel-concrete interface bonding occurred at the elastic stage as steel dilates more than concrete in compression. This adversely affects the confining effect and decrease the elastic modulus. To resolve the problem, it is proposed in this study to use external steel confinement in the forms of rings and ties to restrict the dilation of steel tube. For verification, a series of uni-axial compression test was performed on some CFST columns with external steel rings and ties. From the results, it was found that: (1) Both rings and ties improved the stiffness of the CFST columns and (2) the rings improve significantly the axial strength of the CFST columns while the ties did not improve the axial strength. Lastly, a theoretical model for predicting the axial strength of confined CFST columns will be developed.

• Women's Health Nursing
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• v.23 no.3
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• pp.210-220
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• 2017

Purpose: The aims of the study were to develop mobile application for postpartum care of first-time mothers and to validate it's effect. Methods: Using a nonequivalent control group pretest-posttest design, 52 first-time mothers were recruited (26 each in experimental and control) and the experimental group used the mobile application for 6 weeks after delivery. Postpartum self-care knowledge and confidence, infant care knowledge and confidence, and postpartum depressive mood (Edinburgh Postnatal Depression Scale) were measured before discharge from the hospital and 6 weeks later. Results: Women who have used the postpartum care mobile application reported higher levels of postpartum self-care knowledge (p=.030) and confidence (p=.023) infant care knowledge (p=.001) and confidence (p=.004), while scores of postpartum depression (p=.021) were lower than those in the control group. Conclusion: The postpartum-care mobile application developed in this research may be effective in reinforcing knowledge and confidence for postpartum self-care and infant care and in reducing postpartum depressive mood.