• International Journal of Highway Engineering
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• v.4 no.1 s.11
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• pp.149-159
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• 2002

This study was performed to estimate the high-speed direct tensile strength(DTS1), low-speed direct tensile strength(DTS2) , indirect tensile strength(ITS) resilient modulus(MR) and stiffness index(SI) of sand asphalt mixture based on the absolute viscosity, kinematic viscosity, penetration, softening point and PG grade of binder. DTS2 showed higher correlation with the physical properties than other properties of mixture, and the next was DTS1, ITS, SI and MR in order. Among binder properties, PG grade showed the highest relation with DTS2. Therefore. it was found that the high DTS mixture could be made when the binder with a high PG grade was used. However, since the individual physical property showed a relatively low correlation, various properties were used together in regression analysis. The estimation models of DTS and ITS were over 0.99, respectively. R2 of MR and SI estimation models were over 0.91 and 0.93, respectively. It was concluded that mechanical properties could be estimated with a high coefficient of determination from those physical properties.

• Composites Research
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• v.17 no.3
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• pp.8-14
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• 2004

The effect of moisture absorption on the mechanical properties in carbon fiber reinforced composites has been investigated with various moisture environment such as sea water, tap water and distilled water. It also has been studied about the influence of drying of the immersed specimen for a certain period of time on the mechanical properties. As a result, we found that the ratio of moisture absorption mainly depended on the immersion time in the moisture environment and that of the immersed specimen for a certain period of time decreased with the drying time. We also found that tensile strength decreased with the increasing of the ratio of moisture absorption and the tensile strength decreased by moisture absorption recovered up to some extent by drying the specimen.

• Journal of Korean Clinical Nursing Research
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• v.26 no.3
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• pp.275-284
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• 2020

Purpose: For this study the moderating and mediating effects of resilience on the relationships between work intensity, conflicts in interpersonal relationship and nurses' burnout were investigated. Methods: In this descriptive research 227 nurses who consented to participate in the study were surveyed. The tool included nurses' objective work intensity, subjective work intensity, conflicts in interpersonal relationships, resilience, and burnout. Data were collected from nurses in general hospitals in D city from July to August 2017. Collected data were analyzed using SPSS 23.0 program. Results: Participants' burnout showed a statistically significant difference according to age, marital status, total clinical experience, position, work pattern, frequency of night shifts, work department, and salary. Participants' burnout was significantly positively correlated with subjective work intensity and conflicts in interpersonal relationships, and significantly negatively correlated with resilience. Resilience moderated the relationship between participants' subjective work intensity and burnout, and mediated the relationship between conflicts in interpersonal relationships and burnout. Conclusion: Resilience had a moderating effect on the relationship between subjective work intensity and burnout, and a mediating effect on the relationship between conflicts in interpersonal relationships and burnout. Therefore, further efforts and diverse intervention measures are required to enhance resilience and reduce work intensity and conflicts in interpersonal relationships in order to prevent burnout in nurses.

• Journal of the Korea Institute of Building Construction
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• v.19 no.1
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• pp.47-57
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• 2019

The purpose of this study is to evaluate the improvement effect of adhesion in tension and flexure of polymer cement mortars that have widely used as a repair-reinforcement material in construction field according to adding of polymer dispersions depending on different three types test methods. From the test results, the adhesion performance is improved with a raise in polymer-cement ratio irrespective of the type of polymer. The maximums of A type adhesion in tension, B type adhesion in tension and adhesion in flexure show 1.90 times, 2.17 times and 1.83 times, respectively that of plain cement mortar. The relative strength ratios, B type adhesion in tension and adhesion in flexure of polymer cement mortars to tensile and flexural strengths of plain mortar respectively are in ranges of 50.1% to 101.7% and 73.8% to 132.9% compared to 46.9% of plain mortar. It is apparent that polymer cement mortars with EVA and polymer cement ratios of 10% to 15% are recommended considering its adhesion performance and cost as a repair-reinforcement material in construction field.

• Journal of the Korea Convergence Society
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• v.12 no.12
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• pp.401-409
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• 2021

This study was conducted to investigate the effects of static recovery and dynamic recovery methods on heart rate, blood lactic acid concentration, and blood glucose during recovery after walking at the speed of 80bpm and 130+30bpm upon trekking of forest slopes in Taejo Mountain in Cheonan. 9 men in their 20s and 30s who had no abnormality in walking was subject to this experience. The result of through static recovery and dynamic recovery methods while trekking at the speed of 80bpm and 130+30bpm were analyzed by two-way repeated ANOVA. When there was a significant difference, the repeated method of contrast was applied to compare and analyze. The heart rate at 80bpm condition was significantly different depending on the method(p=.008) and time(p=.000) and there was no significant difference in blood lactic acid concentration for the recovery method(p=.401), but there was a significant difference depending on the time(p=.000). Blood glucose did not show significant difference according to the recovery method(p=.093), and there was significant difference depending on the time of static recovery method(p=.002). The heart rate in 130bpm + 30bpm condition was significantly different depending on to the method(p=.002) and time(p=.000), blood lactic acid concentration was significantly different depending on the method(p=.001) and time(p=.000), and blood glucose concentration was not significantly different between the time(p=090) and the method(p=.721).

• Composites Research
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• v.31 no.3
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• pp.88-93
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• 2018

In this study, damaged composite laminates were repaired by a stepped patch repair method using halloysite nanotube(HNT) and milled carbon(MC) reinforced composite materials with different amount of the particles. And the mechanical and structural effects of the particles on the interface between the damaged and repair surfaces were analyzed. At this time, after exposing them to a harsh environment of high temperature and humidity for a long time, the recovery rate of the material properties relative to the material forming the damaged plate was compared. As a result, at $70^{\circ}C$ high temperature distilled water, the hygroscopicity of the HNT/GFRP composites was significantly different from that of the MC/GFRP composites. Especially, 0.5, 1 wt. % HNT was added, the moisture absorption rate was the lowest and this was the factor that contributed to the mechanical strength increase. On the other hand, MC showed a high hygroscopic resistance only with a small amount, and the strength was different according to the action direction of the load, and the addition amount was also different.

• International Journal of Highway Engineering
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• v.10 no.3
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• pp.57-68
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• 2008

The stabilization techniques in the pavement foundations have advantages in increasing pavement performance and reducing pavement thickness. By mixing the geomaterials and stabilizer, the economical and structurally sound layer can be added in the pavement system. Until now, these techniques have been applied in the field empirically and the design criteria for stabilization has not been established. The purposes of this paper are to evaluate the mechanistic properties of stabilizers used for geomaterials and determine the type and optimum amount of stabilizer for each technique. The unconfined compressive testing and repeated load resilient modulus test were conducted on the coarse grained soils mixed with various types of stabilizer to investigate the strength and deformation characteristics of stabilized geomaterials. It is found from the test that the unconfined compressive strength of stabilized geomaterials is more than ten times higher than that of gradation modified geomaterials. The resilient modulus of stabilized geomaterials increases by $6{\times}10$ times compared to the original soils and tends to increase with increase of volumetric and deviatoric stress, and amount of stabilizer.

• Journal of the Korea Institute of Building Construction
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• v.17 no.3
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• pp.269-277
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• 2017

In this work, as a preliminary experimental works, which focuses on utilizing separated pastes from activated (or radioactive) concrete as solidifying agents for radioactive waste immobilization, were performed. It was found that density of hydrated cement paste, which was lower than that of ordinary portland cement, increased as temperature for heat treatment increased. Highest compressive strength was observed with the specimens that was heat treated at $600^{\circ}C$. However, heat treatment over $700^{\circ}C$ showed higher CaO content that caused higher heat of hydration after in contact with water, lows of workability, and lower strength. Based on experimental results, it is suggested that $600^{\circ}C$ heat treatment is more appropriate for waste cement paste to be used as a solidifying agent.

• Journal of Dental Rehabilitation and Applied Science
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• v.26 no.3
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• pp.339-347
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• 2010

Enhancement of bond strength between new and old composite usually requires increasing the surface roughness to promote mechanical interlocking. This study evaluated the effect of different surface treatments on repair bond strength of resin composite after aging condition. Air abrasion with Al2O3, chairside silicacoating, and silanization provided higher resin-resin bond strength values compared to control group and HF group. Air abrasion is necessary to repair a resin restoration and additional application of silane seems to have good effects on bond strength.

• Restorative Dentistry and Endodontics
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• v.34 no.6
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• pp.515-525
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• 2009

Clinical suggestion for the limitation of application time of NaOCl solution is needed to avoid large reductions in resin-dentin bond strength. The aim of this study was to measure the change of ${\mu}$-tensile bond strength after the various application time of 5.25% NaOCl solution to pulp chamber dentin in endodontic access cavity, and to evaluate the effect of 10% sodium ascorbate application for 10 min on bond strength after the treatment of 5.25% NaOCl solution. In this experiment, there were no statistical differences(p > 0.05) in bond strengths between upper chamber dentin and lower chamber dentin. NaOCl-treated group for 20 min did not show any significant decrease(p > 0.05) in bond strength than non-treated control group. In contrast to that, bond strengths of NaOCl-treated groups for 40 & 80 min were significantly lower(p < 0.05) than that of non-treated control group. 10% sodium ascorbate retreated group for 10 min after 5.25% NaOCl application for 40 min to chamber dentin showed the recovery of bond strength significantly. However, the bond strength of sodium ascorbate retreated group after 5.25% NaOCl application for 80 min was still significantly lower(p < 0.05) compared to the non-treated control group, which means the reductions in resin-dentin bond strength were not fully reversed. On the contrary, sodium ascorbate retreated group after 5.25% NaOCl application for 5 min showed significantly higher(p < 0.05) bond strength compared to the control group, which demonstrates its superior recovery effect. In SEM exminations of specimens retreated with 10% sodium ascorbate after NaOCl application for 40 & 80 min showed that resin tags were formed clearly and densely, but weakly in density and homogeneity of individual resin tag compared to the control specimen.