• 대한공업교육학회지
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• v.37 no.1
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• pp.43-64
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• 2012

The purpose of this study was to analyze the Energy and Transportation Technology Domain about Technology Home Economics textbook Contents of the 7th National Curriculum. 'Jackson's Mill Industrial Arts Curriculum Theory' was used for the content analysis criteria. The results of the study are as follows: First, the sub-systems 'input' and 'process' in contents of the textbooks was represented frequently. However, the 'output', the main contents in transportation technology, was not represented. Second, components of the knowledge, materials, energy and Capital are included in Inputs system. The highest frequency and intensity of the energy and materials were showed. Third, the frequency of the Productive Processes that showed the most. The highest frequency and intensity of Transporting/Moving in Productive Processes were showed. The rest of systems that require the ratio of the intensity values do not meet.

• Journal of the Korean GEO-environmental Society
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• v.14 no.12
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• pp.23-30
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• 2013

Bearing capacity of pile is governed by only skin friction in frozen ground condition, while it is generally governed both by skin friction and end bearing capacity in typically unfrozen ground condition. Skin friction force, which arises from the interaction between pile and frozen soils, is defined as adfreeze bond strength, and adfreeze bond strength is one of the most important key parameters for design of pile in frozen soils. Many studies have been carried out in order to analyze adfreeze bond strength characteristics over the last fifty years. However, many studies for adfreeze bond strength have been conducted with limited circumstances, since adfreeze bond strength is sensitively affected by various influence factors such as intrinsic material properties, pile surface roughness, and externally imposed testing conditions. In this study, direct shear test is carried out inside of large-scaled freezing chamber in order to analyze the adfreeze bond strength characteristics with varying freezing temperature and normal stress. Also, the relationship between adfreeze bond strength and shear strength of the frozen soil obtained from previous study was analyzed. The coefficient of adfreeze bond strength was evaluated in order to predict adfreeze bond strength based on shear strength, and coefficients suggested from this and previous studies were compared.

• 한국체육학회지인문사회과학편
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• v.55 no.2
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• pp.603-615
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• 2016

This study was conducted by performing intensities aerobic exercise for 12 weeks, three times a week targeting 28 middle aged women. The purpose of this study was analyzing factors which affect cognitive function and changes of blood pressure, renin-aldosterone system, neurotransmitter, cognitive function and working memory after treatment. The participants were divided into three groups which are the control group(n=9, non exercise), moderate intensity aerobic exercise group(n=10, 50%V02max), high intensity aerobic exercise group(n=9, 70%V02max). The two-way ANOVA(repeated measure) and multiple regression analysis were carried out to target those three groups before and after treatment. The results were as follows like this. The moderate intensity aerobic exercise increased renin, brain derived neurotrophic factor(BDNF), cognitive function and working memory. Also, it reduced aldosterone, angiotensinII and aldosterone-renin ratio. The high intensity aerobic exercise showed increase BDNF, cognitive function and working memory and decrease systolic. As a result of a multiple regression analysis of factors affecting cognitive function after intensities aerobic exercise, the moderate intensity aerobic exercise affected diastolic blood pressure, decrease of aldosterone-renin ratio and working memory. Also, an increase of BDNF affected cognitive function, the high intensity aerobic exercise affected working memory BDNF and an increase of serotonin affected cognitive function. Therefore, It could be seen that more than moderate intensity exercise increase woman's cognitive function and working memory. Also, there were metabolic factors which affect the increase of cognitive function. To moderate intensity exercise, renin-aldosterone and working memory affected to increase of cognitive function. For high intensity exercise, BDNF and working memory affected to it.

• Journal of Korea Entertainment Industry Association
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• v.13 no.5
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• pp.127-138
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• 2019

This study was a secondary data analysis using statistics from the 13th (2017) Korea Youth Risk Behavior Web-based Survey (KYRBS) to investigate the relationship between health behaviors and physical activity among Korean adolescents. A total of 62,276 adolescents in middle and high schools enrolled in this study. Physical activity utilized moderate and vigorous physical activity variables. Health behaviors used smoking, drinking, eating, sedentary behavior, and sleep duration variables. Statistical analyses were performed applying complex sample analysis method. Chi-square tests were used to compare physical activity according to health behaviors. Multivariate multinomial logistic regression analyses were conducted to examine the relationship between health behaviors and physical activity, adjusted for general characteristics. Current smoking and current drinking were associated with high levels of moderate and vigorous physical activity. Consuming fruits≥1 times/day, vegetables≥3 times/day, and sweet drinks≥3 times/week were associated with high levels of moderate and vigorous physical activity. Eating breakfast≥5 times/week was associated with high levels of moderate physical activity, but not with vigorous physical activity. Sedentary behavior≥2 hour/day was associated with low levels of moderate and vigorous physical activity. Sleep duration<7 hour/day was associated with high levels of moderate physical activity and low levels of vigorous physical activity. These findings suggest that since there is an interrelationship between health behaviors and physical activity among adolescents, intervention programs aiming at promoting physical activity and healthy lifestyles should consider a multiple behavior approach rather than an individual behavior approach.

• The Journal of the Korea Contents Association
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• v.15 no.9
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• pp.384-394
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• 2015

The purpose of this study was to evaluate the push-shear bond strength between five commercial zirconia veneering ceramics and zirconia core cylinder, and to investigate the effect of biaxial flexural strength and zirconia liner glass treatments. The biaxial flexural strengths of the veneering ceramics were evaluated by a piston-on-three-ball test. The bond strengths between the Y-TZP cylinder and zirconia veneering ceramics were evaluated using the push-shear bond strength test. The data was analyzed using two-way ANOVA and Scheffe's test. The biaxial flexural strength of Cercon ceram kiss (CE) was higher than those of the other groups. The glass-treated and Triceram zirconia groups showed the highest value and the Creation ZI(CR) showed the lowest. In all groups, the liner glass treatment groups showed significantly higher push-shear bond strength than those without(P<0.05). The liner glass treatments of zirconia can improve the bond strength between the zirconia ceramic core and veneering ceramics.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.3
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• pp.206-211
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• 2015

Recently, for UHPC (Ulta High Performance Concrete) which is researched actively, as the tensile strength is absolutely influenced on the content of steel fiber, in this paper, experiments of compressive strength, elasticity modulus and tensile strength were performed according to compressive strength and content of steel fiber as variables. By the test results, compressive strength, elasticity modulus and tensile strength are proportioned and have a good correlation and according to content of steel fiber, compressive and tensile strength are also proportioned and have a good correlation. In case of elasticity modulus, the difference between test and present design code is not large, so it is possible to adapt to present design code. On the other hand, in case of tensile strength, as there is no specification of present design code, new prediction equation is proposed by using nonlinear regression analysis and the proposed equation have a good correlation to test results.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.40 no.2
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• pp.177-182
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• 2020

In this study, the effect of nanofibers in cement pastes on the compressive and tensile strength of hardened cement pastes was studied. Two types of nanofibers, nylon 66 nanofibers and carbon nanotube-nylon 66 hybrid nanofibers, were manufactured by electrospinning methodology and mixed in cement powder respectively. The specimens for experiments were prepared by water to cement ratio of 0.5 and cured in water for 28 days. The effect of nanofibers on the increase of the compressive and tensile strength were confirmed by the experimental results. The well-linking effect of nanofibers in the microstructure of the hardened cement pastes has been found by scanning electron microscope (SEM) analysis and well-explained for the increase in mechanical strength. Besides, field emission transmission electron microscope (FE-TEM) analysis and thermal gravimetric analysis (TGA) have also been conducted to analyze the properties of nanofibers as well as the microstructure of the hardened modified cement pastes.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.3
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• pp.28-39
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• 2014

This paper reviews past literatures relevant to fire-resistance properties of high strength concrete and investigates spalling mechanism of high strength concrete in fire. First, literatures were reviewed on spalling occurrence and fire-resistance methods. Second, a chemical change of concrete components in an elevated temperature was presented. Finally, the mechanism of the spalling occurrence and spalling resistance were examined in terms of hybrid fiber content. The focus of the experimental study as part of this research is to investigate the effects of fire on the variation of thermal properties of high strength concrete, which tends to be used in super tall buildings. This experimental study was devised to investigate the fire-resistance performance of high strength concrete containing hybrid fibers. A total of 48 test specimens were exposed to high temperature ranging from $100^{\circ}C$ to $700^{\circ}C$, including room temperature (${\sim}20^{\circ}C$). Test results provide valuable information regarding fire-resistance properties of strength concrete with 100 MPa or greater.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.6
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• pp.63-71
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• 2015

The objective of the present study is to investigate how elevated temperature ranging from $100^{\circ}C$ to $800^{\circ}C$ as well as room temperature affects the variation of mechanical properties of high strength concrete ($over\;f_{ck}=60MPa\;grade$). In this experiment, specimens were exposed for a period of $2^{\circ}C/min$ to temperatures of $20^{\circ}C$, $100^{\circ}C$, $200^{\circ}C$, $300^{\circ}C$ $400^{\circ}C$, $500^{\circ}C$, $600^{\circ}C$, $700^{\circ}C$ and $800^{\circ}C$, respectively. Accordingly, the study investigated the fire resistance performance of high strength concrete mixed with composite fibers which composed with hybrid fibers and steel fibers. After cooling down to ambient temperature, the following basic mechanical properties were then evaluated and compared with reference values obtained prior to thermal exposure: (i) compressive strength in room temperature; (ii) residual compressive strength; (iii) Poisson's ratio; (iv) weight change; (v) SEM analysis & XRD analysis In addition, XRD and SEM Images analyses were performed to investigate chemical and physical characteristics of high strength concrete with composite fibers according to high temperature.

• Composites Research
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• v.35 no.5
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• pp.328-333
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• 2022

In this study, the fabrication conditions of CFRP rebar were controlled to derive the correlation between flexural strength and pore characteristics. The fabrication conditions of CFRP rebar were adjusted for presence or absence of rib, resin temperature, and curing furnace temperature. Flexural strength and pore characteristics of fabricated CFRP rebar were analyzed. The flexural strength of CFRP rebar was changed depending on the fabrication condition, such as the presence or absence of rib, the resin temperature, and the curing furnace temperature. It was confirmed that the flexural strength of CFRP rebar was significantly lowered when the rib was not wound. As a result of Nano X-ray CT analysis, the max. pore diameter was shown in CFRP rebar prepared at a resin temperature of 60℃. According to optical microscopic analysis, the maximum porosity was 6.89% in No. 1, and the minimum porosity was 2.88% in No. 7. The correlation coefficient between porosity used optical microscopy and flexural strength was -0.64, which was higher than the correlation coefficient between porosity or pore size used Nano X-ray CT and flexural strength.