• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.17 no.2
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• pp.93-103
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• 1981

It is well-known that nowadays heat resisting and anti-corrosive materials have been widely used as the components materials of gas turbines, nuclear power plants and engines etc. In the fields of machine production industry. And materials for engine components, like as the exhaust valve of internal combustion engine, have been required to operate under the high temperature range of $700^{\circ}C$-$800^{\circ}C$ and high pressured gas with repeated mechanical load for the high performance of engines. For these components, friction welding for bonding of dissimilar steels can be applied for in order to obtain process shortening, production cost reduction and excellent bonding quality. And age hardening recently has been noticed to the heat resisting materials for further strengthening of high temperature strength, especially high temperature fatigue strength. However, it is difficult to find out any report concerning the effects of age hardening for strengthening high temperature fatigue strength to the Friction welded heat resisting and anti-corrosive materials. In this study the experiment was carried out as the high temperature rotary bending fatigue testing under the condition of $700^{\circ}C$ high temperature to the friction welded domestic heat resisting steels, SUH3-SUS303, which were 10hr., 100hr. aging heat treated at $700^{\circ}C$ after solution treatment 1hr. at $1, 060^{\circ}C$ for the purpose of observing the effects of the high temperature fatigue strength and fatigue fracture behaviors as well as with various mechanical properties of welded joints. The results obtained are summarized as follows: 1) Through mechanical tests and micro-structural examinations, the determined optimum welding conditions, rotating speed 2420 rpm, heating pressure 8kg/mm super(2), upsetting pressure 22kg/mm super(2), the amount of total upset 7mm (heating time 3 sec and upsetting time 2 sec) were satisfied. 2) The solution treated material SUH 3, SUS 303, have the highest inclination gradient on S-N curve due to the high temperature fatigue testing for long time at $700^{\circ}C$. 3) The optimum aging time of friction welded SUH3-SUS 303, has been recognized near the 10hr. at $700^{\circ}C$ after the solution treatment of 1hr. at $1, 060^{\circ}C$. 4) The high temperature fatigue limits of aging treated materials were compared with those of raw material according to the extender of aging time, on 10hr. aging, fatigue limits were increased by SUH 3 75.4%, SUS 303 28.5%, friction welded joints SUH 3-SUS 303 44.2% and 100hr. aging the rates were 64.9%, 30.4% and 36.6% respectively. 5) The fatigue fractures occurred at the side of the base matal SUS303 of the friction welded joints SUH 3-SUS 303 and it is difficult to find out fractures at the friction welding interfaces. 6) The cracking mode of SUS 303, SUH 3-303 is intergranular in any case, but SUH 3 is fractured by transgranular cracking.

• Journal of the Korean Society of Child Welfare
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• no.56
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• pp.133-164
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• 2016

This study investigated the effect of housing poverty in childhood on adolescents' subjective well-being. Specifically, this study examined whether the major factors that have been known to affect adolescents' well-being (i.e., family relationships, peer relationships, school adjustment etc.) mediated the relationship between housing poverty and adolescents' well-being. And then this study aimed to present an empirical evidence for establishing policies against housing poverty in order to enhance adolescent's subjective happiness. Data were derived from the $1^{st}$, $4^{th}$, and $7^{th}$ surveys of the Korea Welfare Panel Study(KOWEPS), and the sample included. 512 high school children in the $7^{th}$ survey. This study utilized structural equation modeling. Housing poverty was measured by the sub-minimum standard housing condition and the household's burden of housing expenditure. Family relationship, as a mediator, was measured by parental involvement in education, parental monitoring, and family conflicts. Another mediator, school adjustment was measured by school environment and school bonding, and the last mediator, peer relationship was measured by friend attachment and peer attachment. The results showed that housing poverty had significant negative effects on the adolescents' subjective well-being. The sub-minimum standard housing condition with inadequate size and facilities negatively affected adolescents' relationships with family directly and subjective well-being indirectly. In addition, the negative family relationships due to the sub-minimum standard housing condition negatively affected adolescents' subjective well-being through school adjustment and peer relationships. The greater the proportion of income a household spends on housing expenditure, the less likely for adolescents to report positive well-being. The sub-minimum standard housing condition had indirect effects through family relationships, whereas the household's housing expenditure directly affected adolescents' subjective well-being. This study suggested the necessity of interventions to alleviate housing poverty for adolescents' families and lays the groundwork for housing poverty policies in Korea.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.5
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• pp.581-589
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• 2021

With the recent increase in the introduction of micro-electric vehicles in Korea, interest in micro-electric vehicle user satisfaction is increasing to revitalize related markets. In this paper, a basic study was conducted on the development of public services using micro-electric vehicle based on the constituent factors of user satisfaction. The survey includes: ① 'Analytic Hierarchy Process (AHP) for selecting the priority factors of user satisfaction of micro-electric vehicles', ② 'A survey of micro-electric vehicles image' to collect data in advance for providing users' preferences and transportation services for micro-electric vehicles, ③ In order to investigate the user satisfaction level of users who actually operated micro-electric vehicles, the order of 'user satisfaction survey of micro-electric vehicle drivers' was conducted. In the Analytic Hierarchy Process (AHP) analysis, it was found that users regarded as important in the order of 'user utilization data', 'vehicle movement data', and 'charging service data'. In the micro-electric vehicle image survey, users perceived micro-electric vehicles more positively in terms of "safety", 'durability', 'Ride comfort', 'design', 'MOOE (Maintenance and other operating expense)', and 'environment-friendly' when comparing micro-electric vehicles with electric motorcycles. In the survey on the user satisfaction of micro-electric vehicle drivers, the use of micro-electric vehicle did not directly affect work performance efficiency, and there was an experience of being disadvantaged on the road due to the size of the micro-electric vehicle, and driving in a cluster of micro-electric vehicle for outdoor advertisements. The city's public relations effect was great, but it was concerned about safety. In the future, based on the results of this study, we plan to build a user satisfaction structural equation model, preemptively discover feedback R&D for micro-electric vehicle utilization services in the public field, and actively seek to discover new public mobility support services.

• The Journal of Korean Academy of Prosthodontics
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• v.59 no.4
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• pp.395-404
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• 2021

Purpose. The purpose of present study was to evaluate the effect of changing structural stability of wax disc on the fit of prosthesis when the milling proceeded in order. Materials and methods. Prepared maxillary left first molar was used to fabricate a Ni-Cr alloy reference model. This was scanned to design crown and then wax pattern was milled, invested and cast to fabricate prosthesis. The wax patterns located in a row centrally within a single wax disc were set into a total of five groups ranging from WM1 group that was first milled to WM5 group that was last milled and the number of each group was set as 10. Silicone replica technique was used to measure the marginal gap, axial internal gap, line angle internal gap, occlusal internal gap. Data was evaluated with one-way ANOVA with significance level set at α = .05 and then Tukey HSD test was conducted for post analysis. Results. Marginal gap measured in each group, it was 40.41 ± 2.15 ㎛ in WM1 group, 40.44 ± 2.23 ㎛ in WM2 group, 39.96 ± 2.25 ㎛ in WM3 group, 39.96 ± 2.48 ㎛ in WM4 group, and 40.57 ± 2.53 ㎛ in WM5 group. No significant difference was found between groups. The significant difference between the groups was also not found in the axial internal gap, line angle internal gap, and occlusal internal gap. Conclusion. Internal and marginal fit of single crown to the sequential order of milling processing in the single machinable wax disc did not seem to be affected by the sequence.

• Korean Journal of Environment and Ecology
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• v.35 no.5
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• pp.548-557
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• 2021

Cypripedium japonicum Thunb. is an endemic plant in East Asia, distributed only in Korea, China, and Japan. At the global level, the IUCN Red List evaluates it as "Endangered Species (EN)," and at the national level in Korea, it is evaluated as "Critically Endangered Species (CR)." In this study, we investigated the characteristics of the age structure and the sustainability of the population based on the data obtained by demographic monitoring conducted for seven years in the natural habitat. C. japonicum habitats were observed in 7 regions of Korea (Pochoen, Gapyeong, Hwacheon, Chuncheon, Yeongdong, Muju, Gwangyang), and 4,356 individuals in 15 subpopulations were identified. The population size and structure differed from region to region, and artificial management had a very important effect on the size and structural change of the population. Population viability analysis (PVA) based on changes in the number of individuals of C. japonicum showed a very diverse tendency by region. And the probability of population extinction in the next 100 years was 0.00% for Pocheon, 10.90% for Gwangyang, 24.05% for Chuncheon, and 79.50% for Hwacheon. Since the above monitored study sites were located within the conservation shelters, which restricted access by humans, unauthorized collection of C. japonicum, the biggest threat to the species, was not reflected in the individual viability. So, the risk of extinction in Korea is expected to be significantly higher than that estimated in this study. Therefore, it is necessary to reflect population information in several regions that may represent various threats to determine the extinction risk of the C. japonicum population objectively. In the future, we should expand the demographic monitoring of the C. japonicum population known in Korea.

• Journal of the Korean Institute of Landscape Architecture
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• v.49 no.1
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• pp.70-82
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• 2021

The purpose of this study is to reveal the tendency of planting design through the analysis of the planting of designer's gardens in the Suncheon Bay National Garden and to derive implications for future garden planting designs. The results of the study are as follows: First, the results of the study show that the practice of tree-based planting is still valid. Large growing trees such as 'Pinus densiflrora', 'Celtis sinensis', 'Zelkova serrata', 'Machilus thunbergii', 'Pinus strobus' overwhelmed the size of the designer's garden(150 to 390㎡). Second, the selection of trees tended to be made considering the designer's intention and the decorative effects rather than by considering the physiological and ecological conditions of the site. Third, among the herbaceous, the rate of the planting of perennials was high. Fourth, the flowering period of planted herbaceous was the most common in summer, followed by spring, fall, and winter. Fifth, the frequency color of the planted herbaceous was the most common in summer, followed by spring, fall, and winter. Fifth, in terms of flower color frequency, the most common was the yellow-series, followed by red-series, blue-series Sixth, average height herbaceous plants(20~60cm) were planted the most(47.4%). Seventh, structural plants that determined the garden's framework depended on trees, and the focal plants mainly utilized were evergreen trees, and the midrange plants were the planted herbaceous plants. The implications derived from the above findings are as follows: First, to ensure the garden's quality and sustainability, the selection of trees should be carefully considered, not considering only the artist's intention but also taking into account the physical and ecological conditions. Second, herbaceous plants can be used in various ways― the garden's focal plants, midrange plants, and ground covers, so more active herbaceous planting needs to be considered. Third, in consideration of the winter landscape, herbaceous planting using characteristics, such as fruits and stems, as well as flower colors should be considered. Fourth, blue and black color herbaceous plants have a noticeable effect even in a small amount, so it is necessary to plant them actively. Fifth, for the design of herbaceous planting, where the individual property of plants can be expressed, the design method should be considered.

• Korean Journal of Heritage: History & Science
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• v.53 no.4
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• pp.188-197
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• 2020

Termites play an important role as decomposers of the forest ecosystem, while simultaneously causing enormous damage to wooden structures. Currently, two species of subterranean termites have been reported in Korea, and termite damage to historical wooden buildings is occurring nationwide due to climate change, forest fertility, and the locational characteristics of historical wooden buildings. Subterranean termites make their nests underground or inside timber. Termites move underground and access wooden structures through the lower parts of the buildings, adjacent to the ground. Once termites attack the wooden structures, it not only spoils the authenticity of cultural heritage structure, but also hampers structural stability due to the decrease in the strength of the material. Therefore, it is important to prevent termite damage before it occurs. Chemical treatments are mainly used in Korea to control and prevent the damage. In foreign countries, physical barriers are also used to prevent entry to wooden buildings, along with chemical treatments. Physical barriers involve installing nets or particles that termites cannot pass through in the lower part of the building, around the pipes, and between the edges of the building or exterior walls and interior materials. Advantages of a physical barrier are that it is an eco-friendly method, maintains long-term effect after installation, and does not require the use of chemical treatments. Prior to applying physical barriers, studies into the characteristics of termite species must be undertaken. In this study, we evaluated the minimum passage size that each caste of Reticulitermes speratus kyushuensis can move through. We found that workers, soldiers, and secondary reproductive termites were able to pass through diameters of 0.7mm, 0.9mm, and 1.1mm respectively. Head height of termites was an important factor in determining the minimum passing size. Results from the current study will be used as a basis to design the mesh size for physical barriers to prevent damage by termites in historical wooden buildings in Korea.

• Asia-Pacific Journal of Business Venturing and Entrepreneurship
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• v.16 no.6
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• pp.69-84
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• 2021

As industrial structural changes in the 4th Industrial Revolution have recently led to the need for fostering high-tech industries and high-tech manufacturing industries have been showing high value-added creation, the importance of high-tech manufacturing ventures has increased a lot as well. As a result of this, the government is actively supporting and fostering them. However, it appears that high-tech manufacturing ventures seem to have a lot of difficulty in securing competitive advantages due to the lack of internal core competencies and experience in the rapidly changing international economic conditions. In order for high-tech manufacturing ventures to strengthen internal core competencies, external collaborations with other companies or institutions which have diverse experience, technology skills and abundant resources are actively promoted. Accordingly, based on resource-based theory and transaction cost theory, the authors analyzed the effects of the high-tech manufacturing ventures'external collaborations on internal core competencies and management performance in this study. In order to verify the hypothesis of this study, the 2020 data on"The Research on the Precision Status of Ventures'compiled by the Ministry of SMEs and Startups since 1999 were utilized. According to the results of this study, the experience of external collaborations had a positive impact on the internal core competencies and non-financial management performance, while there was no direct impact on financial management performance. Moreover, the relationship between the experience of external collaborations and management performance is mediated by the internal core competencies. Additionally, it was found that the internal core competencies positively affected both non-financial and financial management performances, and non-financial management performance again had a significant impact on the financial management performance. Finally, the experience of external collaborations had a positive impact on both development, manufacturing, and marketing factors forming the internal core competencies. However, the impacts of individual factors were different in the management performance. Development and marketing factors were shown to have a significant impact on both non-financial and financial management performance, while the manufacturing factor had a significant impact only on financial management performance.

• Korean Journal of Poultry Science
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• v.49 no.4
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• pp.211-220
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• 2022

Poultry are exposed to extremely high levels of oxidative stress as a consequence of the excessive production of reactive oxygen species (ROS) induced by endogenous and exogenous stressors, such as high-stocking densities, thermal stress, environmental and feed contamination, along with factors associated with intensive breeding systems. Oxidative stress promotes lipid peroxidation, DNA damage, and inflammation, which can have detrimental effects on the health of birds. During the course of evolution, birds have developed antioxidant defense mechanisms that contribute to maintaining homeostasis when exposed to endogenous and exogenous stressors. The primary antioxidant defense systems are enzymatic and non-enzymatic in nature and play roles in protecting cells from ROS attack. Recently, plant flavonoids, which have been established to reduce oxidative stress, have been attracting considerable attention as potential feed additives. Flavonoids are a group of polyphenolic compounds that can be stabilized by binding structural compounds with ROS, and can promote the elimination of ROS by inducing the expression of antioxidant enzymes. However, although flavonoids can contribute to reducing lipid peroxidation and thereby enhance the antioxidant capacity of birds, they have low solubility in the gastrointestinal tract, and consequently, it is necessary to develop a delivery technology that can facilitate the effect intestinal absorption of these compounds. Furthermore, it is important to determine the dietary levels of flavonoids by assessing the exact antioxidant effects in the gastrointestinal tract wherein the concentrations of dietary flavonoids are highest. It is also necessary to examine the expression of transcriptional factors and vitagenes associated with the efficient antioxidant effects induced by flavonoids. It is anticipated that the application of flavonoids as natural antioxidants will become a particularly important field in the poultry industry.

• Journal of Service Research and Studies
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• v.13 no.2
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• pp.181-203
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• 2023

YouTube exhibits a hybrid personality, incorporating traits of both over-the-top (OTT) and personal broadcasting platforms. However, limited research has investigated these hybrid characteristics, particularly in the context of paid YouTube channel memberships. Therefore, building upon consumption value theory and prior literature, this study examines the influence of consumption value factors associated with paid YouTube channel memberships on usage satisfaction and continuance intention. Specifically, the study identifies four perceived consumption value factors (functional, social, emotional, and epistemic values) within the paid YouTube channel membership context and assesses their impact on usage satisfaction and continuance intention. Additionally, the study explores the moderating role of conditional value (the experience of watching live streams on paid YouTube channels) in these relationships. Data was collected via an online survey from Korean adults who subscribed to multiple paid YouTube channel memberships, resulting in 274 responses. The proposed hypotheses were tested using structural equation modeling (SEM). The SEM results indicate that all four consumption value factors significantly influence usage satisfaction, with usage satisfaction in turn positively affecting continuance intention. Furthermore, the study reveals that conditional value moderates the relationships between functional/emotional values and usage satisfaction, as well as between usage satisfaction and continuance intention. This study is the first to focus on YouTube channel paid memberships, which encompass characteristics from both OTT and personal broadcasting platforms. It is anticipated that this research will offer insights to personal broadcasters and stakeholders regarding the motivational factors that impact user satisfaction and encourage subscriptions to channel memberships.