Jaehyun Park;Si-Maek Lee;Beom-Joo Lee;Seon Ju Kim;Hyeong-Min Yoo
Composites Research
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v.36
no.6
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pp.429-434
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2023
In this study, aimed at improving the existing acoustic emission sensor for real time monitoring, a macro-fiber composite (MFC) transducer was employed as the acoustic emission sensor in the gas leak detection system. Prior to implementation, structural analysis was conducted to optimize the MFC's design. Consequently, the flexibility of the MFC facilitated excellent adherence to curved pipes, enabling the reception of acoustic emission (AE) signals without complications. Analysis of AE signals revealed substantial variations in parameter values for both high-pressure and low-pressure leaks. Notably, in the parameters of the Fast Fourier Transform (FFT) graph, the change amounted to 120% to 626% for high-pressure leaks compared to the case without leaks, and approximately 9% to 22% for low-pressure leaks. Furthermore, depending on the distance from the leak site, the magnitude of change in parameters tended to decrease as the distance increased. As the results, in the future, not only will it be possible to detect a leak by detecting the amount of parameter change in the future, but it will also be possible to identify the location of the leak from the amount of change.
Journal of the Korea institute for structural maintenance and inspection
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v.28
no.1
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pp.39-45
/
2024
Seismic safety of expansion joints for piping systems has been underscored by water pipe ruptures and leaks resulting from the Gyeongju and Pohang earthquakes. Metal bellows in piping systems are applied to prevent damage from earthquakes and road subsidence in soft ground. Designed with a series of corrugated segments called convolutions, metal bellows exhibit flexibility to accommodate displacements. Several studies have examined variations in convolution shapes and layers based on the intended performance to be evaluated. Nonetheless, the research on the seismic performance of complex bellows having multiple corrugation heights is limited. In this study, monotonic loading tests, cyclic loading tests, and fatigue tests were conducted to evaluate the shear performance in seismic conditions, of metal bellows with variable convolution heights. Single- and triple-layer bellows were considered for the experimentation. The results reveal that triple-layer bellows exhibit larger maximum deformation and fatigue life than single-layer bellows. However, the high stiffness of triple-layer bellows in resisting internal pressure poses certain disadvantages. The convolutions are less flexible at lower displacements and experience leakage at a rate related to the variable height of the convolutions in certain conditions. At lower deformation rates, the fatigue life is rated higher as the number of layers increase. It converges to a similar fatigue life at higher deformation rates.
The food truck business, which involves selling various types of food from mobile vehicles, has gained significant popularity in urban centers and at events. These food trucks have rapidly expanded due to their relatively low initial investment and high flexibility, attracting customers with unique menus and personalized services. However, as competition increases, the need to manage service quality to boost customer satisfaction and encourage repeat visits has become more critical. Despite this growing importance, there has been limited empirical research on the topic. This study aims to analyze customer experiences with food truck services to gain strategic insights for improving service quality. By applying structural topic modeling to customer review data, the study identified 50 key topics. The process included a comprehensive evaluation of model diagnostics and interpretability to determine the optimal number of topics, ultimately selecting the most relevant ones related to service experiences. The impact of these identified topics on overall customer satisfaction was empirically tested using regression analysis. The results showed that aspects such as "Food Taste," "Friendly Staff," and "Positive Emotion" had a positive influence on customer satisfaction, whereas "Delayed Service," "Negative Emotion," and "Beverage Service" had a negative impact. Based on this analysis, the study proposes concrete methods for food truck operators to systematically analyze customer feedback and use it to drive service improvements and innovation. This research highlights the importance of data-driven decision-making in small business environments like food trucks and contributes to expanding the application of topic modeling in the service industry.
This research had intended to find out regarding the present influences of the Smart Work on the intention to use continuously with the staff members working in the small- and medium-sized enterprises as the subject. And, finally, it had intended to find out about the Smart Work environments of the IT corporations and the non-IT corporations. For this research, the questionnaire survey data were collected from the staff members working at the small- and medium-sized enterprises. Through the questionnaire survey data that were collected, an empirical analysis was carried out. And, through the reliability analysis, the feasibility analysis, the discriminatory feasibility analysis, and the inspection of the degree of suitableness of the structural equation model, finally, the research model was verified and, finally, a difference analysis of the IT corporations and the non-IT corporations was carried out. Regarding the results of the analysis of the research, it appeared that the factors of the job efficiency and the job autonomy of the special characteristics of the job had the positive influences on the usefulness and the job satisfaction, which were the parameters and which were perceived. And it appeared that the time flexibility of the job form could not have any influences on the usefulness and the job satisfaction, which were the parameters and which were perceived. And it appeared that the spatial flexibility had the influences on the job satisfaction only. The perceived usefulness, which was a parameter, had the positive influences on the job satisfaction and the intention to use continuously. And, finally, the job satisfaction had the positive influences on the intention to use continuously. And it appeared that there were the differences, too, between the IT corporations and the non-IT corporations. It is thought that, through the results of this research and through the Smart Work environment, the positive influences on the workers and the organizations could be induced and that a better working environment than previously can be provided to the workers to fit the special characteristics of the corporations.
Kim, Jin Hee;Seo, Yoon Kyung;Han, Joo Won;Oh, Ji Yoon;Kim, Yong Hyun
Applied Chemistry for Engineering
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v.26
no.3
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pp.275-279
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2015
Poly(3,4-ethylenedioxythiophene) : poly(styrenesulfonate) (PEDOT : PSS) has attracted a great deal of attention as a transparent conductive material for organic solar cells or organic light-emitting diodes due to its high electrical conductivity, optical transparency, and excellent mechanical flexibility. It is well known that a solvent doping for PEDOT : PSS thin-films significantly increases the conductivity of films. In this paper, the effect of various kinds of solvent doping and post-treatment on the electrical and structural properties of PEDOT : PSS thin-films is investigated. The solvent doping greatly increases the conductivity of PEDOT : PSS thin-films up to 884 S/cm. A further enhancement of the conductivity of PEDOT : PSS thin-films is achieved by the solvent post-treatment which raises the conductivity up to 1131 S/cm. The enhancement is mainly caused by the depletion of insulating PSS and forming conducting PEDOT-rich granular networks. Strong optical absorption peaks at the wavelength of 225 nm of PEDOT : PSS thin-films indicate the depletion of insulating PSS by post-treatment. We believe that the solvent post-treatment is a promising method to achieve highly conductive transparent PEDOT : PSS thin-films for applications in efficient, low-cost and flexible organic devices.
Journal of the Korea Academia-Industrial cooperation Society
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v.13
no.9
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pp.4277-4283
/
2012
Slip coefficient, whose value is dependent on the condition of contact surface at the friction joint of high tension bolt, is determined by slip load. Because contact area affects slip load, contact area that varies with bolt hole size is also related to the slip coefficient. In this study, we manufactured 32 specimens and performed bending and tension tests in order to examine changes in slip coefficient and load with material type, bolt diameter, and size of bolt hole. Slip load of specimens with oversize bolt hole had strength that was more than 80% higher than the slip load of specimens with standard bolt hole, and it also exceeded the design slip strength. In addition, we observed significant correlation between net-section ratio and slip ratio of specimens with oversize and standard bolt hole. However, some differences between the specimens are thought to have been caused by reduction in initial axial force of high tension bolt, which is an important parameter of slip coefficient. It is self-evident that increased bolt hole size would lead to decrease in design strength as it reduces both slip coefficient and bolt axial force. Nevertheless, we suggest that some flexibility in regulation of bolt hole, as long as it does not threaten the structural stability, may be a positive factor in terms of workability and efficiency.
Kim, Sang-Young;Kang, Min-Sung;Koo, Jae-Mean;Seok, Chang-Sung
Transactions of the Korean Society of Mechanical Engineers A
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v.34
no.10
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pp.1411-1417
/
2010
CFRP (Carbon Fiber Reinforced Plastic) has received considerable attention in various fields as a structural material, because of its high specific strength, high specific stiffness, excellent design flexibility, favorable chemical properties, etc. Most products consisting of several parts are generally assembled by mechanical joining methods (using rivets, bolts, pins, etc.). Holes must be drilled in the parts to be joined, and the strength of the components subjected to static and fatigue loads caused by stress concentration must be decreased. In this study, we experimentally evaluated the variation in the residual strength of a holenotched CFRP plate subjected to fatigue load. We repeatedly subjected the hole-notched specimen to fatigue load for a certain number of cycles, and then we investigated the residual strength of the hole-notched specimen by performing the fracture test. From the results of the test, we can observe the initiation of a directional crack caused by the applied fatigue load. Further, we observed that the residual strength increases with a decrease in the notch effect due to this crack. It was evaluated that the residual strength increases to a certain level and subsequently decreases. This variation in the residual strength was represented by a simple equation by using a model of the decrease in residual strength for plain plate, which was developed by Reifsnider and a stress redistribution model for hole-notched plate, which was developed by Yip.
Journal of Korean Library and Information Science Society
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v.43
no.1
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pp.261-285
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2012
The purpose of this study is to confirm that the user benefit criteria can be applied as the user benefit criteria of children's libraries by examining the theoretical validity of the user benefit criteria and furthermore, by clarifying and verifying the mutual relation between the user benefit criteria and the child development area. For such a purpose, this study collected data from 247 users of children's libraries in the country and collected data was analyzed using the structural equation modeling. The result of analysis is as follows. First, the relation between physical development and behavioral facilitation, emotional development and physiological maintenance, cognitive development and perceptual maintenance, and the development of social skills and social facilitation was appropriate. Second, usability, safety and diversity was valid as an index of behavioral facilitation, self-esteem, amenity and peacefulness was valid as an index of physiological maintenance, esthetic sense, dynamics and flexibility was valid as an index of perceptual maintenance, and leisure, communication and territoriality was valid as an index of social facilitation. Third, children who prefer physical development prefer the benefit of behavioral facilitation, children who prefer emotional development prefer the benefit of physiological maintenance, children who prefer cognitive development prefer the benefit of perceptual maintenance and children who prefer the development of social skills prefer the benefit of social facilitation.
Since the 1980s, the western welfare states have experienced a wide spectrum of socio-economic changes; changes in population composition, the economic globalization, the post-industrialization, an increasing flexibility in the labor market. etc. This study examines the trend of poverty in welfare states, and analyzes how those socio-economic changes are related to it. For these purposes, this study first calculates the poverty indices for several years in 10 welfare states using the Luxembourg Income Study database, and then decomposes the index by subpopulation and income sources. Major findings of this study can be summarized as follows. First of all, the welfare state in general has experienced an increasing trend in the degree of poverty since the 1980s. In particular, poverty has greatly intensified in the United Kingdom and the Netherlands. Many other welfare states including Canada, Germany, Sweden, and Norway have also experienced substantial increases in poverty. The increasing trend of poverty is not wholly due to changes in population composition such as increases in the aging population and one-parent(mother) families. Contrary to the traditional belief, these population groups are not as much poor as the working-age population. In particular, the degree of poverty in the elderly is less severe than in the working-age group. Furthermore, since the 1980s the market income poverty in the aging population has shown a decreasing trend in many welfare states. The degree and trend of poverty in one-parent families vary greatly across countries, owing to the labor market and income transfer policies. The most important reason for the increasing poverty trend in the welfare state is that the degree of poverty has been deepening in the working-age population. Especially, the market income poverty of the working-age population has considerably increased in every country except the Netherlands. Structural changes in the economy and the labor market may drive the increasing trend of poverty. Further studies and deliberate anti-poverty policies are needed to tackle the factors relating to the increase in the market income poverty.
Kim, Sung Il;Lee, Pil Goo;Lee, Jung Whee;Yeo, In Ho
Journal of Korean Society of Steel Construction
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v.18
no.6
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pp.793-804
/
2006
Various PSC and steel-concrete composite railway bridges are being developed for short-medium spans with structural and economic efficiency. According to the design concept, the prestressed composite girder bridge has the advantages of being lightweight and having low girder depth, with the capacity for long spans. However, the dynamic behavior under a passing train is one of the critical issues concerning these railway bridges designed with more flexibility. Therefore, it is very important to evaluate the modal parameters before performing dynamic analyses. In this paper, real-scale prestressed composite girders were fabricated as a test model and modal testing was carried out to evaluate modal parameters including natural frequency and modal damping ratio. During the modal testing, a digitally controlled vibration exciter as well as an impact hammer was applied to obtain frequency-response functions, and the modal parameters were also evaluated after the fracture of test models. With application of reliable properties from modal tests, the estimation of dynamic performances of prestressed composite girder railway bridges can be obtained from various parametric studies on dynamic behavior under the passage of a moving train.
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