• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.616-623
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• 2012

Turbopump is a key component in liquid rocket engines, and reducing weight while maintaining structural safety is one of the major concerns of turbopump designers. To reduce the weight aluminium alloy castings instead of steel casings are introduced. The casting process is especially useful for enhancement of productivity and for reduction of product costs. But, since castings are used in space vehicle engines, reliability cannot be compromised therefore proper design, production process and thorough investigation should be performed to ensure structural integrity. In this study inlet casings for a fuel pump are casted with A356.0-T6 alloy and using one of them a burst test is conducted to ensure structural integrity. Structural analysis is performed for simulation, and with multiple strain gages strains are measured and compared with predictions.

• Structural Engineering and Mechanics
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• v.8 no.2
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• pp.165-180
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• 1999

The cost effectiveness of using steel roof systems for residential buildings is becoming increasingly apparent with the decrease in manufacturing cost of steel components, reliability and efficiency in construction practices, and the economic and environmental concerns. While steel has been one of the primary materials for structural systems, it is only recently that its use for residential buildings is being explored. A comprehensive system for the design of residential steel roof truss systems is presented. In the first stage of the research the design curves obtained from the AISI-LRFD code for the manufactured cross-sections were verified experimentally. Components of the truss systems were tested in order to determine their member properties when subjected to axial force and bending moments. In addition, the experiments were simulated using finite element analysis to provide an additional source of verification. The second stage of the research involved the development of an integrated design approach that would automatically design a lowest cost roof truss given minimal input. A modified genetic algorithm was used to handle sizing, shape and topology variables in the design problem. The developed methodology was implemented in a software system for the purpose of designing the lowest cost truss that would meet the AISI code provisions and construction requirements given the input parameters. The third stage of the research involved full-scale testing of a typical residential steel roof designed using the developed software system. The full scale testing established the factor of safety while validating the analysis and design procedures. Evaluation of the test results indicates that designs using the present approach provide a structure with enough reserve strength to perform as predicted and are very economical.

• Nuclear Engineering and Technology
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• v.23 no.1
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• pp.20-29
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• 1991

The system analysis for Korean nuclear power reactor option is made on the basis of reliability, cost minimization, finite uranium resource availability and nuclear engineering manpower supply constraints. The reference reactor scenarios are developed considering the future electricity demand, nuclear share, current nuclear power plant standardization program and manufacturing capacity. The levelized power generation cost, uranium requirement and nuclear engineering professionals demand are estimated for each reference reactor scenarios and nuclear fuel cycle options from the year 1990 up to the year 2030. Based on the outcomes of the analysis, uranium resource utilization, reliability and nuclear engineering manpower requirements are sensitive to the nuclear reactor strategy and associated fuel cycle whereas the system cost is not. APWR, CANDU longrightarrow FBR strategy is to be the best option for Korea. However, APWR, CANDU longrightarrow Passive Safe Reactor(PSR）longrightarrowFBR strategy should be also considered as a contingency for growing national concerns on nuclear safety and public acceptance deterioration in the future. FBR development and establishment of related fuel cycle should be started as soon as possible considering the uranium shortage anticipated between 2007 and 2032. It should be noted that the increasing use of nuclear energy to minimize the greenhouse effects in the early 21st century would accelerate the uranium resource depletion. The study also concludes that the current level of nuclear engineering professionals employment is not sufficient until 2010 for the establishment of nuclear infrastructure.

• The Journal of the Korea Contents Association
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• v.21 no.9
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• pp.644-651
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• 2021

This study used a qualitative research method to derive meaning through intensive interviews on stress, focusing on the subjective perceptions and experiences of college students about COVID-19. The study participants were 12 college students enrolled at University Y in Gyeonggi-do, and the questionnaires were 'How has your daily life changed due to COVID-19?' and 'What changes have you made in your environment due to COVID-19?', 'What kind of comfort/inconvenience did you experience due to COVID-19?'As a result of analyzing the stress experienced by university students due to COVID-19, the stress factors were found to be four types: concerns about academic quality, anxiety about disconnection from social relationships, burden due to decrease in jobs (part-time jobs), and health and safety anxiety. The results of this study, it seems that the university's efforts to optimize online classes, seeking social relationships through non-face-to-face, preparing policies for job creation for college students, and health management measures due to COVID-19 should be discussed.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.15 no.8
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• pp.2827-2848
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• 2021

Mobile Crowdsourcing (MCS) has become an emerging paradigm evolved from crowdsourcing by employing advanced features of mobile devices such as smartphones to perform more complicated, especially spatial tasks. One of the key procedures in MCS is to collect answers from mobile users (workers), which may face several security issues. First, authentication is required to ensure that answers are from authorized workers. In addition, MCS tasks are usually location-dependent, so the collected answers could disclose workers' location privacy, which may discourage workers to participate in the tasks. Finally, the overhead occurred by authentication and privacy protection should be minimized since mobile devices are resource-constrained. Considering all the above concerns, in this paper, we propose a lightweight and privacy-preserving answer collection scheme for MCS. In the proposed scheme, we achieve anonymous authentication based on traceable ring signature, which provides authentication, anonymity, as well as traceability by enabling malicious workers tracing. In order to balance user location privacy and data availability, we propose a new concept named current location privacy, which means the location of the worker cannot be disclosed to anyone until a specified time. Since the leakage of current location will seriously threaten workers' personal safety, causing such as absence or presence disclosure attacks, it is necessary to pay attention to the current location privacy of workers in MCS. We encrypt the collected answers based on timed-release encryption, ensuring the secure transmission and high availability of data, as well as preserving the current location privacy of workers. Finally, we analyze the security and performance of the proposed scheme. The experimental results show that the computation costs of a worker depend on the number of ring signature members, which indicates the flexibility for a worker to choose an appropriate size of the group under considerations of privacy and efficiency.

• Journal of dental hygiene science
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• v.19 no.2
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• pp.107-112
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• 2019

Background: Good oral health is important for systemic body health and quality of life. Spray oral cleansers are increasingly preferred because of their convenience of carrying and the ease of oral hygiene management. In addition, many kinds of oral cleanser products containing various ingredients with antibacterial, washing, and moisturizing effects are being manufactured. However, concerns about the safety and side effects of oral sprays are increasing, and there is very little information regarding the use and care of oral sprays is available to consumers. This study aimed to investigate the effects of oral spray on oral bacteria and tissue to elucidate the factors that need to be considered when using oral sprays. Methods: The effects of oral spray on the growth of dental plaque bacteria was assessed using disk diffusion assays. Cytotoxicity and morphological changes in oral epithelial cells were observed by microscopy. The effects of oral spray on dental plaque growth were also confirmed on specimens from permanent incisors of bovines by Coomassie staining. Results: The pH of spray products, such as Perioe Dental Cooling, Cool Sense, and Dentrix, were 3.65, 3.61, and 6.15, respectively. All tested spray products showed strong toxicity to dental plaque bacteria and oral epithelial cells. Compared with those on the control, dental plaque bacteria deposits on the enamel surface increased following the use of oral spray. Conclusion: Three types of oral spray, namely Perioe Dental Cooling, Cool Sense, and Dentrix, strongly inhibited the growth of dental plaque bacteria and oral epithelial cells. The oral spray ingredient enhanced dental plaque growth on the enamel surface. Users should be informed of precautions when using oral sprays and the need for oral hygiene after its use.

• Annals of Coloproctology
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• v.34 no.6
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• pp.306-311
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• 2018

Purpose: Hartmann operation is widely recognized as a useful procedure, especially in emergencies involving the rectosigmoid colon. One of the surgeon's foremost concerns after Hartmann operation is future colostomy reversal, as colostomy reversal after a Hartmann procedure is associated with relatively high morbidity and mortality. Laparoscopic surgical techniques continue to prove useful for an ever-increasing variety of indications. We analyzed the outcomes of laparoscopic Hartmann colostomy reversals at our center. Methods: We retrospectively analyzed the hospital records of 170 patients who had undergone Hartmann operation between January 2010 and June 2017 at Wonkwang University Hospital. Among 68 Hartmann colostomy reversals, we evaluated and compared the outcomes of 3 groups of patients: 29 patients in the open colostomy reversal group (OG) who had undergone laparotomies for Hartmann reversals, 19 patients in the conversion group (CG) whose laparoscopic procedures had required conversion to a laparotomy, and 20 patients in the laparoscopy group (LG). Results: The overall reversal rate for Hartmann colostomies was 40.5% during this time period. The duration of hospital stay was significantly shorter among LG patients ($10.15{\pm}2.94days$) than among OG patients ($16{\pm}9.5days$). The overall complication rate among OG patients was higher than that among LG patients (adjusted odds ratio, 8.78; P = 0.01). The most common complication was postoperative ileus (19.1%). Conclusion: If no contraindications to laparoscopy exist, surgeons should favor a laparoscopic reversal of Hartmann operation over an open reversal.

• Pediatric Gastroenterology, Hepatology & Nutrition
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• v.22 no.3
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• pp.217-224
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• 2019

Purpose: Various publications on the use of sedation and anesthesia for diagnostic procedures in children have demonstrated that no ideal agent is available. Although propofol has been widely used for sedation during esophagogastroduodenoscopy in children, adverse events including hypoxia and hypotension, are concerns in propofol-based sedation. Propofol is used in combination with other sedatives in order to reduce potential complications. We aimed to analyze whether the administration of midazolam would improve the safety and efficacy of propofol-based sedation in diagnostic esophagogastroduodenoscopies in children. Methods: We retrospectively reviewed the hospital records of children who underwent diagnostic esophagogastroduodenoscopies during a 30-month period. Demographic characteristics, vital signs, medication dosages, induction times, sedation times, recovery times, and any complications observed, were examined. Results: Baseline characteristics did not differ between the midazolam-propofol and propofol alone groups. No differences were observed between the two groups in terms of induction times, sedation times, recovery times, or the proportion of satisfactory endoscopist responses. No major procedural complications, such as cardiac arrest, apnea, or laryngospasm, occurred in any case. However, minor complications developed in 22 patients (10.7%), 17 (16.2%) in the midazolam-propofol group and five (5.0%) in the propofol alone group (p=0.010). Conclusion: The sedation protocol with propofol was safe and efficient. The administration of midazolam provided no additional benefit in propofol-based sedation.

• The Journal of the Korea Contents Association
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• v.21 no.4
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• pp.555-564
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• 2021

This study evaluates the social value orientation, well-being of the elderly and care needs of elderly that elderly care services are identified and seeks future service development directions through a desire survey. As of October 2019, 1,501 elderly living alone who used basic care services for the single elderly households for more than 3 months were sampled, and frequency analysis, technical statistical analysis, t-test, and variance analysis were conducted. The survey found that social value orientation averages 90.93, and the sense of well-being of the elderly is 71.29 points. As a result of the analysis of variance and post-hoc analysis, the well-being of the elderly was statistically significant in groups well aware of their social value orientation. In addition, key words such as "loneliness", "lonely Death", and "safety" were derived for concerns that may arise when the service is discontinued. Based on the results of this study, it could be used as basic data to explore the development direction of the new "elderly care services" and to establish a care system for senior citizens in preparation.

• Journal of Korean Society on Water Environment
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• v.37 no.5
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• pp.398-404
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• 2021

The use of water purifiers has been increasing every year due to increased drinking water safety concerns raised by the water pollution accidents occasionally reported. Currently, more than 10 million water purifiers have been distributed in Korea, and the estimation of the purifier sales reaches two million units per year. As a result, the number of used water purifier filters that must be replaced on a regular basis has gradually increased. However, regardless of the considerations for the capacity of used filters remaining, water purifier filters were replaced and collected at regular intervals. The high cost of disposal of the used filters by landfill or incineration were required. Thus, in this study, the current status and trends of recycling technologies for used water purifier filters were reviewed. It is noted that there was insufficient statistical data to understand the current status of the difference between the number of used water filters discarded and the number of those recycled. Most studies on the recycling of old water purifier filters have concentrated on pretreatment and cleaning methods for sediment filters and membrane filters, with the goal of extending the lifespan of used filters. Further, the study suggested future study directions on the recycling of used water purifier filters, which could be useful information on establishing environmental policy to promote the recycling of used filters.