• International Journal of Aeronautical and Space Sciences
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• v.17 no.4
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• pp.565-578
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• 2016

A probabilistic based systems approach is addressed in this study for the reliability prediction of solid rocket motors (SRM). To achieve this goal, quantitative Failure Modes, Effects and Criticality Analysis (FMECA) approach is employed to determine the reliability of components, which are integrated into the Fault Tree Analysis (FTA) to obtain the system reliability. The quantitative FMECA is implemented by burden and capability approach when they are available. Otherwise, the semi-quantitative FMECA is taken using the failure rate handbook. Among the many failure modes in the SRM, four most important problems are chosen to illustrate the burden and capability approach, which are the rupture, fracture of the case, and leak due to the jointed bolt and O-ring seal failure. Four algorithms are employed to determine the failure probability of these problems, and compared with those by the Monte Carlo Simulation as well as the commercial code NESSUS for verification. Overall, the study offers a comprehensive treatment of the reliability practice for the SRM development, and may be useful across the wide range of propulsion systems in the aerospace community.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.10
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• pp.1125-1131
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• 2009

O-rings are commonly used in machines as a seal. Due to prolonged use the surface of an O-ring can degrade which can lead to leakage as well as contamination. Damage of O-rings used in vacuum applications such as sputter is caused by various mechanisms. Particles detached from the O-ring may cause significant problems on the performance of the system in the vacuum chamber. Therefore, understanding the tribological behavior of O-rings is important to tackle the damage caused by repeated contact. In this work, FKM rubber was used for friction and wear tests conducted to investigate the tribological behavior of O-rings. A reciprocating type of a tribo-tester was used for the tests. The friction coefficient between the steel ball and the FKM specimen was quite high. Also, in order to identify the wear behavior, the surface of the FKM specimen was characterized using both optical and scanning electron microscopes. Evidence of wear due to adhesion and extrusion could be found. The results of this work will aid in improving the durability of O-rings.

• Journal of Yeungnam Medical Science
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• v.37 no.3
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• pp.217-225
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• 2020

Background: This study was performed to provide a long-term bacterial seal through the formation of reparative dentin bridge, calcium silicate-based pulp capping materials have been used at sites of pulpal exposure. The aim of this study was to evaluate the mineralization-inducing potentials of calcium silicate-based pulp capping materials (ProRoot MTA [PR], Biodentine [BD], and TheraCal LC [TC]) in human dental pulp cells (HDPCs). Methods: Specimens of test materials were placed in deionized water for various incubation times to measure the pH variation and the concentration of calcium released. The morphology of HDPCs cultured on the specimens was examined using a confocal laser scanning microscope (CLSM). Alizarin red S staining and alkaline phosphatase assays were used to evaluate mineralization-inducing potentials of the capping materials. Results: BD showed the highest calcium release in all test periods, followed by PR and TC. (p<0.05). All experimental groups showed high alkalinity after 1 day, except at 14 days. BD showed the highest cell viability compared with PR and TC after 1 and 3 days, while TC showed the lowest value (p<0.05). The CLSM analysis showed that cells were well adhered and expressed actin filaments for all pulp capping materials. Mineralization by PR and BD groups was higher than that by TC group based on alizarin red S staining. BD showed significantly higher alkaline phosphatase activity than PR and TC, while TC showed the lowest value (p<0.05). Conclusion: Within the limitations of the in vitro study, BD had higher mineralization-inducing potential than PR and TC.

• Biomolecules & Therapeutics
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• v.6 no.3
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• pp.261-268
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• 1998

Propolis is a lipophilic, natural product prepared by mixing the exudates collected from various plants by honeybees with beeswax for the purpose of using to seal hive walls and to strengthen the borders of combs. Because of its versatile bioactivities, propolis has been attracting many investigators'interest. But the pharmacological studies on propolis has, to date, been exclusively performed for an alcohol extract, there is few information of water extract. Therefore, in this study, we investigated the various effects of water extract of Chinese propolis. The water extract of propolis and its fractions of organic solvents showed strong antioxidative activities, especially ether and ethylacetate fractions, and reduced the lipid peroxidation of rat liver in viro. Additionally the ether fraction of propolis (10 mg/ml) inhibited the activity of hyaluronidase by 50%. In vivo, the water extract of propolis considerably decreased s-GOT, s-GPT and s-LDH activities which represent for the hepatotoxicity induced by $CCl_4$ in rats, and prolonged the MST (Medium revival tinge) and ILS (Increasing in MST over control) by 18% in mice which inoculated with sarcoma 180 ascites cells. These results suggest that the water extract of propolis has various bioactivities as well as the alcohol extract.

• Restorative Dentistry and Endodontics
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• v.28 no.1
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• pp.57-63
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• 2003

The purpose of the present study were to evaluate microleakage of a fourth generation dentin-bonding agent following a walking bleaching treatment, to determine the effect of temporary postbleaching dressing with calcium hydroxide on microleakage and to investigate the effect of delayed intracoronal restoration on microleakage. The results of this study were as follows : 1. Bleached groups showed more microleakage than unbleached group 2. Immediately restored group following bleaching procedure showed the highest microleakage score. 3. One-week delayed restorations showed less microleakage but there were no statistically significant difference between group II and III. 4. Provisional dressing with calcium hydroxide had no influence on microleakage. It is necessary to know the time that has elapsed from the bleaching treatment to the restoration procedure to achieve optimal seal, as well as to reduce the risk of microleakage in adhesive restoration.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.10
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• pp.2203-2208
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• 2011

In this paper, we describe application service development for secure land and marine transport based on CSD (Conveyance Security Device) systems. Based on CSD systems, we present application service and security service according to relevant standards as well as test procedure of developed services. Exploiting temperature, moisture, impact sensors, state monitoring function of container freight was developed to prevent disaster during transportation in addition to security function with CSD. For confidentiality of messages exchanged among application service entity and CSD systems, Encryption and decryption functions going by RC5 and AES-128 algorithms were implemented at desktop PC and 8 bit CPU environments, respectively. Measuring the elapsed time during encryption and decryption shows that two algorithms are allowable for the application service.

• Journal of Families and Better Life
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• v.26 no.3
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• pp.101-114
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• 2008

Eater Seal, the child care experts, observes that children with disability significantly benefit from receiving appropriated care along side their peers. Typically developing children serve as role models from which children with disabilities learn age-appropriated communications and social behavior. Therefore the children with disability can actively participate in well-designed child care settings. But unfortunately in Seoul, Korea, only 2% of children with disability are taken care of in child care centers. And even the disabled children at the child care centers are mostly mentally or emotionally disabled because the building, programs and services of the centers are restrictive to the children with severe physical disabilities. This study reviewed Korean domestic physical environment of child care centers for children with disabilities. Questionnaire survey was conducted to 103 centers located in Seoul by mail. Our survey revealed that they need more areas for nursing room and special rooms and the accessibility to buildings has to be improved. Also, there are no elevators in all buildings surveyed. Accessibility to toilet is noted as significant problem, especially wet floors in toilets. In a nursing room, a space for psychological rest and special education is needed for children with mental disability. Technical specifications on how to make buildings and facilities accessible for the children with disability should be developed. The goal of this study is to provide basic information to develop domestic design guidelines to ensure that the child care centers are safe, convenient, and usable for everyone possible.

• Journal of the Korean housing association
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• v.18 no.5
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• pp.121-131
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• 2007

Eater Seal, the child care experts, observes that children with disability significantly benefit from receiving appropriated care along side their peers. Typically developing children serve as role models from which children with disabilities team age-appropriated communications and social behavior. Therefore the children with disability can actively participate in well-designed child care settings. But unfortunately in Seoul, Korea, only 2% of children with disability are taken care of in child care centers. And even the disabled children at the child care centers are mostly mentally or emotionally disabled because the building, programs and services of the centers are restrictive to the children with severe physical disabilities. This study reviewed Korean domestic physical environment of child care centers for children with disabilities. 15 centers located in Seoul were surveyed. Our survey revealed that the accessibility to buildings is poor. There are many places with difference in height of floors. Also, there are no elevators in all buildings surveyed. Accessibility to toilet is noted as significant problem, especially wet floors in toilets. In a nursing room, a space for psychological rest and special education is needed for children with mental disability. Technical specifications on how to make buildings and facilities accessible for the children with disability should be developed. The goal of this study is to provide basic information to develop domestic design guidelines to ensure that the child care centers are safe, convenient, and usable for everyone possible.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.251-253
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• 2010

In the leakage test of a Main Oxidizer shut-off valve, gas leakage was found on the middle flange with a metal conical seal. The structural analysis was performed for three models with different numbers of bolts and flange shapes and then one model was selected in consideration of the minimum axial gap deformation as well as the weight increment due to the change of flange shapes. Experimental leakage tests for the simulated flanges of the selected model has resulted in no gas leakage, and consequently the structural analysis method for the design of the middle flanges has proved feasible.

• Nuclear Engineering and Technology
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• v.49 no.5
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• pp.928-940
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• 2017

An experiment using the $Prim{\ddot{a}}rkreisl{\ddot{a}}ufe$ Versuchsanlage (PKL) was performed for the OECD/NEA PKL-3 Project as a counterpart to a previous test with the large-scale test facility (LSTF) on a cold leg smallbreak loss-of-coolant accident with an accident management (AM) measure in a pressurized water reactor. Concerning the AM measure, the rate of steam generator (SG) secondary-side depressurization was controlled to achieve a primary depressurization rate of 200 K/h as a common test condition; however, the onset timings of the SG depressurization were different from each other. In both tests, rapid recovery started in the core collapsed liquid level after loop seal clearing, which caused whole core quench. Some discrepancies appeared between the LSTF and PKL test results for the core collapsed liquid level, the cladding surface temperature, and the primary pressure. The RELAP5/MOD3.3 code predicted the overall trends of the major thermal-hydraulic responses observed in the LSTF test well, and indicated a remaining problem in the prediction of primary coolant distribution. Results of uncertainty analysis for the LSTF test clarified the influences of the combination of multiple uncertain parameters on peak cladding temperature within the defined uncertain ranges.