• Journal of Environmental Health Sciences
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• v.40 no.6
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• pp.469-476
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• 2014

Objectives: The purpose of this study was to identify the stains causing infections in dental clinics by analyzing bacterial contamination, as well as to suggest improvements for infection control in dental clinics. Methods: In this study, a questionnaire survey of 47 dental hospitals and clinics located in Gyeonggi-do and Incheon, South Korea was administered from June 2013 to September 2013 and used to investigate the practice rates of infection control by dental hygienists and to analyze the bacterial contamination levels in dental offices. Results: In the studied institutions, the bacterial contamination levels of water lines were $20.9{\times}10^3$ colony forming units (CFU)/mL for three-way syringes, $12.7{\times}10^3CFU/mL$ for high-speed handpieces and $9.8{\times}10^3CFU/mL$ for gargling water. The bacterial contamination levels of surfaces were $44.9{\times}10^3CFU/mL$ in cuspidors, higher than in unit chairs ($2.9{\times}10^3CFU/mL$) and light handles ($6.7{\times}10^3CFU/mL$). The mean bacterial cell count of water lines and surfaces was relatively high in all establishments founded 11 years ago or more, and the mean bacterial cell count of waterline handpieces was $6.27{\times}10^3CFU/mL$ in establishments founded between one and five years ago, $11.16{\times}10^3CFU/mL$ six to ten years ago and $20.04{\times}10^3CFU/mL$ 11 years ago or more, which suggests that earlier foundation is associated with higher bacterial contamination levels with a statistical difference (p<0.01). Similarly, the mean bacterial cell count of cuspidors using water from water lines was also $70.16{\times}10^3CFU/mL$ in at least 11-year-old establishments, statistically significantly higher among in one- to five-year-old ($4.61{\times}10^3CFU/mL$) and six- to ten-year-old clinics ($47.89{\times}10^3CFU/mL$) (p<0.05). Conclusion: This study may be utilized to improve the bacterial contamination levels in dental offices by controlling the characteristics and environmental factors of dental offices that affect the microbial contamination of waterlines and surfaces in such institutions.

• Applied Biological Chemistry
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• v.50 no.2
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• pp.87-94
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• 2007

A bacterium which has high enzymatic activities such as amylase, cellulase and protease was isolated from Korean traditional soybean food, doenjang. The isolated bacterium was identified to Bacillus subtilis HS25 by the test of morphological and biochemical properties according to Bergey's Manual of Systematic Bacteriology and API 50 CHL kit, and by the 16S rDNA sequence. The isolated B. subtilis HS25 had a potent antibacterial activity against food born causative or pathogenic bacteria. B. subtilis HS25 is endospore forming cell and contained flagella and abundant viscous material at the out layer of cell wall. It was rod type bacterium $(0.5{\sim}0.8{\times}3{\sim}5{\mu}m)$ having biochemical characteristics such as gram staining(+), catalase(+), oxidase(-) and hydrolysis of esculin(+). The optimal medium compositions for production of antibacterial substance in the B. subtilis HS25 were 1% of soluble starch, 0.5% of yeast extract, 0.5% of peptone and 0.05% of MgCl$_2{\cdot}6H_{2}O$. The optimum temperature and pH of the growth of the B. subtilis HS25 was 35$^{\circ}C$ and pH 7.5, respectively. The antibacterial activity was more high in neutral to a little alkaline pH (6.5-10.5) than in acidic pH. The optimal shaking speed to grow and to produce antibacterial substance of the B. subtilis HS25 was 160${\sim}$200 rpm. The optimal culture time for antibacterial activities of the bacterium were shown to be in the range of 12-36 hr.

• Korean Journal of Mineralogy and Petrology
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• v.36 no.2
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• pp.95-106
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• 2023

Quartz (SiO₂) is among the major rock-forming minerals in the earth's crust. The atomistic structures of SiO₂ may evolve during diverse frictional processes. The reduction of friction of quartz-rock accompanied by its amorphization, hydration, and formation of silica gel provides mineralogical insights into earthquakes and related phenomena. Ball milling, together with rotary shear experiments have been useful to infer the atomic origins of such processes. In this study, optimal experimental conditions for ball milling for amorphization of SiO₂ were determined by taking into account various process variables. The crystallinity of SiO₂ gradually decreased and became amorphous as the ball milling time increased at a high milling speed. The degree of wear of the milling media and its effect on the amorphization of SiO₂ were analyzed using distinct milling materials (zirconia, stainless steel). The amount of ball wear increased with increasing milling time. Furthermore, the worn stainless steel particles from balls tend to interact with amorphized SiO₂ to form Si-O-Cr. These results aid in understanding the process of atomistic structural changes caused by ball milling of divserse materials with relatively high hardness, such as SiO₂, and understanding various geological friction processes.

• Journal of Intelligence and Information Systems
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• v.22 no.1
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• pp.107-118
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• 2016

The advent of 5G mobile communications, which is expected in 2020, will provide many services such as Internet of Things (IoT) and vehicle-to-infra/vehicle/nomadic (V2X) communication. There are many requirements to realizing these services: reduced latency, high data rate and reliability, and real-time service. In particular, a high level of reliability and delay sensitivity with an increased data rate are very important for M2M, IoT, and Factory 4.0. Around the world, 5G standardization organizations have considered these services and grouped them to finally derive the technical requirements and service scenarios. The first scenario is broadcast services that use a high data rate for multiple cases of sporting events or emergencies. The second scenario is as support for e-Health, car reliability, etc.; the third scenario is related to VR games with delay sensitivity and real-time techniques. Recently, these groups have been forming agreements on the requirements for such scenarios and the target level. Various techniques are being studied to satisfy such requirements and are being discussed in the context of software-defined networking (SDN) as the next-generation network architecture. SDN is being used to standardize ONF and basically refers to a structure that separates signals for the control plane from the packets for the data plane. One of the best examples for low latency and high reliability is an intelligent traffic system (ITS) using V2X. Because a car passes a small cell of the 5G network very rapidly, the messages to be delivered in the event of an emergency have to be transported in a very short time. This is a typical example requiring high delay sensitivity. 5G has to support a high reliability and delay sensitivity requirements for V2X in the field of traffic control. For these reasons, V2X is a major application of critical delay. V2X (vehicle-to-infra/vehicle/nomadic) represents all types of communication methods applicable to road and vehicles. It refers to a connected or networked vehicle. V2X can be divided into three kinds of communications. First is the communication between a vehicle and infrastructure (vehicle-to-infrastructure; V2I). Second is the communication between a vehicle and another vehicle (vehicle-to-vehicle; V2V). Third is the communication between a vehicle and mobile equipment (vehicle-to-nomadic devices; V2N). This will be added in the future in various fields. Because the SDN structure is under consideration as the next-generation network architecture, the SDN architecture is significant. However, the centralized architecture of SDN can be considered as an unfavorable structure for delay-sensitive services because a centralized architecture is needed to communicate with many nodes and provide processing power. Therefore, in the case of emergency V2X communications, delay-related control functions require a tree supporting structure. For such a scenario, the architecture of the network processing the vehicle information is a major variable affecting delay. Because it is difficult to meet the desired level of delay sensitivity with a typical fully centralized SDN structure, research on the optimal size of an SDN for processing information is needed. This study examined the SDN architecture considering the V2X emergency delay requirements of a 5G network in the worst-case scenario and performed a system-level simulation on the speed of the car, radius, and cell tier to derive a range of cells for information transfer in SDN network. In the simulation, because 5G provides a sufficiently high data rate, the information for neighboring vehicle support to the car was assumed to be without errors. Furthermore, the 5G small cell was assumed to have a cell radius of 50-100 m, and the maximum speed of the vehicle was considered to be 30-200 km/h in order to examine the network architecture to minimize the delay.

• Information Systems Review
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• v.6 no.2
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• pp.269-284
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• 2004

Induced from government policy to boost regional economic competitiveness, regional informatization forming e-community has been the subject included in the various regional informatization master plans in Korea. However, few cases are reported for its successful implementation mainly due to the lack of profitable business model to encourage investment. On the other hand, most efforts to build smart apartments, part of the home networking in a broad sense, has been pursued from the different directions. Telecommunication giant such as Korea Telecom tries to find new source of revenue exploiting enhanced broad band technology. Also, construction companies started constructing housing complexes equipped with built-in high speed network infrastructure as a means to differentiation to other competitors. The contents providing community portal has become mandatory in the sense of bearing the cost from customer side who are willing to adopt those services for new smart house. Our research motivation stems from exploring critical value aspects of realizing the profitability of this emerging new business model, that is, industry convergence model. In this paper, mainly from the survey results of the Korean smart apartment complexes, we reported recent home networking services development in Korea, and value propositions from the business model perspective. Merged business model components of telecommunications, construction, and internet contents are analyzed to provide the insights for future directions.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.6
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• pp.1726-1732
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• 2008

Injection molding is one of plastic forming technology which can easily mass-produce plastic parts with various and even complex shape. The technology has lots of difficulties in making a good part due to phase change of material, high applied pressure, and fast melt flow speed in the cavity. To overcome the problems, they had to make trial and error method until the CAE(Computer Aided Engineering) could be a tool for concurrent engineering. In this paper, we investigate the optimal design for a plastic DVD tray part by systematic approach of the commercial CAE program. In design, we should consider two objectives which are both dimensional stability and cost-down. The dimension of the part is crucial because the tray should carry a DVD correctly, but the part is too thin to injection-mold easily. In order to improve the moldability, the mold is designed in the form of stack mold which is a kind of 4 hot runner system. In first, we changed the stack-mold system with one hot-runner to cost down, and decided the optimal position of the gate. After that, we investigate the effect of both the layout of cooling channels and the cooling temperature on the shrinkage of the DVD tray. A optimal simulation approach, the gate design is 2Gate#3 and the layout is Case2 cooling line as the optimal temperature of $70^{\circ}C$. The Moldflow and PC+ABS are used for the CAE program and material respectively.