• Journal of Mechanical Science and Technology
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• 제18권6호
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• pp.979-989
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• 2004

Numerical simulations have been performed to investigate tip clearance effect on through-flow and performance of a centrifugal compressor which has the same configuration of impeller with six different tip clearances. Secondary flow and loss distribution have been surveyed to understand the flow mechanism due to the tip clearance. Tip leakage flow strongly interacts with mainstream flow and considerably changes the secondary flow and the loss distribution inside the impeller passage. A method has been described to quantitatively estimate the tip clearance effect on the performance drop and the efficiency drop. The tip clearance has caused specific work reduction and additional entropy generation. The former, which is called inviscid loss, is independent of any internal loss and the latter, which is called viscous loss, is dependent on every loss in the flow passage. Two components equally affected the performance drop as the tip clearances were small, while the efficiency drop was influenced by the viscous component alone. The additional entropy generation was modeled with all the kinetic energy of the tip leakage flow. Therefore, the present paper can provide how to quantitatively estimate the tip clearance effect on the performance and efficiency.

• Journal of Korean Elementary Science Education
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• 제21권2호
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• pp.263-288
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• 2002

'Science Garden' is a science program that develops acquirements of science & technology at an early stage through experiential study and inspire the spirit of scientific inquiry by carrying out laboratory work, science movie, science lecture, scientific work, outdoor activities, computer classes and science experiment which is hard to do through the regular educational course. It is targeted grade 4,5,6 students during summer and winter vacation. 'Science Garden' is conducted by selective participation freely. It is a wholelistic activity that develops children's potential talents or creativities, improves interest and attitude toward science, and also gives opportunity for self-realization by extending capacity for inquiry to show each student's ability. This study is observed and is compared how it is conducted in elementary school using qualitative study. This study is used narrative observation, in-depth interview and document analysis. Objects of narrative observation are two elementary schools, each from Jellabukdo and Gyeonggido, and 7 teachers were interviewed in-depthly. Here are results of the study. 1 A teacher in school G never takes part in student activities, tends to be indifferent to classes, but focuses on observation and experiment in laboratory. And feedback or evaluation about student's activity is never done. On the other hand, a teacher in school S guides students to understand the principals of science on themselves, and wide variety forms of activities such as role playing, discussion, and games are being done. But an effort to evaluate student's activity is not being made properly. 2. Teachers set a high valuation on the need of 'Science Garden'. Observing the way of conducting 'Science Garden', usually teachers who is in charge of science for official work is selected as a teacher in charge, and groan under a heavy burden of conducting it without anyone's help. Participating students are selected by volunteering or teacher's recommendation, but because of low Participation rate, teachers have difficulty in conducting it. Plan for conducting ‘science Garden’ is made 20 days before it, after getting an official document from Office of Education, refering to booklets produced by National Jungang Science Institute, or data from Office of Education, and internet. Teachers evaluate rarely Most school principals have interest in 'Science Garden' but parents are not well aware of it, The budget is made at the same time with the plan, and scale is varied between 200,000∼500,000 won. Because of the improper way of selecting teacher in charge, difficulty in selecting students, heavy works caused by planning, conducting the program, as well as reporting teacher's work, and lack of parents' awareness, 'Science Garden' has been conducted formally and superficially. Next gives you direction to change, for the right way of conducting' Science Garden'. It is important to motivate competent teachers to instruct students actively. For students' active participation, They should publicize thoroughly beforehand, and develope 'Science Garden' program for teachers to be able to make better use of it. Evaluation of student activities and program should be done in the aspect of developing students’ faculties. Beside of school facilities, they need to put diverse local facilities and places to practical use for immediate natural experience. And not only separate schools but also associated form of schools to conduct it is necessary.

• Nuclear Engineering and Technology
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• 제53권12호
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• pp.3879-3891
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• 2021

A heat pipe residual heat removal system is proposed to be incorporated into the reactor driven subcritical (RDS) facility, which has been proposed by MIT Nuclear Reactor Laboratory for testing and demonstrating the Fluoride-salt-cooled High-temperature Reactor (FHR). It aims to reduce the risk of the system operation after the shutdown of the facility. One of the main components of the system is an air-cooled heat pipe heat exchanger. The alkali-metal high-temperature heat pipe was designed to meet the operation temperature and residual heat removal requirement of the facility. The heat pipe model developed in the previous work was adopted to simulate the designed heat pipe and assess the heat transport capability. 3D numerical simulation of the subcritical facility active zone was performed by the commercial CFD software STAR CCM + to investigate the operation characteristics of this proposed system. The thermal resistance network of the heat pipe was built and incorporated into the CFD model. The nominal condition, partial loss of air flow accident and partial heat pipe failure accident were simulated and analyzed. The results show that the residual heat removal system can provide sufficient cooling of the subcritical facility with a remarkable safety margin. The heat pipe can work under the recommended operation temperature range and the heat flux is below all thermal limits. The facility peak temperature is also lower than the safety limits.

• Journal of Dental Rehabilitation and Applied Science
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• 제21권2호
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• pp.183-189
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• 2005

There is no single or simple answer for effective communication between laboratory technician and clinical dentist. Love-hate could be used to describe the relationship between dentists and their labs. Great lab work can make a dentists life much easier and can result in getting many referrals. However, if the lab work is not up to par and/or late, it can add stress and agony to a dentists practice. Also the opposition is right. If the preparations are calibrated, the impressions clear, and the bite registrations accurate, most labs can do their work reasonably well. Unfortunately, many cases received by labs are barely adequate, especially when it comes to reading margins, which are frequently created by the imagination of the person trimming the dies. In other words, both dentists and lab technicians need to be able to understand how each party operates so that solutions to problems can be found. Effective communication with the laboratory is critical if any degree of success is desired.

• Safety and Health at Work
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• 제13권2호
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• pp.155-162
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• 2022

Background: Workers are exposed to several risks in academic laboratories due to the presence of potentially hazardous substances. The main objective of this study was to assess the prevalence of accident occurrence and associated risk factors among laboratory workers at the scientific laboratories of the public university in Lebanon and the impact of safety measures training and availability. Methods: In this observational study, a survey was conducted for one year in scientific laboratories at faculties of the public university. Results: Among the participants (N = 220), 45.0% have had accidents; the main cause was exposure to chemicals (73.7%) and more specifically by inhalation (45.4%). Females (85.9%) were more exposed to accidents than males. Laboratory workers with a master's degree, a full-time schedule, and more than ten years of experience were significantly more exposed to accidents (p < 0.05). A significant association was found between accident occurrence and training on management of hazardous products (p = 0.044), risks related to workplace (p = 0.030), eyewash and emergency shower (p < 0.001), first aid (p = 0.012), and facial protection availability (p = 0.019). In spite of the lack of safety culture and efficient training on laboratory safety, participants have shown a very good perception regarding safety measures to be applied in case of work accidents. Conclusion: Based on our findings, the prevalence of accident occurrence is elevated among lab workers at the public university. The impact of regular training on laboratory safety preventive measures is of great importance to ensure the efficiency of occupational health and safety in scientific laboratories.

• Journal of Magnetics
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• 제10권1호
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• pp.36-39
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• 2005

We report element-resolved and interface-sensitive magnetization reversals investigated from an oppositely exchange-biased NiFe/FeMn/Co structure by employing soft x-ray resonant Kerr rotation measurements. We have found not only switchable uncompensated antiferromagnetic regions with its sizable thicknesses at both interfaces of the FeMn layer but also their strong coupling to the individual ferromagnetic layers. These experimental results provide a better insight into experimentally observed reductions in exchange-bias field on the basis of an interface-proximity model proposed in this work.

• Journal of Science Education
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• 제34권2호
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• pp.327-341
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• 2010

The purpose of this study is to obtain science high school students' perceptions of scientists and their work before and after the Green Investigation program with scientists. This study also attempts to determine whether the program affected the participants' perceptions of scientists and their work. A modified DAST was carried out with 64 high school students. Findings revealed that Korean science high school students had normal perceptions of scientists, such as images of 20 to 30 year old males wearing laboratory coats and working alone in research labs with test tubes, flasks, and several machines in the background. After the intervention, students drew fewer typical items representing scientists and had significantly different perceptions of their work places between the pretest (M=1.69, SD=1.14) and posttest (M=1.96, SD=1.24, t=4.43, p<0.001) with the eta squared statistics (.24). These findings reflect the need for continued efforts of developing green investigation programs with scientists for students. Some future studies based on this study are also introduced.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권3호
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• pp.1785-1801
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• 2017

In recent years, image encryption algorithms have been developed rapidly in order to ensure the security of image transmission. With the assistance of our previous work, this paper proposes a novel chaotic image encryption algorithm based on self-adaptive model and feedback mechanism to enhance the security and improve the efficiency. Different from other existing methods where the permutation is performed by the self-adaptive model, the initial values of iteration are generated in a novel way to make the distribution of initial values more uniform. Unlike the other schemes which is on the strength of the feedback mechanism in the stage of diffusion, the piecewise linear chaotic map is first introduced to produce the intermediate values for the sake of resisting the differential attack. The security and efficiency analysis has been performed. We measure our scheme through comprehensive simulations, considering key sensitivity, key space, encryption speed, and resistance to common attacks, especially differential attack.

• Geomechanics and Engineering
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• 제14권1호
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• pp.91-98
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• 2018

Length of a vehicle is an important variation to generate different variants of an automotive platform. This parameter is usually adjusted by embedding dimensional flexibility into different components of the Body in White (BIW) including the floor pan. Due to future uncertainties, it is not necessarily possible to define certain values of wheelbase for the future products of a platform. This work is performed to add flexibility into the design process of a length-variable floor pan. By means of this analysis, the cost and time consuming process of optimization is not necessary to be performed for designing the different variants of a product family. Stiffness and mass of the floor pan are two important functional requirements of this component which directly affect the occupant comfort, dynamic characteristics, fuel economy and environmental protection of the vehicle. A combination of Genetic algorithm, GMDH-type of artificial neural networks and TOPSIS methods is used to optimally design the floor pan associated with arbitrary length of the variant in the defined system range. The correlation between the optimal results shows that for a constant mass of the floor pan, the first natural frequency decreases by increasing the length of this component.

• Nuclear Engineering and Technology
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• 제54권8호
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• pp.3117-3129
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• 2022

Deeply understanding the phase change of thin liquid sodium film inside wick pore is very important for further studying high-temperature sodium heat pipe's heat transfer. For the first time, the evaporation and condensation of thin liquid sodium film are investigated by the Lennard-Jones potential of molecular dynamics. Based on the startup and normal operation of the sodium heat pipe, three different cases are simulated. First, the equilibrium is achieved and the Mass Accommodation Coefficients of the three cases are 0.3886, 0.2119, 0.2615 respectively. Secondly, the non-equilibrium is built. The change of liquid film thickness, the number of gas atoms, the net evaporation flux (J_net), the heat transfer coefficient (h) at the liquid-gas interface are acquired. Results indicate that the magnitude of the J_net and the h increase with the basic equilibrium temperature. In 520-600 K (the startup of the heat pipe), the h has approached 5-6 W m^-2 K^-1 while liquid film thickness is in 11-13 nm. The fact shows that during the initial startup of the sodium heat pipe, the thermal resistance at the liquid-gas interface can't be negligible. This work is the complement and extension for macroscopic investigation of heat transfer inside sodium heat pipe. It can provide a reference for further numerical simulation and optimal design of the sodium heat pipe in the future.