• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.3
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• pp.58-64
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• 2003

Pogo is the instability resulting from the interaction between rocket structure and propulsion system of liquid propellant rocket. The coupling of structure and propulsion system can lead to severe problem in rocket. For the analysis of pogo, a time-invariant linearized mathematical model is developed for a selected flight time. Propulsion system is modeled using element representations for each components. Rocket structure is modeled using FEM. Form the results of modal analysis of structure, the behavior of structure can be represented. System equations for coupling structure and propulsion system are composed. The stability in obtained by the eigen solution of system matrix. The optimization of the design variables such as size, place of accumulator for suppressing pogo instability in carried out. This article of study can be used to determine the degree of stability, and guide the design of pogo suppression system.

• Journal of Educational Research in Mathematics
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• v.9 no.1
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• pp.263-278
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• 1999

Computer with various powerful functions has profound potential for mathematics instruction and learning. As computer technology progress, its applicability to mathematics education become more comprehensive. Not only its functional development but various psychological positions also changed the way computer technology utilized in mathematics education. In behaviorist's perspective, computer viewed as a teaching machine and constructivist viewed computer as microworld where students could explore various mathematical contents. Both theoretical positions emphasized individual aspect of learning because behaviorist tried to individualize learning using computer and constructivist focused on the process of individual construction. But learning is not only a individual event but also a social event. Therefore we must take social aspect into account. This is especially important when it comes to computer based learning. So far, mathematics loaming with computer weighed individual aspect of loaming. Even in microworld environment, learning should be mediated by teacher and collaborative learning activities. In this aspect, the roles of teacher and peers are very important and socio-cultural perspective sheds light on the computer based learning. In socio-cultural perspective, the idea of scaffold is very important in learning and students gradually internalize the social dimension and scaffolding is gradually faded. And in the zone of proximal development, teacher and more competent peers guide students to formulate their own understanding. In sum, we must take following points into account. First of all, computer should not be viewed as a medium for individualized teaming. That is, interaction with computer should be catalyst for collaborative activities with peers. So, exploration in computer environment has to be followed by small group activities including small group discussion. Secondly, regardless of the role that computer would play, teacher should play a crucial role in computer based learning. This does not mean teacher should direct every steps in learning process. Teacher's intervention should help student construct actively. Thirdly, it is needed to conceptualize computer in learning situation as medium. This would affect learning situation and result in the change of pre-service and in-service teacher training. Computer to be used effectively in mathematics classroom, researches on assessment of computer based learning are needed.

• Journal of the Korean housing association
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• v.19 no.1
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• pp.57-66
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• 2008

In the past, strong social bands, which had spontaneous communities, existed in Korean traditional society. However, while it's developing through industrialization; monolithic apartment houses were introduced which causes less interaction between neighbors. With the growing attention to the higher living quality, various schemes to revitalize the community spirits have been groped, including to improve in hardhearted neighborhood relationships and to cope with the dreariness in the city. With the development of the internet and the spread of 'digital home', the communities in cyber space have been especially revitalized since the information-oriented society. In a move to strengthen the communities in apartment complexes, this study tries to find the revitalization scheme for virtual communities in apartment complexes by analyzing the contents of its web sites and understanding the world of virtual community. These are compared and analyzed. The related virtual communities ("cafe" or "blogs") are also analyzed. The results are as follows. 1) There are some differences among the contents provided by apartment virtual community developing companies, still, it could be categorized into four types; "apartment complex introduction and management information" "community revitalization" "living guide" "individual services" 2) The contents provided by self-organized communities of residents neither require additional charge nor special membership for information while the formation is not systematized. 3) In the comparison of apartment virtual community developing companies with residents self-organized communities, "apartment complex introduction and management information" on freeboard, notice, request and Q&A, and "community revitalization" on communication board are both provided throughout the web sites. 4) The contents provided by apartment virtual community developing companies makes the information available in a wide range with managers, on the other hand, self-organized communities emphasize on showing attachment and concern of residents and requiring communications between neighborhoods.

• The KSFM Journal of Fluid Machinery
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• v.7 no.1 s.22
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• pp.17-23
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• 2004

Aeroacoustic characteristics of sirocco fan used in Over-The-Range (OTR) has been analyzed in this paper. A microwave hood combination over the gas range is short for the OTR. The flow phenomena of the double-sided sirocco fan was analyzed numerically and experimentally by using commercial code and three dimensional PIV for flow visualization. Also, microphone array is used in order to understand acoustic characteristics of OTR. Two dimensional unsteady flow and acoustic simulation is tried to qualitatively estimate the effects of tonal noise and broadband noise on the overall sound pressure level. It is found that tonal sound is generated from the strong interaction between the impeller and cutoff while broadband sound is generated from the strong secondary flows along the scroll surface. To reduce the noise level, the V-shape cut-off was applied to improve the sound quality by reducing tonal noise. So the peak noise at BPF (Blade Passing Frequency) was almost reduced. The shape of flow-guide to suppress the secondary flow over the scroll surface was carefully checked. It is found that this affects flow pattern at the fan exit and reduces the broad band noise. Through this numerical and experimental study, the sound pressure level was lowered by 4dBA compared to that of the previous fan at the operating point.

• The KSFM Journal of Fluid Machinery
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• v.18 no.3
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• pp.46-52
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• 2015

Pump-turbine system is widely used by the hydropower industry for stabilizing the electrical grid in the vast growing economy of most developed countries. This study only investigates the Fluid-structure Interaction (FSI) analysis of the pump-turbine system at various operating conditions. The FSI analysis can show how reliable each component of the system is by providing the engineer with a better understanding of high stress and deformation points, which could reduce the lifespan of the pump-turbine. Pump-turbine components are categorized in two parts, pressurized static parts and movable stressed parts. The fixed parts include the spiral casing, top and bottom cover, stay vane and draft tube. The movable parts include guide vanes and impeller blades. Fine hexahedral numerical grids were used for CFD calculation and fine tetrahedral grids were used for structural analysis with imported load solution mapping greater than 90 %. The maximum equivalent stress are much smaller than the material yield stress, and the maximum equivalent stress showed an increasing tendency with the varying of operating conditions from partial to excessive at both modes. In addition, the total deformation of all the operating conditions showed a small magnitude, which have quite small influence on the structural stability. It can be conjectured that this system can be safely implemented.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.39 no.5
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• pp.45-55
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• 2002

In this paper, we describe an outdoor augmented reality system using GPS tracking for position and attitude information. The system consist of a remote mobile operation unit and a ground operation unit. The remote mobile operation unit includes a real-time image acquiring device, a GPS tracking device, and a wireless data transceiver; the ground operation unit includes a wireless transceiver, a virtual image generating device, and an image superimposing device. The GPS tracking device for measurement of position and attitude of the remote mobile operation unit was designed by TANS Vector and RT-20 for DGPS. The wireless data transceiver was for data transmission between the remote mobile operation unit and the ground operation unit. After the remote mobile operation unit was installed on a vehicle and a helicopter, the system was evaluated to verify its validity in actual applications. It was found that the implemented system could be used for obtaining real-time remote information such as construction simulation, tour guide, broadcasting, disaster observation, or military purpose.

• Journal of Korean Elementary Science Education
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• v.22 no.1
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• pp.121-129
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• 2003

The enhancement of inquiry skills has been emphasized as a important objective of science education for a long time. Of these, the observation is not only a simple and basic skill, but also a very important skill, in aspect of gathering informations about the nature of all things around us, through interaction between the sense organs of body and objectives. The purpose of this study is to investigate the results of observations about the grasshopper(Oxya chinesis), made by the elementary student from the 3rd to the 6th grade, and to make use of them as the basic materials for the observative teaming and the evaluation of the observation ability. Through this study, the collected items of observation are as follows For grasshopper, a total of observation items is 95, 70 using the sight sense, 13 using the tactile sense,7 using the olfactory sense. 3 using the palate sense and 2 using the auditory sense. In this study, the findings of elementary student's observation are as follows. 1. On the whole, most of students have observed mainly by the sight and the tactile sense, when observing the grasshopper. 2. It is showed a tendency that the observation ability of student is increased with the higher grade in elementary school. 3. As the grade ascends. the observations with operating are increased, also the quantitative expression and interpretation about them are increased. 4. In the case of same grade, there is no significant difference between students' gender, though girls' ability of the observation showed somewhat higher than boys' 5. Occasionally, the interpretations on the observative facts made by student, are inaccurate. Basis on the above results, we suggested some directions for the improvement of the observative learning program in science classroom of elementary school. First, the teacher have to serve as a guide and encouragement in the observative learning class, to be accomplished the various observation, which all the sensory organ can be used by student than the sight sense. Second, to get elevated the ability of observation, it is necessary that some experimental tools(magnifying lens, stereoscope, auxiliary implements etc.) are utilized. Third, the teacher have to make often endeavors showing an example of operation, to be activated the atmosphere of operative observation.

• Korean Journal of Health Education and Promotion
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• v.30 no.5
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• pp.61-77
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• 2013

Objectives: The purpose of this study was to evaluate program methods for effective smoking cessation and prevention through systematic review of studies published during recent 3 years in Korea. Methods: Electronic searches were conducted in DBPIA, RISS, KISS and other databases looking for studies published from 2010 to 2012 that dealt with the effects of intervention on smoking prevention and cessation. A total of 25 studies were included in the final analysis. Three independent reviewers critically evaluated the study quality and evidence of effectiveness based on The Community Guide methodology. Results: Multi-component intervention showed strong evidence of effectiveness for adolescents and sufficient evidence for patient smokers. Cognitive-behavioral intervention for adolescents and child-parent interaction program for adults demonstrated sufficient evidence of effectiveness on the smoking cessation and its determinants. There was insufficient evidence showing effectiveness of smoking prevention programs. Conclusion: Improving the quality and quantity of the intervention studies on smoking could help to expand evidence base for effective intervention methods and strategies on smoking.

• Korean Journal of Acupuncture
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• v.27 no.2
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• pp.79-94
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• 2010

Objectives : Many researchers in western societies raised questions on methodological limitations of randomized controlled trial (RCT) for studying Complementary and Alternative Medicine (CAM), and they have tried to find alternatives to RCT. Some of them recently have interest in health service research as one of the alternatives. Discussing the significance of health services research in CAM studies will be helpful to guide the researchers in Korea who are also interested in developing an appropriate research methodology for traditional Korean medicine. Methods : Previous studies on methodological issues of studying CAM and health service researches published in western societies until 2009 were searched mainly from Pubmed. The definition, main research domains, and research methods of health service research and the significance of it for researches on CAM were summarized. Results & Conclusions : Health service researches are important in two aspects. First, health service researches evaluate the actual practice of CAM, including the individualized diagnosis as well as treatment and interaction between practitioners and patients. Second, when evaluating the outcomes, they put an emphasis on subjective evaluation by patients as well as objective evaluation by doctors. Thus, it can reflect the treatment goals of CAM which is improving the overall quality of life and the physical and psychological health. Therefore, health services researches such as descriptive studies, qualitative studies, outcomes studies including economic evaluation, and whole systemic research should be more utilized in order for studying traditional Korean medicine.

• Korean Journal of Soil Science and Fertilizer
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• v.48 no.5
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• pp.464-468
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• 2015

Our government has performed to support the nation-wide application of customized fertilizer based on soil-testing results and crop nutrient balance in order to promote the environment-friendly agriculture and to respond the global environment guide-line since 2010. This study was performed at the selected local paddy fields (Hwaseong-si, Uiseong-gun and Miryang-si) with different soil chemical properties in 2012. The contents of amino acids measured showed an increasing trend with fertilization, and glutamic acid was the most abundant amino acid followed by aspartic acid, leucine and alanine. However, valine, isoleusine, tyrosine and lysine were not significantly affected by fertilization. The significant differences in grain N, expressed as a crude protein, and amino acids dose was observed between experimental sites (p<0.001), treatments (p<0.01 to 0.001) and interaction of both factors (p<0.01 to 0.001). In our experiment the following order of carbon skeleton backbones to produce amino acids was observed irrespective of experiment sites and fertilization: ${\alpha}$-ketoglutarate > oxalate > pyruvate > 3-phosphoglycerate > phosphoenolpyruvate. In conclusion, customized fertilizer had no difference in amino acids compared to the conventional-NPK practice which was higher than in no fertilization, and also the normal paddy represented slightly higher amino acids compared to the reclaimed. Further study based on the present results is required to investigate what is main factor to amino acids between genetic and environmental factors.