• Journal of Communications and Networks
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• v.8 no.3
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• pp.339-350
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• 2006

Several novel concepts and tools have revolutionized our understanding of the Internet topology. Most of the existing efforts attempt to develop accurate analytical models. In this paper, our goal is to develop an effective conceptual model: A model that can be easily drawn by hand, while at the same time, it captures significant macroscopic properties. We build the foundation for our model with two thrusts: a) We identify new topological properties and b) we provide metrics to quantify the topological importance of a node. We propose the jellyfish as a model for the inter-domain Internet topology. We show that our model captures and represents the most significant topological properties. Furthermore, we observe that the jellyfish has lasting value: It describes the topology for more than six years.

• Journal of the Korean earth science society
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• v.30 no.1
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• pp.111-126
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• 2009

The purpose of this study was to derive the criterions of each type of mental models on the plate boundaries and to investigate high school students' mental models on these concepts. The 11th grade student participants were requested to draw the collisional, convergent, and divergent boundaries and were interviewed individually. The drawings and the data gathered through the interviews were analyzed qualitatively. The mental models on the plate boundaries were classified as 'naive model', 'unstable model', 'causal model', and 'conceptual model'. The criterions for analyzing the mental models were the differentiations of the lithospheric plates and the mantle, the explanations of the motion of the plates and lower mantle, the demonstrations of topographical features of the plate boundaries and the causal relationships between the mantle convection and the topographical features. The findings revealed that the students holding 'the naive model' and 'the unstable model' were unable to relate the mantle convection and the three boundaries. In contrast, the students holding 'the causal model' and 'the conceptual model' were able to explain that the mantle convection causes the three boundaries. Also, the types of epistemological belief were different depending on their mental models. Students holding the naive model and the unstable model tended to rely upon the external authorities.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.1
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• pp.154-164
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• 2017

This work conducts a validation study for the XH-59A helicopter using a rigid coaxial rotor system in order to establish the techniques of the conceptual design and performance analysis for the lift-offset compound rotorcraft. As a tool for conceptual design and performance analysis, NDARC (NASA Design and Analysis of Rotorcraft) is used for the present study. An assumed mission profile is considered for the conceptual design of the XH-59A. As a validation result of the design, the dimensions and weight of the XH-59A are appropriately designed when compared to the target values since the relative error is less than 0.5%. Then, performance analyses are conducted for the designed XH-59A model with and without auxiliary propulsion in hover and forward flight conditions. The present analyses show good validity since the prediction results compare well with both the flight test and previous analyses. Therefore, the techniques for the conceptual design and performance analysis of the lift-offset compound helicopter are overall considered to be appropriately established. In addition, this study investigates the influence of the lift-offset on the rotor effective lift-to-drag ratio of the XH-59A helicopter with auxiliary propulsion. As a result, the improvement of the rotor effective lift-to-drag ratio can be obtained by appropriately increasing the lift-offset in high-speed flight.

• Journal of the Korean Society for Library and Information Science
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• v.33 no.4
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• pp.133-156
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• 1999

The purpose of this paper is to show how conceptual data modeling can enhance current information retrieval (IR) systems. The conceptual database design provides for: 1) data mining capability to discover new knowledge based on the relationships between entities, and 2) integrating current separate databases into one IR system (e.g., integrating ISI Citation, a thesaurus, and bibliographic databases into one retrieval system) . Further, as new user requirements are unfolded, modifications of IR systems based on conceptual data modeling will be much easier to make than they were in the current IR systems because conceptual modeling facilitates flexible modifications. The enhanced Entity-Relationship (ER) model was employed in this study to develop conceptual schemas of IR data.

• Journal of The Korean Association For Science Education
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• v.24 no.3
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• pp.621-637
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• 2004

In science education, the research on students' conceptions has been started in early 1970. From the early 1980, the research on students' conceptions stimulated the research on conceptual change. Recently, mental model has been a theoretical background in concrete arguments on "how students' conceptions are constructed or created?" Mental model has been studied early in cognitive psychology, and several researchers have studied it partially in science education area. In this study, we compared different theories that explained students' conceptions in, mainly, physics. Further we discussed the possibility of mental model as a theory that could integrate different explanations about students' conceptions from different theory.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.2
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• pp.781-790
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• 2013

This research focuses on development of the conceptual cost estimation models for I.L.M box girder bridge. The current conceptual cost estimation for public construction projects is dependent on governmental average unit price references which has been regarded as inaccurate and unreliable by many experts. Therefore, there have been strong demands for developing a better way of conceptual cost estimating methods. This research has proposed three different conceptual cost estimating method for a P.S.C. girder bridge built with the I.L.M method. Model (I) attempts to seek the proper breakdown of standard works that are accountable for more than 95 percentage in total cost and calculates the amount of standard work's materials from the standard section and volume of I.L.M box girder bridge. Model (II) utilizes a correlation analysis (coefficient over 0.6 or more) between breakdown of standard works and input data that would be considered available information in preliminary design phase. Model(III) obtains conceptual estimating through multiple-regression analysis between the breakdown of standard works and all of input data related to them. In order to validate the clustering of coverage in the preliminary design phase, the variation of I.L.M cost coverage from multiple-regression analysis[model(III)] has been investigated which result in between -3.76% and 11.79%, comparing with AACE(Association for the Advancement of Cost Engineering) which informs its variation between -5% and +15% in the design phase. The model proposed from this research are envisioned to be improved to a great distinct if reliable cost date for P.S.C. girder bridges can be continually collected with reasonable accuracies.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.4D
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• pp.595-601
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• 2011

There is currently applied to the unit cost per a distance (KRW/km) for estimating the conceptual cost of civil work on basic planning stage of high speed railroad. This unit cost is an arithmetic average value based on historical data, which could be in big error. It also is difficult to explain the deficiency comparing the estimated cost derived from next basic design stage. This study provides the conceptual estimation model using by the parametric method and regression analysis. Independent variables are the distance and the geological materials (earth, weathered rock, soft-rock, hard-rock), extracting from the actual data to 36 contracts. The deviation between the unit costs estimated using the developed model and the actual cost data is presented in the range from -0.4% to +31%. This range is acceptable compared the typical range "-30% to + 50%". This model will improve the accuracy of existing method and be expected to contribute to effective total cost management and the economic aspects, reduce the financial expenditure.

• Journal of The Korean Association For Science Education
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• v.17 no.2
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• pp.179-189
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• 1997

In this study, a conceptual change model for effective laboratories was developed and its instructional effect on students' achievement, the acquisition of scientific conceptions, and the attitudes toward science was investigated. Considering several conceptual change models in literature and Korean educational situations, the conceptual change model was developed. The model consists of 5 stages; preliminary, prediction, exploration, consolidation and reconstruction, and application. The treatment and control groups (2 classes) were selected from a middle school in Seoul, and taught about the changes of states, density, and dissolution for three weeks. Prior to instruction, the Group Assessment of Logical Thinking and the Learning Approach Questionnaire were administered, and their scores were used as covariate and / or blocking variable. To examine students' alternative conceptions before the instructions, a pre-conceptions test was also administered. After the instructions, students' achievement, the acquisition of scientific conceptions, and the attitudes toward science were measured with a researcher-made achievement test, a post-conceptions test, and the subtests of the Test of Science-Related Attitudes, respectively. The results indicated that the score of the treatment group was significantly higher than that of the control group in the post-conceptions test. The students in the treatment group had also less alternative conceptions than those in the control group. However, there were no significant differences for the achievement and the attitudes toward science. Educational implications are discussed.

• Journal of The Korean Association For Science Education
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• v.35 no.6
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• pp.971-984
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• 2015

The purpose of this study is twofold: to theoretically review the 'resources-based view' (RBV) developed by D. Hammer and his colleagues as an alternative cognitive theory and to illustrate the usefulness of the theory by applying it to interpret a science learning activity in which undergraduate students worked together to construct a model of the seasons. The theoretical review was based on the exploration of relevant literature and dealt mainly with three types of resources: conceptual, epistemological, and practical resources. The trial application revealed that scientific models have been developed through the combination of different pieces of conceptual resources activated from participants, rather than emerging as unitary wholes. However, all the activated resources were not included into a model, and some of the conceptual resources acted as constraints to constructing a scientific model. The implications included that science educators should be attentive and responsive to students' resources and help them use the resources productively to learn science.

• Journal of Educational Research in Mathematics
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• v.17 no.2
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• pp.147-162
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• 2007

This paper reports an analysis of 19 Chinese and Korean middles school mathematics teachers' understanding of division by fractions. The study analyzes the teachers' responses to the teaching task of generating a real-world situation representing the meaning of division by fractions. The findings of this study suggests that the teachers' conceptual models of division are dominated by the partitive model of division with whole numbers as equal sharing. The dominance of partitive model of division constraints the teachers' ability to generate real-world representations of the meaning of division by fractions, such that they are able to teach only the rule-based algorithm (invert-and-multiply) for handling division by fractions.