• Geomechanics and Engineering
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• v.10 no.5
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• pp.657-676
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• 2016

In this paper, the active lateral earth pressure is evaluated using the stress characteristics or slip line method. The lateral earth pressure is expressed as the lateral earth pressure coefficients due to the surcharge, the unit weight and cohesion of the backfill soil. Seismic horizontal and vertical pseudo-static coefficients are used to consider the seismic effects. The equilibrium equations along the characteristics lines are solved by the finite difference method. The slope of the ground surface, the wall angle and the adhesion and friction angle of the soil-wall interface are also considered in the analysis. A computer code is provided for the analysis. The code is capable of solving the characteristics network, determining active lateral earth pressure distribution and calculating active lateral earth pressure coefficients. Closed-form solutions are provided for the lateral earth pressure coefficients due to the surcharge and cohesion. The results of this study have a good agreement with other reported results. The effects of the geometry of the retaining wall, the soil and soil-wall interface parameters are evaluated. Non-dimensional graphs are presented for the active lateral earth pressure coefficients.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2000.11a
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• pp.10-10
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• 2000

For low Earth orbit, the atmosphere causes orbit altitude to decrease, If this decrease is not corrected by the satellite propulsive unit, the orbit decoys continuously unit reaches the dense atmosphere and satellite life ends. If active orbit maintenance is mode by satellite propulsive unit then fuel consumption is necessary, which must be considered in the satellite design. Especially interesting is the method for evaluating the fuel consumption role for maintenance of elliptical orbit developed in this paper.(omitted)

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.4 no.3
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• pp.215-225
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• 1999

To study the vertical variations of major elements, trace elements and rare earth elements(REEs) contents in deep-sea sediments, six cores from Korea Deep-sea Environmental Study area(KODES) were analyzed. Topmost sediment layers of KODES area are divided into two Units; brown-colored and peneliquid Unit I and pale brown-colored and relatively solidified Unit II. Contents of major elements, REEs, Cu, Sr and Rb in each Unit are almost same, while contents of Mn, Ni and Co in Unit I are two or three times higher than those in Unit II. R-mode factor analysis represents that surface sediments are composed of alumino-silicate phase (AI-Ti-K-Mg-Fe-Rb-Ce), apatite phase (Ca-P-Cu-Sr-Trivalent Rare Earth Elements) and Mn-oxide phase(Mn-Ni-Co). Factor scores in silicate and apatite phases in each Unit are nearly same, whereas those in Mn-oxide phase in Unit I is higher than those in Unit II. While NilCu ratio in Unit I is two times higher than that in Unit II. We interprete the geochemical fractionation of Ni and Cu as a result that Ni can be remobilized in oxygen-depleted micro-environment in Units I and II and then easily reprecipitated in Unit I, while most of Cu supplied together with organic material is decomposed mostly in Unit I and sorbed into apatite.

• Journal of the Korean earth science society
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• v.28 no.4
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• pp.393-404
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• 2007

The purpose of this study was to identity scientific models included in the Earth domain of the $10^{th}$ grade science textbooks. Three earth science-related chapters in each of 11 trade books were analyzed. A framework was developed and used to classify a scientific model from three different perspectives: medium of representation, method of representation, and mobility of a model. Results showed that the science textbooks utilized domain-specific models in which the nature of sub-areas of earth science was embedded. That is, the unit of 'Change of the Earth' included many iconic models that represented the inaccessible inner structure of the earth and the movement of the tectonic plates. These were also two-dimensional pictorial and static models. In the chapter of 'Atmosphere and Oceans', symbolic and diagrammatic models were dominant in use, which included weather maps and contour line graphs of sea surface temperature and salinity. The unit of 'Solar System and Galaxies' showed the highly frequent use of iconic and analogical models for the large-scale celestial objects and their movements. Implications for earth science education and relevant research were discussed.

• Aerospace Engineering and Technology
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• v.10 no.2
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• pp.20-28
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• 2011

The electro-optical payload of a low-earth orbit satellite is thermally decoupled with the bus, which supports a payload for a mission operation. The payload has a cooling unit of FPA(Focal Plane Assembly) which has a thermal behavior increasing its temperature instantly during an operation in order to dissipate a waste heat into the space. The FPA cooling unit should include a radiator and heatpipes with a sufficient performance in worst hot condition, and a heater design to maintain its temperature above a minimum allowable temperature in the worst cold condition. In this paper, we analyzed the thermal requirements and the heater design constraints from the thermal analysis results for the current thermal design of the FPA cooling unit and the design elements of the better heater design were found.

• Journal of the Korean earth science society
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• v.32 no.3
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• pp.324-333
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• 2011

The opinion, that the history of science should be introduced to science lesson, has been continuously emphasized by a group of people who supported the needs of science and scientific process, nature of science, and the interaction between science and society. When the importance of the integrated science education is emphasized, the history of science is suggested as an effective curriculum for it. To respond to this identified interest, we developed a lesson of the history of science by selecting the contents of the history of science as subject topics of the integrated science and by utilizing the findings of previous studies related to the history of science in science educations. To develop the history of science class as a subject of integrated science, we chose 'the age of the earth' as a unit. After the pilot test of the unit in secondary school students, the possibility of offering the lesson as a regular course was examined with analysis of the students' reactions showing its effectiveness.

• Journal of the Korean Society of Earth Science Education
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• v.3 no.1
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• pp.28-35
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• 2010

This study is aiming to determine the effect of learning dimensions oriented elementary science lecture on scientific attitude, academic achievement, and logical thinking based on 'Earth' section in the 2nd semester of the 5th grade. Analyzing sub-categories of dimension in each lecture before teaching, a teaching and a learning plans based on dimension 3 and 4 were devised and applied. The result of this study is as follows: Firstly, when sub-categories of Earth section in the 2nd semester of the 5th grade in elementary schools were examined, the unit '5-2-4. Volcanoes and Rocks' was missing 8 of total 28 sub-units, while '5-2-7. Solar families' unit was covering all sub-units of every learning dimension. Secondly, learning dimensions 3 and 4 centered elementary school teaching caused significant difference in scientific attitude. Especially, among other sub-categories of scientific attitudes, 'Social meaning of Science', 'Attitude toward Science lessons' were better improved. Thirdly, learning dimensions 3 and 4 based elementary school lectures didn't bring significant difference to academic achievement. Fourthly, learning dimensions 3 and 4 oriented elementary lessons didn't imply significant difference in sub-logics of logical thinking, however proved to be helpful for students of transitional age.

• Journal of the Korean earth science society
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• v.32 no.5
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• pp.474-484
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• 2011

This study presents how a professional development program (PD) of K-12 teachers affects participants' use of the earth system approach and their perceptions of using the urban environment for their science teaching and lesson unit development. This study utilized mixed methods to collect and analyze the data. Eleven urban teachers' pre-post lessons (45 lessons) were analyzed quantitatively using a lesson plan analysis tool, modified by the author, and their lesson reflections were analyzed qualitatively. The findings of this study show that the PD program influences the teachers to choose more topics and content knowledge based on the earth system approach and to assess the topics and content knowledge with more appropriate methods. Specifically, the teachers use more urban environmental factors/topics in their post lesson to teach the environmental topics of urban area. However, according to the statistical analysis of pre-and postlesson plan scores, the accuracy of the earth system knowledge that participants used in their lessons did not change significantly (p<0.05) (Table 4), which means that the PD program did not affect the improvement of the teacher's content knowledge in earth system science. Implications of this study are discussed.

• Journal of Soil and Groundwater Environment
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• v.15 no.6
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• pp.46-52
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• 2010

Derivative analysis, based on the derivative of the drawdown as a function of time (i.e., rate of drawdown change), was applied to the evaluation of hydraulic parameters of the aquifer as an aid of the aquifer test interpretation based on the Theis solutions. Pumping tests were conducted at a coastal fractured aquifer in Muan county, Korea, of which the drawdown data, measured at the two observation wells, were used for derivative analysis. Wellbore storage and transition period were hard to identify at conventional log-log and semi long plots, but was easily recognized by distinctive curves of positive unit slope, hump and negative unit slope in the derivative plot. For the observation well of OW-2 at which wellbore storage and transition lasted over an hour, conventional aquifer analysis would suffer from the uniqueness problems and in further result in erroneous hydraulic parameters. Derivative analysis was found to be effective for distinguishing the drawdown data directly reflecting the aquifer property from those reflecting non aquifer effects such as wellbore storage and transition, which offers a unified methodology to yield correct hydraulic parameters from aquifer test data.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.333-336
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• 2003

Designed transformer-less inverter for photovoltaic and small unit windturbine power system. This system consisted of boost chopper circuit of multiple-switching method and foil bridge PWM inverter. Transformer-less system was adapted to reduce cost and size. But in this system, earth-leakage current have to be considered. So, to solve this problem, we used PWM inverter switching method to reduce the earth-leakage current which flows in accordance with the variation of DC input common mode voltage.