• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.3
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• pp.30-35
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• 2021

The present study examined the effects of various guide fin structures and boundary parameters on the thermal performance of heat exchangers used in heat recovery thermoelectric generators. The heat transfer rate and pressure drop of the heat exchangers without fins, with circular fins, with triangular fins, and with combined circular and triangular fins were simulated numerically using ANSYS 19.1 commercial code to confirm the effect of the guide fin structures. The heat transfer rate of the heat exchanger with combined fins was 27.0%, 5.2%, and 1.5% higher than those without fins, with circular fins, and with triangular fins, respectively. The pressure drop characteristic of the heat exchanger with the combined fins was 28.3% higher than that without fins but 9.2% and 10.5% lower than those with circular fins and with triangular fins, respectively. The heat exchanger with combined fins as the optimal model showed the highest heat transfer rate of 5664.9 W and pressure drop of 1454.02 Pa for highest hot gas temperature, maximum flow rates of hot gas and coolant, and lowest coolant temperature.

• Journal of Korean Elementary Science Education
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• v.41 no.1
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• pp.30-43
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• 2022

In this study, elementary students' science communication competence was investigated based on the grammatical features expressed in their language-use in classroom discourse and science writings. The classes were designed to integrate the evidence-based reasoning framework and traditional learning cycle and were conducted on fifth graders in an elementary school. Eight elementary students' discourse data and writings were analyzed using lexico-grammatical resource analysis, which examined the discourse text's content and logical relations. The results revealed that the student language used in analyzing data, interpreting evidence, or constructing explanations did not precisely conform to the grammatical features in science language use. However, they provided examples of grammatical metaphors by nominalizing observed events in the classroom discourses and those of causal relations in their writings. Thus, elementary students can use science language grammatically from science language-use experiences through listening to a teacher's instructional discourses or recognizing the grammatical structures of science texts in workbooks. The opportunities in which elementary students experience the language-use model in science learning need to be offered to understand the appropriate language use in the epistemic context of evidence-based reasoning and learn literacy skills in science.

• Economic and Environmental Geology
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• v.56 no.3
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• pp.277-291
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• 2023

To analyze the crustal velocity structures beneath 21 broadband seismic stations in Gangwon Province, South Korea, we first applied the H-κ stacking method to 139 teleseismic event data (Mw ≥ 5.8 and the epicentral distance of 30° - 90°) occurring between March 18, 2019 and December 31, 2022 to estimate the Moho depths and V_p/V_s ratios beneath each station. The Moho depths and V_p/V_s ratios from the H-κ stacking method range from 24.9 to 33.2 km depth and 1.695 - 1.760, respectively, and the estimated V_p/V_s ratios were applied to the joint inversion of receiver functions and surface wave dispersion to obtain 1-D crustal velocity models beneath each station. The resulting Moho depths range from 25.9 to 33.7 km depth, similar to the results from the H-κ stacking method. Moho depth results from the both methods are generally consistent with Airy's isostasy. The 1-D crustal velocity models confirm that the existence of 2 km thick low-velocity layers with P-wave velocities of 5 km/s or less at some stations in the Taebaeksan basin, and at the stations CHNB and GAPB in northern Gangwon Province, which are located above the Cenozoic sedimentary layer. The station SH2B, although not overlying a sedimentary layer, has a low P-wave velocity near the surface, which is probably due to various factors such as weathering of the bedrock. We also observe a velocity inversion with decreasing velocity with depth at all stations within 4 - 12 km depths, and mid-crustal discontinuities possibly due to density differences in the rocks at around 10 km depth below some stations.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.1381-1388
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• 2011

Recently, Because of weight lighting and tighten safety regulations of the railway vehicle railroad weight lighting and safety improvement technology is internationally required. Slide step for moving the passenger to high flatform in the railroad vehicle is recognized of important parts. However, Due to high price and weight, it is limited. In this research, In order to apply for railroad, it was redesigned to optimize part count and reduce the price and weight. By choosing honeycombcore as a part for enduring high weight and weight lighting, We produce honeycombpanel of sandwich structure which a different kind connected by using existing stainless(STS304)steel and thermo plasticity glue. Finally, we can find that honeycombpanel is suitable for weight lighting and high weight. As well as, with test result, we can prove that low-high platform railway system will be optimized, if steps are applied to honeycombpanel.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.3
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• pp.331-336
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• 2013

In this paper, plasma modeling is achieved using fluid dynamics, thereby electron density is derived. The way proposes the key to overcoming the limitations of conventional researches which adopt simplified plasma model. The result is coupled with Maxwell-Boltzmann system in order to calculate scattering waves in various incident angle. The first part is dedicated to perform plasma modeling in dielectric barrier discharge(DBD) structure. Suzen-Huang model is adopted among various models due to the fact that it uses time independent variables to calculated potential and electron distribution in static system. The second part deals with finite difference time domain(FDTD) scheme which computes the scattered waves when the modulated Gaussian pulse is incident. Founded on it, radar cross section(RCS) is observed. Consequently, RCS is decreased by 1~2 dB with DBD plasma. The result is analogous to the RCS measurement in other researches.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.1
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• pp.561-568
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• 2014

A modular fish-bone girder pier consists of one main girder system named as "Spine Girder". Therefore, this pier can be most affected by torsion as well as flexural bending. The design considerations of the fish-bone girder pier are proposed to assure the reasonable design in this study. In order to investigate the behavior characteristics, structural analysis F.E model is developed, and the verification of the developed model is performed by comparison with experimental data. From the investigation of the structural behavior, the vertical stiffener is required at the bottom of bone-beams to prevent the excessive local stress. Also, it is found that the normal stress of the flange and the shear stress of the web and flange are dominantly affected by the warping torsion and pure torsion, respectively.

• Journal of the Earthquake Engineering Society of Korea
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• v.18 no.1
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• pp.53-61
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• 2014

RC shear wall sections which have irregular shapes such as T, ㄱ, ㄷ sections are typically used in low-rise buildings in Korea. Pushover analysis of building containing such members costs a lot of computation time and needs professional knowledge since it requires complicated modeling and, sometimes, fails to converge. In this study, a method using an equivalent column element for the shear wall is proposed. The equivalent column element consists of an elastic column, an inelastic rotational spring, and rigid beams. The inelastic properties of the rotational spring represent the nonlinear behavior of the shearwall and are obtained from the section analysis results and moment distribution for the member. The use of an axial force to compensate the difference in the axial deformation between the equivalent column element and the actual shear wall is also proposed. The proposed method is applied for the pushover analysis of a 5- story shear wall-frame building and the results are compared with ones using the fiber elements. The comparison shows that the inelastic behavior at the same drift was comparable. However, the performance points estimated using the pushover curves showed some deviations, which seem to be caused by the differences of estimated yield point and damping ratios.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.6
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• pp.67-72
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• 2020

Life tests are essential in reducing the catastrophic damage caused by the accidents of large machinery such as aircraft and ships. However, life tests are challenging to implement due to the high costs and time required to test the life of large machinery parts. Therefore, it is advantageous and convenient to apply accelerated life test techniques for key components to reduce costs and time. In fact, extensive research has already been conducted on these techniques. However, recently, there have been cases in which an experimental value was applied to the shape parameter of the Weibull distribution used in the reliability test, but the test time was not significantly reduced. Therefore, in this paper, the shape parameters are estimated from the probability density function of the Weibull distribution for the analysis of an accelerated life test for bladder accumulators, which are core components of military helicopters. The test time was derived based on the number of samples and confidence level by substituting it into the test time equation. Next, the accelerated life test time was calculated using the steady-state test time with an acceleration factor obtained from the Arrhenius model. The steady-state life test required approximately 15,000 H, whereas the accelerated life test time for one sample at 100 ℃ was 34% shorter than that of the steady-state life test.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.8
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• pp.43-53
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• 2001

Wavelength conversion devices are essential to build an expanding all-optical network, and various types of wavelength conversion techniques are being researched. Among them, wavelength conversion based on the cross phase modulation in a directionally coupled semiconductor optical amplifier has been introduced and the concept has been experimentally proved. In this paper, a split-step method is applied to properly model the mentioned wavelength converter in the time-domain and various characteristics have been analyzed. It is shown that the present modeling approach can explain the results of the reported experimental results. Furthermore the wavelength conversion is shown to be well performed when the input signal wave and the converted wave travels in the opposite direction. The simulation shows that the positive and negative chirping appear simultaneously at both the leading and trailing of edges of the optical pulse.

• Journal of the Korean earth science society
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• v.35 no.7
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• pp.501-517
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• 2014

Based on a summary of the previous studies on columnar joints, this study presents research strategies and subjects to understand a formation of columnar joints, and its application in South Korea as follows; geometry of colonnade and entablature, formation mechanism and pattern change, surface morphology and internal structure, platy joint at the top and the bottom of columnar joints, crack patterns in drying starch-water slurries, using numerical models and computer graphics on joint formation, scale and geometry concerned with occurrence of volcanic rock, petrological and mineralogical study of the host rock. Additionally, more research is needed, such as deformation of column pattern during the hot state, secondary landform by alteration and weathering on the Earth's surface such as rock stream, tor and tafoni. This study will take an active role in research of columnar joint and the Cenozoic lava flow of South Korea. Results of this study will be useful to the activation of geotourism and geological field study.