• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.6
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• pp.193-200
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• 2023

This paper investigates the effect of directional alignment of steel fibers using an electromagnetic field on the flexural fracture behavior of steel fiber reinforced concrete. A specially designed and manufactured solenoid, capable of aligning steel fibers in the longitudinal direction of the beam specimen, was employed for this purpose. Beam specimens with a design strength of 30 MPa were produced, and failure tests were conducted on specimens exposed to electromagnetic fields and those without exposure. Experimental variables included the mixing ratio and aspect ratio of steel fibers. The results of the experiments revealed a slight increase in flexural strength and crack mouth opening displacement at the maximum load for specimens exposed to the electromagnetic field. Notably, a significant enhancement in fracture energy was observed.

• Journal of the Korean Geotechnical Society
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• v.34 no.10
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• pp.61-74
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• 2018

In this study, the pull-out behavior of tunnel type anchorage of suspension bridges was analyzed based on results from laboratory size model tests and numerical analysis. Tunnel type anchorage has found its applications occasionally in both domestic and oversea projects, therefore design method including failure mode and safety factor is yet to be clearly established. In an attempt to improve the design method, scaled model tests were conducted by employing simplified shapes and structure of the Ulsan grand bridge's anchorage which was the first case history of its like in Korea. In the model tests, the anchorage body and the surrounding rocks were made by using gypsum mixture. The pull-out behavior was investigated under plane strain conditions. The results of the model tests showed that the tunnel type anchorage underwent wedge shape failure. For the verification of the model tests, numerical analysis was carried out using ABAQUS, a finite element analysis program. The failure behavior predicted by numerical analysis was consistent with that by the model tests. The result of numerical analysis also showed that the effect of Poisson's ratio was negligible, and that a plugging type failure mode could occur only when the strength of the surrounding rocks was 10 times larger than that of anchorage body.

• Journal of the Earthquake Engineering Society of Korea
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• v.15 no.6
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• pp.67-80
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• 2011

This paper presents the results of shaking table tests on a 1:5 scale 10-story R.C. wall-type residential building model. The following conclusions are drawn based on the test results. (1) The model responded linear elastically under the excitations simulating an earthquake with a return period of 50 years, and showed a nonlinear response under the excitations simulating the design earthquake of Korea. (2) The model showed a significant strength drop under the maximum considered earthquake, with a return period of 2400 years. (3) The major portion of the resistance to lateral inertia forces came from the walls used for the elevator and stair case. (4) Finally, the damage and failure modes appear to be due to the flexural behavior of walls and slabs. A significant deterioration of stiffness and an elongation of the fundamental periods were observed under increased earthquake excitations.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.4
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• pp.19-26
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• 2018

This study evaluates the shear performance of reinforced concrete members with web opening reinforcement. A total of 4 reinforced concrete members with or without openings were cast then tested. The main variables investigated were with or without of web openings and with or without of web opening reinforcement, respectively. The proposed web opening reinforcement was a rectangle and rhombus-shaped spiral considering of construct ability. Test result showed that the proposed web reinforcement had improved shear capacity and ductility of the specimens. It was found that the web opening reinforcement proposed in this study had a positive effect on the shear strength and crack control of RC beams with web openings. In addition, it was confirmed that the analytical results by the current design codes underestimates the test results of the specimens with the proposed web opening reinforcement.

• Journal of the Korean Society of Earth Science Education
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• v.11 no.1
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• pp.21-37
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• 2018

The purpose of the study is to visualize the concept of water circulation in elementary school students through science behavioral system. Elementary school students found it difficult to understand concepts related to the water cycle. Most of the elementary school children think it rains because the clouds are heavier. It is most difficult to explain invisible concepts to elementary school children. Also, experiments in current textbooks are likely to disrupt scientific concepts. Accordingly, conventional water cycle, dew, fog, and cloud experiments were integrated into one system. The researchers then developed a device that allowed students to see the water's circulation at a glance. It is intended to enable integrated thinking on evaporation, condensation and precipitation. In addition, a instruction program to guide students using the system has been developed to demonstrate its effectiveness. Employing a quasi-experimental design, the participants were measured on their concepts of evaporation, condensation, and water circulation before and after participation. The findings indicated that the experiment is more effective in changing the concepts of evaporation, condensation, and water circulation than in previous experiments. Also, the optimal conditions for making use of the device were found, and there were no various experimental parameters, such as condensation.

• Journal of KIISE
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• v.43 no.12
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• pp.1365-1375
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• 2016

One of the most important capabilities for autonomous service robots working in living environments is to recognize and understand the correct context in dynamically changing environment. To generate high-level context knowledge for decision-making from multiple sensory data streams, many technical problems such as multi-modal sensory data fusion, uncertainty handling, symbolic knowledge grounding, time dependency, dynamics, and time-constrained spatio-temporal reasoning should be solved. Considering these problems, this paper proposes an effective dynamic context management and spatio-temporal reasoning method for intelligent service robots. In order to guarantee efficient context management and reasoning, our algorithm was designed to generate low-level context knowledge reactively for every input sensory or perception data, while postponing high-level context knowledge generation until it was demanded by the decision-making module. When high-level context knowledge is demanded, it is derived through backward spatio-temporal reasoning. In experiments with Turtlebot using Kinect visual sensor, the dynamic context management and spatio-temporal reasoning system based on the proposed method showed high performance.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.13 no.6
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• pp.10-24
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• 2014

In-vehicle warning information systems(IWIS) is an effective countermeasure for preventing traffic crashes. It provides drivers with warnng messages about upcoming hazards to draw proper evasive maneuvering. This study developed a methodology for evaluating the effectiveness of IWIS based on an integrated index to identify driver's responsive behavior. The proposed index consists of characteristics of longitudinal and lateral behavior of vehicle maneuverings. Also, a method to assign mixed-weights in the context of multi-criteria decision making framework was adopted to develop the evaluation method. It is expected that the outcome of this study is useful in designing more effective in-vehicle warning information systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.12A
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• pp.1219-1225
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• 2007

In this paper, we propose a new quasi-orthogonal space-time block code(QO-STBC) achieving full rate and full diversity for general QAM and quasi-static Rayleigh fading channels with four transmit antennas. This code possesses the quasi orthogonal property like the conventional minimum decoding complexity QO-STBC(MDC-QO-STBC), which allows independently a maximum likelihood(ML) decoding to only require joint detection of two real symbols. By computer simulation results, we show that the proposed code exhibits the identical BER performance with the existing MDC-QO-STBC. However, the proposed code has an advantage in the transceiver implementation since the original coding scheme may be modified so that increases of peak-to-average power ratio occur at only two transmit antennas, but the MDC-QO-STBC does at all of transmit antennas.

• Journal of the Korea Society of Computer and Information
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• v.27 no.3
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• pp.201-207
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• 2022

In this paper, we propose a movie recommendation model that uses the users' ratings as well as their reviews. To understand the user's preference from multicriteria perspectives, the proposed model is designed to apply attribute-based sentiment analysis to the reviews. For doing this, it divides the reviews left by customers into multicriteria components according to its implicit attributes, and applies BERT-based sentiment analysis to each of them. After that, our model selectively combines the attributes that each user considers important to CF to generate recommendation results. To validate usefulness of the proposed model, we applied it to the real-world movie recommendation case. Experimental results showed that the accuracy of the proposed model was improved compared to the traditional CF. This study has academic and practical significance since it presents a new approach to select and use models in consideration of individual characteristics, and to derive various attributes from a review instead of evaluating each of them.

• Journal of Elementary Mathematics Education in Korea
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• v.11 no.2
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• pp.117-136
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• 2007

The purpose of this study was to analyze the effects of mathematics learning through tessellation activities on the improvement of spatial sense and to find out a better mathematics teaching method that could further develop spatial sense. For this purpose, the following questions were attempted; Can mathematics learning using tessellation activities develop spatial sense? In odor to test this hypothesis, twenty-four fifth graders of a class were selected at random. And the experimental group was divided into four groups according to gender and academic performance. The groups were protested and post-tested to determine results based on the quasi-experimental design(i.e. one-group pretest-post test design). The process of this study was checking spatial sense for a common evaluation of experimental group. In this study, tangram, pattern block, and GSP was used for mathematics learning through tessellation activities during each independent-study, discretion-activity, and math class. The instrument used in this study was a spatial sense test and pretest and post-test were implemented with the same instrument(i.e. K-WISC-III Activity Test). In conclusion, mathematics learning through tessellation activities with tangram, pattern block, and GSP is an effective teaching and learning method for the improvement of the spatial sense.