• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.1
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• pp.1-6
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• 2021

Concrete structures gradually age due to deterioration of materials or excess loads and environmental factors, and their performance decreases, affecting the usability and safety of structures. Although external tension construction methods are widely used among the reinforcement methods of old bridges, it is insufficient to identify the effects and effects of reinforcement depending on the level of aging. Therefore, in this study, a four-point loading experiment was conducted on the subject with the non-reinforced and external tensioning method to confirm the reinforcement effect of the external tensioning method, assuming the aging of the structure as a reduction in the compressive strength and tensile reinforcement of concrete, to analyze the behavior of the reinforcement and confirm the reinforcement effect. As a result of the experiment, it was difficult to identify the amount of reinforcement in the extreme condition due to early elimination of the anchorage. Therefore, compliance with the regulations on anchor bolts is required when applying the external tension reinforcement method. Crack load and yield load increased depending on whether external tension was reinforced, but before the crack, the stiffness before and after reinforcement was similar, making it difficult to confirm the reinforcement effect.

• Resources Recycling
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• v.31 no.5
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• pp.42-51
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• 2022

Aggregate resources in Korea are expected to run out owing to an increase in development demand and construction investment. Recycled concrete aggregates (RCA), extracted from waste concrete, have a lower quality than natural aggregates. However, RCA can produce concrete similar in quality to the normal concrete by aggregate pretreatment, use of admixtures, and quality control. RCA are most suitable for use in precast concrete products such as sidewalk blocks and revetment blocks. Herein, the feasibility of producing revetment blocks using recycled aggregate concrete (RAC), similar in quality to normal concrete, was analyzed. The amount of RCA was varied, and moderate high early strength cement and steam curing were used to produce the concrete test blocks. In the block test, the load resistance characteristics of the blocks were evaluated to determine optimal RAC and glass fiber reinforced polymer (GFRP) rebar compositions. Thus, the variable that reduced the cement content was determined at the same level as that of natural aggregate concrete by the control of steam curing. In the concrete block test, although this depends on the reinforcement ratio, the RAC block exhibited the same or better performance than a normal concrete block. Therefore, the low quality of RCA in RAC is no longer a problem when concrete mixing and curing are controlled and appropriate reinforcement is used.

• Korean Journal of Remote Sensing
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• v.38 no.6_2
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• pp.1643-1652
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• 2022

Deposited Marine Debris(DMD) can negatively affect marine ecosystems, fishery resources, and maritime safety and is mainly detected by sonar sensors, lifting frames, and divers. Considering the limitation of cost and time, recent efforts are being made by integrating underwater images and artificial intelligence (AI). We conducted a comparative study of You Only Look Once Version 5 (YOLOv5) and You Only Look Once Version 7 (YOLOv7) models to detect DMD from underwater images for more accurate and efficient management of DMD. For the detection of the DMD objects such as glass, metal, fish traps, tires, wood, and plastic, the two models showed a performance of over 0.85 in terms of Mean Average Precision (mAP@0.5). A more objective evaluation and an improvement of the models are expected with the construction of an extensive image database.

• Korean Journal of Remote Sensing
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• v.38 no.6_2
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• pp.1633-1641
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• 2022

Urban population concentration and indiscriminate development are causing various environmental problems such as air pollution and heat island phenomena, and causing human resources to deteriorate the damage caused by natural disasters. Urban trees have been proposed as a solution to these urban problems, and actually play an important role, such as providing environmental improvement functions. Accordingly, quantitative measurement and analysis of individual trees in urban trees are required to understand the effect of trees on the urban environment. However, the complexity and diversity of urban trees have a problem of lowering the accuracy of single tree detection. Therefore, we conducted a study to effectively detect trees in Dongjak-gu using high-resolution aerial images that enable effective detection of tree objects and You Only Look Once Version 5 (YOLOv5), which showed excellent performance in object detection. Labeling guidelines for the construction of tree AI learning datasets were generated, and box annotation was performed on Dongjak-gu trees based on this. We tested various scale YOLOv5 models from the constructed dataset and adopted the optimal model to perform more efficient urban tree detection, resulting in significant results of mean Average Precision (mAP) 0.663.

• Journal of the Korean Society for Library and Information Science
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• v.56 no.3
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• pp.241-264
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• 2022

Bibliographic metadata can help researchers effectively utilize essential publications that they need and grasp academic trends of their own fields. With the manual creation of the metadata costly and time-consuming. it is nontrivial to effectively automatize the metadata construction using rule-based methods due to the immoderate variety of the article forms and styles according to publishers and academic societies. Therefore, this study proposes a two-step extraction process based on rules and deep neural networks for generating bibliographic metadata of scientific articlles to overcome the difficulties above. The extraction target areas in articles were identified by using a deep neural network-based model, and then the details in the areas were analyzed and sub-divided into relevant metadata elements. IThe proposed model also includes a model for generating reference summary information, which is able to separate the end of the text and the starting point of a reference, and to extract individual references by essential rule set, and to identify all the bibliographic items in each reference by a deep neural network. In addition, in order to confirm the possibility of a model that generates the bibliographic information of academic papers without pre- and post-processing, we conducted an in-depth comparative experiment with various settings and configurations. As a result of the experiment, the method proposed in this paper showed higher performance.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.4
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• pp.73-80
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• 2022

This study evaluated changes in fluidity and rheological properties over time for 3D printed composite materials, and evaluated compressive strength and splitting tensile strength properties for laminated and molded specimens. The composite material for 3D printing starts to change rapidly after 30 minutes of extrusion, and the viscosity of the material tends to be maintained up to 90 minutes, but it was confirmed that construction within 60 minutes after mixing is effective. The compressive strength of the laminated test specimen showed equivalent or better performance at all ages compared to the molded test specimen. In the stress-strain curve of the laminated specimen, the initial slope was similar to that of the molded specimen, but the descending slope was on average 1.9 times higher than that of the molded specimen, indicating relatively brittle behavior. The splitting tensile strength of the P-V laminated specimen was about 6% lower than that of the molded specimen. It is judged that this is because the interfacial adhesion force against the vertical load is affected by the pattern direction of the laminated test specimen.

• Korean small business review
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• v.42 no.4
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• pp.251-283
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• 2020

The purpose of this study is to provide assistance to the establishment of related policies to improve the level of acceptance and use of smart factories for SMEs in Korea. To this end, the Unified Technology Acceptance Model (UTAUT) was extended to select additional factors that could affect the intention to accept technology, and to demonstrate this. To achieve the research objective, a questionnaire composed of 7-point Likert scales was prepared, and a survey was conducted for manufacturing-related companies. A total of 136 questionnaires were used for statistical processing. As a result of the hypothesis test, performance expectation and social influence had a positive (+) positive effect on voluntary use, but effort expectation and promotion conditions did not have a significant effect. As an extension factor, the network effect and organizational characteristics had a positive (+) effect, and the innovation resistance had a negative effect (-), but the perceived risk had no significant effect. When the size of the company is large, the perceived risk and innovation resistance are low, and the level of influencing factors for veterinary intentions, veterinary intentions, and veterinary behaviors are excluded. Through this study, factors that could have a positive and negative effect on the adoption (reduction) of smart factory-related technologies were identified and factors to be improved and factors to be reduced were suggested. As a result, this study suggests that smart factory-related technologies should be accepted.

• Journal of Korean Elementary Science Education
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• v.41 no.4
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• pp.673-689
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• 2022

To understand seasonal changes it is necessary to understand the relationship between celestial bodies in a three-dimensional space, and to this end, modeling activities in which students directly construct, use, evaluate, and modify three-dimensional models are important. In this study, the process of elementary school students using globes and light bulbs to model Earth's motion in a three-dimensional space as a cause of seasonal changes was analyzed. Seventeen sixth graders participated in the modeling process. After exploring phenomena and concepts related to seasonal change, students constructed models using globes and bulbs and used them to explain seasonal changes. Video data recording students' modeling process, students' activity sheets, and transcripts of post-interview were used as research data, and data triangulation was conducted. The modeling level analysis framework was also developed based on previous studies. In particular, the framework was developed in detail in this study in consideration of the concept of Earth's motion as well as understanding model and implementing modeling. In the final analysis framework, the 3D modeling level was classified from level 1 to level 3, and student performance that may appear at each level was specified. As a result of the study, there were two main levels of modeling using globes for elementary school students to explain seasonal changes. The rotation and tilt of the axis of rotation and revolution of the earth were considered but the level at which empirical evidence was not used (level 2), the level at which empirical evidence was used to explain seasonal chages (level 3). However, even when students use empirical evidence, it did not lead to the construction of a scientific model. In this study, the cause was explored in relation to the characteristics of the tool used for modeling.

• Journal of Aerospace System Engineering
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• v.16 no.6
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• pp.54-63
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• 2022

Recently, electric propulsion aircraft with various propeller mounting positions have been under construction. The position of the propeller relative to the wing can significantly affect the aerodynamic performance of the aircraft. Placing the propeller in front of the wing produces a complex swirl flow behind or around the propeller. The up/downwash induced by the swirl flow can alter the wing's local effective angle of attack, causing a change in the aerodynamic load distribution across the wing's spanwise direction. This study investigated the influence of the distance between a propeller and a wing on the aerodynamic loads on the wing. The swirl flow generated by the propeller was modelled using an actuator disk theory, and the wing's aerodynamics were analysed with the VSPAERO tool. Results of the study were compared to wind tunnel test data and established that both axial and spanwise distance between the propeller and the wing positively affect the wing's lift-to-drag ratio. Specifically, it was observed that the lift-to-drag ratio increases when the propeller is positioned higher than the wing.

• Journal of the Korean Geotechnical Society
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• v.38 no.12
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• pp.67-78
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• 2022

In this study, the measurement results of the coastal deep soft ground buried in the upper part of the dredged clay were analyzed and compared with the current specification standards. Based on the results, a suitable proposal was suggested for the selection, installation, data arrangement, and analysis of each instrument used in the deep soft ground improvement construction. The pore water pressure meter has a range of 1.5 times or more of the expected measurement range, considering the field conditions of the soft ground. The groundwater level meter installed in the horizontal drainage layer checks the change in the groundwater level during the embanking as well as the performance of the catchment well and the horizontal drainage layer. Therefore, it is important to manage so that the groundwater level exists inside the horizontal drainage layer during embanking. It is enough to install the inclinometer in the gravel layer below the soft ground or weathered rock with an N value of 40 or more for the deep soft ground. It seems desirable to install a screw type for differential settlement meter. However, the screw type should not settle due to its own weight. Considering that it is a dredged landfill where subsidence occurs significantly, it is sufficient to manage the tolerance of leveling at about 10 mm (L is the one-way distance (km)).