• The Journal of the Acoustical Society of Korea
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• v.43 no.3
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• pp.351-360
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• 2024

With the increasing use of drone technology, the Unmanned Aerial Vehicle (UAV) is now being utilized in various fields. However, this increased use of drones has resulted in various issues. Due to its small size, the drone is difficult to detect with radar or optical equipment, so acoustical tracking methods have been recently applied. In this paper, a method of localization of multiple drones using the acoustic characteristics of the quadcopter drone is suggested. Because the acoustic characteristics induced by each rotor are differentiated depending on the type of drone and its movement state, the sound source of the drone can be reconstructed by spatially clustering the results of the estimated positions of the blade passing frequency and its harmonic sound source. The reconstructed sound sources are utilized to finally determine the location of multiple-drone sound sources by applying the source localization algorithm. An experiment is conducted to analyze the acoustic characteristics of the test quadcopter drones, and the simulations for three different types of drones are conducted to localize the multiple drones based on the measured acoustic signals. The test result shows that the location of multiple drones can be estimated by utilizing the acoustic characteristics of the drone. Also, one can see that the clarity of the separated drone sound source and the source localization algorithm affect the accuracy of the localization for multiple-drone sound sources.

• Journal of Space Technology and Applications
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• v.4 no.1
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• pp.48-61
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• 2024

In this paper, we introduce the concept of the cube satellite Chungnam National University Laser Unity Bus (CLUB), which can provide an integrated infrastructure for various ground-space laser applications. With the advent of the new space era, the rapid expansion of space utilization has begun to reveal the limitations of conventional radio frequencies. As space missions diversify, lasers are garnering attention as a viable alternative. Between ground and space, lasers are applied in various fields including satellite laser ranging (SLR), laser weapons, and laser communication. However, laser used between the ground and space are significantly influenced by the Earth's atmosphere. Consequently, understanding the atmospheric effects on laser propagation is crucial. In particular, atmospheric turbulence, which refracts and distorts laser beams, intensifies closer to the Earth's surface, exerting a greater impact on the uplink than on the downlink. While downlink verification is facilitated by ground detection, verifying the uplink poses challenges due to the necessity of space-based detection. In response to these challenges, we propose the idea of cube satellite as a means to enhance understanding and verification of laser propagation in the uplink. Additionally, we present the results of conceptual design by analyzing requirements, focusing on mission design of the CLUB cube satellite, following the stages of systems engineering for systematic cube satellite development.

• Journal of Advanced Technology Convergence
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• v.3 no.3
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• pp.9-15
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• 2024

This paper details research on the optimized design and fabrication of a 4x4 microstrip array antenna intended for X-Band applications. The study focuses on achieving the desired resonance frequency and gain by modifying the microstrip patch and array antenna parameters, including substrate type and patch size. It presents results from designing and fabricating a 4x4 array antenna with optimum substrate materials to enhance X-Band resonance characteristics and gain. The antenna dimensions are 10mm(W)x7.4mm(L)x 0.79mm(H), with an Rogers RO 4350B dielectric substrate (ε_r=3.54) and an inset-fed feeding method to minimize antenna size. Both the single patch and 4x4 array antennas demonstrated stable SWR (<1.5) and a gain of 18.5dBi at the target frequency of 10.3GHz in simulations. The fabricated antenna showed performance consistent with simulation results. This antenna design is suitable for X-Band applications, including military, satellite communications, and biomedical fields.

• Korean Journal of Remote Sensing
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• v.40 no.4
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• pp.343-350
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• 2024

Since the release of Meta's Segment Anything Model (SAM), a large-scale vision transformer generation model with rapid image segmentation capabilities, several studies have been conducted to apply this technology in various fields. In this study, we aimed to investigate the applicability of SAM for water bodies detection and extraction using the QGIS Geo-SAM plugin, which enables the use of SAM with satellite imagery. The experimental data consisted of Compact Advanced Satellite 500 (CAS500)-1 images. The results obtained by applying SAM to these data were compared with manually digitized water objects, Open Street Map (OSM), and water body data from the National Geographic Information Institute (NGII)-based hydrological digital map. The mean Intersection over Union (mIoU) calculated for all features extracted using SAM and these three-comparison data were 0.7490, 0.5905, and 0.4921, respectively. For features commonly appeared or extracted in all datasets, the results were 0.9189, 0.8779, and 0.7715, respectively. Based on analysis of the spatial consistency between SAM results and other comparison data, SAM showed limitations in detecting small-scale or poorly defined streams but provided meaningful segmentation results for water body classification.

• The Journal of Bigdata
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• v.8 no.2
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• pp.1-13
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• 2023

Current analysis of air passengers mainly relies on statistical methods, but there are limitations in analyzing detailed aspects such as travel routes, number of regional passengers and airport access times. However, with the advancement of big data technology and revised three data acts, big data-based transportation analysis has become more active. Mobile communication data, which can precisely track the location of mobile phone terminals, can serve as valuable analytical data for transportation analysis. In this paper, we propose a air passenger Origin/Destination (O/D) extraction algorithm based on mobile communication data that overcomes the limitations of existing air transportation user analysis methods. The algorithm involves setting airport signal detection zones at each airport and extracting air passenger based on their base station connection history within these zones. By analyzing the base station connection data along the passenger's origin-destination paths, we estimate the entire travel route. For this paper, we extracted O/D information for both domestic and international air passengers at all domestic airports from January 2019 to December 2020. To compensate for errors caused by mobile communication service provider market shares, we applied a adjustment to correct the travel volume at a nationwide citizen level. Furthermore correlation analysis was performed on O/D data and aviation statistics data for air traffic users based on mobile communication data to verify the extracted data. Through this, there is a difference in the total amount (4.1 for domestic and 4.6 for international), but the correlation is high at 0.99, which is judged to be useful. The proposed algorithm in this paper enables a comprehensive and detailed analysis of air transportation users' travel behavior, regional/age group ratios, and can be utilized in various fields such as formulating airport-related policies and conducting regional market analysis.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.4
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• pp.259-265
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• 2024

Shape memory alloy (SMA)-textile actuators have attracted significant attention across various fields, including soft robotics and wearable technology. These smooth actuators are developed by combining SMA and simple textile fibers and then knitting them into two loop patterns known as the knit (K-loop) and plain (P-loop) patterns. Both loops are distinguished by opposite bending characteristics owing to loop head geometry. However, the knitting processes for these actuator sheets require expertise and time, resulting in high production costs for knitted loop actuation sheets. This study introduces a novel method by which to assess the strain in SMA textile-based actuators, which experience large deformations when subjected to voltage. Owing to the highly nonlinear constitutive equations of the SMA material, developing an analytical model for numerical analysis is challenging. Therefore, this study employs a novel approach that utilizes a linear constitutive equation to analyze large deformations in SMA material with nonlinear geometry considerations. The user-defined material (UMAT) subroutine integrates the linear constitutive equation into the ABAQUS software suite. This equivalent unit cell (EUC) model is validated by comparing the experimental bending actuation results of K-loops and P-loops.

• Journal of Korea Water Resources Association
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• v.57 no.8
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• pp.493-507
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• 2024

RANS-based CFD analysis is widely applied in various engineering fields, including practical hydraulic engineering, due to its high computational efficiency. However, problems of non-physical behavior in the analysis of two phase flow, such as free surfaces, have long been raised. The two-equation turbulence models used in general RANS-based analysis were developed for single phase flow and simulate unrealistically high turbulence energy at the interface where there are abrupt changes in fluid density. To solve this issue, one of the methods recently developed is the buoyancy-modified turbulence model, which has been partially validated in coastal engineering, but has not been applied to open channel flows. In this study, the applicability of the buoyancy-modified turbulence model is evaluated using the VOF method in the open-source program OpenFoam. The results of the uniform flow showed that both the buoyancy-modified k-𝜖 model and the buoyancy-modified k-ω SST model effectively simulated the reduction of turbulence energy near the free surface. Specifically, the buoyancy-modified k-ω SST model accurately simulated the vertical velocity distribution. Additionally, the model is applied to dam-break flows to examine cases with significant surface variation and cavity formation. The simulation results show that the buoyancy-modified turbulence models produce varying results depending on the VOF method and shows non-physical behavior different from experimental results. While the buoyancy-modified turbulence model is applicable in cases with stable surface shapes, it still has limitations in general application when there are rapid changes in the free surface. It is concluded that appropriate adjustments to the turbulence model are necessary for flows with rapid surface changes or cavity formation.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.24 no.5
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• pp.53-59
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• 2024

This study presents the design and implementation of a camera-based 6DoF (6 Degrees of Freedom) tracking and pose estimation system. In particular, we propose a method for accurately estimating the positions and orientations of all fingers of a user utilizing a 6DoF robotic arm. The system is developed using the Python programming language, leveraging the Mediapipe and OpenCV libraries. Mediapipe is employed to extract keypoints of the fingers in real-time, allowing for precise recognition of the joint positions of each finger. OpenCV processes the image data collected from the camera to analyze the finger positions, thereby enabling pose estimation. This approach is designed to maintain high accuracy despite varying lighting conditions and changes in hand position. The proposed system's performance has been validated through experiments, evaluating the accuracy of hand gesture recognition and the control capabilities of the robotic arm. The experimental results demonstrate that the system can estimate finger positions in real-time, facilitating precise movements of the 6DoF robotic arm. This research is expected to make significant contributions to the fields of robotic control and human-robot interaction, opening up various possibilities for future applications. The findings of this study will aid in advancing robotic technology and promoting natural interactions between humans and robots.

• The Journal of the Acoustical Society of Korea
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• v.43 no.5
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• pp.536-546
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• 2024

Music has a close connection with human emotions, and this relationship has been explored in various fields. Recently, research has been attempted to quantify these subjective emotions based on biosignals such as brain signals. However, emotional changes when listening to music, as measured by heart rate, which can be easily measured in daily life, are not sufficiently known. In this study, we investigated how changing emotions are expressed through variations in heart rate during music listening. The electrocardiogram (ECG) was measured while participants listened to music, and the emotional characteristics of preference, familiarity, arousal, and valence after listening were evaluated using Likert scale scores to analyze the correlation between changes in heart rate and emotional characteristics. The study confirmed that smaller changes in heart rate were associated with lower preference, higher arousal, and more negative emotional valence, while larger heart rate differences were associated with higher preference, lower arousal, and more positive emotional valence. This study demonstrates that heart rate can be used to objectively predict emotional changes due to music listening, and it is expected to have applications in various music-related industries in the future.

• Korean Journal of Soil Science and Fertilizer
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• v.31 no.2
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• pp.197-203
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• 1998

Although biological metabolism in soil is very important for evaluating the soil properties, most of researches have concerned mainly about physical and chemical sides. In this study, biological characteristics were examined to demonstrate the biota in the plastic film house soils. Contents of organic matter and phosphate in soil were increased with cultivation period. ECs of soil cultivated spinach and melon were $3.59dS\;m^{-1}$ and $3.46dS\;m^{-1}$ respectively: these values were higher than that of rose and flower, which were $1.23dS\;m^{-1}$ and $1.32dS\;m^{-1}$ respectively. The population of fluorescent Pseudomonas strains of the soil cultivated flowers: $113.8{\times}10^4{\sim}129.7{\times}10^4cfu\;g^{-1}$ was higher than that of leafy vegetables: $40.7{\times}10^4{\sim}97.9{\times}10^4cfu\;g^{-1}$ and fruiting vegetables: $25.0{\times}10^4{\sim}91.7{\times}10^4cfu\;g^{-1}$. However the number of Fusarium strains of the soil cultivated with flowers: $3.8{\times}10^2{\sim}4.0{\times}10^2cfu\;g^{-1}$ was lower than that of leafy vegetables: $4.3{\times}10^2{\sim}16.3{\times}10^2cfu\;g^{-1}$ and fruiting vegetables: $7.6{\times}10^2{\sim}30.0{\times}10^2cfu\;g^{-1}$. In relation to the cultivation period, the habitation density of aerobic bacteria, mesophilic Bacillus, thermophilic Bacillus, and fluorescent Pseudomonas strains was the highest in the soil cultivated over 11 years, but diversity index showed negative correlation with cultivation period. Microbial biomass C in these soils had positive correlation with each number of microorganisms including aerobic bacteria, actinomycetes, and strains of mesophilic Bacillus as well as the total number of these microorganisms.