• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.10
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• pp.738-746
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• 2019

Instead of hydraulic actuation systems, an electromechanical actuation system is more efficient in terms of weight, cost, and test evaluation in the thrust vector control of the 7-ton gimbal engine used in the Korea Space Launch Vehicle-II(KSLV-II) $3^{rd}$ stage. The electromechanical actuator is a kind of servo actuator with position feedback and uses a BLDC motor that can operate at high vacuum. In the case of the gimballed rocket engine, a synthetic resonance phenomenon may occur due to a combination of a vibration mode of the actuator itself, a bending mode of the launcher structure, and an inertial load of the gimbals engine. When the synthetic resonance occurs, the control of the rocket attitude becomes unstable. Therefore, the requirements for the stiffness have been applied in consideration of the gimbal engine characteristics, the support structure, and the actuating system. For the 7-ton gimbal engine of the KSLV-II $3^{rd}$ stage, the stiffness requirement of the actuation system is $3.94{\times}10^7N/m$, and the direct drive type electromechanical actuator is designed to satisfy this requirement. In this paper, an equivalent stiffness analysis model of a direct drive electromechanical actuator designed based on the stiffness requirements is proposed and verified by experimental results.

• The Journal of the Acoustical Society of Korea
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• v.38 no.5
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• pp.593-600
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• 2019

The similarity in tones between speakers can lower the performance of speaker verification. To improve the performance of speaker verification systems, we propose a multi-task learning technique using deep neural network to learn speaker information and age information. Multi-task learning can improve generalization performances, because it helps deep neural networks to prevent hidden layers from overfitting into one task. However, we found in experiments that learning of age information does not work well in the process of learning the deep neural network. In order to improve the learning, we propose a method to dynamically change the objective function weights of speaker identification and age estimation in the learning process. Results show the equal error rate based on RSR2015 evaluation data set, 6.91 % for the speaker verification system without using age information, 6.77 % using age information only, and 4.73 % using age information when weight change technique was applied.

• Journal of Convergence for Information Technology
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• v.7 no.2
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• pp.43-51
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• 2017

Background/Objectives : The purpose of this study is to propose a multi-threaded web crawl using queues that can solve the problem of time delay of single processing method, cost increase of parallel processing method, and waste of manpower by utilizing multiple bots connected by wide area network Design and implement. Methods/Statistical analysis : This study designs and analyzes applications that run on independent systems based on multi-threaded system configuration using queues. Findings : We propose a multi-threaded web crawler design using queues. In addition, the throughput of web documents can be analyzed by dividing by client and thread according to the formula, and the efficiency and the number of optimal clients can be confirmed by checking efficiency of each thread. The proposed system is based on distributed processing. Clients in each independent environment provide fast and reliable web documents using queues and threads. Application/Improvements : There is a need for a system that quickly and efficiently navigates and collects various web sites by applying queues and multiple threads to a general purpose web crawler, rather than a web crawler design that targets a particular site.

• Journal of the Korean Society for Railway
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• v.18 no.6
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• pp.543-551
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• 2015

Quick-hardening track (QHT) is a construction method which is used to change from old ballast track to concrete track. Sufficient time for construction is important, as the construction should be done during operational breaks at night. Most of the time is spent on exchanging the ballast layer. If it is possible to apply the ballast non-exchange type of quick-hardening track, it would be more effective to reduce the construction time and costs. In this paper, pouring materials with high permeability are suggested and a construction method involving a layer separation pouring process considering the void condition is introduced in order to develop ballast non-exchange type of QHT. The separate pouring method can secure the required strength because optimized materials are poured into the upper layer and the lower layer for each void ratio condition. To ensure this process, a rheology analysis was conducted on the design of the pouring materials according to aggregate size, the aggregate distribution, the void ratio, the void size, the tortuosity and the permeability. A polymer series was used as the pouring material of the lower layer to secure the void filling capacity and for adhesion to the fine-grained layer. In addition, magnesium-phosphate ceramic (MPC) was used as the pouring material of the upper layer to secure the void-filling capacity and for adhesion of the coarse-grained layer. As a result of a mechanics test of the materials, satisfactory performance corresponding to existing quick-hardening track was noted.

• The Journal of Korean Institute of Information Technology
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• v.15 no.12
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• pp.181-188
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• 2017

As a population of leisure activities grows and diversifies, there is a great demand for portable and environment-friendly power generation systems. A small wind power generation system is emerging as a suitable power generation equipment to meet these needs. The most important thing when developing a small portable wind turbine is to reduce the weight of the generator and increase the efficiency. The existing 300W wind turbine generator weighs about 10kg, which is heavy to carry. Therefore, a new generator weighing less than 4kg to make it easy to carry with high efficiency has been developed. In addition, considering complicated characteristics of wind volume and topography of Korea, a small wind turbine that can be used in urban and rural areas individually was constructed. Through basic designing and optimization, the lightweight and efficient generator was manufactured. It is a 300W wind turbine designed and fabricated with reduced weight as a prototype. The average output voltage of the generator was 24.7V at 900rpm no-load test. On a load test with the average line voltage 36.8V and the average phase current 2.62A, when the mechanical input was 339.84W, an average voltage output of the generator was measured as 289.5W with efficiency of 85.18%. The generator weight was 3.84kg.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.4
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• pp.399-404
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• 2021

From 1 January 2020, the limit for Sulphur in fuel oil used on board ships operating outside designated emission control areas will be reduced to 0.5 %. This regulation by international maritime organization (IMO) is able to significantly reduce the amount of Sulphur oxides (SOx) discharging from ships and should have environmental advantages and health for all over the world. To meet the regulation, in these days, wet scrubber system is being actively developed. However, this process leads to make washing wastewater. In this study, we evaluated ion exchange resin system in accordance with scrubber wastewater discharge regulation by IMO. Theoretical wastewater used as feed solution of lab scale water treatment systems. The results revealed that nitrate ion was removed selectively in spite of high TDS wash wastewater solution depending on ion exchange resin property. Moreover, it was possible to improve efficiency of the system by optimizing operating conditions.

• Journal of the Korean Institute of Gas
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• v.25 no.5
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• pp.11-18
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• 2021

Since hydrogen has the lower minimum ignition energy than that of gasoline, hydrogen could be also appropriate for the IC engine systems. However, due to the low ignition energy, there might be a 'back-fire' and 'pre-ignition' problems with hydrogen SI(Spark-ignition) combustion. In this research, cooling effects of intake gas mixture on the improvement of the maximum power output were evaluated in a 2.4 L SI engine. There were two ways to cool intake gas mixtures. The first one was cooling intake fresh air by adjusting inter-cooler system after turbocharger. The other one was cooling hydrogen fuel before supplying by using heat ex-changer. Cooling hydrogen was performed under natural aspired condition. The result showed that cooling fresh air from 40 ℃ to 20~30 ℃ improved the maximum brake power up to 6.5~8.6 % and cooling hydrogen fuel as -6 ℃ enhanced the maximum brake power likewise.

• Journal of Wetlands Research
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• v.23 no.4
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• pp.307-316
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• 2021

Due to rapidly increased urbanization, impervious area has been extended and concerns about urban flooding has been increased as well. A lot of effort has been made to restore the urban water circulation. Low Impact Development (LID) technology that consist of retention, infiltration, and evapotranspiration has begun to attract attention to simulate the hydrologic phenomenon before and after development. Many researches on the technique is being actively conducted. In this study, the effect on reducing runoff in urban catchment was analyzed and evaluated by applying LID techniques using SWMM and six scenarios. A SWMM-LID model was built for the Gasan 1 rainwater pumping station basin, and Green Roof and Permeable Pavement were selected as LID techniques to be applied. As a result, the reduction effect of the permeable pavement was larger than green roof. In the future, the results could be used to design a LID facility using the characteristics of the watershed, and other urban water resource factors such as river and groundwater levels that affect each other should be considered, so that the entire system can be considered.

• KIPS Transactions on Software and Data Engineering
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• v.10 no.9
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• pp.359-366
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• 2021

A number of construction companies in Korea invest considerable human and financial resources to construct a system for managing apartment defect data and for categorizing repair tasks. Thus, this study proposes machine learning models to automatically classify defect complaint text-data into one of the sub categories of 'finishing work' (i.e., one of the defect repair tasks). In the proposed models, we employed two word representation methods (Bag-of-words, Term Frequency-Inverse Document Frequency (TF-IDF)) and two machine learning classifiers (Support Vector Machine, Random Forest). In particular, we conducted both binary- and multi- classification tasks to classify 9 sub categories of finishing work: home appliance installation work, paperwork, painting work, plastering work, interior masonry work, plaster finishing work, indoor furniture installation work, kitchen facility installation work, and tiling work. The machine learning classifiers using the TF-IDF representation method and Random Forest classification achieved more than 90% accuracy, precision, recall, and F1 score. We shed light on the possibility of constructing automated defect classification systems based on the proposed machine learning models.

• Journal of the Korea Organic Resources Recycling Association
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• v.29 no.3
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• pp.17-25
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• 2021

This study was conducted to investigate effects of mixture with dried food waste powder (FWP) and mixed organic fertilizer (MOF) on growth of pakchoi. As compared with non-fertilizer treatment (NF) or control (MOF treatment), growth of pakchoi in FWP treatments (2,500 kg/ha, 5,000 kg/ha, 10,000 kg/ha) was inhibited by salt (NaCl) content in the FWP. In comparison with control, mixtures of MOF and FWP (FWP10, FWP20, and FWP30 treatment) were not significantly different, and their salt content correlated with pakchoi growth factors negatively (P<0.05). Applied of FWP10, (FWP10: 2,500 kg/ha, 2FWP10: 5,000 kg/ha, 3FWP10: 7,500 kg/ha, 4FWP10: 10,000 kg/ha), growth factors of FWP10, 2FWP10 and 3FWP10 treatment were not significantly different than those of chemical fertilizer treatment, and of 4FWP10 decreased. Correlation coefficient between NaCl supply by FWP10 application and growth factor was negative (P<0.01). These results indicated that FWP was used as another source of organic fertilizer, and the organic fertilizers blending with FWP inhibited a pakchoi growth by increase of salt content containing in the them or of salt supplying amount after their application.