• Journal of Space Technology and Applications
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• v.1 no.1
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• pp.23-32
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• 2021

The high-level Space Situational Awareness (SSA) objective is to provide to the users dependable, accurate and timely information in order to support risk management on orbit and during re-entry and support safe and secure operation of space assets and related services. Therefore the risk assessment for the re-entry of space objects should be managed nationally. In this research, the Software for Re-Entry Prediction of space objects (SREP) was developed for national SSA system. In particular, the rate of change of the drag coefficient is estimated through a newly proposed Drag Scale Factor Estimation (DSFE), and is used for high-precision orbit propagator (HPOP) up to an altitude of 100 km to predict the re-entry time and position of the space object. The effectiveness of this re-entry prediction is shown through the re-entry time window and ground track of space objects falling in real events, Grace-1, Grace-2, Tiangong-1, and Chang Zheng-5B Rocket body. As a result, through analysis 12 hours before the final re-entry time, it is shown that the re-entry time window and crash time can be accurately predicted with an error of less than 20 minutes.

• Journal of The Korean Association of Information Education
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• v.22 no.6
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• pp.651-660
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• 2018

To determine the educational effects of collaborative story creation activities using the Entry programming language, we instructed first year students at the national university of education on these activities for three weeks and analyzed the changes in their software (SW) education capacity and story creating ability. The completed analysis showed no significant changes in the students' SW education capacity as related to information literacy, computational thinking, and learner competency; however, the students' ability to create stories increased significantly. Although students struggled to learn story creation using Entry, they gradually found that the activities were useful and their interest in creating stories grew. Therefore, we suggest expanding the number of subject curriculum activities using Entry in order to improve SW education capacity as well as the subject capacity for student teachers.

• Journal of The Korean Association of Information Education
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• v.19 no.4
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• pp.459-466
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• 2015

The content of software education for elementary school students in the 2015 revisions to the national curriculum are not sufficient because class time dedicated to software education has been limited to 17 hours in fifth and sixth grades. In this study, I developed the algorithm and programming model for Korea. I analyzed domestic and international software education curricula as well as training platforms, such as Code.org, Blockly Games, and Entry. The suggested algorithm and programming framework is known as the Rainbow system, which is divided into 7 steps, 14 criteria, and 3 content areas--understanding the algorithm, the actual programming, and evaluation of the program. Using the Rainbow system, once students have completed a level they can be promoted to the next stage, regardless of their grade.

• Journal of Information Processing Systems
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• v.14 no.1
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• pp.228-238
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• 2018

With the rapid advancement of Internet services, there has been a dramatic increase in services that dynamically provide Internet resources on demand, such as cloud computing. In a cloud computing service, because the number of users in the cloud is changing dynamically, it is more efficient to utilize a flexible network technology such as software-defined networking (SDN). However, to efficiently support the SDN-based cloud computing service with limited resources, it is important to effectively manage the flow table at the SDN switch. Therefore, in this paper, a new flow management scheme is proposed that is able to, through efficient management, speed up the flow-entry search speed and simultaneously maximize the number of flow entries. The proposed scheme maximizes the capacity of the flow table by efficiently storing flow entry information while quickly executing the operation of flow-entry search by employing a hash index. In this paper, the proposed scheme is implemented by modifying the actual software SDN switch and then, its performance is analyzed. The results of the analysis show that the proposed scheme, by managing the flow tables efficiently, can support more flow entries.

• Geomechanics and Engineering
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• v.22 no.6
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• pp.541-552
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• 2020

With the increasing tension of current coal resources and the increasing depth of coal mining, the gob-side entry retaining technology has become a preferred coal mining method in underground coal mines. Among them, the technology of the gob-side entry retaining with the high-water filling material can not only improve the recovery rate of coal resources, but also reduce the amount of roadway excavation. In this paper, based on the characteristics of the high-water filling material, the technological process of gob-side entry retaining with the high-water filling material is introduced. The early and late stress states of the filling body formed by the high-water filling materials are analyzed and studied. Taking the 8th floor No.3 working face of Xin'an coal mine as engineering background, the stress and displacement of surrounding rock of roadway with different filling body width are analyzed through the FLAC^3D numerical simulation software. As the filling body width increases, the supporting ability of the filling body increases and the deformation of the surrounding rock decreases. According to the theoretical calculation and numerical simulation of the filling body width, the filling body width is finally determined to be 3.5m. Through the field observation, the deformation of the surrounding rock of the roadway is within the reasonable range. It is concluded that the gob-side entry retaining with the high-water filling material can control the deformation of the surrounding rock, which provides a reference for gob-side entry retaining technology with similar geological conditions.

• Ocean Systems Engineering
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• v.8 no.2
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• pp.183-199
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• 2018

The open source software OpenFOAM is utilised to simulate the water entry and hydrodynamic impact process of 2D wedges and ship hull sections. Incompressible multiphase flow solver interDyMFoam is employed to calculate the free fall of structure from air into water using dynamically deforming mesh technique. Both vertical and oblique entry of wedges of various dead-rise angles have been examined. A convergence study of dynamics as well as kinematics of the flow problem is carried out on successively refined meshes. Obtained results are presented and compared to the experimental measurements showing good agreement and reasonable mesh convergence of the solution.

• Journal of the Korea Society of Computer and Information
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• v.24 no.1
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• pp.239-246
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• 2019

In this paper, we propose an effective software education donation model for the social care class. The types of software education for elementary, middle, and high school for the social care class are in the order of after school classes, club activities, creative experiences, and regular classes. In elementary school students, it is effective to precede visual programming education based on block coding and to conduct curriculum convergence with SW and HW at the beginning, and high school students are carrying out text programming education like Python. Software education for social care class The contribution activity model can be classified into five types such as geographically difficult area, multicultural family areas, orphanage, reformatory, and basic livelihood security recipient. In addition, the survey results show that the students' interest in software education and their satisfaction are all very high at 96%. Effective software education for the social care class In the donation model, the lecturers consist of responsible professors, lecturers, and assistant instructors. Software training for the social care class is effective on a year-by-year basis, so that students can feel authenticity and trust. Software education contents focus on visual programming and physical computing education in elementary or middle school, and text programming and physical computing education in high school. It is necessary to construct a software education donor matching system that helps efficient management of software education donations by efficiently matching schools (consumers: elementary, middle, high school) and software education donors(suppliers).

• Journal of Korean Society of Transportation
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• v.28 no.6
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• pp.25-32
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• 2010

This study deals with the roundabout by flare of entry and exit. The goal is to analyze the relative effectiveness of roundabout by flare of entry and exit. In pursuing the above, this study gives the particular attentions to comparing the performances using VISSIM software. The main results analyzed are as follows. First, the single and double roundabouts are analyzed to have LOS F in the case of total entering vehicles of 2,400pcph and 4,400pcph Second, the roundabouts by entry flare analyzed to have LOS F in the case of total entering vehicles of 2,800~3,200pcph and the roundabouts by entry and exit flare analyzed to have LOS F in the case of total entering vehicles of 3,200~3,600pcph. Finally, result of comparative analysis of roundabout and roundabout by flare of entry and exit, capacity of roundabout by flare of entry and exit are located between 1-lane roundabout and 2-lane roundabout. therefore it analyzed that roundabout by flare of entry and exit can be added to new type roundabout.

• Journal of Internet Computing and Services
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• v.22 no.2
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• pp.11-17
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• 2021

Software-defined networking provides a programmable and flexible way to manage the network by separating the control plane from data plane. However, the limited switch memory restricts the number of flow entries in the flow table used to forward packets. This leads to flow table overflow and flow entry reinstallation, which severely degrade the network performance. Therefore, this paper proposes a comprehensive policy for timely eviction of inactive flow entries to optimally maintain flow tables usage. In particular, statistics of user datagram protocol flow entries are periodically sampled to enable the inactive entries to be evicted early. Through traffic-based experiments, we found that the proposed system reduces the number of overflow occurrences and flow entries reinstallation compared to the random and FIFO policies.

• International journal of advanced smart convergence
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• v.8 no.4
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• pp.147-153
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• 2019

Recently, the perception of software education, which had been considered as a field of education for programmers in this field, is changing in response to recent changes with the trend of 4th industrial revolution. Major counties competitively invest in software education and the target age group for software education is also on the decline. However, the traditional text-based programing languages such as JAVA and Python, have a high entry barrier. To address the shortcoming, a variety of methods have been recently proposed for the effective software education for kindergarten and elementary school student. In this paper, we propose a robot-based coding education system with steps for coding education for effective software education. The proposed method is divided into three stages, depending on the level of the student being trained in the software coding education to interact with robots. The proposed stages consists of unplugged coding using a remote control, coding using a graphic-based programming language and text- based coding. We conducted an experiment with performing separate missions while providing propoer tutorials for each stage to verify the effectiveness of the proposed software education system.