• Education of Primary School Mathematics
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• v.24 no.4
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• pp.217-231
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• 2021

The purpose of this study was to investigate the effects of flipped learning through EBSmath on Students' 'rate and ratio' learning. By increasing demands for change in education, an innovative teaching and learning paradigm, 'Flipped Learning', has been presented and drawing attentions. In South Korea, Flipped Learning is also highly recognized for its effectiveness by many scholars and various media. However, this innovative learning model has limitations in application and expansion due to the excessive burden of class preparation of teachers. As remote learning becomes more active, it would be possible to overcome the limitations of Filliped learning by using the platform provided by the Korea Educational Broadcasting System (EBS). EBSmath is an online learning module that is designed to assist students' self-directed learning. Thus, EBSmath would reduce teachers' burden to prepare mathematics classes for the application of Flipped Learning; and led to students' better understanding of mathematical concepts and problem solving. In this study, the effect of Flipped Learning through EBSmath on learning 'rate and ratio' was investigated. In order to scrutinize the effects of flipped learning, students' achievement and mathematical disposition were examined and analyzed. Students' achievement, specifically, was divided into two subcategories: concept understanding and problem solving. As a result, Flipped learning through EBSmath had a positive effect on students' 'rate and ratio' problem solving. In addition, a statistically significant change was identified in the 'willingness', which is subdomain of students' mathematical disposition.

• The Journal of the Acoustical Society of Korea
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• v.38 no.2
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• pp.184-192
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• 2019

Compared to 31-mode rings, 33-mode rings are highly utilized as wide bandwidth underwater acoustic transducers because the electro-mechanical coupling and piezoelectric constant d are high. On the other hand, the 31-mode ring is an axial symmetry structure, so it is possible to model it as a simple two-dimensional asymmetrical model for numerical analysis, but the 33-mode ring requires a three-dimensional numerical analysis. That is, a lot of computing resources and computation time are required. In this study, the effective material properties of an equivalent 31-mode ring were derived to simulate the electro-mechano-acoustical responses of the 33-mode ring transducer. Using the effective material properties derived from this study, a numerical analysis of rings in vacuum, air backed rings in water, and FFR (Free Flooded Ring) transducers were performed to compare the responses of 33-mode rings.

• Journal of the Korean Geotechnical Society
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• v.35 no.10
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• pp.33-45
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• 2019

In this study, in order to recycle a large amount of rocks and weathered mudstones produced by civil engineering projects such as railways and highways, as materials for roadbeds or embankment materials, circumferential specimens with a diameter of 5 cm and a height of 10 cm were made. A mudstone that weathered rapidly during rainfall was collected from Pohang construction sites. The weathered mudstone passed through a 2 mm sieve. It was prepared with the cement ratio, the sand ratio, curing condition and curing days. Three specimens were prepared according to each condition and then the unconfined compressive test, durability test and SEM analysis were performed to evaluate the engineering properties of the cemented soil. In the case of 28 days cured specimen, the strength of under-water cured specimens was 32-55% and the durability index was about 15% higher than air cured specimens. In addition, when the CR increased from 8% to 16%, the unconfined compressive strength (UCS) of pure mudstone cemented soil under water increased by about 1.6 times and the durability index increased by about 1.9 times. When the SR increased from 0% to 50%, the UCS of the specimen with SR = 10% was slightly less than or equal to specimen with SR = 0%. Then, as the SR became 30-50%, the UCS increased up to 51%. Unlike the UCS, the durability index increased continuously as the SR increased. As a result of SEM analysis, when SR was 50% rather than SR = 0%, the contact between sand particles increased and they were connected to each other. Such contact between these particles resulted in the increase of strength.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.12
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• pp.60-66
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• 2020

Torrential rain causes landslide damage every year. In particular, the 2011 downpour caused landslides at numerous points throughout Mt. Woomyeon, which resulted in considerable damage to people and property. Because it occurred in an urban area, this case became a major social issue and received public attention. Measures were quickly implemented for multilateral investigations and recovery. Landslides caused by heavy rain are greatly affected by rainfall at the time. Landslides from the upper part erode the flow path, increasing the size, causing much damage to the lower part. This study selected a rural village area among the damaged areas of Mt. Woomyeon, and analyzed the change in terrain profile before and after a landslide using the DSM data obtained from airborne LiDAR. This area can be divided into three hydrological basins. For each basin, the analysis was performed on the average slope of each part of the flow path, as well as the erosion and deposition due to soil flow. As a result of the analysis, it was estimated that the total amount of soil from the Jeonwon village was 15,300㎥. These field data based on GIS can be used as basic information to predict damage in the case of a similar disaster, and it can be helpful in analyzing the results of various debris flow simulations.

• Journal of Advanced Navigation Technology
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• v.24 no.6
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• pp.566-572
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• 2020

In a wireless power transmitter, the characteristics and effects of wireless power transmission between two induction coils are investigated, and a power converter circuit and a battery charger/discharger circuit using wireless power transmission technology are proposed. The advantage of wireless power transmitters and wireless chargers is that, instead of the existing plug-in-mounted wired charger (OBC; on-board charger), the user can wirelessly charge the battery without connecting the power source when charging power to the battery. There is. In addition, the advantage of wireless charging can bring about an energy efficiency improvement effect by using the secondary side rectifier circuit and the receiving coil, but the large-capacity long-distance wireless charging method has a limitation on the transmission distance, so many studies are currently being conducted. The purpose of the study is to study the transmitter circuit and receiver circuit of a wireless power transmission device using a primary coil, a secondary coil, and a half bridge series resonance converter, which can transmit power of a non-contact type power transmitter. As a result, a new topology was applied to improve the power transmission distance of the wireless charging system, and through an experiment according to each distance, the maximum efficiency (95.8%) was confirmed at an output of 3 kW at an 8 cm transmission distance.

• 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.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.23 no.4
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• pp.157-164
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• 2023

This paper suggests O(n²) polynomial time heuristic algorithm for corporate tax structure optimization problem that has been classified as NP-complete problem. The proposed algorithm constructs tax tree levels that the target holding company is located at root node of Level 1, and the tax code categories(T_e) 1,4,3,2 are located in each level 2,3,4,5 sequentially. To find the maximum tax-relief path from source(S) to target(T), firstly we connect the minimum witholding tax rate _minr_w(u, v) arc of node u point of view for transfer the profit from u to v node. As a result we construct the spanning tree from all of the source nodes to a target node, and find the initial feasible solution. Nextly, we find the alternate path with minimum foreign tax rate _minr_fi(u, v) of v point of view. Finally we choose the minimum tax-relief path from of this two paths. The proposed heuristic algorithm performs better optimal results than linear programming and Tabu search method that is a kind of metaheuristic method.

• Proceedings of the Plant Resources Society of Korea Conference
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• 2022.09a
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• pp.113-113
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• 2022

도라지(Platycodon grandiflorum)는 초롱꽃과 도라지속에 속하는 여러해살이풀로 7~8월에 보라색이나 흰색의 꽃을 피우고, 뿌리는 다육질로 원주형 또는 분지형이다. 잎은 거의 엽병이 없는 대생이며, 종자는 난형으로 3개의 모서리가 있다. 항염증 성분인 플라티코딘이 들어있어 편도염을 비롯한 후두염, 폐렴 등에 효과가 있어 우리나라 약용작물 재배면적의 상위를 차지하고 있는 주요 작물이다. 최근, 백수오, 감초 등 심근성 약용작물은 뿌리의 수확 비용 절감을 위해 용기재배가 도입되고 있다. 본 연구는 도라지 용기재배에 적합한 용기의 규격과 고온 경감을 위한 용기 재료 선발을 위해 수행하였다. 도라지 용기재배에 적합한 용기의 규격 선발은 기본 용기로 플라스틱 플륨관을 사용하였고, 높이는 40cm로 고정하여 직경을 10, 20, 30cm로 처리하였다. 2019년 4월 하순에 도라지 종자를 파종하여 용기 규격별로 각각 1주(10cm), 4주(20cm), 8주(30cm)를 남겨 두고 솎음 다음, 2020년 10월 하순에 수확하였다. 도라지의 생육 및 수량성을 조사한 결과, 용기의 직경이 증가함에 따라 근장, 근경, 근중 등 지하부 생육이 우수한 경향이었다. 또한, 10a당 수량은 노지재배 749kg에 비해 직경 10cm 778kg, 20cm 849kg, 30cm 1,156kg로 직경 30cm가 가장 우수하였다. 직경이 증가할수록 수량성이 증가하였으나 직경 30cm 이상의 용기는 수확 시 노동력이 증가하고, 배양토 비용이 증가하여 사용하지 않았다. 고온 경감을 위한 용기 재료 선발은 흰색과 검정색 플라스틱 플륨관을 높이 40cm × 직경 30cm 규격으로 절단하여 2020년 4월에 도라지 종자를 파종하였고, 2021년 10월 하순에 수확하였다. 이 중 검정색 용기는 무처리(대조), 유공, 반유공, 흰색부직포, 반사필름 처리를 하였다. 도라지의 수량성을 조사한 결과, 검정색 용기 중 유공처리가 무처리 대비 수량이 21%(1,080 → 1,304kg/10a) 증가하였다. 위의 결과로 도라지는 직경 30cm의 검정색 유공 용기가 용기재배에 적합한 것으로 판단되었다.

• Korean Journal of Heritage: History & Science
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• v.57 no.1
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• pp.22-36
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• 2024

In 1993, a large number of relics was found in Cheongju Sanesa Buddhist Temple. They show superiority as bronze-based products, and are especially important in since they provide much information about the time of their creation. However, there are many opinions about the time they were hoarded: in the middle of the 13^th century, late in the 13^th century, early in the 14^th century, etc. This study estimates the time they were hoarded to be some time in April 1291 during the invasion of Kădīn (哈丹) in the Yuan Dynasty. Kădīn's troops invaded the Goryeo Dynasty, then went through Yangpyeong and Wonju in January 1291 and appeared in Yeongi-hyeon on May 1 of that year. Based on records, this study verified that the troops passed through Cheongju on their way from Chungju to Yeongi-hyeon (currently Sejong-si) and pointed out that the invasion route of the troops was the background for the hoarding of Sanesa relics. The estimation that the Sanesa relics were hoarded in 1291 when Kădīn's invasion was going on makes it possible to reasonably clear up the era of the relics in which the Heavenly Stems called gānzhī (干支) Muo (戊午), Gyeongshin (庚申), Giyu(己酉) etc. were written. That is, Giyu Geumgo is presumed to be the year 1249, Muo Hyangro 1258, Gyeongshin Hyangwan 1260, etc.

• Journal of the Korean association of regional geographers
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• v.6 no.3
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• pp.1-36
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• 2000

Periodic markets of the later Choson dynasty had undergone fundamental changes during the late Chosun dynasty and Japanese colony period. This paper aims to analyse the spatial distributions and changes of the periodic markets in the middle stream of Han-River in this era in the use of the survey of documentary records and fieldwork. Before the early 1910s, long distance transportation was made by riverboats, short distance transportation was done by porters and pack animals. Because goods such as rice, soybean and salt were very heavy and needed long distance transport, they were mainly transported by riverboats. Accordingly, riverports on the shore of river played important roles in exporting and importing goods as nodes of long distance transportation. The opening of railroad Seoul-Busan, the construction of new roads(Sinjakno) of 1910s and the use of oxcarts produced striking changes in the spatial distribution and hierarchy structure of periodic markets. These changes also had influence on the outflow and inflow of goods in the middle stream of Han-River. In the parr of outflow of goods, it seems that the line linking Icheon city-Yongin city-Anseong city played a role in making the boundaries of the marketing areas between goods trams ported by the rail road Seoul-Busan and goods done by Han River river boats. Anseong, Osan and Suwon periodic markets located around railroad stations occupied the higher positions than those of other regions in the hierarchial structure of periodic markets. Their marketing areas could nearly overwhelm those of riverports located in the middle stream region of Han River and extend to the middle stream region of Han River as a result of decrease of transport cost through using of oxcarts and railroads. the opening of railroad Suwon-Yeoju(Suryoson) and railroad Cheonan-Janghawon(Cheonjangson) brought about changes of the structure of long distance trade again. In a part of outflow of goods, it seems that as a result of the new opening of their railroads periodic markets around railroads seized a large portion of the marketing area of the southern part of Yoju and Ichon area and therefore made extreme change in rivershipping of Han River. In the inflow part of goods, goods transported by riverboats from the downstream of Han River before the opening of railroad were imported directly from railroad stations. Accordingly, rivershipping and riverports declined. And because goods were imported by way of great periodic markets and supplied to small periodic markets and consumers before the opening of railroad, but supplied from railroad stations to small periodic markets and consumers after the opening of railroad. The volume of turnover of such great periodic markets as Anseong, Osan and Suwon periodic markets therefore declined. On the other hand, because Yangpyong area had not been yet included within the sphere of influence of railroad until 1930s, it heavily depended on rivershipping of Han River as before. But the opening of railroad Seoul-Wonju(jungangson) brought about decline of rivershipping in Yangpyong and Wonju area.