• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.10a
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• pp.574-577
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• 2007

While disk can be overwritten on updating data, because flash memory can not be overwritten on updating data, new data are updated in new area. If data are frequently updated, garbage collection, which is achieved by erasing blocks, should be performed to reclaim new area. Hence, because the number of erase operations is limited due to characteristics of flash memory, every block should be evenly written and erased. However, if data with access locality are processed by cost benefit algorithm with separation of hot block and cold block, though the performance of processing is high, wear-leveling is not even. In this paper, we propose CB-MB (Cost Benefit between Multi Bank) algorithm in which hot data are allocated in one bank and cold data in another bank, and in which role of hot bank and cold bank is exchanged every period. CB-MB showed that its performance was similar to that of others for uniform workload, however, the method provides much better performance than that of others for workload of access locality.

• Journal of Digital Convergence
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• v.18 no.7
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• pp.111-122
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• 2020

The current study aimed to examine university students' perceptions of the positive effects of L2 oral presentations in terms of communication skills and future employment. The participants were 13 undergraduate students enrolled in L2 oral presentation classes at the beginner or intermediate level. This study followed a qualitative research approach using in-depth and semi-structured interviews as the primary method. The findings revealed that students largely exhibited the benefits of oral presentations in three ways: by enhancing L2 proficiency, building confidence in public speaking, and gaining competitive advantages in their future careers. As a challenge for L2 learners, oral presentations were considered fundamental to develop effective communication skills in academic and professional contexts.

• The KIPS Transactions:PartA
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• v.12A no.2 s.92
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• pp.171-180
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• 2005

In distributed systems data are replicated and stored at several nodes to increase the availability and overall performance. Here Quorum protocol doffing a certain set of replicas required for read/write operation exists for global concurrency control. One of the representative replication Protocols - the Tree Quorum protocol - has a drawback of rapidly growing number of replicas as the level increases, while the Grid protocol requires the same operation cost even without any failure. In this paper, thus, we propose a new replication protocol called hybrid protocol which capitalizes the merits of the existing protocols and solves the problems of them at the same time. The proposed hybrid protocol has very low operation cost in the absence of failure like the tree quorum protocol, and has relatively lower operation cost and higher availability than existing protocols when failure occurs by employing tree architecture as the overall organization while each level of the tree is organized as a row of a grid architecture. It is thus effective to be applied to survival storage system. We conduct cost and availability analysis of the proposed protocol through mathematical modeling, and response time and throughput are compared with those of the Tree Quorum protocol through computer simulation.

• Journal of KIISE
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• v.42 no.1
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• pp.7-14
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• 2015

Storage Class Memory(SCM) has been considered as a next-generation storage device because it has positive advantages to be used both as a memory and storage. However, there are significant problems of data consistency in recently proposed file systems for SCM such as insufficient data consistency or excessive data consistency-control overhead. This paper proposes a novel data consistency-control scheme, which changes the write mode for log data depending on the modified data ratio in a block, using a rollback-recovery scheme instead of the Write Ahead Logging (WAL) scheme. The proposed scheme reduces the log data size and the synchronization cost for data consistency. In order to evaluate the proposed scheme, we implemented our scheme on a Linux 3.10.2-based system and measured its performance. The experimental results show that our scheme enhances the write throughput by 9 times on average when compared to the legacy data consistency control scheme.

• The Journal of Korean Institute of Next Generation Computing
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• v.15 no.1
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• pp.86-98
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• 2019

Recently, the trend of building container-based PaaS (Platform-as-a-Service) is expanding. Container-based platform technology has been a core technology for realizing a PaaS. Containers have lower operating overhead than virtual machines, so hundreds or thousands of containers can be run on a single physical machine. However, recording and monitoring the storage logs for a large number of containers running in cloud computing environment occurs significant overhead. This work has identified two problems that occur when detecting a file system change event of a container running in a cloud computing environment. This work also proposes a system for container file system event detection in the environment by solving the problem. In the performance evaluation, this work performed three experiments on the performance of the proposed system. It has been experimentally proved that the proposed monitoring system has only a very small effect on the CPU, memory read and write, and disk read and write speeds of the container.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.22 no.4
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• pp.17-22
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• 2022

With the spread of web services, data types are becoming more diversified. In addition to the form of storing data such as images, videos, and texts, the number and form of properties and metadata expressing the data are different for each data. In order to efficiently process such unstructured data, a key-value store is widely used for state-of-the-art applications. LSM-Tree (Log Structured Merge Tree) is the core data structure of various commercial key-value stores. LSM-Tree is optimized to provide high performance for small writes by recording all write and delete operations in a log manner. However, there is a problem in that the delay time and processing speed of user requests are lowered as batches of deletion operations for expired data are inserted into the LSM-Tree as special key-value data. This paper presents a Filtered LSM-Tree (FLSM-Tree) that solves the above problem by separating the deleted key from the main tree structure while maintaining all the advantages of the existing LSM-Tree. The proposed method is implemented in LevelDB, a commercial key-value store and it shows that the read performance is improved by up to 47% in performance evaluation.

• Journal of Gifted/Talented Education
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• v.26 no.4
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• pp.699-719
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• 2016

Alternate pictures that are proven to be equivalent are in high demand to assess creative thinking and language skills. This study aimed to investigate the equivalence of three pictures ('Dog owners,' 'Lost Dog,' and 'Overslept') recently developed for use in a creative writing task. Middle school students (N=183) wrote a story in English based on one of the three prompts distributed randomly. Four writing features (fluency, syntactic complexity, lexical diversity, and temporality) were analyzed with Coh-Metrix and MANCOVA. The three prompts were largely equivalent in their capacity to detect differences among writers in all the features of writing. The difficulty levels of the three prompts, however, were not necessarily the same. Two prompts, Dog Owners and Lost Dog, were verified as equivalent prompts, and therefore, they are recommended as alternate forms to assess creative language skills in repeated measurements. The Overslept prompt had greater facility in eliciting diverse words and more temporal connectives in composing stories. The differential difficulty shown among the prompts suggests that the validity of using different picture versions in repeated assessment remains questionable unless those versions undergo equivalence verification.

• Journal of the Korean earth science society
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• v.35 no.2
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• pp.147-158
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• 2014

The purpose of this study was to explore changes of elementary science class in student oriented group inquiry activities using a Science Writing Heuristic (SWH) template that enhance scaffolding of inquiry. The changes focused on students' written reports and perceptions of their learning environment as well as discourse patterns. One fourth-grade class of 29 students participated in this study, and a developed work sheet of science writing was utilized to scaffold student's inquiry activities. Four units in the first-semester text book for fourth grade of the-, 2007 Educational Curriculum Revision were chosen for scaffolding inquiry, and sixteen lessons of instruction were all videotaped. For investigating students' written reports, a framework based on the aspects of science inquiry by Millar (2010) was used to evaluate the coherence between student inquiry activities and their claims. Secondly, a regular fourth-grade class was selected as the control group and was compared with the experiment group using the pre- and post-test of the survey on the perception of science class and science. Lastly, students' discourse patterns of the beginning science lesson were compared with those of the closing lesson. We found that the coherence in the last class increased significantly in students' written reports compared to the first one. Findings also indicated that students' perceptions on their learning environment moved toward student-centered. Based on our discourse patterns analysis, the last class was more student-centered from being teacher-centered than the first one.

• Journal of Elementary Mathematics Education in Korea
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• v.15 no.3
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• pp.619-640
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• 2011

The study aims the introducing the items for the assessment of mathematical thinking including mathematical reasoning, problem solving, and communication and the analyzing on the responses of the 5th grade pupils. We categorized the area of mathematical reasoning into deductive reasoning, inductive reasoning, and analogy; problem solving into external problem solving and internal one; and communication into speaking, reading, writing, and listening. And we proposed the examples of our items for each area and the 5th grade pupils' responses. When we assess on pupil's mathematical reasoning, we need to develop very appropriate items needing the very ability of each kind of mathematical reasoning. When pupils solve items requesting communication, the impact of the form of each communication seem to be smaller than that of the mathematical situation or sturucture of the item. We suggested that we need to continue the studies on mathematical assessment and on the constitution and utilization of cognitive areas, and we also need to in-service teacher education on the development of mathematical assessments, based on this study.

• The Journal of the Korea Contents Association
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• v.20 no.1
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• pp.573-580
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• 2020

The purpose of this study was to explore and to suggest the effective teaching methods for university students to improve their speaking abilities through peer assessment-feedback and self assessment-feedback based presentation and debate class. The objects and content of the study were the students who took a class "Reading and Communication" of H university, and here examine closely the speaking activities and their effects during the integrated activities of 'reading, speaking and writing'. In speaking education peer and self assessment feedback is to form an emotional consensus among the students and encourage active participation, and enable self-discovery and communication learning to students. As a result of the study, it was found that the variety speaking practice had a very positive effect on the attitude of speaking and the psychological aspect, and it was confirmed that the evaluation and feedback activities had a meaningful learning effect on the students. Effective speech education and guidance measures should be continuously studied and developed.