• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.9
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• pp.703-709
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• 2020

Pintle injector is known to have been adopted as injector of Lunar Module Descent Engine (LMDE) and contributed to success of the Apollo program and recently used in merlin engine. In this study, 500N Lab-Scale pintle injector thruster was manufactured and the combustion experiment with LOx/GCH4 was conducted. However, the proto-type thruster was showed some problems, such as low combustion efficiency and melting of pintle tip. To solve these problems, the flow guide in pintle tip was suggested through the CFD simulation. After addition of flow guide module, the combustion efficiency increased and pintle tip did not melt until the end of combustion.

• Journal of the Korean Society for information Management
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• v.33 no.4
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• pp.27-57
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• 2016

The objective of this study is to explore the strategies to promote the use of the subject guide for Korean modern literature. To meet this objective this study conducted a survey on users' awareness of the subject guide service and sought out experts' opinions to identify the strategies to promote and improve the subject guide for Korean modern literature. The study proposes the following strategies: 1) Conduct promotional activities utilizing a variety of social media; 2) provide education for the user to enhance understanding of the utility of the subject guide; 3) build a website dedicated to the subject guide service for Korean modern literature; 4) provide an efficient subject-specific bibliography service by improving the quality of the subject guide, by offering full texts, ongoing content updates, and coordination with other institutions and agencies; and 5) tailor the service to user characteristics such as gender, age, occupation, and education level. Suggestions for future directions include research on the collaborative system, additional specific promotional strategies to promote the use of the subject guide, and development of evaluation indicators of the subject guide for Korean modern literature.

• Journal of KIISE:Computing Practices and Letters
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• v.14 no.2
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• pp.181-185
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• 2008

Layered video multicast such as RLM Receiver-driven layered multicast) is a premising technique for delivering streaming video to a set of heterogeneous receivers over ALM(Application Layer Multicast) as well as over IP multicast. However, this approach may suffer from unnecessary fluctuation of video quality due to overlapped and failed join-experiments. Though a shared teaming scheme was introduced to resolve these problems, it may cause high control overhead and slow convergence problem when used with ALM. In this paper, we propose a new shared learning scheme for ALM-based layered video multicast which reduces control overhead and convergence latency while keeping the number of fluctuation reasonably small. The simulation results show that the proposed scheme performs better than an ALM-based layered video multicast with shared learning in terms of control overhead and convergence latency.

• Journal of KIISE
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• v.43 no.11
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• pp.1216-1222
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• 2016

The advent of large-scale web services has resulted in gradual increase in the amount of data used in those services. These big data are managed efficiently by DBMS such as MySQL and MariaDB, which use InnoDB engine as their storage engine, since InnoDB guarantees ACID and is suitable for handling large-scale data. To improve I/O performance, InnoDB caches data and index of its database through a buffer pool. It also supports multiple buffer pools to mitigate lock contentions. However, the multiple buffer pool scheme leads to the additional data consistency overhead. In this paper, we analyze the overhead of the multiple buffer pool scheme. In our experimental results, although multiple buffer pool scheme mitigates the lock contention by up to 46.3%, throughput of DMBS is significantly degraded by up to 50.6% due to increased disk I/O and fsync calls.

• The Journal of the Korea Contents Association
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• v.11 no.12
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• pp.347-356
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• 2011

The aim of this study was to determine the prevalence of self-assessment halitosis and to offer the basic information that establishes a strategy of effective health promotion and to enhance the quality of life. This study performed a questionnaire survey. The questionnaire was filled out by the 362 adults, who lived in Incheon Metropolitan City from May to July, 2010. The data were analyzed using a Chi-square test in the SPSS version 12.0 program. The prevalence rate of self-assessment halitosis was 24.3%. Hypertension, diabetes, medication and inadequate oral hygiene practice were significantly associated with self-assessment halitosis. Other factors of self-assessment halitosis were older age and occupation. As a result, dental professionals have to investigate a systemic disease history thoroughly. And they have to educate regular checkup of oral health and to perform a continuous feedback. The self-assessment halitosis has a negative influence on mental health and social life, so dental professionals must take into consideration about the halitosis.

• The Journal of the Korea Contents Association
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• v.17 no.8
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• pp.144-151
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• 2017

The aim of this cross-sectional study was to investigate the relationship between regular interdental cleaning and periodontal condition. A total of 319 pregnant women were recruited at 21 to 24 weeks of gestation. Information on demographics, health status and health behaviors including regulary use of interdental cleaning aids, that can influence periodontal condition was collected. Full mouth periodontal probing was performed. Periodontitis was defined as CAL of 4.0 mm or greater on 2 or more sites not on the same tooth. Gingivitis was defined as 15 percent and more sites showed bleeding on probing. Gingival crevice fluid sample was collected for bacterial analysis. We studied a total of 319 subjects, comprised of 116 subjects who use interdental cleaning device regularly and 203 subjects who didn't. Subjects who do not use interdental cleaning regularly had 2.3 times higher risk of gingivitis and 2.7 times of periodontitis, 2.3 times more amount of P. gingivalis. There was a significant relationship between regular interdental cleaning and periodontal condition in Korea.

• Journal of KIISE:Computing Practices and Letters
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• v.15 no.12
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• pp.963-967
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• 2009

The Log-structured File System (LFS) collects all modified data into a memory buffer and writes them sequentially to a segment on disk. Therefore, it has the potential to utilize the maximum bandwidth of storage devices where sequential writes are much faster than random writes. However, as disk space is finite, LFS has to conduct cleaning to produce free segments. This cleaning operation is the main reason LFS performance deteriorates when file system utilization is high. To overcome painful cleaning and reduced performance of LFS, we propose the segment space recycling (SSR) scheme that directly writes modified data to invalid areas of the segments and describe the classification method of data and segment to consider locality of reference for optimizing SSR scheme. We implement U-LFS, which employs our segment space recycling scheme in LFS, and experimental results show that SSR scheme increases performance of WOLF by up to 1.9 times in HDD and 1.6 times in SSD when file system utilization is high.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.12
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• pp.6111-6117
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• 2012

This paper is a type of business representatives who are responsible for the burden he want to relieve. In addition, to ensure transparency and to contribute to the Elimination of irregularities in cracking down on overcharging to research. In order to avoid duplicate entry of fixed checkpoints of modern equipment was installed in the automatic collection of information inspection. And, if the information is the same information to crack down imposed the Road Fine system linkage system Constrution CALS system to research. Land administration office imposed a fine after confirmation information to crack down on the auditory system, the auditory crackdown imposed fine and proceed to determine the status of your work since. This study was carried out and any future crackdown on overcharging gathering information for the efficient production of surgical intervention for improved accuracy considering that frequency.

• Journal of KIISE:Databases
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• v.27 no.2
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• pp.227-237
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• 2000

A Web database System is a large-scaled multimedia application system that has multimedia processing facilities and cooperates with relational/Object-Oriented DBMS. Conventional hypertext modeling methods and DB gateway have limitations for Web database because of their restricted versatile presentation abilities and inefficient concurrency control caused by bottleneck in cooperation processing. Thus, we suggest a Dynamic Navigation Model & Virtual Graph Structure. The Dynamic Navigation Model supports implicit query processing and dynamic creation of navigation spaces, and introduce node-link creation rule considering navigation styles. We propose a mapping methodology between the suggested hypertext model and the relational data model, and suggest a dynamic allocation scheduling technique for query processing server based on weighted value. We show that the proposed technique enhances the retrieval performance of Web database systems in processing complex queries concurrently.

• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.6
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• pp.89-102
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• 2010

In this paper, a study on the future-oriented actuator introduces the future technology and future direction in aerospace and several industry fields. In particular, the mechanical linkage or hydraulic and pneumatic actuators which have the higher output-to-weight ratio have been used a lot in the past as the aircraft's flight control device. Most recently, Fly-By-Wire system has been used in aircraft and the flight control system has been changed in more electric and all electric systems. Electrohydraulic actuators and electric actuators have been developed continually, because they have better efficiency, safety and lower cost for the flight control system of aircraft. Also, to improve the weight condition, accuracy and response of actuator, new field actuators using new materials have been developed. In this paper we clearly proposed the actuator design and detailed technology development trend for next generation actuation system in aerospace and new field.