• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.6
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• pp.609-615
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• 2011

A two-dimensional Stokes flow past a vertical plate in a channel is analyzed. The vertical plate is located at the center of the channel, and plane Poiseuille flow exists far upstream and downstream of the vertical plate. The Stokes approximation is used, and the flow is investigated analytically using the method of eigenfunction expansion and the point collocation method. From the analysis, the stream function and pressure distribution are obtained, and the pressure and shear stress distributions on the plate and channel wall are calculated. The additional pressure drop induced by the vertical plate and the force exerted on it are calculated as functions of the length of the vertical plate. For a typical length of the vertical plate, the streamline pattern and pressure distribution are shown. In addition, numerical analysis of laminar flow with a small Reynolds number is carried out to analyze the effect of a small Reynolds number on the flow pattern.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.442-448
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• 2008

This paper presents an approach to define an optimal piezoactuator length to actively control structural vibration. The optimal ratio of the piezoactuator length against beam length when a pair of piezoceramic actuator and accelerometer is used to suppress unwanted vibration with direct velocity feedback (DVFB) control strategy is not clearly defined so far. It is well known that direct velocity feedback (DVFB) control can be very useful when a pair of sensor and actuator is collocated on structures with a high gain and excellent stability. It is considered that three different collocated pairs of piezoelectric actuators (20, 50 and 100 mm) and accelerometers installed on three identical clamped-clamped beams (300 * 20 * 1 mm). The response of each sensor-actuator pair requires strictly positive real (SPR) property to apply a high feedback gain. However the length of the piezoactuator affects SPR property of the sensor-actuator response. Intensive simulation and experiment shows the effect of the actuator length variation is strongly related with the frequency range of SPR property. A shorter actuator gave a wider SPR frequency range as a longer one had a narrower range. The shorter actuator showed limited control performance in spite of a higher gain was applied because the actuation force was relatively small. Thus an optimal length ratio (actuator length/beam length) was suggested to obtain relevant performance with good stability with DVFB strategy. The result of this investigation could give important information in the design of active control system to suppress unwanted vibration of smart structures with piezoelectric actuators and accelerometers.

• Journal of the Society of Naval Architects of Korea
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• v.50 no.2
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• pp.111-119
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• 2013

The concept of the natural frequency is useful for understanding the characters of oscillating systems. However, when a circular cylinder floating horizontally on the water surface is heaving, due to the hydrodynamic forces, the system is not governed by the equation like that of the harmonic one. In this paper, in order to shed some lights on the more correct use of the concept of the natural frequency, a problem of the heaving circular cylinder is analyzed in the frequency domain. Previously, it was thought that the theory of Ursell (1949) could not be used to get the added mass and wave-making damping for short waves, however, they were obtained by applying an accurate collocation method to the theory in this study. Using the so developed numerical method, we found the added mass and wave-making damping of the circular cylinder for the entire range of the frequency. Then, the MCFR(Modulus of Complex Frequency Response) was used to locate the frequency corresponding to the local maximum of MCFR and we define it as the natural frequency. Comparing our results with the previous investigation, we found that the pressure distribution on the cylinder gets close asymptotically to that of a cylinder in infinite fluid OR close to that of the cylinder, that the approximation of the natural frequency by Lee (2008) is different from our new value only by 0.64%, and that the approximation of the heaving system by an equivalent damped harmonic oscillation is not proper by the reason that is clearly shown from the comparison of the shape of the corresponding MCFRs.

• Journal of Korea Multimedia Society
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• v.20 no.9
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• pp.1541-1550
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• 2017

The increasing number of multimedia content offered to the user demands content recommendation. In this paper, we propose a system for recommending content related to the content that user is watching. In the proposed system, relationship information between content is generated using relationship information between representative keywords of content. Relationship information between keywords is generated by analyzing keyword collocation frequencies in Internet news corpus. In order to handle big corpus data, we design an architecture that consists of a distributed search engine and a distributed data processing engine. Furthermore, we store relationship information between keywords and relationship information between keywords and content in NoSQL to handle big relationship data. Because the query optimizer of NoSQL is not as well developed as RDBMS, we propose query optimization techniques to efficiently process complex queries for recommendation. Experimental results show that the performance is improved by up to 69 times by using the proposed techniques, especially when the number of requested related keywords is small.

• Journal of the Korean Society for information Management
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• v.25 no.3
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• pp.65-82
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• 2008

The purposes of this study are to explore FRBR utilities such as work clustering and expression clustering and problems of application of the FRBR by developing work and expression clustering algorithm and implementing it into cataloging system, and to suggest new cataloging rules for FRBR and guideline of MARC description to improve FRBR work clustering. FRBR was suggested by necessitation of collocation function of bibliographic records according to increase of searching materials and multi-version materials, but FRBRization has some problems such as imperfect conversion of bibliographic records to FRBR records and inappropriateness of current cataloging rules for FRBR. Bibliographic records must be processed by FRBR algorithm to construct FRBRized system, but bibliographic records and current cataloging rules couldn't perfectly support FRBRization. Therefore cataloging rules and guidelines of MARC description for FRBR are needed. For constructing FRBRized cataloging system in Korea, it is needed to find problems and solution through FRBR practical application such as developing FRBR algorithm and applying it to cataloging records.

• Annual Conference on Human and Language Technology
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• 1999.10e
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• pp.105-109
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• 1999

영-한 기계번역 중 변환 단계에서 한국어 문장을 생성하기 위해서는 구구조 변환 후 조사 및 대역어 선택으로 이루어진다. 그러나 하나의 영어 단어는 여러 개의 한국어 의미들을 가지고 있기 때문에 문장에서 사용된 영어의 정확한 의미에 해당하는 한국어 대역어를 선택하는 것은 번역의 질을 높이고 시스템의 성능에 매우 중요한 역할을 한다. 특히 용언 및 체언의 대역어 선택은 문장에서 서로 간의 의미적인 관계를 고려하여야 올바른 대역어를 선택할 수 있다. 기존에는 전자 사전에 용언과 체언간의 연어 정보(collocation information)를 구축하여 대역어 선택의 문제를 해결하려고 하였으나 연어 정보가 사전에 존재하지 않을 때 올바른 대역어를 선택할 수 없었다. 또한 용언과 체언의 관계를 나타내는 조사를 선택하기 위하여 격(case)을 세분화하여 사전을 구축하였으나 격의 분류 및 사전을 구축할 경우 격을 선택하는 어려움이 있었다. 이에 따라 본 논문에서는 문형(sentence pattern)에 의한 방법으로 용언의 대역어 및 용언이 갖는 필수격 체언의 조사와 대역어 선택방법을 제안한다. 문형의 구조적인 정보에는 용언과 체언의 의미적 역할(thematic role)을 하는 조사 및 용언이 갖는 필수격 체언의 의미 자질(semantic feature)을 갖고 있다. 이러한 의미 자질을 wordnet과 한/영 및 영/한 사전을 이용하여 의미 지표(semantic marker)를 갖는 문형 사전을 구축한다. 또한 의미 지표를 갖는 문형 사전을 기반으로 조사 및 대역어 선택 알고리즘을 개발한다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.4
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• pp.493-499
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• 2007

The Taylor expansion expresses a differentiable function and its coefficients provide good approximations for the given function and its derivatives. In this study, m-th order Taylor Polynomial is constructed and the coefficients are computed by the Moving Least Squares method. The coefficients are applied to the governing partial differential equation for solid problems including crack problems. The discrete system of difference equations are set up based on the concept of point collocation. The developed method effectively overcomes the shortcomings of the finite difference method which is dependent of the grid structure and has no approximation function, and the Galerkin-based meshfree method which involves time-consuming integration of weak form and differentiation of the shape function and cumbersome treatment of essential boundary.

• Nuclear Engineering and Technology
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• v.26 no.2
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• pp.212-224
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• 1994

A numerical method has been developed for studying the dynamics of a flexible cylinder in a coaxial cylindrical duct, immersed in inviscid flow. The unsteady inviscid fluid-dynamic force acting on the oscillating cylinder has been estimated more rigorously by means of a spectral collocation method without simplification of governing equations. This numerical approach is applicable to the system haying wider annular gap and/or shorter length of cylinder as compared to existing potential theory. The governing equation of the unsteady flow was obtained from Laplace equation. The equation of cylinder motion coupled with the fluid motion was discretized by Galerkin's method, from which the dynamic behaviour of the system has been evaluated. The effect of the length of the cylinder and the annular gap on the critical flour velocity, where the system loses stability by buckling, was investigated. To validate the numerical method, the potential flow theory developed by Hobson based on thin film approximation has been improved. Typical results of the present numerical theory on the dynamics and stability of the system are compared with those of available existing theory and the present approximate results. Good agreement was found between the results. It was also found that a nondimensional critical flow velocity becomes larger as increasing the annular gap and decreasing the length of cylinder.

• Journal of the Korean Institute of Intelligent Systems
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• v.14 no.1
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• pp.28-32
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• 2004

Till now, Korean spelling proofreading system has corrected words of a sentence from the relationship of a collocation or the grammatical information of the sentence. In this paper, we propose a system that corrects a word using the relationship among the sememes in a single sentence and substitutes an apt word for a word of the sentence that has the meaningful mistake by a mistyping. The proposed system makes several sentences that are able to communicate with each sememe. The substantives forms meaning tree according to the meaning of the word and the predicate of a sentence defines the meaningful relationship between a substantives of the subject and the object. After this system compares and analyzes the relationship of meaning, it corrects the mistyping of a word in a single sentence that includes an error. If the system finds out the semantic error by the mistyping, it applies the spelling proofreading method that proposed in this paper.

• Journal of the Korean Society for information Management
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• v.28 no.1
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• pp.23-42
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• 2011

This study is to compare the descriptive cataloging rules between AACR2 and RDA, and then to find a direction of future cataloging and KCR 4. RDA is new cataloging rules that embody the International Cataloging Principles(2009), FRBR and FRAD. It is a structure of bibliographic control of all kinds of resources, and the rules can be flexibly applicable in the international cataloging community. It is critical to embody RDA in KCR 4 because RDA is likely to affect the future cataloging through its collocation function and relation function to construct semantic web of OPAC. This study analyzed the descriptive rules of work, expression, and manifestation based on RDA draft(2008) of JSC for Development of RDA. It analyzed the changes in the cataloging rules from AACR2 to RDA in such descriptive areas as title, type of resources, statement of responsibility, edition, publication, physical description and series in the manifestation level, and the preferred access points in both expression and work levels. The findings of this study will provide implications in revising KCR4.