• Journal of Korean Association for Spatial Structures
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• v.11 no.3
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• pp.137-145
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• 2011

Due to architectural requirement, the attention of single layered freeform spatial structure is increasing nowadays. Because the node of single layered structure should resist the bending and axial forces simultaneously, it is necessary to develop a new proper type of node in detail. In this study, a new type of node for single layered freeform spatial structure was proposed. And the structural performance for the node was analytically evaluated using the commercial FEM software(ABACUS). As a result, a node prototype was selected and the proposed node showed good structural behaviors.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.8
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• pp.801-808
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• 2004

In this paper, we proposed the grating parallel plate waveguide structure for converting a linearly polarized wave to a circularly polarized wave. For the design of the polarizer, the moment method and Floquet's theorem are applied under two assumptions that the incident wave is a plane wave and the structure is infinitely periodic. In order for the more precise design, we performed the near-field analysis for the finite polarizer structure using MATLAB. By comparing with the measured results obtained by the near-field arrangement, we verified the correctness of our near-field analysis. By taking the ideal assumptions considered in the initial design procedure into account, newly designed modified dimensions for the polarizer was suggested which give improved performance.

• Proceedings of the Korean Society of Computational and Applied Mathematics Conference
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• 2003.09a
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• pp.2.1-2
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• 2003

WLAN의 매체 특성상 AP beacon영역 내의 모든 STA들은 다른 STA의 송수신 데이터 내용에 접근할 수 있다. 따라서 상호 또는 그룹 간의 데이터프라이버시와 상호인증 서비스는 무선 랜의 중요한 이슈중의 하나이다. 무선랜을 통한 네트워크 접속 보안으로는 사용자와 AP 사이의 무선 접속구간 보안과 AP와 AS사이의 유선 구간 보안으로 정의되며, 상대적으로 취약한 무선 구간 보안이 초점이 된다. 현재 무선 구간 보안에는 WEP이 사용된다. 그러나 WEP 방식은 WEP 키와 IV 크기가 작고, 노출된 공유키를 사용하며, 암호 알고리즘(RC4)와 무결성 알고리즘(CRC-32)이 근본적으로 취약하다. 이러한 문제에 대한 해결 방법으로 IEEE 802.11i는 두 가지 접근 방식을 채택하였다. 하나는 WEP의 보안 문제점을 소프트웨어적으로 개선한 TKIP이고 다른 하나는 기존의 WEP과는 하드웨어적으로 상이한 AES을 기반으로 한 CCMP이다. 이 논문에서는 각 알고리즘에 대한 키의 흐름 및 그 안전성을 분석하였다. 이러한 방법을 통해 WEP 구조의 보안상의 취약점을 확인하고, TKIP이 WEP을 대체할 수 있을 만큼의 안전성을 갖는지를 검증한다. 또한 고려될 수 있는 공격 모델을 제시하고, 이에 대하여 알고리즘에 부가적으로 요구되는 보완점에 대해 논한다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.8
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• pp.1-11
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• 2004

A comprehensive study has been made for the investigation of the convergence and stability characteristics of the LU scheme for solving the Navier-Stokes equations on unstructured meshes. For this purpose the characteristics of the LU scheme was initially studied for a scalar model equation. Then the analysis was extended to the Navier-Stokes equations. It was shown that the LU scheme has an inherent stiffness in the streamwise direction. This stiffness increases when the grid aspect ratio becomes high and the cell Reynolds number becomes small. It was also shown that the stiffness related to the grid aspect ratio can be effectively eliminated by performing proper subiteration. The results were validated for a flat-plate turbulent flow.

• Journal of Internet Computing and Services
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• v.6 no.1
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• pp.65-72
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• 2005

Flash memories are one of best media to support portable computers in mobile computing environment. The features of non-volatility, low power consumption. and fast access time for read operations are sufficient grounds to support flash memory as major database storage components of portable computers. However. we need to Improve traditional transaction management scheme due to the relatively slow characteristics of flash operation as compared to RAM memory. In order to achieve this goal. we devise a new scheme called flash-aware transaction management (FATM). FATM improves transaction performance by exploiting SRAM and W-Cache, We also propose a simulation model to show the performance of FATM. Based on the results of the performance evaluation, we conclude that FATM scheme outperforms the traditional scheme.

• The Journal of the Korea Contents Association
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• v.17 no.7
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• pp.538-545
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• 2017

Moisture evaporates, when concrete is exposed to fire, not only at concrete surface but also at inside the concrete to adjust the equilibrium and transfer properties of moisture. The equilibrium properties of moisture are described by means of water vapor sorption isotherms, which illustrate the hysteretical behavior of materials. In this paper, the prediction method of the moisture distribution inside the concrete members at fire is presented. Finite element method is employed to facilitate the moisture diffusion analysis for any position of member. And the moisture diffusivity model of high strength concrete by high temperature is proposed. To demonstrate the validity of this numerical procedure, the prediction by the proposed algorithm is compared with the test result of other researcher. The proposed algorithm shows a good agreement with the experimental results including the vaporization effect inside the concrete.

• Proceedings of the Korean DIstribution Association Conference
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• 2006.02a
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• pp.105-136
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• 2006

이 연구는 농협 하나로마트를 표본점포로 하여 슈퍼마켓의 점포성과에 미치는 영향요인을 규명하기 위한 것이다. 기존의 유통관련 선행연구가 소비자조사를 통한 점포선택이론 중심으로 접근하였다면, 본 연구는 소매공급 측면에서 접근했다는 점과 소매입지모델 뿐만 아니라 소매경영이론 측면에서 내적요인까지 아울러 접근함으로써 슈퍼마켓의 점포성과에 대한 영향관계를 종합적으로 접근하여 규명하고자 시도하였다는 점에서 그 의의를 갖는다. 본 연구의 접근은 슈퍼마켓 경영에서 환경요인인 외적요인과 역량요인인 내적요인에서 점포성과에 영향을 미칠 것으로 기대되는 다양한 변수들을 선정하고, 이 변수들에 대한 검증을 통해 슈퍼마켓의 점포성과에 미치는 영향관계를 분석하였다. 분석의 신뢰도와 설명력을 높이기 위하여 변수별, 요인별 접근을 시도하였으며, 대상점포의 설명력을 높이기 위하여 동업계 편균대비 비교분석과 도시와 농촌간의 입지유형별 특성과 차이점을 규명하고자 하였다. 연구결과 현실적 측면에서 채용가능한 결과를 도출할 수 있었다. 본 연구가 대형 슈퍼마켓이 향후 유망업태로 주목받고 있는 상황에서 농협 하나로마트를 표본으로 하여 슈퍼마켓의 점포성과에 영향을 미치는 요인을 규명하고자 하였으나, 향후 슈퍼마켓의 점포출점, 전략수립, 점포운영 등에서 실질적인 방향성을 제시할 수 있도록 연구가 보강되어야 할 것이며, 나아가 타 업태 및 업종에 일반화될 수 있도록 기대한다.

• The KIPS Transactions:PartD
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• v.11D no.7 s.96
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• pp.1459-1466
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• 2004

As the area of software application is increased. the software is becoming larger and more complex. In addition, development of the high quality software within the limits of the budget is strongly demanded. Many methodologies, such as software process improvement, object-ori-ented development, requirement-engineering, and software metrics have been introduced in the software development process in order to attain such objectives. Among those techniques. Requirements-Engineering gives basic guideline to develop high quality software. In other word. in order to develop high quality software, requirements should be elicited, and described. And with proper reviews and management. the quality of requirements can be improved. In this paper, quantitative measurement method that is based on IEEE Std-830-1998 for the require-ment-specifications is proposed.

• Water for future
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• v.29 no.5
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• pp.173-184
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• 1996

In this study, a two-dimensional shallow-water equation was used to develop the mathematical model for computing water levels and flow distribution. In the discretization equations, based on the finite volume method (FVM), the third order Runge-Kutta method and the third order upwind scheme were introduced to handle the unsteady and vconvective terms in the governing equations. To determine the accuracy of the developed model, it was applied to the rectangular horizontal channel in a frictionless flow. The water depth and velocity obtained by the numerical model were found to agree closely with the exact solution. The model was also applied to the rectangular channel with both the symmetric and the non symmetric constriction. The velocity distribution of the flow and the propagation of the flood wave were simulated and the results well described the flow characteristics.

• Korean Journal of Optics and Photonics
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• v.21 no.4
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• pp.139-145
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• 2010

A complete modeling of erbium-doped Bismuth-oxide fibers with a high doping concentration is presented. A 6-level amplifier system that incorporated clustering-induced concentration quenching, cooperative upconversion, pump excited state absorption (ESA), and signal ESA, was adopted for the modeling. The accuracy of the modeling was verified by comparing the calculated gain and noise figure with experimentally obtained ones.