• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.2
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• pp.123-130
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• 2015

This paper presents a new formulation for transient simulations of microwave propagation in heterogeneous unbounded domains. In particular, perfectly-matched-layers(PMLs) are introduced to allow for wave absorption at artificial boundaries used to truncate the infinite extent of the physical domains. The development of the electromagnetic PML targets the application to engineering mechanics problems such as structural health monitoring and inverse medium problems. To formulate the PML for plane electromagnetic waves, a complex coordinate transformation is introduced to Maxwell's equations in the frequency-domain. Then the PML-endowed partial differential equations(PDEs) for transient electromagnetic waves are recovered by the application of the inverse Fourier transform to the frequency-domain equations. A mixed finite element method is employed to solve the time-domain PDEs for electric and magnetic fields in the PML-truncated domain. Numerical results are presented for plane microwaves propagating through concrete structures, and the accuracy of solutions is investigated by a series of error analyses.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.3
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• pp.1053-1058
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• 2010

Infinite element approach has been widely used to analysis soil-structure interaction, in which the soil domain is treated as infinite domain. However, most of the developed infinite element has been formulated in the frequency domain rather than the time domain to include the frequency contents of the earthquake or vibration wave. Due to that, those approaches have a critical limitation which is restricted to the linear elastic analysis. To main objective of this research is to develop the infinite element in the time domain to cooperate the inelastic soil and structure behavior. Developed infinite element is verified with the results of finite element analysis modeled in large domain. The nonlinear analysis also conducted to demonstrate the application of developed infinite element. Hence, based on above-mentioned statements, it can be concluded that the propose approach would assist for structure-seismic design.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.4
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• pp.81-87
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• 2003

In this paper, the feasibility of using Shannon's sampling theorem to reconstruct exact mode shapes of a structural system from a limited number of sensor points and localizing damage in that structure with reconstructed mode shapes is investigated. Shannon's sampling theorem for the time domain is reviewed. The theorem is then extended to the spatial domain. To verify the usefulness of extended theorem, mode shapes of a simple beam are reconstructed from a limited amount of data and the reconstructed mode shapes are compared to the exact mode shapes. On the basis of the results, a simple rule is proposed for the optimal placement of accelerometers in modal parameter extraction experiments. Practicality of the proposed rule and the extended Shannon's theorem is demonstrated by detecting damage in laboratory beam structure with two-span via applying to mode shapes of pre and post damage states.

• Journal of the Korean BIBLIA Society for library and Information Science
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• v.27 no.3
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• pp.25-50
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• 2016

Archives and Records Management Studies is being developed its own independent domains. However, the existing library classification scheme such as the KDC don't properly reflect the characteristics of Archives and Records Management Studies. This classification scheme has the irrational part of the arrangement of the subject items and should be required to rearrange subdivision of the subject areas. In this study, According to the characteristics of Archives and Records Management Studies, It is set up 8 subject areas, Records Management (General), the law and polices of records management, the collection and appraisal of the records, the documentary organization, recording information services, preservation of the records, archives management, archives and records center, etc. After analyzing the major contemporary library classification system such as KDC, DDC, NDC, UDC, LCC, then It is suggested that improvement measures through analyzing classification status and keywords of the Archives and Records Management data contained in Korean National Bibliography. In Archives and records management studies, The contents of the eight subject areas related to the field are changed to allow integration with KDC 028.

• Journal of Science Education
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• v.32 no.1
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• pp.19-32
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• 2008

The purpose of this study was to identify the influence of using the concept cartoons about middle school students' science attitude in the lessons on water cycle unit. For the purpose, they were developed to the learning program with concept cartoon and the instrument for the science attitude which has four categories; attitudes about science, attitudes about science subject, learning motives for science subject, and scientific attitudes. The research method was designed to quasi-experimental design. The concept cartoon was provided to the experimental group during nine lessons. Before and after the lessons in all two groups, the pre-post tests with the instrument were performed. The results from twice t-tests were shown that the domain of learning motives for science subject was only improved. From these, it were indicated that the concept cartoon was not effective all areas in science attitude, therefore the use in science lessons need to be restricted within narrow purpose.

• Journal of the Korean Society of Radiology
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• v.12 no.2
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• pp.193-199
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• 2018

In this research, 15 patients were diagnosed with 1.5T and 3.0T MRI instruments (Philips, Medical System, Achieva) to minize Ferromagnetic artifact and find the optimized Tesla. Based on the theory that the 3.0T, when compared to 1.5T, show relatively high signal-to-ratio(SNR), Scan time can be shortened or adjust the image resolution. However, when using the 3.0T MRI instruments, various artifact due to the magnetic field difference can degrade the diagnostic information. For the analysis condition, area of interest is set at the background of the T1, T2 sagittal image followed by evaluation of L3, L4, L5 SNR, length of 3 parts with Ferromagnetic artifact, and Histogram. The validity evaluation was performed by using the independent t test. As a result, for the SNR evaluation, mere difference in value was observed for L3 between 1.5T and 3.0T, while big differences were observed for both L4, and L5(p<0.05). Shorter length was observed for the 1.5T when observing 3 parts with Ferromagnetic artifact, thus we can conclude that 3.0T can provide more information on about peripheral tissue diagnostic information(p<0.05). Finally, 1.5T showed higher counts values for the Histogram evaluation(p<0.05). As a result, when we have compared the 1.5T and 3.0T with SNR, length of Ferromagnetic artifact, Histogram, we believe that using a Low Tesla for Spine MRI test can achieve the optimal image information for patients with disk operation like PLIF, etc. in the past.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05b
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• pp.148-153
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• 1998

핵연료 피복관용 신합금을 개발하기 위한 기초연구로서 Zr-xNb계 합금과, Zr-0.8Sn-xNb계 합금을 각각 4종씩 선정하였다. 이들 합금을 판재시편으로 가공한 뒤 Autoclave를 이용하여 36$0^{\circ}C$에서 부식 시험을 실시하였다. 부식과정에서 생성되는 산화막의 미세구조를 관찰하기 위해 천이 전 영역에서 동일두께를 갖도록 부식시편을 준비하여 산화막/금속계면에 대해 SEM관찰을 실시하였다. 또한 석출물의 크기와 부식과의 관계를 조사하기 위하여 부식전의 시편에 대해 TEM관찰을 실시하였다. Zr-xNb 2원계 합금에서는 Nb함량이 적을수록 부식저항성이 증가하는 경향을 보이는데, 0.2Nb가 첨가된 합금이 가장 우수한 부식저항성을 보였다. Zr-0.8Sn-xNb 3원계에서도 천이 전 영역에서는 2원계 합금과 마찬가지로 Nb함량이 적을수록 부식저항성이 증가하나, 천이 후 영역에서는 이런 경향이 바뀌는 것이 관찰되었다. 이는 Sn이 첨가됨으로서 Nb가 부식에 미치는 영향이 달라지기 때문이라 생각된다. 산화막 관찰결과, 순수 Zr은 결정립계를 따라서 산화막이 급격히 성장하는 반면에, Zircaloy-4합금은 매우 균일한 산화막 계면을 유지한다. Zr-xNb계 합금과 Zr-0.8Sn-xNb계 합금에서도 내식성이 우수한 합금은 균일한 산화막/금속 계면을 유지하는 것이 관찰되었다.

• Journal of the Korean Ceramic Society
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• v.38 no.4
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• pp.360-364
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• 2001

고상반응법(solid-state reaction)으로 산화물 초전도체 Bi$_{2+x}$ Sr$_{1.8}$ $CaCu_2$$O_{8+\delta}$(-0.2$\leq$x$\leq$0.2)을 제조하여 조성변화에 따른 산소량과 Bi 이온의 하전가(valence)가 구조변조의 주기에 미치는 영향을 조사하였다. 2212상의 단일상 고용한계는 -0.1$\leq$x$\leq$0.1 영역이었다. 이 영역에서 x의 증가에 따라 격자상수 c는 감소를 보이며, 온셋 임계온도 Tc$^{on}$ 과 산소량은 증가하는 경향을 보였다. 또한, Bi 이온의 하전기와 구조변조의 주기는 단일상 고용한계 영역 내에서 x의 증가에 따라 감소하는 경향을 보이고 있다. 구조변조의 주기는 산소량이 증가함에 따라 감소하고 Bi 이온의 하전가 증가에 따라 증가함을 보였다. 즉, 산소의 절대량과 Bi 이온의 하전가에 따라 구조변조의 주기가 변화하는 것을 알 수 있었다.

• 한국정보교육학회:학술대회논문집
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• 2008.01a
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• pp.192-197
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• 2008

초등학교 수학과 도형 학습은 매우 추상적인 분야로 직관적인 이해를 돕기 위해 다양한 구체적인 조작이 요구되는데, 그 중에서 컴퓨터를 활용한 도형 학습은 학생들의 구체물을 이용한 학습의 한계를 극복할 수 있는 장점이 있다. 특히 Flex와 Flash를 이용하면 입체도형의 가상물의 제작 및 동적인 학습은 물론 사용상의 제약이 적어 시,공간의 한계를 극복할 수 있다. 본 연구에서는 초등학교 수학과 제 7차 교육과정의 입체도형 영역을 분석하여 학습요소를 추출하고 플래시의 드로잉 메서드를 바탕으로 학습요소별로 속성과 메서드를 정의하고 클래스를 설계하여 입체도형 객체를 생성하고 플렉스의 컴포넌트로 구성된 학습 어플리케이션의 틀을 설계하여 입체도형 객체가 플렉스의 어플리케이션 내에서 사용이 가능하도록 설계 개발하였다. 본 연구가 갖는 의의는 첫째, 초등학교 수학과 수준에 맞는 속성과 메서드를 갖도록 개발한 입체도형 객체를 활용하여 학습자의 입체도형에 자유로운 탐구활동 기회를 제공하여 보다 직관적이고 구체적으로 도형학습을 할 수 있도록 돕는다. 둘째, 플렉스를 활용함으로서 학습자의 쉬운 접근을 돕고 학습 어플리케이션 틀을 활용하여 기존에 개발되어 있는 수학과 플래시 파일들을 활용한 다른 수학과 영역의 학습 어플리케이션 설계 및 개발의 시간과 노력을 단축시키는데 있다.

• Proceeding of EDISON Challenge
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• 2013.04a
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• pp.403-408
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• 2013

본 논문은 EDISON_CFD를 이용하여 관상동맥 분지관에서 점도에 따른 유체의 유동현상에 관하여 연구를 하였다. 뉴턴유체인 물의 점성계수 일때와 비뉴턴유체인 혈액의 Carreau model에서의 영전단율 점성계수(${\eta}_0$)와 무한전단율 점성계수(${\eta}_{\infty}$)일 때의 유동현상을 살펴보았다. 그 결과 점도가 증가할수록 재순환 영역에서 유체의 속도가 감소하였고 CF 및 CP값이 감소하는 구간의 수가 증가하여 벽면의 저전단응력으로 인해 생기는 재순환영역의 수가 증가하는 것으로 나타났다.