• 산업기술연구
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• 제27권A호
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• pp.47-53
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• 2007

A theoretical model based on Rayleigh-Ritz method is proposed to predict the resonance frequency of a W/T(Wind Turbine) tower structure supported by guy cables. In order to verify the validity of the theoretical model, a reduced W/T tower system is manufactured and tested. Frequency response and mode data are determined by modal testing and finite element analysis is performed to calculate the natural frequency of the tower model. Numerical and experimental results are compared with those by the theoretical analysis. Parametric study by the theoretical model shows how the cable tension and cable elasticity influence the resonance frequency of the W/T tower structure. Finally, vibration response under various rotating speed is investigated to examine the possibility of severe resonance.

• Steel and Composite Structures
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• 제24권4호
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• pp.383-390
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• 2017

This paper highlights the experimental and numerical investigations performed on a tubular T-joint fabricated from circular hollow sections under axial compressive loads applied at the brace. Tests were performed on a reference joint and the joint wrapped with Carbon Fiber Reinforced Polymer (CFRP). The Nitowrap EP carbon fiber with Nitowrap 410 resin serve as a composite material is used for wrapping the T-joint. Schematic diagram of the fabricated tubular joint for the experimental test setup, along with the experimental and numerical results are presented. After performing these experiments, it has been demonstrated that the joint wrapped with CFRP has a better strength and lesser deflection than a reference joint. Finite element analysis carried out in Ansys reveals that the results were in good correlation with the experimental values.

• 전자통신동향분석
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• 제31권5호
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• pp.99-109
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• 2016

IETF Path Computation Element(PCE) 그룹에서는 데이터 전송을 위한 전달 경로를 찾는 엔진 기능을 중심으로 표준화를 진행하고 있다. 망의 상태, 위상, 자원 가용성, 정책을 기반으로 최적의 자원을 할당하는 경로 계산 기능과 구조, 프로토콜 등을 정의하는데 MPLS/GMPLS 망의 제어 평면 프로토콜 기반 전송을 위주로 출발하여 광, 회선 망에서의 적용과 서비스 표준이 실제 사례를 뒷받침하여 발전되었고 현재는 데이터 센터 네트워크, SDN, IoT 분야에서의 활용이 활발하게 논의되고 있다. 본고에서는 경로 계산 기능의 분산을 주요 목적으로 하여 이제는 범용의 전달망 관리 분야로 확대 적용되는 추세의 active stateful PCE와 Traffic Engineering Database (TED), Label Switched Path DB(LSP-DB), PCE Protocol(PCEP) 등을 포함한 관련 표준 현황을 살펴보고 향후 통합 전달망 제어 관리 진화 방향을 소개하고자 한다.

• Structural Engineering and Mechanics
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• 제29권1호
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• pp.77-89
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• 2008

Presence of high degree of orthotropy enhances shear lag phenomenon in laminated composite box-beams and it persists till failure. In this paper three key parameters governing shear lag behavior of laminated composite box beams are identified and defined by simple expressions. Uniqueness of the identified key parameters is proved with the help of finite element method (FEM) based studies. In addition to this, for the sake of generalization of prediction of shear lag effect in symmetrical laminated composite box beams a feed forward back propagation neural network (BPNN) model is developed. The network is trained and tested using the data base generated by extensive FEM studies carried out for various b/D, b/tF, tF/tW and laminate configurations. An optimum network architecture has been established which can effectively learn the pattern. Computational efficiency of the developed ANN makes it suitable for use in optimum design of laminated composite box-beams.

• Steel and Composite Structures
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• 제16권6호
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• pp.611-637
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• 2014

A single plate shear connection, or shear tab, is a very popular shear connection due to its merit in ease of construction and material economy. However, problems in understanding the connection behavior, both in terms of strength and ductility, have been well-documented. Suggestions or design model for single plate connections in AISC Design Manual have been altered several times, with the latest edition settling down to giving designers pre-calculated design strength tables if the connection details agree with given configurations. Results from many full-scale tests and finite element models in the past suggest that shear strength of a bolt group in single plate shear connections might be affected by yield strength of plate material; therefore, this research was aimed to investigate and clarify effects of plate yield strength and thickness on shear strength of the bolt group in the connections, including the validity of using a plate thickness/bolt diameter ratio ($t_p/d_b$) in design, by using finite element models. More than 20 models have been created by using ABAQUS program with 19.0- and 22.2-mm A325N bolts and A36 and Gr.50 plates with various thicknesses. Results demonstrated that increase of plate thickness or plate yield strength, with the $t_p/d_b$ ratio remained intact, could significantly reduce shear strength of the bolt group in the connection as much as 15 percent. Results also confirmed that the $t_p/d_b$ ratio is a valid indicator to be used for guaranteeing strength sufficiency. Because the actual ratio recommended by AISC Design Manual is $t_p/d_b$ + 1.6 (mm) for connections with a number of bolts less than six and plate yield strength in construction is normally higher than the nominal value used in design, it is proposed that shear strength of a bolt group in single plate connections with a number of bolts equal or greater than seven be reduced by 15 percent and the $t_p/d_b$ ratio be limited to 0.500.

• 한국생물공학회:학술대회논문집
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• 한국생물공학회 2002년도 생물공학의 동향 (X)
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• pp.257-260
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• 2002

Dissolved oxygen level of cell culture media has a critical effect on cellular metabolism, which governs specific productivity of recombinant proteins and mammalian cell growth However, in the cores of cell aggregates or cell-immobilized beads, oxygen level frequently goes below a critical level. Mammalian cells have a number of genes induced in the lower level of oxygen, and the genes contain a common cis-acting element (-RCGTG-), hypoxia response element (HRE). By binding of hypoxia inducible factor-l (HIF-I) to the HRE, promoters of hypoxia inducible genes are activated, which is a survival mechanism. In this work, to develop a CHO cell capable of producing recombinant proteins in immobilization and high density cell culture efficiently, mammalian expression vectors containing human tissue-type plasminogen activator (t-PA) gene controlled by HRE were constructed and stably transfected into the CHO cells. In $Ba^{2+}$ -alginate immobilization culture, CHO/pCl/dhfr/2HRE-t-PA cells produced 2 folds higher recombinant t-PA activity than CHO/pCl/dhfrlt-PA cells without $CoCl_2$ treatment. Furthermore, in repeated fed batch culture, productivity of t-PA in immobilized CHO/pCI/dhfr/2HRE-t-PA cells was 121 ng/ml/day, total production of 0.968 mg/day at 11 days culture while CHO/pCIIdhfrlt-PA cells was 22.8 ng/ml/day. All these results indicate that HRE is very useful for the enhancement of protein productivity in mammalian cell cultures.

• 전자공학회논문지SC
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• 제44권4호통권316호
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• pp.55-60
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• 2007

3.0 T 이상의 고자장 MRI의 경우 특히 body 영상에서는 전자기파의 특성상 피촬영체 내부의 자장 불균일도가 매우 심하여 부분적으로 SAR(Specific Absorption Ratio)가 인체 허용치 이상으로 높아지는 경우가 있다. 본 연구에서는 3.0 T Body MRI에서 이와 같은 문제점을 극복하기 위한 병렬전송 고주파 코일 (parallel-transmission radio frequency coil)의 element 구조와 동작 방법을 최적화하고 FDTD 시뮬레이션을 통하여 유용성을 검증토록 하였다. 이를 위해 3가지 형태의 전송 고주파 코일 element에 대하여 여러 가지 parameter를 실험 및 시뮬레이션을 통해 비교하였으며 각각의 element에 독립적으로 공급되는 고주파 펄스는 코일 내부의 피촬영체에 적절한 자장의 크기와 초소의 SAR를 가지면서 자장의 균일도를 향상시키는 방향으로 최적화하였다. 예로 3.0 T Body MRI에서 $25cm{\times}8cm$ 코일 요소를 12 채널로 구성하는 방식의 경우 최적화 이전에는 70% 이상의 자장의 불균일도를 보인 반면 최적화 후에는 26% 이하로 개선시킬 수 있었다. 따라서 본 연구에선 제안된 코일구조는 (초)고자장 MRI에도 유용하게 적용될 것으로 판단된다.

• 대한지구과학교육학회지
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• 제15권2호
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• pp.224-234
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• 2022

이 연구의 목적은 2022년부터 국정 발행체제에서 검정 발행체제로 전환되는 초등학교 과학과 교과용도서의 창의·융합 활동에 나타난 STEAM 요소와 융합유형을 분석하고자 하였다. 이 연구를 위해 창의·융합 활동이 제시된 6종의 초등학교 과학 3~4학년 교과서를 선정하여 각 출판사별, 학년-학기별, 과학 분야별로 창의·융합 활동에 나타난 STEAM 요소를 분석하고 각 출판사별로 융합유형을 분석하였다. 이 연구의 결과는 다음과 같다. 첫째, 교과서의 창의·융합 활동에 나타난 STEAM 요소의 전체 빈도와 각 요소별 비율이 출판사별로 다르게 나타났다. 그러나 모든 출판사에서 과학(S) 요소를 제외한 나머지 4개의 요소 중 예술(A) 요소의 비율이 높고, 수학(M) 요소의 비율이 매우 낮은 경향은 공통적으로 나타났다. 둘째, 전체적으로 융합된 STEAM 요소의 수가 많을수록 교과서에 나타나는 비율은 낮았고, STEAM 요소의 융합유형 비율은 출판사 마다 다르게 나타났다. 셋째, 매 학년-학기별로 예술(A) 요소, 기술(T), 공학(E) 요소의 비율 편차는 크지 않았으나 수학(M) 요소의 비율 편차는 크게 나타났다. 넷째, '운동과 에너지'와 '물질' 분야에는 기술(T)과 공학(E) 요소가 많이 나타난 반면 '지구와 우주', '생명', 그리고 '통합' 분야에는 예술(A) 요소가 매우 많이 나타났다.

• 대한기계학회논문집A
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• 제27권7호
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• pp.1159-1169
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• 2003

This paper investigates the effects of T-stress and plastic hardening mismatch on the interfacial crack-tip stress field via finite element analyses. Plane strain elastic-plastic crack-tip fields are modeled with both MBL formulation and a full SEC specimen under pure bending. Modified Prandtl slip line fields illustrate the effects of T-stress on crack-tip constraint in homogeneous material. Compressive T-stress substantially reduces the interfacial crack-tip constraint, but increases the J-contribution by lower hardening material, J$\_$L/. For bimaterials with two elastic-plastic materials, increasing plastic hardening mismatch increases both crack-tip stress constraint in the lower hardening material and J$\_$L/. The fracture toughness for bimaterial joints would consequently be much lower than that of lower hardening homogeneous material. The implication of unbalanced J-integral in bimaterials is also discussed.

• 대한기계학회논문집A
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• 제30권8호
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• pp.873-879
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• 2006

To investigate applicability of the reference stress approach as simplified inelastic stress analysis to estimate local creep rupture, detailed finite element stress analyses of a T-piece pipe with different inner pressure and system loading levels are performed. The reference stresses are obtained from the finite element (FE) limit analysis based on elastic-perfectly-plastic materials, from which the local reference stress for creep rupture is determined from R5. The resulting inelastic stresses are compared with elastic stresses resulting from linear elastic FE calculations. Furthermore they are also compared with the stresses from full elastic-creep FE analyses. It shows that the stresses estimated from the reference stress approach compare well with those from full elastic-creep FE analysis, which are significantly lower than the elastic stress results. Considering time and efforts for full inelastic creep analysis of structures, the reference stress approach is shown to be a powerful tool for creep rupture estimates and also to reduce conservatism of elastic stress analysis significantly.