• Journal of the Earthquake Engineering Society of Korea
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• v.5 no.6
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• pp.21-27
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• 2001

In this paper, a nonlinear finite element procedure is presented for the dynamic analysis of reinforced concrete shells. A computer program, named RCAHEST(reinforced concrete analysis in higher evaluation system technology), for the analysis of reinforced concrete structures was used. A 4-node flat shell element will drilling rotational stiffness is used for spatial discretization. The layered approach is used to discretize behavior of concrete and reinforcement through the thickness. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. The smeared crack approach is incorporated. Solution of the equations of motion is obtained by numerical integration using Hilber-Hughes-Taylor(HHT) algorithm. The proposed numerical method for the nonlinear dynamic analysis of reinforced concrete shells is verified by comparison with reliable analytical results.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.4
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• pp.353-367
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• 2003

This paper describes the extension of the numerical model, which was developed to simulate the nonlinear behavior of reinforced concrete (RC) structures subjected to monotonic in plane shear and introduced in the companion paper, to simulate effectively the behavior of RE structures under cyclic loadings. While maintaining all the basic assumptions adopted in defining the constitutive relations of concrete under monotonic loadings, a hysteretic stress strain relation of concrete, which across the tension compression region, is defined. In addition, unlike previous simplified stress strain relations, curved unloading and reloading branches inferred from the stress strain relation of steel considering the Bauschinger effect we used. The modifications of the stress strain relation of steel are also introduced to reflect pinching effect depending on the shear span ratio and an average stress distribution in a cracked RC element. Finally, correlation studies between analytical results and experimental studies are conducted to establish the validity of the proposed model.

• The Microorganisms and Industry
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• v.27 no.1
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• pp.2-17
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• 2001

Cyclomaltodextrinase(CDase, EC 3.2.1.54), maltogenic amylase(EC 3.2.1.133). neopullulanase(EC 3.2.1.135)는 cyclomaltodextrin(CD), pullulan 및 전분을 가수분해하는 효소들이다. 이 효소들은 $\alpha$-1,4-Ο-glycosidic 결합에 작용하여 CD와 전분을 말토오스로 pullulan을 panose로 가수분해할 뿐만 아니라 올리고당들을 다양한 당 수용체 분자들의 C-3, C-4. C-6 수산기로 전이시키는 활성도 갖고 있다. 이러한 특성들은 기존의 $\alpha$-amylase를 비롯한 판수화물 분해효소들과 뚜렷이 구별되는 것으로 전분 분해효소들의 분류체계에 새로운 기준점을 제시한다고 하겠다. 본 총설에서는 CDase, maltogenic amylase, neopullulanase처럼 pullulan이나 전분보다 CD를 훨씬 더 잘 분해하는 효소들과 Thermoactinomyces vulgaris amylase II(TVA II)처럼 CD를 분해하기는 하나 pullulan을 더 잘 분해하는 효소들의 생화학적, 효소적, 구조적 특성들을 종합하여 소개하고자 하였다. 이 효소들은 40~60% 정도로 아미노산 서열이 동일하고, 세포 내에 존재하며, 분자량이 62~90 kDa로 $\alpha$-amylase보다 다소 크다. 아미노산 서열 비교분석 및 maltogenic amylase와 TVA II 등의 3차구조 분석 결과, 이 효소들은 아미노 말단에 보통 $\alpha$-amylase에는 존재하지 않는 약 130개 아미노산으로된 영역을 갖고 있어 이를 매개로 이합체를 형성할 수 있는 것으로 나타났다. 이합체-단위체 평형은 염 농도, 효소 농도, 산도 등에 의해 조절되고 단위체와 이합체 모두 효소환성을 갖고 있으나, 기질 특이성이 다르며 단위체는 전분을, 이합체는 CD를 선호하는데 이는 이합체 형성 시 활성부위의 구조적 변화에 따른 것으로 분석되었다. 본 총설에서는 CD 분해효소들의 다양한 기질 특이성을 올리고머 형성 등의 구조적 특성과 관련하여 논함으로써 관련 효소들의 분류체계를 보다 명확히 할 수 있는 자료를 제공하고자 하였으며, 이러한 효소들의 생리적 기능 및 산업적 이용에 대해 제안하고자 하였다.

• Applied Chemistry for Engineering
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• v.31 no.2
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• pp.215-219
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• 2020

In this study, nanoporous iron oxide layers were fabricated by the anodization of 304 series stainless steel. K₂HPO₄/glycerol solution was used as an electrolyte for anodization. We investigated the anodization behavior according to various parameters such as electrolyte concentration, reaction temperature, applied voltage, and reaction time. As a result of anodization, we confirmed that the anodic growth rate of oxide layer on 304 series stainless steel increased with increasing the electrolyte temperature and applied potential. In order to form well-ordered porous nanostructures, the electrolyte temperature was at 160 ℃, and the applied potential was at 30 V in 10 wt% K₂HPO₄/glycerol electrolyte.

• Journal of the Korean Chemical Society
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• v.63 no.2
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• pp.73-77
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• 2019

We compared methodologies based on the density functional theory (DFT), e.g., time-dependent DFT (TD-DFT), TD-DFT within Tamm-Dancoff approximation (TDA-DFT), and spin-unrestricted DFT (UDFT), that are usually employed to optimize the geometries of ${\pi}$-conjugated molecules in their lowest lying triplet excited ($T_1$) state. As a model system for ${\pi}$-conjugated molecules, we employed 1,2,3,4,5-pentacyano-6-phenyl-benzene. In conjunction with 6-31G(d) basis sets, we made use of gap-tuned range-separated ${\omega}B97X$ functional which is often employed recently in the calculations of molecular excited states. Near the equilibrium geometries, we found that the important difference between the geometries derived at UDFT level and those at TD-DFT or TDA-DFT methods: more stable ground-state energies but higher triplet excitation energies for UDFT derived geometries. In the studies, we discuss such differences in more detail.

• Journal of the Korean Electrochemical Society
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• v.24 no.1
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• pp.7-12
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• 2021

In this study, we investigated the formation of the metal oxide nanostructure by anodization of aluminum 3104H18 alloy. The anodization was performed in pyrophosphoric acid (H4P2O7) electrolyte. By the control of anodization condition such as concentration of electrolyte, anodization temperature and applied voltage, nanoporous or nanofiber structures were obtained. The optimal anodization condition to form nanofiber structures are 75 wt% of H4P2O7 at 30 V and 20℃. When anodization was performed at over 40 V, nanoporous structures were formed due to accelerated dissolution reaction rate of nanofiber structures or increasing thickness of channel wall.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.8A
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• pp.1417-1427
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• 2001

본 논문에서는 밀리미터파를 이용하여 사용자에게 양방향 무선 멀티미디어의 구현을 가능케 하는 LMDS 송수신 모듈을 설계, 구현하였다. 제작된 LMDS 송수신 모듈은 신서사이져, 혼합기, 저잡음 증폭기, 고출력 증폭기, 듀플렉서 등으로 구성하였으며, 전체적으로는 전원부와 제어부를 통하여 이상여부를 감시하며, 송수신 모듈에 이상이 발생했을 때 이를 보호할 수 있도록 구현하였다. 여기서 DAVIC 표준에 맞도록 IF부 대역은 0.95∼1.45GHz의 500MHz 대역폭에서 동작하도록 제작하였고, 상하향 혼합기는 격리도 특성을 최대화하였으며, 이를 위해 하이브리드 링형을 이용한 다이오드 평형 구조를 적용하여 설계하였다. 혼합기로 주입되는 Local 주파수는 안정도가 높아야 함으로 유전체 공진형 발진기로 구현하였다. 또한 저잡음 증폭기와 고출력 증폭기는 정보통신부에서 공고한 3사 주파수 대역을 모두 수용할 수 있도록 24GHz∼26.5GHz의 대역에서 정상적인 동작을 할 수 있도록 설계하였으며, 특히 저잡음 증폭기는 잡음 환경에서 작은 신호를 손실 없이 얻을 수 있도록 잡음지수를 최소화하고, 30dB 이상의 충분한 이득이 구현되도록 하였다. 고출력 증폭기는 15dBm 이상의 출력을 송신하면서도 선형성에 문제가 없도록 혼변조왜곡(IMD) 특성을 고려하여 설계하였다. 그리고 듀플렉서는 우수한 주파수 선택도와 낮은 삽입손실 특성을 갖도록 송수신 필터 모두 5개의 공진기를 포함한 Chebyshev형 구조를 갖으며 생산성이 뛰어난 모노리딕형으로 구현하여, LMDS 송수신 성능을 구현하였다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.3
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• pp.275-281
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• 2011

When a flat bar type metal specimen for general tension test is subject to incremental uniaxial tension, a narrow plastic shear band, so called luders band, is generated at some instance. This band typically has an angle to the axis of specimen and many early researches have been done to investigate the condition and angle of this localized deformation phenomenon by many researchers. This study follows the procedure of Thomas(1961) under plane stress boundary condition. $J_2$ plasticity theory, balance of linear momentum, and constitutive equations are used to derive the angle of luders band under plain strain boundary condition. The result was confirmed by other angle based on acoustic tensor theory.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.1
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• pp.93-103
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• 1994

Two beam/column elements are developed in order to analyze the geometric nonlinear plane irames including the effects of internal hinge and transverse shear deformation. In the case of the first element (finite segment method), tangent stiffness matrix is derived by directly integrating the equilibrium equations whereas in the case of the second element (finite element method) elastic and goemetric stiffness matrices are calculated by using the hermitian polynomials including the effects of internal hinge and shear deformation as the shape function. Numerical results are presented for the selected test problems which demonstrate that both elements represent reliable and highly accurate tools.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.3
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• pp.305-319
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• 2000

Numerical solution lot frictional contact problems of nonlinearly deformable bodies having large deformation is presented. The contact conditions on the possible contact points are expressed by using the contact error vector, and the iterative scheme is used to reduce the contact error vector monotonically toward zero. At each iteration the solution consists of two steps : The first step is to revise the contact force by using the contact error vector given by the previous geometry, and the second step is to compute the displacement and the contact error vector by solving the equilibrium equation with the contact force given at the first step. Convergence of the iterative scheme to the correct solution is analyzed, and the numerical simulations we performed with a rigid-plastic membrane and a nonlinear elastic beam.