• Bulletin of the Korean Chemical Society
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• 제35권1호
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• pp.45-50
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• 2014

A fully packed capillary electrochromatographic (CEC) microchip with an on-column micro-solid phase extraction (SPE) bed for the preconcentration and separation of organic analytes was prepared. A linear microchannel with monodisperse colloidal silica packing was formed on a cyclic olefinic copolymer microchip with two reservoirs on both ends. Silver-cemented silica packing frit structure was formed at the entrance of the microchannel by electroless plating treatment as a base layer. A gold coating was formed on it by reducing $Au^{3+}$ to gold with hydroxylamine. Finally micro-SPE bed was formed by self-assembly adsorption of 1-dodecanethiol on it. Micro-SPE beds were about 100-150 ${\mu}m$ long. Approximately $10^3$ fold sensitivity enhancements for Sulforhodamine B, and Fluorescein in nM concentration levels were possible with 80 s preconcentration. Basic extraction characteristics were studied.

• Steel and Composite Structures
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• 제51권2호
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• pp.173-183
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• 2024

This study investigates a new seismic retrofit system that utilizes rotational friction dampers and axial springs. The retrofit system involves a steel frame with rotational friction dampers (RFD) at beam-column joints and linear springs at the corners, providing energy dissipation and self-centering capabilities to existing structures. The axial spring acts as a self-centering mechanism that eliminates residual deformations, while the friction damper mitigates seismic damage. To evaluate the seismic performance of the proposed retrofit system, a series of cyclic loading tests were carried out on a steel beam-column subassembly equipped with the proposed devices. An analytical model was then developed to validate the experimental results. A performance point ratio (PPR) was presented to optimize the design parameters of the retrofit system, and a performance-based seismic design strategy was developed based on the PPR. The retrofit system's effectiveness and the presented performance-based design approach were evaluated through case study models, and the analysis results demonstrated that the developed retrofit system and the performance-based design procedure were effective in retrofitting structures for multi-level design objectives.

• Steel and Composite Structures
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• 제12권5호
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• pp.445-464
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• 2012

In order to evaluate the dynamic behavior of passive energy dissipation system, two steps need to be considered for prediction of structural response in the presence of ductile element in an off-centre bracing system. The first is a detailed analysis of the proposed ductile element and the second is the effect of this ductile element on an off-centre bracing system. The use of ductile bracing system is expanding in steel structures in order to increase the force reduction factor. Therefore, regarding the nonlinear behavior of steel material used in an off-centre bracing systems and using ductile element in OBS bracing systems, the seismic evaluation of the mentioned systems seems to be necessary. This paper aims to study linear and nonlinear behavior of steel frames with off-centre bracing system and ductile element, in order to get the best position of these bracing elements. To achieve this purpose, the modeling has been done with ANSYS software. The optimum eccentricity has been obtained by modeling three steel frames with different eccentricities and evaluating the results of them. The analytical results showed that the model OBS-C with 0.3 eccentricities has higher performance among the models.

• 한국정보과학회논문지:시스템및이론
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• 제32권11_12호
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• pp.692-704
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• 2005

컴퓨터 하드웨어의 급속한 발전으로 그래픽 프로세서 유닛(Graphics Processor Units : GPUs)은 굉장한 메모리 대역폭과 산술 능역을 보유하게 되어 범용 계산에 많이 활용되고 있으며, 특히 계산 집약적인 물리 기반 시뮬레이션(physics based simulation)의 GPU 구현이 활발하게 연구되고 있다. 물리 기반 시뮬레이션의 기본이 되는 미분방정식 풀이 과정에서 삼중대각행렬(tridiagonal matrix) 시스템은 유한차분(finite-difference) 근사에 의해서 자주 나타나는 선형시스템으로 물리 기반 시뮬레이션 관점에서 삼중대각행렬 시스템의 빠른 풀이는 중요한 연구 분야이다. 본 논문에서는 GPU에서 삼중대각행렬 시스템 풀이를 빠르게 구현할 수 있는 방법을 제안한다. 벡터 프로세서(vector processor) 계산에서 삼중대각행렬 시스템 풀이 방법으로 널리 사용되는 cyclic reduction 또는 odd-even reduction 알고리즘을 GPU에서 구현하였다. 본 논문에서 제안한 방법을 삼중대각행렬 시스템 풀이 방법으로 잘 알려져 있는 Thomas 방법과 GPU를 이용한 선형시스템 풀이에서 좋은 성과를 보이고 있는 conjugate gradient 방법과 비교할 때 상당한 성능 향상을 얻을 수 있었다. 또한, 열전도(heat conduction) 방정식, 이류 확산(advection-diffusion) 방정식, 얕은 물(shallow water) 방정식에 의한 물리 기반 시뮬레이션의 GPU 구현에 본 논문에서 제안한 방법을 사용하여 1024x1024 격자의 계산 영역에서 초당 35프레임 이상의 놀라운 성능을 보여주었다.

• 한국도로학회논문집
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• 제14권5호
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• pp.1-9
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• 2012

PURPOSES: A viscoelastic axisymmetric finite element analysis code has been developed for stress analysis of asphalt pavement structures. METHODS: Generalized Maxwell Model (GMM) and 4-node isoparametric element were employed for finite element formulation. The code was developed using $C^{+}^{+}$ computer program language and named as KICTPAVE. For the verification of the developed code, a structural model of a pavement system was constructed. The structural model was composed of three layers: asphalt layer, crushed stone layer, and soil subgrade. Two types of analysis were considered for the verification: (1)elastic static analysis, (2)viscoelastic time-dependent analysis. For the elastic static analysis, linear elastic material model was assigned to all the layers, and a static load was applied to the structural model. For the viscoelastic time-dependent analysis, GMM and linear elastic material model were assigned to the asphalt layer and all the other layers respectively, and a cyclic loading condition was applied to the structural model. RESULTS: The stresses and deformations from KICTPAVE were compared with those from ABAQUS. The analysis results obtained from the two codes showed good agreement in time-dependent response of the element under the loading area as well as the surface deformation of asphalt layer, and horizontal and vertical stresses along the axisymmetric axis. CONCLUSIONS: The validity of KICTPAVE was confirmed by showing the agreement of the analysis results from the two codes.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1999년도 가을 학술발표회 논문집
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• pp.387-394
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• 1999

Artificial Neural Network (ANN) is a computational model inspired by the structure and operations of the brain. It is massively parallel system consisting of a large number of highly interconnected and simple processing units. The purpose of this paper is to verify the applicability of ANN to predict experimental results through the use of measured experimental data. Although there have been accumulated data based on hysteretic characteristics of structural element with cyclic loading tests, it is difficult to directly apply them for the analysis of elastic and plastic response. Thus, simple models with mathematical formula such as Bi-Linear Model, Ramberg-Osgood Model, Degrading Tri Model, Takeda Model, Slip type Model, and etc, have been used. To verify the practicality and capability of this study, ANN is adapted to several models with mathematical formula using numerical data To show the efficiency of ANN in nonlinear analysis, it is important to determine the adequate input and output variables of hysteretic models and to minimize an error in ANN process. The application example is Beam-Column joint test using the ANN in modeling of the linear and nonlinear hysteretic behavior of structure.

• Structural Monitoring and Maintenance
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• 제7권4호
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• pp.319-344
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• 2020

Inverse analysis of non-linear reinforced concrete bridge pier using recursive Gaussian filtering for in-situ condition assessment is the main theme of this work. For this purpose, minimum variance unbiased estimation using unscented sigma points is adopted here. The uniqueness of this inverse analysis lies in its approach for strain based updating of engineering demand parameters, where appropriate bound and constrained conditions are introduced to ensure numerical stability and convergence. In this analysis, seismic input is also identified, which is an added advantage for the structures having no dedicated sensors for earthquake measurement. First, the proposed strategy is tested with a simulated example whose hysteretic properties are obtained from the slow-cyclic test of a frame to investigate its efficiency and accuracy. Finally, the experimental test data of a full-scale bridge pier is used to study its in-situ condition in terms of Park & Ang damage index. Overall the study shows the ability of the augmented minimum variance unbiased estimation based recursive time-marching algorithm for non-linear system identification with the aim to estimate the engineering damage parameters that are the fundamental information necessary for any future decision making for retrofitting/rehabilitation.

• 대한치과보철학회지
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• 제51권4호
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• pp.315-322
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• 2013

연구 목적: 내측연결형 임플란트와 지대주의 연결체에 반복하중을 부여하였을 때 수직 침하를 평가하고자 하였다. 연구 재료 및 방법: 외측연결형 임플란트와 내측연결형 임플란트에 세 종류의 시멘트유지형 지대주를 각각 장착하였다. 즉, 외측연결형 지대주(Ext 그룹), 내측연결형 1-piece 지대주(Int-1 그룹), 내측연결형 2-piece 지대주(Int-2 그룹)를 사용하였으며, 각 그룹마다 7개의 시편을 준비하였다. 임플란트-지대주 연결체에 수직하중을 적용하기 위하여 임플란트 받침대에 고정한 후, 4 Hz의 빈도로 $150{\pm}10N$의 반복하중을 가하였다. 수직침하량은 0, 5, 10, 50, 100, 1,000, 5,000, 10,000회의 반복하중 후에 각각 측정하였다. 반복측정분산분석(RM-ANOVA)를 이용하여 반복하중의 영향을 분석하였으며, 패턴변화를 관찰하기 위하여 선형혼합모형(linear mixed model)을 사용하였다. 유의수준은5% 로 설정하였다. 결과: 10,000회 반복하중 후 수직침하량은, Ext 그룹에서 $0.714{\pm}0.488{\mu}m$, Int-1그룹에서 $5.286{\pm}1.604{\mu}m$, Int-2 그룹에서 $11.429{\pm}1.902{\mu}m$를 나타내었다. 패턴분석에서는, Int-1 그룹 및 Int-2 그룹에서 지속적인 수직침하가 관찰되었으며, Ext그룹에서는 수직침하현상이 관찰되지 않았다. 결론:10,000회 반복하중 후의 선형혼합모형을 통한 분석에서, Ext그룹은 수직침하현상을 보이지 않았으나, Int-1 및 Int-2 그룹은 지속적인 수직침하현상을 나타내었다. 또한, Int-2그룹에서 Int-1그룹보다 더 많은 수직침하량이 관찰되었다.

• 공업화학
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• 제3권1호
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• pp.138-147
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• 1992

기능성 전극(chemically modified electrodes)을 이용한 전기촉매반응을 조사하였다. 고분자 지지체로서 음이온 교환이 가능한 poly-[1-methyl-3-(pyrrol-1-ylmethyl) pyridinium]을 사용하였는데 이는 정전류 방법으로 직접 전극표면에 중합시켰다. 전극표면에 코팅되는 필름의 두께는 중합시 전체 전하량으로 조절하였으며, SEM을 이용하여 두께를 측정하였고, 필름의 두께와 전하량과의 직선관계를 조사하였다. 전기촉매반응에 활성을 갖는 ferro/ferricyanide 이온은 빠른속도로 이온교환이 가능하였으며, 이온교환되는 양은 cyclic voltammetry 실험 결과 1.2~1.3M이었다. 필름내에 존재하는 ferro/ferricyanide 이온이 ascorbic acid 산화반응의 매개체임을 cyclic votammetry 실험을 통하여 알 수 있었고, RDE 실험을 통하여 반응속도론적 파라미터를 규명하였는데 본 실험의 조건에서 Saveant 등의 모델 중 ER+S에 해당됨을 알 수 있었다. 이상적인 모델인 R+S가 되기 위하여 기능성 전극이 갖추어야 할 조건을 제시하였다.

• 한국공간정보시스템학회:학술대회논문집
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• 한국공간정보시스템학회 2004년도 춘계 학술발표회 논문집 제1권1호(통권1호)
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• pp.279-286
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• 2004

An accumulated crack damage which propagates progressively with time was frequently observed on several engineering structures, This paper numerically demonstrates this damage process on large cooling tower shells under thermal and wind loads. Damage states under varying loads are investigated and the influence of this progressive damage process on the life-cycle of cooling towers discussed. The paper presents briefly some fundamentals of the geometrically and physically non-linear numerical analysis employed for reinforced concrete, especially concerning the models used for concrete, steel reinforcement and the bond between them. As a numerical example an existing cooling tower with noticeable meridian crack damage is analysed. The existing damage state of the cooling tower is determined by quasi-static analyses for temperature, hygric and cyclic wind leading. The change in the dynamical behaviour of the structure as mirrored in its natural frequencies and mode shapes is presented and discussed. Finally, the example shows that such damage processes develop progressively over the life-time of the structures.