• 대한수학회보
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• 제50권2호
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• pp.353-373
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• 2013

In this paper, a class of delayed predator-prey models of prey migration and predator switching is considered. By analyzing the associated characteristic transcendental equation, its linear stability is investigated and Hopf bifurcation is demonstrated. Some explicit formulae for determining the stability and the direction of the Hopf bifurcation periodic solutions bifurcating from Hopf bifurcations are obtained by using the normal form theory and center manifold theory. Some numerical simulations for justifying the theoretical analysis are also provided. Finally, biological explanations and main conclusions are given.

• 한국가스학회:학술대회논문집
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• 한국가스학회 2005년도 추계학술발표회 논문집
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• pp.49-58
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• 2005

화학공장의 취약점을 파악하여 안전성을 경제적으로 확보할 수 있는 대안에 대한 설비별 안전투자비용과 그에 따른 편익을 산출하고, 분석함으로써 경제적인 안전 투자 대안을 사업주에게 제시함으로써 안전투자 의사결정의 기초자료로 활용하도록 한다. 이를 통하여 화학공장의 안전 활동 및 안전 투자의 효율성을 증진시키고 안전성 향상을 위한 화학공장의 안전투자가치를 정립하기 위함이다.

• Asia pacific journal of information systems
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• 제13권2호
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• pp.87-104
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• 2003

Though much attention has been paid to offer various multimedia services by many online service providers, the study on consumer behavior of online information service users are yet to be further explored in various aspects. This study develops a mathematical model for analyzing online consumer's usage patterns, contrasted to the existing media selection theory and flow concept about usage behavior of information services. We demonstrated using some case examples that online information consumption can be viewed not only as a cognitive behavior interacting with online media, but also as an economically rational behavior depending on consumer's perceived cost and time spending. The results obtained in this paper will surely serve as a theoretical foundation for justifying the consumer's behavior and WTP (willingness to pay) for various online contents consumption empirically.

• 대한기계학회논문집A
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• 제33권11호
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• pp.1239-1243
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• 2009

To evaluate the structural integrity of the nuclear seismic category penetration cooling water pump under the seismic service conditions the seismic analysis was performed in accordance with IEEE-STD-344 code. The finite element computer program, ANSYS, Version 10.0, is used to perform both a mode frequency analysis and an equivalent static seismic analysis of the pump assembly. The mode frequency analysis results show the fundamental natural frequency is greater than 33 Hz and does not exist in seismic range, thus justifying the use of the static analysis. The stresses resulted from various loadings and their combinations are within the allowable limits specified in the above mentioned IEEE code. The results of the seismic evaluation fully satisfied the structural acceptance criteria of the IEEE code. Accordingly the structural integrity on the pump assembly was proved.

• Animal cells and systems
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• 제2권4호
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• pp.451-454
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• 1998

Gulgastrura reticulosa, first described by Yosii (1966) as a monotypic new genus from a Korean limestone cave, was reviewed for its systematic position by c1adistic analysis of morphological characteristics, investigation of its intermaulting period and reproductive cycle as well as allozyme and 18S rDNA analysis. The great extent of divergence was strongly suggested by its combined lack of sensory organs (third antennal organ, postantennal organ, eyes, pseudocelli) with simultaneous development of an 'apical organ'at the tip of the antennae. The obvious divergence from any existing Collembola families was additionally supported by the extremely prolonged intermoulting period as well as by the low strap value it showed with Onychiuridae as obtained by 18S DNA sequence analysis. All these were considered Justifying the creation of a new family, Gulgastruridae, but still revealing more allied to Onychiuvidae rather than to Hypogastruridae.

• 한국콘텐츠학회:학술대회논문집
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• 한국콘텐츠학회 2005년도 추계 종합학술대회 논문집
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• pp.284-288
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• 2005

인터넷 원격교육이 보편화되어 가고 있는 현시점에서 인터넷 원격교육의 교육적 효과에 대한 검증은 매우 필요한 연구 대상이라고 할 수 있다. 면대면 교육이 아닌 인터넷원격교육의 문제점에 대한 분석은 교육적 효과에 대한 검증에서 반드시 거쳐야하는 중요성을 내포하고 있다. 본 연구는 인터넷 원격교육에 참가한 학생들을 대상으로 한 설문을 바탕으로 문제점에 대한 분석을 실시하였다. 문제점을 환경적문제, 학생자신의 문제, 교수설계문제, 운영상의문제의 4가지 카타고리로 구분하고 카타고리별 문제점들을 도출하여 설문을 통해 문제의 심각도를 분석하였다. 또한 각 문제들의 성별, 직업유무, 나이에 따른 차이 유무를 통계적 방법론을 통하여 검증하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 B
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• pp.569-571
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• 1998

In this paper, a new method of conrolling chaotic nonlinear systems is proposed. Firstly, the dynamics of a chaotic nonlinear system is separated into a linear part and a nonlinear part. Secondly, the nonlinear part is approximated using a radial basis function network (RBFN) and canceled from the controlled system. Then, the resulting system has only the linear part added with very weak nonlinearity. Finally, a simple linear state feedback control law is designed for the linear part. In the meanwhile, a theorem justifying this concept is presented and proved. Comparing with the feedback linearization, the proposed method can be applied regardless of the functional form of the controlled dynamics. The proposed method is applied by simulation to the Duffing system and the Lorenz system and satisfactory results are obtained.

• Structural Engineering and Mechanics
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• 제53권6호
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• pp.1167-1182
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• 2015

In this study, the stresses and electric potential redistributions of a cylinder made from functionally graded piezoelectric material (FGPM) are investigated. All the mechanical, thermal and piezoelectric properties are modeled as power-law distribution of volume fraction. Using the coupled electro-thermo-mechanical relations, strain-displacement relations, Maxwell and equilibrium equations are obtained including the time dependent creep strains. Creep strains are time, temperature and stress dependent, the closed form solution cannot be found for this constitutive differential equation. A semi-analytical method in conjunction with the Mendelson method of successive approximation is therefore proposed for this analysis. Similar to the radial stress histories, electric potentials increase with time, because the latter is induced by the former during creep deformation of the cylinder, justifying industrial application of such a material as efficient actuators and sensors.

• Computers and Concrete
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• 제16권5호
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• pp.683-701
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• 2015

When approached using nonlinear finite element (FE) techniques, structural analyses generate, for real RC structures, large complex numerical problems. Damage is a major part of concrete behavior, and the discretization technique is critical to limiting the size of the problem. Based on previous work, the ${\mu}$ damage model has been designed to activate the various damage effects correlated with monotonic and cyclic loading, including unilateral effects. Assumptions are formulated to simplify constitutive relationships while still allowing for a correct description of the main nonlinear effects. After presenting classical 2D finite element applications on structural elements, an enhanced simplified FE description including a damage description and based on the use of multi-fiber beam elements is provided. Improvements to this description are introduced both to prevent dependency on mesh size as damage evolves and to take into account specific phenomena (permanent strains and damping, steel-concrete debonding). Applications on RC structures subjected to cyclic loads are discussed, and results lead to justifying the various concepts and assumptions explained.

• 산업경영시스템학회지
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• 제13권21호
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• pp.73-79
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• 1990

The quality and cost of manufacturing products is a significant problem in view of duality assurance, but the quality level of the incoming materials is not considered to determine in the economic order quantity of conservative inventory model. A typical situation we face is the difference of quantity between order quantity and the determined outgoing quantity after acceptance inspection. In this paper we present a procedure to reduce the difference of order(ingoing) quantity and outgoing quantity of incoming materials a method of justifying the acceptance plans whether accept or not by comparing with ingoing outgoing quality.