• 대한수학회지
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• 제48권4호
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• pp.669-689
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• 2011

The notion of quasi-Einstein manifolds arose during the study of exact solutions of the Einstein field equations as well as during considerations of quasi-umbilical hypersurfaces. For instance, the Robertson-Walker spacetimes are quasi-Einstein manifolds. The object of the present paper is to study Lorentzian quasi-Einstein manifolds. Some basic geometric properties of such a manifold are obtained. The applications of Lorentzian quasi-Einstein manifolds to the general relativity and cosmology are investigated. Theories of gravitational collapse and models of Supernova explosions [5] are based on a relativistic fluid model for the star. In the theories of galaxy formation, relativistic fluid models have been used in order to describe the evolution of perturbations of the baryon and radiation components of the cosmic medium [32]. Theories of the structure and stability of neutron stars assume that the medium can be treated as a relativistic perfectly conducting magneto fluid. Theories of relativistic stars (which would be models for supermassive stars) are also based on relativistic fluid models. The problem of accretion onto a neutron star or a black hole is usually set in the framework of relativistic fluid models. Among others it is shown that a quasi-Einstein spacetime represents perfect fluid spacetime model in cosmology and consequently such a spacetime determines the final phase in the evolution of the universe. Finally the existence of such manifolds is ensured by several examples constructed from various well known geometric structures.

• Smart Structures and Systems
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• 제15권6호
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• pp.1569-1582
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• 2015

Two hyperbolic displacement models are used for the bending response of simply-supported orthotropic laminated composite plates resting on two-parameter elastic foundations under mechanical loading. The models contain hyperbolic expressions to account for the parabolic distributions of transverse shear stresses and to satisfy the zero shear-stress conditions at the top and bottom surfaces of the plates. The present theory takes into account not only the transverse shear strains, but also their parabolic variation across the plate thickness and requires no shear correction coefficients in computing the shear stresses. The governing equations are derived and their closed-form solutions are obtained. The accuracy of the models presented is demonstrated by comparing the results obtained with solutions of other theories models given in the literature. It is found that the theories proposed can predict the bending analysis of cross-ply laminated composite plates resting on elastic foundations rather accurately. The effects of Winkler and Pasternak foundation parameters, transverse shear deformations, plate aspect ratio, and side-to-thickness ratio on deflections and stresses are investigated.

• 대한물리치료과학회지
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• 제2권2호
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• pp.517-531
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• 1995

This article reviews the concepts of motor ability and motor skill and the models, theories, and treatment approaches of motor contorl. Reflex, hierarchical, and systems models of motor control are discussed. And muscle reeducation, neurodevelopment, motor relearning program, and contemporary task-oriented approach is also discussed. We consider that the concept of motor control is being changed and the treatment approach also is being changed. There are a number of reasons, the first is traditional trteatment approach has limitation. Second is theories of motor control is contineously developed. Third is new approach is coming to us. therefore, the therapists shoulder strive for acquisition of motor skill and motor ability. This article hope the successful integration of models and treatment approaches and its application in physical therapy practice.

• 산업경영시스템학회지
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• 제10권16호
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• pp.173-182
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• 1987

Motivation models based on the Psychology have contributed to Predict and understand individual behaviors. During the many period, a various type of motivation models have been experimented by the researchers(i.e., need theory that is the first theory in motivation and equity theory, expectancy theory, reinforcement theory, and goal-setting theory centered on cognitive mechanisms). This article's objectives is to analyze motivation models mentioned above in the point of cognitive views (cognitive processes and cognitive mechanisms). Accordingly, the article's structure is consisted of five parts as follows. Part 1. Introduction. Part 2. The theoritical backgrounds of motivation. Part 3. The major theories of motivation. Part 4. The cognitive analysis of motivation theories. Part 5. Conclusion.

• 한국과학교육학회지
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• 제25권6호
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• pp.698-709
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• 2005

When modeling students' conceptual understanding, there are several different frameworks, among which are the alternative conception framework and the mental model framework, which converge to suggest a form of knowledge representation. However, little research has explained how they are different from each other and from memory. The purpose of this study was to develop a new mental model theory that integrates the different terminologies and their background theories, which refer to students' ideas not only in science education, but also in other research areas. For this purpose, at first, we compared different terminologies including alternative conception, p-prim, and mental models, and the underlying theories used for representing students' ideas in learning science. Through such comparison, we tried to find the relationship among them. We reviewed related literature and synthesized the results from both cognitive science (related research areas) and science education approaches, especially, Vosniadou's mental model theory. Based on reviewing previous studies, we have developed a preliminary mental model theory 'an integrated theoretical structure of mental models'. We applied the new mental model theory to interpret data on students' ideas about circular motion from our previous research. We expect our new mental model theory will help us understand how students form their own ideas in science from an integrated perspective.

• Advances in nano research
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• 제7권4호
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• pp.265-275
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• 2019

In this work, the effect of size on the axial buckling behavior of single-layered graphene sheets embedded in elastic media is studied. We incorporate Eringen's nonlocal elasticity equations into three plate theories of first order shear deformation theory, higher order shear deformation theory, and classical plate theory. The surrounding elastic media are simulated using Pasternak and Winkler foundation models and their differences are evaluated. The results obtained from different nonlocal plate theories include the values of Winkler and Pasternak modulus parameters, mode numbers, nonlocal parameter, and side lengths of square SLGSs. We show here that axial buckling behavior strongly depends on modulus and nonlocal parameters, which have different values for different mode numbers and side lengths. In addition, we show that in different nonlocal plate theories, nonlocality is more influential in first order shear deformation theory, especially in certain range of nonlocal parameters.

• 보건교육건강증진학회지
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• 제27권2호
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• pp.141-149
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• 2010

Objectives: This paper aims to compare the intervention development steps of the revised PRECEDE-PROCEED model and the Intervention Mapping model. Methods: Concepts and structure of the intervention development step of each model are reviewed with examples. Results: The revised PRECEDE-PROCEED model and the Intervention Mapping model share characteristics in intervention development in employing PRECEDE assessments, applying a social ecological framework and behavior theories for intervention building, emphasizing multi-interventions at multiple levels, and involving stakeholders and existing resources in intervention development. A detailed explanation of the intervention alignment and matrix building is provided with illustration of examples. Conclusion: Intervention development should not be done compartmentally but in line with other steps in a planning model to sustain the program logic. For successful application of planning models for intervention development, solid understanding of the models and behavior theories are required. Multisectoral collaboration is also critical for the successful application.

• Smart Structures and Systems
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• 제13권4호
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• pp.659-683
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• 2014

The static analysis of structures with arbitrary cross-section geometry and material lamination via a refined one-dimensional (1D) approach is presented in this paper. Higher-order 1D models with a variable order of expansion for the displacement field are developed on the basis of Carrera Unified Formulation (CUF). Classical Euler-Bernoulli and Timoshenko beam theories are obtained as particular cases of the first-order model. Numerical results of displacement, strain and stress are provided by using the finite element method (FEM) along the longitudinal direction for different configurations in excellent agreement with three-dimensional (3D) finite element solutions. In particular, a layered thin-walled cylinder is considered as first assessment with a laminated conventional cross-section. An atherosclerotic plaque is introduced as a typical structure with arbitrary cross-section geometry and studied for both the homogeneous and nonhomogeneous material cases through the 1D variable kinematic models. The analyses highlight limitations of classical beam theories and the importance of higher-order terms in accurately detecting in-plane cross-section deformation without introducing additional numerical problems. Comparisons with 3D finite element solutions prove that 1D CUF provides remarkable three-dimensional accuracy in the analysis of even short and nonhomogeneous structures with arbitrary geometry through a significant reduction in computational cost.

• International Journal of Aeronautical and Space Sciences
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• 제13권4호
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• pp.458-467
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• 2012

In this study, the linear viscoelastic response of a rectangular laminated plate is investigated. The viscoelastic properties, expressed by two basic spring-dashpot models, that is Kelvin and Maxwell models, is assumed in the range to investigate the influence of viscoelastic coefficients to mechanical behavior. In the present study, viscoelastic responses are performed for two popular equivalent single-layered theories, such as the first-order shear deformation theory (FSDT) and third-order shear deformation theory (TSDT). Compliance and relaxation modulus of time-dependent viscoelastic behavior are approximately determined by Prony series. The constitutive equation for linear viscoelastic material as the Boltzmann superposition integral equation is simplified by the convolution theorem of Laplace transformation to avoid direct time integration as well as to improve both accuracy and computational efficiency. The viscoelastic responses of composite laminates in the real time domain are obtained by applying the inverse Laplace transformation. The numerical results of viscoelastic phenomena such as creep, cyclic creep and recovery creep are presented.

• 동의생리병리학회지
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• 제27권5호
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• pp.540-552
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• 2013

This study focuses on discussing several issues that we encounter when we 'modernize' the fundamental theories of Korean Medicine(KM): It is pertinent to set the boundaries of the "fundamental theories" of the KM. The boundaries can be set based on: a) setting the medicine and the philosophy of medicine apart and b) re-evaluating the traditional theories of KM based on the needs of the modern practitioners of KM. The fundamental theories of KM should focus on how effectively they can observe, explain, and predict the clinical cases. The clinical cases and observations should not be distorted in order to satisfy the theory. "The modernization of KM" can be defined as the change in traditional medicine to fit the needs of the contemporary world, while not losing the focus and the nature of the KM. The fundamental theories of KM will play a key role in modernizing the KM, as the focus and the inherent nature of the KM comes from these fundamental theories. The modernization of the fundamental theories of KM will be crucial to both possible models of future healthcare system-the plural healthcare system, or the western medicine-centric integrated healthcare system. The modernization will also help in advancing the future medical studies. The key to modernization of the fundamental theories of the KM is in translating the key terms of KM in modern light. As a solution, this study suggests paying attention to the 'scientific metaphors', and especially to the 'theory-constitute metaphors' among those. More in-depth studies need to be done on these.