• Title, Summary, Keyword: generalized gradients

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Oxygen Potential Gradient Induced Degradation of Oxides

  • Martin, Manfred
    • Journal of the Korean Ceramic Society
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    • v.49 no.1
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    • pp.29-36
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    • 2012
  • In many applications of functional oxides originally homogeneous materials are exposed to gradients in the chemical potential of oxygen. Prominent examples are solid oxide fuel cells (SOFCs) or oxygen permeation membranes (OPMs). Other thermodynamic potential gradients are gradients of electrical potential, temperature or uni-axial pressure. The applied gradients act as generalized thermodynamic forces and induce directed fluxes of the mobile components. These fluxes may lead to three basic degradation phenomena of the materials, which are kinetic demixing, kinetic decomposition, and morphological instabilities.

Buckling analysis of FGM Euler-Bernoulli nano-beams with 3D-varying properties based on consistent couple-stress theory

  • Hadi, Amin;Nejad, Mohammad Zamani;Rastgoo, Abbas;Hosseini, Mohammad
    • Steel and Composite Structures
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    • v.26 no.6
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    • pp.663-672
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    • 2018
  • This paper contains a consistent couple-stress theory to capture size effects in Euler-Bernoulli nano-beams made of three-directional functionally graded materials (TDFGMs). These models can degenerate into the classical models if the material length scale parameter is taken to be zero. In this theory, the couple-stress tensor is skew-symmetric and energy conjugate to the skew-symmetric part of the rotation gradients as the curvature tensor. The material properties except Poisson's ratio are assumed to be graded in all three axial, thickness and width directions, which it can vary according to an arbitrary function. The governing equations are obtained using the concept of minimum potential energy. Generalized differential quadrature method (GDQM) is used to solve the governing equations for various boundary conditions to obtain the natural frequencies of TDFG nano-beam. At the end, some numerical results are performed to investigate some effective parameter on buckling load. In this theory the couple-stress tensor is skew-symmetric and energy conjugate to the skew-symmetric part of the rotation gradients as the curvature tensor.

ON NONSMOOTH OPTIMALITY THEOREMS FOR ROBUST OPTIMIZATION PROBLEMS

  • Lee, Gue Myung;Son, Pham Tien
    • Bulletin of the Korean Mathematical Society
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    • v.51 no.1
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    • pp.287-301
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    • 2014
  • In this paper, we prove a necessary optimality theorem for a nonsmooth optimization problem in the face of data uncertainty, which is called a robust optimization problem. Recently, the robust optimization problems have been intensively studied by many authors. Moreover, we give examples showing that the convexity of the uncertain sets and the concavity of the constraint functions are essential in the optimality theorem. We present an example illustrating that our main assumptions in the optimality theorem can be weakened.

Consistent couple-stress theory for free vibration analysis of Euler-Bernoulli nano-beams made of arbitrary bi-directional functionally graded materials

  • Nejad, Mohammad Zamani;Hadi, Amin;Farajpour, Ali
    • Structural Engineering and Mechanics
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    • v.63 no.2
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    • pp.161-169
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    • 2017
  • In this paper, using consistent couple stress theory and Hamilton's principle, the free vibration analysis of Euler-Bernoulli nano-beams made of bi-directional functionally graded materials (BDFGMs) with small scale effects are investigated. To the best of the researchers' knowledge, in the literature, there is no study carried out into consistent couple-stress theory for free vibration analysis of BDFGM nanostructures with arbitrary functions. In addition, in order to obtain small scale effects, the consistent couple-stress theory is also applied. These models can degenerate into the classical models if the material length scale parameter is taken to be zero. In this theory, the couple-tensor is skew-symmetric by adopting the skew-symmetric part of the rotation gradients as the curvature tensor. The material properties except Poisson's ratio are assumed to be graded in both axial and thickness directions, which it can vary according to an arbitrary function. The governing equations are obtained using the concept of Hamilton principle. Generalized differential quadrature method (GDQM) is used to solve the governing equations for various boundary conditions to obtain the natural frequencies of BDFG nano-beam. At the end, some numerical results are presented to study the effects of material length scale parameter, and inhomogeneity constant on natural frequency.

A Generalized Model for Homogenized Reflectors

  • Pogosbekyan, Leonid;Kim, Yeong-Il;Kim, Young-Jin;Joo, Hyung-Kook
    • Proceedings of the Korean Nuclear Society Conference
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    • pp.40-45
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    • 1996
  • A new concept of equivalent homogenization is proposed. The concept employs new set of homogenized parameters: homogenized cross sections (XS) and interface matrix (IM), which relates partial currents at the celt interfaces. The idea of interface matrix generalizes the idea of discontinuity factors (DFs), proposed and developed by K.Koebke and K.Smith. The method of K.Smith can be simulated within framework of new method, while the new method approximates heterogeneous cell better in case of the steep flux gradients at the cell interfaces. The attractive shapes of new concept are: improved accuracy, simplicity of incorporation in the existing codes, equal numerical expenses in comparison to the K.Smith's approach. The new concept is useful for: (a) explicit reflector/baffle simulation; (b) control blades simulation; (c) mixed UO2/MOX core simulation, The offered model has been incorporated in the finite difference code and in the nodal code PANBOX. The numerical results show good accuracy of core calculations and insensitivity of homogenized parameters with respect to in- core conditions.

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Simulation of the gas exchange process for single-cylinder 4-stroke cycle spark ignition engine (단기통 4사이클 스파아크 점화기관 흡.배기 과정의 시뮬레이션)

  • 윤건식;유병철
    • Journal of the korean Society of Automotive Engineers
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    • v.7 no.1
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    • pp.24-34
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    • 1985
  • The study of unsteady gas exchange processes in the inlet and exhaust systems of the single-cylinder 4-stroke cycle spark ignition engine is presented in this paper. The generalized method of characteristics including friction, heat transfer, change of flow area and entropy gradients was used for solving the equations defining the gas exchange process. The path line calculation was also conducted to allow for calculation of the gas composition and entropy change along the path lines, and of the variable specific heat due to the change of temperature and composition. As the result of the simulation, the properties at each point in the inlet and exhaust pipe, pressure and temperature in the cylinder, and charging efficiency were obtained. Pumping loss and residual gas fraction were also computed. The effect of engine speed, exhaust and inlet pipe length on the pumping loss and charging efficiency were studied showing that the results were in agreement with what has been known from experiments.

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Simulation of the single-cylinder 2-stroke cycle compression ignition engine (단기통 2사이클 압축점화기관의 시뮬레이션)

  • 유병철;김정순
    • Journal of the korean Society of Automotive Engineers
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    • v.8 no.1
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    • pp.62-74
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    • 1986
  • The simulation of power cycle and unsteady gas exchange processes in the inlet and exhaust systems of the single-cylinder 2-stroke cycle compression ignition engine was studied in this paper. In power cycle process, the single-zone model proposed by Whitehouse and Way was used, and the convective and radiative heat transfer from cylinder contents to surroundings was considered. To solve the equations for gas exchange process, the generalized method of characteristics including area change, friction, heat transfer and entropy gradients was used. Also with the path line calculation, the entropy change along the path line and the variation of specific heat due to the change of temperature and the composition of cylinder gas were considered. As a result of the simulation, the change of pressure and temperature in the cylinder against the crank angle, the rate of net heat release, and the change of properties at each point in the inlet and exhaust pipe against the crank angle were obtained. The engine performances under various operating conditions were also calculated.

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NUMERICAL SIMULATION OF HIGH-SPEED FLOWS WITH SHOCK WAVE TURBULENT BOUNDARY LAYER INTERACTIONS (충격파와 난류경계층의 상호작용에 대한 수치해석)

  • Moon S. Y.;Sohn C. H.
    • 한국전산유체공학회:학술대회논문집
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    • pp.51-59
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    • 2000
  • The Interactions of shock wave with turbulent boundary layers in high-speed flows cause complex flowfields which result in increased adverse pressure gradients, skin friction and temperature. Accurate and reliable prediction of such phenomena is needed in designing high-speed propulsion systems. Such analyses of the complex flowfields require sophisticated numerical scheme that can resolve interactions between shock wave and boundary layers accurately. Therefore the purpose of the present. article is to introduce an accurate and efficient mixed explicit-implicit generalized Galerkin finite element method. To demonstrate the validity of the theory and numerical procedure, several benchmark cases are investigated.

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Invasion of Ambrosia artemisiifolia L. (Compositae) in the Ukrainian Carpathians Mts. and the Transcarpathian Plain (Central Europe)

  • Song, Jong-Suk;Prots, Bohdan
    • Animal cells and systems
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    • v.2 no.2
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    • pp.209-216
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    • 1998
  • The invasion of Ambrosia artemisiifolia in the Ukrainian Carpathians Mts. and the Transcarpathian Plain in Central Europe was reconstructed on the basis of floristic records. The first spontaneous occurrence was dated from the beginning of the 1940s. Within the next 55 year period, the distributional spread speed of the species was of 67.6 $km^2/y$ (by the average data). The occupied area by A. artemisiifolia in the range of the studied areas is about $3716.5km^2$ now. The features of behavior of the invader and the habitat preference were determined. The frequency of occurrence by sociologic-ecological classification was carried out. The generalized model of correlations among the gravitation, the active temperature sum and the disturbance gradients and the frequency of occurrence of the species was presented. The scheme of the invasion stages of A. artemisiifolia is reflected in the population status changes of the species during the areal dynamics.

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Gaussian Response Curves Fitting for Ecology Data (생태학 자료에 대한 가우시안 반응곡선 적합)

  • Jeong, Hyeong Chul
    • Journal of the Korean Data Analysis Society
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    • v.20 no.5
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    • pp.2307-2318
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    • 2018
  • In this study, the Gaussian response regression and Gaussian logistics regression to describe the species occurrence along the environmental gradients is considered. In ecology, the occurrence of species is generally influenced by environmental variables and follows the Gaussian curve form. Using Gaussian curves, optimal environmental conditions, tolerance of environmental factors, peak abundance or peak abundance probability can be estimated for the expression of the species. In this study, Poisson regression or logistic regression analysis, which is a generalized linear model, is used to estimate the Gaussian curve. These models are applied to the spider data of Aart, Smeenk (1975) and the occurrence of the spider, the probability of occurrence of the spider are estimated on the environmental gradients. However, it is not possible to estimate the Gaussian curve unless the species abundance is followed by a uni-modal distribution. In this study, the univariate Gaussian response curve estimation is limited by the analysis with one environmental variable.