• Title/Summary/Keyword: theoretical models

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Modeling of the Tensile Strength of Unsaturated Granular Soil Using Soil-water Characteristic Curve (흙-수분 특성 곡선을 이용한 불포화모래의 인장강도 모델링)

  • Kim Tae-Hyung;Kim Chan-Kee;Kim Tae-Hoon
    • Journal of the Korean Geotechnical Society
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    • v.20 no.7
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    • pp.171-181
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    • 2004
  • This study was conducted to explore the tensile strength models in granular soil at the full range of unsaturated state. Direct tension experiments were carried out with a newly developed direct tension technique. The measured experimental data were compared with theoretical models developed by Rumpf and Schubert for monosized ideal particulate solids at the unsaturated state. To do this, the soil-water characteristic curve obtained from a suction-saturation experiment was used to define the unsaturation state and the negative pore water pressure with different water content levels, which are important factors in theoretical tensile strength models. The nonlinear behavior of the tensile strength for unsaturated granular soil at the pendular state is appropriately simulated with Rumpf's model. For the funicular and capillary states, the predicted trend by Schubert's model is properly matched with the experimental data: tensile strength steadily increases and reaches a maximum value and then decreases until it reaches zero. This comparison supports the concept that the tensile strength of unsaturated real granular soil can be approximately simulated with theoretical models.

Structural Alignment: Conceptual Implications and Limitations (구조적 정렬: 개념적 시사점과 한계)

  • Lee Tae-Yeon
    • Korean Journal of Cognitive Science
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    • v.17 no.1
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    • pp.53-74
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    • 2006
  • Similarity has been considered as one of basic concepts of cognitive psychology which is useful for explaining cognitive structure and process. MDS models(Shepard, 1964; Nosofsky, 1991) and Contrast model(Tversky, 1977) were proposed as early models of similarity comparison process. But, there have been a lot of theoretical doubts about the conceptual validity of similarity as a result of empirical findings which could not be explained by early models. Goldstone(1994) assumed that similarity could be defined by alignment processes, and suggested structural alignment as a prospective alternative for solving conceptual controversies so far. In this study, basic assumption and algorithms of MDS models(Shepard, 1944; Nosofsky, 1991) and Contrast model(Tversky, 1977) were described shortly and some theoretical limitations such as arbitrariness of selective attention and correlated structures were discussed as well. The conceptual characteristics and algorithms of SIAM(Goldstone, 1994) were described and how it has been applied to cognitive psychology areas such as categorization, conceptual combination, and analogical reasoning were reviewed. Finally, some theoretical limitations related with data-driven processing and alternative processing and possible directions for structural alignment were discussed.

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Quasi-Likelihood Approach for Linear Models with Censored Data

  • Ha, Il-Do;Cho, Geon-Ho
    • Journal of the Korean Data and Information Science Society
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    • v.9 no.2
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    • pp.219-225
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    • 1998
  • The parameters in linear models with censored normal responses are usually estimated by the iterative maximum likelihood and least square methods. However, the iterative least square method is simple but hardly has theoretical justification, and the iterative maximum likelihood estimating equations are complicatedly derived. In this paper, we justify these methods via Wedderburn (1974)'s quasi-likelihood approach. This provides an explicit justification for the iterative least square method and also directly the iterative maximum likelihood method for estimating the regression coefficients.

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GRAVITATIONAL LENSING AND THE GEOMETRY OF THE UNIVERSE

  • Park, Myeong-Gu
    • Publications of The Korean Astronomical Society
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    • v.7 no.1
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    • pp.79-87
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    • 1992
  • New and improved data on the gravitational lens systems discovered so far are compared with the theoretical predictions of Gott, Park, and Lee (1989, GPL). Systems lensed by a single galaxy, compatible with assumptions of GPL, support flat or near-flat geometry for the universe. But the statistical uncertainty is too large to draw any definite conclusion. We need more lens systems. Also, the probability of multiple image lensing and mean separation of the images averaged over the source distribution are calculated for various cosmological models. Multiple-image lens systems and radio ring systems are compared with the predictions. Although the data reject exotic cosmological models, it cannot discriminate among conventional Friedmann models yet.

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Assessment of Slip Factor Models at Off-Design Condition (탈설계 조건에서의 미끄럼 계수 모텔들의 평가)

  • Yoon, Sung-Ho;Baek, Je-Hyun
    • Proceedings of the KSME Conference
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    • 2000.11b
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    • pp.410-415
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    • 2000
  • Slip factor is defined as an empirical factor being multiplied to theoretical energy transfer for the estimation of real work input of a centrifugal compressor. Researchers have tried to develop a simple empirical model, for a century, to predict a slip factor. However most these models were developed on the condition of design point assuming inviscid flow. So these models often fail to predict a correct slip factor at off-design condition. In this study, we summarized various slip factor models and compared these models with experimental and numerical data at off-design condition. As a result of this study, Wiesner's and Paeng and Chung's models are applicable for radial impeller, but all the models are not suitable for backswept impeller. Finally, the essential avenues for future study is discussed.

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Potational Viscous Damping of On-substrate Micromirrors (기판에 인접한 미소거울의 회전 점성감쇠)

  • Kim, Eung-Sam;Han, Ki-Ho;Cho, Young-Ho;Kim, Moon-Uhn
    • The Transactions of the Korean Institute of Electrical Engineers C
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    • v.50 no.5
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    • pp.243-248
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    • 2001
  • In this paper, we present theoretical and experimental study on the viscous damping of the on-substrate torsional micromirrors, oscillating near the silicon substrates. In this theoretical study, we develop theoretical models and test structures for the viscous damping of the on-substrate torsional micromirrors. From a finite element analysis, we estimate the theoretical damping coefficients of the torsional micromirrors. From a finite element analysis, we estimate the theoretical damping coefficients of the torsional micromirrors, fabricated by the surface-micromaching process. From the electrostatic test of the fabricated devices, frequency-dependent rotationalvelocity of the micromirrors has been measured at the atmospheric pressure using devices, frequency-dependent rotational velocity of the micromirrors has been measured at the atmospheric pressure using the Mach-Zehnder interferometer system. Experimental damping coefficients have been extracted from the least square fit of the measured rotational velocity within the filter bandwidth of 150 kHz. We have compared the theoretical values and the experimental results on the dynamic performance of the micromirrors. The theoretical analysis overstimates the resonant frequency in the amount of 15%, while underestimating the viscous damping in the factors of 10%.

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Theoretical Stiffness of Cracked Reinforced Concrete Elements (철근콘크리트 부재의 균열 후 강성 이론)

  • 김장훈
    • Journal of the Korea Concrete Institute
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    • v.11 no.5
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    • pp.79-88
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    • 1999
  • The purpose of this paper is to develop a mathematical expression for computing crack angles based on reinforcement volumes in the longitudinal and transverse directions, member end-fixity and length-to-width aspect ratio. For this a reinforced concrete beam-column element is assumed to possess a series of potential crack planes represented by a number of differential truss elements. Depending on the boundary condition, a constant angle truss or a variable angle truss is employed to model the cracked structural concrete member. The truss models are then analyzed using the virtual work method of analysis to relate forces and deformations. Rigorous and simplified solution schemes are presented. An equation to estimate the theoretical crack angle is derived by considering the energy minimization on the virtual work done over both the shear and flexural components the energy minimization on the virtual work done over both the shear and flexural components of truss models. The crack angle in this study is defined as the steepest one among fan-shaped angles measured from the longitudinal axis of the member to the diagonal crack. The theoretical crack angle predictions are validated against experimentally observed crack angle reported by previous researchers in the literature. Good agreement between theory and experiment is obtained.

Behavioral Symptoms in Nursing Home Residents with Dementia: Developing a Nursing Practice Model

  • Kim, Hyo Jeong
    • Korean Journal of Adult Nursing
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    • v.18 no.3
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    • pp.488-499
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    • 2006
  • Purpose: Behavioral symptoms in dementia (BSD) are one of the most disturbing behaviors to caregivers and a major reason for nursing home placement. Behavioral symptoms are often treated with psychotropic drugs (PD), however, the effect of such drugs for the frail elderly dementia patient is not certain because of their critical adverse effects. Theoretical model applicable to nursing practice for BSD in nursing homes, which is essential in guiding and evaluating such interventions, is absent. This article presents the process of developing a theoretical model of BSD in nursing homes. Method: Using Walker and Avants' theory synthesis method, three behavior models and two system models were incorporated into the proposed model to provide the theoretical and analytical explanation of the relationships between PD usage, its determinants, and BSD. Results: Resident variables and nursing home variables related to the two focal concepts (i.e., PD usage and BSD) were identified. Resident variables include demographical characteristics such as age and gender, and dementia-compromised functions such as cognitive and functional impairment. Nursing home variables include facility characteristics such as ownership type and size, and physical and psychosocial environment. Conclusion: The proposed model suggests that fulfillment of resident unmet needs through improvement of physical and psychosocial environment may produce better health outcomes of nursing home residents with BSD. Assessment and intervening environmental triggers of such behaviors are also suggested to be prior to the PD usage.

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Crack detection in rectangular plate by electromechanical impedance method: modeling and experiment

  • Rajabi, Mehdi;Shamshirsaz, Mahnaz;Naraghi, Mahyar
    • Smart Structures and Systems
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    • v.19 no.4
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    • pp.361-369
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    • 2017
  • Electromechanical impedance method as an efficient tool in Structural Health Monitoring (SHM) utilizes the electromechanical impedance of piezoelectric materials which is directly related to the mechanical impedance of the host structure and will be affected by damages. In this paper, electromechanical impedance of piezoelectric patches attached to simply support rectangular plate is determined theoretically and experimentally in order to detect damage. A pairs of piezoelectric wafer active sensor (PWAS) patches are used on top and bottom of an aluminum plate to generate pure bending. The analytical model and experiments are carried out both for undamaged and damaged plates. To validate theoretical models, the electromechanical impedances of PWAS for undamaged and damaged plate using theoretical models are compared with those obtained experimentally. Both theoretical and experimental results demonstrate that by crack generation and intensifying this crack, natural frequency of structure decreases. Finally, in order to evaluate damage severity, damage metrics such as Root Mean Square Deviation (RMSD), Mean Absolute Percentage Deviation (MAPD), and Correlation Coefficient Deviation (CCD) are used based on experimental results. The results show that generation of crack and crack depth increasing can be detectable by CCD.

Design and behaviour of double skin composite beams with novel enhanced C-channels

  • Yan, Jia-Bao;Guan, Huining;Wang, Tao
    • Steel and Composite Structures
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    • v.37 no.5
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    • pp.517-532
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    • 2020
  • This paper firstly developed a new type of Double Skin Composite (DSC) beams using novel enhanced C-channels (ECs). The shear behaviour of novel ECs was firstly studied through two push-out tests. Eleven full-scale DSC beams with ECs (DSCB-ECs) were tested under four-point loading to study their ultimate strength behaviours, and the studied parameters were thickness of steel faceplate, spacing of ECs, shear span, and strength of concrete core. Test results showed that all the DSCB-ECs failed in flexure-governed mode, which confirmed the effective bonding of ECs. The working mechanisms of DSCB-ECs with different parameters were reported, analysed and discussed. The load-deflection (or strain) behaviour of DSCB-ECs were also detailed reported. The effects of studied parameters on ultimate strength behaviour of DSCB-ECs have been discussed and analysed. Including the experimental studies, this paper also developed theoretical models to predict the initial stiffness, elastic stiffness, cracking, yielding, and ultimate loads of DSCB-ECs. Validations of predictions against 11 test results proved the reasonable estimations of the developed theoretical models on those stiffness and strength indexes. Finally, conclusions were given based on these tests and analysis.