• 한국지반공학회논문집
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• 제20권7호
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• pp.171-181
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• 2004

본 연구는 불포화 상태 전 범위에 대한 사질토의 인장강도 모델화 가능성을 조사하기 위해 실시 되었다. 새로 개발된 직접인장시험기법을 이용하여 인장시험이 실시되었다. 측정된 결과는 Rumpf 및 Schubert가 동일크기의 이상적인 구에 대해 개발한 이론적인 인장강도 모델들에 의한 예측 값과 비교 되었다. 이를 위해 석션-포화실험을 통해 얻어진 흙-수분특성곡선을 이용하여 이론모델에 있어 중요한 요소인 불포화상태(pendular, funicular, capillary) 구분 및 음의 간극수압 값을 산정하는데 사용하였다. Pendular 상태에서 불포화모래의 비선형 거동이 Rumpf의 모델에 의해 적절이 묘사되었다. Funicular 및 capillary상태의 경우, 함수비가 증가함에 따라 인장강도가 증가하다 최고 값이 도달한 후 다시 감소하는 실험 측정치의 경향도 Schubert의 모델에 의해 적절히 묘사되었다. 본 비교 연구는 이상적인 단일 크기의 입자에 대해 개발된 이론적인 모델이 다양한 크기를 갖는 불포화 사질토의 인장강도를 예측할 수 있다는 가능성을 뒷받침해준다.

• 인지과학
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• 제17권1호
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• pp.53-74
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• 2006

유사성은 인지구조와 그 처리과정을 설명하는 중요한 개념으로 알려져 있으며 유사성 비교과정을 설명하기 위해 제안된 대표적인 초기모형으로는 다차원 척도모형(Shepard, 1964; Nosofsky, 1991)과 대비모형(Tversky, 1977)이 있다. 그러나 초기 모형에 의해 설명되기 어려운 경험적 연구결과들이 발표되면서 유사성의 개념적 타당성에 대한 의문이 제기되었다. Goldstone(1994)은 유사성이 속성차원간의 정렬과정에서 정의된다고 가정하고, 구조적 정렬 개념을 유사성을 둘러싼 개념적 논쟁들을 해결할 수 있는 유망한 대안으로 제안하였다. 본 연구에서는 우선 초기 유사성모형들의 기본 가정과 알고리즘을 개관한 후 속성차원에 대한 선택적 주의의 임의성이나 속성차원들 사이에 존재하는 상관적 구조와 같이 초기 유사성 모형들에 의해 설명되기 어려운 개념적 문제들을 살펴보았다. 그리고 SIAM(Goldston,, 1994)의 개념적 특징과 알고리즘을 알아본 후 구조적 정렬 개념이 범주화, 명사결합, 유추 추리 등의 인지심리학 분야들에 어떻게 적용되었는지를 개관하였다. 끝으로 자료 주도적 처리와 대안적 처리과정의 가능성과 관련된 SIAM의 한계점을 검토하고 가능한 발전방향에 대해 논의하였다.

• Nuclear Engineering and Technology
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• 제56권4호
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• pp.1165-1203
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• 2024

In the paper we validate theoretical models of the pulse against experimental data from the Jozef Stefan Institute TRIGA Mark II research reactor. Data from all pulse experiments since 1991 have been collected, analysed and are publicly available. This paper summarizes the validation study, which is focused on the comparison between experimental values, theoretical predictions (Fuchs-Hansen and Nordheim-Fuchs models) and calculation using computational program Improved Pulse Model. The results show that the theoretical models predicts higher maximum power but lower total released energy, full width at half maximum and the time when the maximum power is reached is shorter, compared to Improved Pulse Model. We evaluate the uncertainties in pulse physical parameters (maximum power, total released energy and full width at half maximum) due to uncertainties in reactor physical parameters (inserted reactivity, delayed neutron fraction, prompt neutron lifetime and effective temperature reactivity coefficient of fuel). It is found that taking into account overestimated correlation of reactor physical parameters does not significantly affect the estimated uncertainties of pulse physical parameters. The relative uncertainties of pulse physical parameters decrease with increasing inserted reactivity. If all reactor physical parameters feature an uncorrelated uncertainty of 10 % the estimated total uncertainty in peak pulse power at 3 $ inserted reactivity is 59 %, where significant contributions come from uncertainties in prompt neutron lifetime and effective temperature reactivity coefficient of fuel. In addition we analyse contribution of two physical mechanisms (Doppler broadening of resonances and neutron spectrum shift) that contribute to the temperature reactivity coefficient of fuel. The Doppler effect contributes around 30 %-15 % while the rest is due to the thermal spectrum hardening for a temperature range between 300 K and 800 K.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제28권1호
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• pp.1-21
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• 2024

This review comprehensively explores the evolution, theoretical underpinnings, variations, and applications of diffusion models. Originating as a generative framework, diffusion models have rapidly ascended to the forefront of machine learning research, owing to their exceptional capability, stability, and versatility. We dissect the core principles driving diffusion processes, elucidating their mathematical foundations and the mechanisms by which they iteratively refine noise into structured data. We highlight pivotal advancements and the integration of auxiliary techniques that have significantly enhanced their efficiency and stability. Variants such as bridges that broaden the applicability of diffusion models to wider domains are introduced. We put special emphasis on the ability of diffusion models as a crucial foundation model, with modalities ranging from image, 3D assets, and video. The role of diffusion models as a general foundation model leads to its versatility in many of the downstream tasks such as solving inverse problems and image editing. Through this review, we aim to provide a thorough and accessible compendium for both newcomers and seasoned researchers in the field.

• Journal of the Korean Data and Information Science Society
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• 제9권2호
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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.

• 천문학논총
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• 제7권1호
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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.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집B
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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.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제50권5호
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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%.

• 콘크리트학회논문집
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• 제11권5호
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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.

• 성인간호학회지
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• 제18권3호
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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.