• 한국전기전자재료학회논문지
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• 제32권4호
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• pp.276-280
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• 2019

In this study, we investigated the crystal defects and grain boundary properties in a ZZCCC ($ZnO-Zn_2BiVO_6-Co_3O_4-Cr_2O_3-CaCO_3$) varistor, with the liquid-phase sintering aid $Zn_2BiVO_6$ developed by our laboratory. The ZZCCC varistor sintered at $1,200^{\circ}C$ exhibited excellent nonlinear current-voltage characteristics (${\alpha}=63$), with oxygen vacancy ($V_o^*$ ; 0.35 eV) as a main defect, and an apparent activation energy of 1.1 eV with an electrically single grain boundary. Therefore, among the various additives to improve the electrical properties of ZnO varistors, if $Zn_2BiVO_6$ is used as a liquid phase sintering aid, it will be ideal to use Co for the oxygen vacancy and Ca for the electrically single grain boundary. This will allow the good properties of ZnO varistors to be maintained up to high sintering temperatures.

• 영어어문교육
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• 제13권1호
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• pp.211-233
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• 2007

Caryl Churchill achieved spacial politics to resist dominant ideology in Cloud Nine. It is suggested that heterotopia is a counter-site to the places which are controlled by colonialism and sexuality. Churchill juxtaposes African colony of Victorian period in the first act and modern London in the second act. It implies that individuals are similarly oppressed by dominant ideology until now though several conditions for individuals are drastically improved. White heterosexual men in the play try to build their utopia to keep their privileges. If they find anything abnormal to their standard, they systematically classify people and organize them into the different ranks and levels to seclude them from their utopia. Actually, the ideal people in the ideal place are oppressed by patriarchal ideology, compulsory heterosexuality, and colonialism which are covertly associated with gender. Therefore, Churchill uses the cross-casting to challenge the artificiality of gender, sexuality, generation and race in the play. People realize that they need to find their own desires free from gender, compulsory heterosexuality, ethnic, and race and their subjectivity flowing in and out of space. It is the site that all the binary oppositions are deconstructed and creates new multiple nodes to expand the boundary of their communities to heterotopia in real places.

• 복식문화연구
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• 제18권6호
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• pp.1261-1273
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• 2010

The advent of various arts and remarkable development of mass media since 1980s accelerate fashion photographs' advancement. The expression of fashion through photographs can represent characteristics of ages, societies, cultures, traits of designers and techniques of photographers. In addition, that is the tool which contains economical role as a product and artistic role as photos. Therefore, this study examines hyprt-reality images in editorial fashion photographs. Hyper-reality means the reproduction which represents the reality of life more actually. Hyper-reality through photographs elevates reality of virtual things and creates the confused situation which haunts the boundary between reality and reproduction. This study classifies the hyper-reality in editorial fashion photographs into three groups by their external traits, ideal reality, collapse of reality, and restoration of reality. First, ideal reality is represented as harmony among fashion, characters, and space, causality of fashion with time and circumstances, positive will, and melting with nature. Second, collapse of reality is expressed as in harmony between fashion and situation, violence, fetishism and symbol of death. Third, restoration of reality is shown as recurrence to nature and images of utopia to express dignity of life.

• 에너지공학
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• 제26권1호
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• pp.9-22
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• 2017

A combined thermal and flow analysis was carried out to study the behavior and performance of a small, commercial LTD (Low-Temperature-Differential) heat engine. Laminar-flow solutions for annulus and channel flows were employed to estimate the viscous drags on the piston and the displacer and the pressure difference across the displacer. Temperature correction factors were introduced to account for the departure from the ideal heat transfer processes. The analysis results indicate that the work required to overcome the viscous drags on engine moving parts and to move the displacer is much smaller than the moving-boundary work produced by the power piston for temperature differentials in the neighborhood of $20^{\circ}C$ and engine speeds below 10 RPS. A comparison with experimental data reveals large degradations from the ideal heat transfer processes. Thus, heat-transfer devices inside the displacer cylinder are recommended.

• 대한토목학회논문집
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• 제14권5호
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• pp.1033-1042
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• 1994

2차원 경계요소-유한요소 연계법을 사용하여 구형 수조구조물의 동적거동 특성을 파악하였다. 비점성, 비압축성 이상유체의 운동은 경계요소법으로 모델링하였으며 구조물의 운동은 유한요소법으로 모델링하였다. 경계요소법의 적용시 Singularity를 소거한 경계적분식을 사용하였다. 유체와 구조물의 경계면에서 적합조건과 평형조건을 만족시킴으로써 경계요소와 유한요소를 연계하였다. 유체-구조물 상호작용의 영향은 유체의 부가질량행렬과 유체 유동에 의한 강성행렬로 연계된 유체-구조물계에 반영된다. 연계된 유체-구조물계의 고유치 문제로부터 수조구조물의 고유진동수외 고유모드를 구하였으며 수평 및 수직 자바운동에 의하여 수조구조물에 발생하는 유체동압력과 자유수면의 유동도 산출하였다.

• 대한조선학회논문집
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• 제56권1호
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• pp.94-101
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• 2019

Underwater acoustic power should be measured in a free field, but it is not easy to implement. In practice, the measurement could be performed in a reverberant field such as a water-filled steel tank and concrete tank. In this case, the structure and the acoustic field are strongly or weakly coupled according to material properties of the steel and water. So, characteristics of the water tank must be investigated in order to get the accurate underwater acoustic power. In detail, modal frequencies, mode shapes of the structure and frequency response functions of the acoustic field could represent the characteristics of the reverberant water tank. In this paper, the structure-acoustic coupling has been investigated on a reverberant water tank numerically and experimentally. The finite element analysis has been carried out to estimate the structural and acoustical modal parameters under the dry and water-filled conditions, respectively. In order to investigate the structure-acoustic coupling effect, the numerical analysis has been performed according to the structure stiffness change of the water tank. The acoustic frequency response functions were compared with the numerical analysis and acoustic exciting test. From the results, the structural modal frequencies of the water-filled condition have been decreased compared to those of the dry condition in the low frequency range. The acoustic frequency response functions under the coupled boundary conditions showed different patterns from those under the ideal boundary conditions such as the pressure release and rigid boundary condition, respectively.

• 건축역사연구
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• 제17권4호
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• pp.83-95
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• 2008

This study was firstly to reflect upon the background of the generation and the urban spatial value and significance of the medieval plaza. The main aim of this study was to extract the spatial determinants which give the great influence on the formation of the medieval plaza and in addition the endogenous rules and aesthetical grounds regarding the respective elements. Especially they could be applied to the design guideline. They are dimension(volume and scale), shape, elevation as the morphological elements and enclosure, proportion, grade difference, spatial sequence and plaza group as the spatial determinants and visual sequence, visual or spatial boundary, approaching axis and perspective effect as the aesthetic and visual elements and function(use), human behaviour as the social-behavioral elements and otherwise, for instance, plaza furniture, ground decoration and vegetation. This study was intended to analyze each elements based on the classical historical literatures and to suggest the planning conditions for composing the ideal plaza referring to the cases and literature review on the medieval plaza and finally is expected to contribute to the plaza design methodology.

• Nuclear Engineering and Technology
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• 제41권3호
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• pp.335-346
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• 2009

This paper deals with a hydroelastic vibration analysis of two rectangular plates partially coupled with a liquid, which is bounded by two plates and two rigid side walls. The wet displacement of each plate is assumed to be a combination of the modal functions of a dry uniform beam with a clamped boundary condition. As the liquid is assumed to be an ideal liquid, the displacement potential satisfying the Laplace equation is determined so that the liquid boundary conditions can meet the requirements at the rigid surfaces and the free liquid surface. The wet dynamic modal functions of each plate are expanded by using the finite Fourier transform to obtain an appropriate form of the compatibility requirement along the contacting surfaces between the plates and the liquid. The liquid-coupled natural frequencies of the plates are derived by using the Rayleigh-Ritz method. Finite element analyses using commercial software are carried out to verify the proposed theory. It is observed that the theoretical method agrees excellently with the three-dimensional finite element analyses results. The effects of the liquid depth and the liquid thickness on the normalized natural frequencies are investigated to identify the dynamic characteristics of the liquid coupled system.

• Journal of Power Electronics
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• 제16권2호
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• pp.584-597
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• 2016

This paper focuses on an improvement in the transient performance of Boost converters when the load changes abruptly. This is achieved on the basis of the nature trajectory in Boost converters. Three key aspects of the transient performance are analyzed including the storage energy change law in the inductors and capacitors of converters during the transient process, the ideal minimum voltage deviation in the transient process, and the minimum voltage deviation control trajectory. The changing relationship curve between the voltage deviation and the recovery time is depicted through analysis and simulations when the load suddenly increases. In addition, the relationship curve between the current fluctuation and the recovery time is obtained when the load suddenly decreases. Considering the aspects of an increasing and decreasing load, this paper proposes the transient performance synthetic optimized trajectory and control laws. Through simulation and experimental results, the transient performances are compared with the other typical three control methods, and the ability of proposed synthetic trajectory and control law to achieve optimal transient performance is verified.

• 한국융합학회논문지
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• 제7권4호
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• pp.181-190
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• 2016

The objective of this study is to find the effective stiffness and compressive strengths of a unit-cell pinwheel truss and double pinwheel truss model designed following a double helical geometry similar to that of the DNA (deoxyribonucleic acid) structure in biology. The ideal solution for their derived relative density is correlated with a ratio of the truss thickness and length. To validate the relative stiffness or relative strength, ABAQUS software is used for the computational model analysis on five models having a different size of truss diameter from 1mm to 5mm. Applied material properties are stainless steel type 304. The boundary conditions applied were fixed bottom and 5 mm downward displacement. It was assumed that the width, length, and height are all equal. Consequently, it is found that the truss model has a lower effective stiffness and a lower effective yielding strength.