• Bulletin of the Korean Chemical Society
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• v.32 no.2
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• pp.451-454
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• 2011

The traditional BCS superconductors $AOs_2O_6$ (A=K, Rb, and Cs) were investigated to find the relationship between their structures and superconducting transition temperatures. The $T_c$ decreases with increasing the unit cell parameter of $AOs_2O_6$. This is in contrast to the case of conventional BCS superconductivity in a single bond model, where $T_c$ may increase with increasing the the unit cell parameter since the DOS at Fermi level increases as the unit cell parameter increases. Instead, the $T_c$ of a $\beta$-pyrochlore oxide is proportional to the lattice softness of the compound.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.8
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• pp.1-7
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• 2008

In this paper, we propose a lossy MTM transmission line unit cell and retrieve the parameter values related with radiation effects. Based on this unit cell model, we plot dispersion diagrams and analyze resonance conditions. We also discuss the input impedance or admittance behavior when we terminate the load as open or short. Then, we examine the quality factor and return loss bandwidth. We also design a very compact unit cell antenna using the provided lossy MTM-TL model. The results based on EM simulations and measurements are shown to be in good agreement with those based on circuit simulation.

• Computers and Concrete
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• v.7 no.6
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• pp.497-510
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• 2010

For better estimation of elastic property of concrete composites, the effect of Interfacial Transition Zone (ITZ) has been found to be significant. Numerical concrete composites models have been introduced using Finite Element Method (FEM), where ITZ is modeled as a thin shell surrounding aggregate. Therefore, difficulties arise from the mesh generation. In this study, a numerical concrete composites model in 3D based on FEM and random unit cell method is proposed to calculate elastic modulus of concrete composites with ITZ. The validity of the model has been verified by comparing the calculated elastic modulus with those obtained from other analytical and numerical models.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.7
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• pp.736-745
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• 2009

Fuel cells convert a fuel together with oxygen in a highly efficient electrochemical reaction to electricity and water. Since the electrochemical reaction in the fuel cell stack dose not generate any noise, Fuel cell systems are expected to operated much quieter than combustion engines. However, the tonal noise and the broad band noise caused by a centrifugal compressor and an electric motor cause which is required to feed the ambient air to the cathode of the fuel cell stack with high pressure. In this study, the multi-camber perforated muffler is used to reduce noise. We propose optimized muffler model using an axiomatic design method that optimizes the parameters of perforated muffler while keeping the volume of muffler minimized.

• Journal of the Korean Society of Industry Convergence
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• v.19 no.3
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• pp.109-124
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• 2016

The objective of this paper is to find the density, stiffness, and strength of truss-wall diamond corrugation model combined with pinwheel truss inside space. The truss-wall diamond corrugation (TDC) model is defined as a unit cell coming from solid-wall diamond corrugation (SDC) model. Pinwheel truss-wall diamond corrugation (P-TDC) model is made by TDC connected with pinwheel structure inside of the space. Derived ideal solutions of P-TDC is based on truss-wall and pinwheel truss model at first. And then it is compared with Gibson-Ashby's ideal solution. To validate the ideal solutions of the P-TDC, ABAQUS software is used to predict the density, strength, and stiffness, and then each of them are compared to the ideal solution of Gibson-Ashby with a log-log scale. Applied material property is stainless steel 304 because of having cost effectiveness. Applied parameters for P-TDC are 1 thru 5 mm diameter within fixed opening width as 4mm. In conclusion, the relative Young's modulus and relative yield strength of the P-TDC unit model is reasonable matched to the ideal expectations of the Gibson-Ashby's theory. In nearby future, P-TDC model is hoped to be applied to make sandwich core structure by advanced technologies such as 3D printing skills.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.7
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• pp.2939-2944
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• 2011

The performance and efficiency of a Molten Carbonate Fuel Cell system will improve with the aids of numerical simulations such as finite element analysis. For best simulation results, the virtual model must accurately reflect the actual model including the material properties. It is very difficult, however, to make a detailed numerical model of the stack that consists of hundreds of layers of unit cells composed of various materials like metal, ceramics, polymer, etc. Instead, a practical approach is to find a homogenized material property of the stack as a whole as an approximate replacement. In this paper, the compression ratio of a unit cell is introduced, and a new method is proposed to estimate the homogeneous material properties for both the active and the manifold regions of the stack under the assumption that the compressive deformation occurs only at the separators and matrices in the unit cells. The estimated properties are applied successfully to simulating an actual stack.

• Journal of the Korea Convergence Society
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• v.10 no.4
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• pp.139-145
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• 2019

This paper investigated the strength and stiffness of composite truss unit structures. The model used is a core-filled model combining the Kagome model and the cube truss model. The material properties used for the analysis are 304 stainless steel with elastic modulus of 193 GPa and yield stress of 215 MPa. The theoretical equation is derived from the relative elasticity relation of Gibson - Ashby ratio, the analysis was performed using Deform 3D, a commercial tool. In conclusion, the relative elasticity for this unit model correlates with 1.25 times the relative density and constant coefficient, elasticity is inversely proportional to pore size. The relative compressive strength has a correlation with relative density of 1.25 times. Proof of this is a real experiment, the derived theoretical relationship should further consider mechanical behavior such as bending and buckling. In the future, it is hoped that the research on the elasticity and the stress according to the structure of the three-dimensional space will be continued.

• Asian Pacific Journal of Cancer Prevention
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• v.13 no.6
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• pp.2935-2941
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• 2012

Biological response modifiers (BRMs) can alter interactions between the immune system and cancer cells to boost, direct, or restore the body's ability to fight disease. Mice with ethylnitrosourea- (ENU) induced leukemia were here used to monitor the therapeutic efficacy of lipopolysaccaride (LPS), Bacillus Calmette Guerin (BCG) and sheep erythrocytes (SRBC). Flow cytometry based CD34+ positivity analysis, clonogenicity, proliferation and ultrastructure studies using scanning electron microscopy (SEM) of stem cells in ENU induced animals with and without BRMs treatment were performed. BRMs improved the stem-stromal relationship structurally and functionally and might have potential for use as an adjunct in human stem cell therapy.

• International Journal of Automotive Technology
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• v.5 no.1
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• pp.47-53
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• 2004

In this paper, a modified and representative unit cell model was employed to study the crush behaviour of a closed cell metallic foam. The unit cell which captures the main geometrical features of the metallic foam considered was used to simulate crush behaviour in metallic foams. Both analytical using limit analysis and numerical using the finite element method were used to study the collapse behaviour of the cell. The analytical crushing stress of the foam was compared with FE results and was found to be in good agreement.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.2 s.233
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• pp.253-261
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• 2005

In decades, a substantial body of work on a unified viscoplastic model which considers the mechanism of plastic deformation and creep deformation has developed. The systematic scheme for numerical analysis of unified model is necessary because the dominant failure mechanism is the defect growth and coalescence in materials. In the present study, the unified viscoplastic model for materials with defects suggested by Suquet and Michel was employed for numerical analysis. The constitutive equations are integrated based on the generalized mid-point rule and implemented into a finite element program (ABAQUS) by means of user-defined subroutine (UMAT). To evaluate the validity of the developed UMAT code and the assessment of the adopted viscoplastic model, the results obtained from the UMAT code was compared with the numerical reference solution and experimental data. The unit cell analysis also has been investigated to study the effect of strain rate, temperature, stress triaxiality and initial defect volume fraction on the growth and coalescence of the defect.