• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.10
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• pp.1239-1249
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• 2013

In this study we establish a process to predict hardening behavior considering the Bauschinger effect for zircaloy-4 sheets. When a metal is compressed after tension in forming, the yield strength decreases. For this reason, the Bauschinger effect should be considered in FE simulations of spring-back. We suggested a suitable specimen size and a method for determining the optimum tightening torque for simple shear tests. Shear stress-strain curves are obtained for five materials. We developed a method to convert the shear load-displacement curve to the effective stress-strain curve with FEA. We simulated the simple shear forward/reverse test using the combined isotropic/kinematic hardening model. We also investigated the change of the load-displacement curve by varying the hardening coefficients. We determined the hardening coefficients so that they follow the hardening behavior of zircaloy-4 in experiments.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.528-535
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• 2011

In the present, the formation of shear band under a simple shear deformation is investigated using a rate-independent elastic-plastic constitutive relations. Moreover, the strain gradient terms are incorporated to obtain a non-local plastic constitutive relation, which in turn represented using combined two-back stress hardening model. Then, the continuum damage model is also included to the proposed model. The post-localization behavior are studied by introducing a small imperfection in a work piece. The strain gradient affects the shear localization significantly such that the intensity of shear band decreases as the strain gradient coefficient increases when the J2 flow theory is employed.

• Journal of the Korean Geotechnical Society
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• v.17 no.1
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• pp.131-139
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• 2001

화강토와 관련된 지반문제의 거동예측을 위한 수치해석의 적용이 양적인 면에서는 많이 확대되어왔지만 해석결과에 지대한 영향을 미치는 구성방정식 등 수치해석 모델링을 개선하고자 하는 노력은 부족하였다. 화강토 거동의 특징은 내재적 결합력으로 인한 구조화의 거동을 나타내는 것이며, 항복면이 평균유효응력 축에 대칭이고 Non-associated 소성거동을 보인다는 점이다. 본 연구에서는 이러한 화강토 거동을 표현하기 위하여 일반화된 한계상태모델을 도입하고, 이를 화강토의 경화거동 모델링이 가능하도록 확장하였다. 제안된 모델을 이용한 삼축시험의 유한요소 시뮬레이션 결과는 측정결과와 좋은 일치를 보였다. 화강토 지반내 터널에 대한 유한요소해석을 수행한 결과, 비선형 탄성모델과 조합된 확장된 한계상태모델이 현장계측결과와 잘 일치하는 결과를 주었다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.272-278
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• 2011

In the present work, FEM analyses are carried out to investigate the fractures occurred within the structural part in the course of combustion experiment. The loss of structural integrity stems from the localized deformation and the damage induced due to a severe change in the thermal load. Moreover, the two-back stress evolution model is proposed using the Armstrong-Frederick and the Phillips' rules to depict the plastic deformation, and the continuum damage mechanics is also incorporated into the present model. It is noted that the present model is able to formulate a wide range of constitutive description with ease. The numerical results depicts that a severe strain localization and damage evolution can be obtained depending on the dominant back stress.

• Elastomers and Composites
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• v.48 no.2
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• pp.133-140
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• 2013

Carbon fiber reinforced polymer (CFRP) composites consist of carbon fibers in a polymer matrix. Recently, CFRP composites having high thermal stability and low outgassing are finding their use in high performance materials for aerospace and electronics applications under high temperature and high vacuum conditions. Cyanate ester resin is one of the most suitable matrix resins for this purpose. In this study, proper combination of cyanate ester and catalyst, curing behavior, and cure cycle were determined by chemorheology. Optimum condition was found to be catalyst content of 100 ppm and curing temperature of $150^{\circ}C$. Thermal stability and outgassing of cured resin composition were analyzed and the results showed thermal decomposition temperature of $385^{\circ}C$ and total mass loss of 0.29%. The CFRP prepregs and subsequent composites were fabricated by predetermined resin composition and the cure condition. Tensile moduli of the composites were compared with theoretical models and the results were very consistent.

• Transactions of Materials Processing
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• v.17 no.3
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• pp.161-169
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• 2008

In the present work, the two-back stress model is proposed and continuum damage mechanics (CDM) is incorporated into the plastic constitutive relation in order to describe the plastic deformation localization and the damage evolution in a deforming continuum body. Coupling between damage mechanics and isothermal rate independent plasticity is performed using the kinematic hardening rule, which in turn is formulated by combining the nonlinear Armstrong-Frederick rule and the Phillips rule. The numerical analyses are carried out within h deformation theory. It is noted that the damage evolution within a work piece accelerates the plastic deformation localization such that the material with lower hardening exponent results in a rapid shear band formation. Moreover, the results from the numerical analysis reflected closely with the micro-structures around the fractured regime. The effects of the various hardening parameters on deformation localization are also investigated. As the nonlinear strain rate description in the back stress evolution becomes dominant, the strain localization becomes intensified as well as the damage evolution.

• Journal of Dairy Science and Biotechnology
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• v.32 no.1
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• pp.17-29
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• 2014

GRAS probiotics can be used to modulate intestinal microbiota and to alleviate various gastrointestinal disorders. In several recent studies, researchers have explored the potential expansion and usability of probiotics to reduce the risk factors associated with diseases, including obesity, hypercholesterolemia, arterial hypertension, hyperhomocysteinemia, and oxidative stress. In this review, our aim was to clarify the mechanism underlying interactions between hosts (animal or human) and probiotics and the beneficial effects of probiotics on human health.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.10
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• pp.1057-1068
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• 2014

This paper proposes elastic-plastic constitutive relations for a composite material with two phases-inclusion and matrix phases-using a homogenization scheme. A thermodynamic framework is employed to develop non-local plasticity constitutive relations, which are specifically represented in terms of the second-order gradient terms of the internal state variables. A combined two back-stress evolution equation is also established and the degradation of the state and internal variables is expressed by continuum damage mechanics in terms of the damage factor. Then, deformation localization is analyzed; the analysis results show that the proposed model yields a wide range of shear band formation behaviors depending on the evolution of the specific internal state variables. The analysis results also show good agreement with the results of simplified Rice instability analyses.

• Journal of Chest Surgery
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• v.31 no.12
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• pp.1119-1126
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• 1998

Background: In this study, we investigated the early time course of expression of the major histocompatibility(MHC) antigens, intercellular adhesion molecule-1(ICAM-1), vascular cell adhesion molecule-1(VCAM-1), interleukin-6 and the histopathological changes in the coronary arteries of cardiac allografts exchanged between inbred mice strains that differ in one loci of class I major histocompatibility antigen (B10.BR to B10.A). Material and Method: No immunosuppressive therapy was used. Both allografts and the hearts of the recipients were harvested at 7(group 1, n=6), 15(group 2, n=6), 21(group 3, n=6), and 30(group 4, n=6) days after transplantation. They were examined by immunohistochemistry, microscopy and morphometry. All allografts had contractions at the time of harvest. Result: A strong MHC class I antigen expression was present on the endothelial and medial cells of the coronary arteries in group 1 and remained unchanged in the rest of the groups. However, MHC class II reactivity was none or very little at any time. Mild to moderate ICAM-1 expression was observed on the endothelial cells, but not on the medial cells at any time by 30 days. VCAM-1 expression was strong both on the endothelial and medial cells at any time. Moderate degree expression of interleukin-6 was observed from 7 to 30 day specimens. Histopathologically, percentage of affected vessels(vessels with intimal thickening) was less than 10 % in 7 day group and increased up to 50 % at 30 days. Mean percent narrowing of the lumen of the affected vessels revealed less than 20 % at 7 days and 40 % at 30 days. The area occupied by tropomyosin positive cells in the intimal lesion, graded from 0 to 3, showed gradual increase but remained between grade 0 to 1 by 30 days. Medial integrity was also well preserved at any time. Moderate perivascular mononuclear cell infiltration was observed at 7 days and it was progressively increased upto 30 days. Recipients' heart revealed no positive immunopathologic findings. Conclusion: In this study, the early time course of progression of the transplantation vasculopathy was demonstrated in the murine heterotopic heart transplant model.

• Journal of the Korean Society of Food Science and Nutrition
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• v.37 no.6
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• pp.708-713
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• 2008

The effects of administration alone or mixed of Angelica keiskei and turmeric extract on blood lipids were evaluated in hypercholesterolemic diet or P-407-induced hyperlipidemic rats. In the study 1, female Sprague-Dawley rats weighing 160-180 g were divided into each groups and fed high cholesterol diets for 8 weeks. Experimental groups were administered with following diets: basal diet (Normal), high cholesterol diets (1% cholesterol). We did the oral administration for evaluation in experimental groups: C (vehicle), A (angelica extract), T (turmeric extract), AT (angelica extract, turmeric extract/ 1:1 complex). The concentrations of serum total cholesterol, and LDL-cholesterol were decreased by 6.8%, 9.8% in A group, by 22.1%, 28.8% in C group and by 28.2%, 35.6% in AT group, compared to the C group, respectively. HDL-cholesterol levels were not different among the experimental groups. In the study 2, we induced the hypertriglyceridemia in rats by intraperitoneal injection of P-407 (0.5 g/kg) once per three days. From the next day after P-407 injection beginning, we did the oral administration as the study 1. Angelica keiskei extract, turmeric extract and complex extract decreased serum triglyceride by 17.2%, 19.7% and 48.3%, respectively. These results suggested that Angelica keiskei and turmeric extract complex might have synergistic effect in lowering total cholesterol, LDL-cholesterol and triglyceride in hyperlipidemic rats.