• Journal of the Korea Concrete Institute
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• v.27 no.1
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• pp.55-63
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• 2015

Prefabrication technologies are making bridge construction safer and less disruptive to the environment and traveling public, making bridge designs more constructible and, improving the quality and durability by shifting site work to a more controllable environment. Modular bridge substructures with concrete-filled steel tube (CFT) piers and composite pier caps were suggested to realize accelerated bridge construction. The precast segmental pier cap consists of a composite pier table and precast prestressed segments on the table. The pier table has embedded steel section to mitigate stress concentration at the connection by small tubes. Each bridge pier has four or six CFT columns which connect to the pier cap. Shear strength of the pier cap was obtained by extending vertical reinforcing bars from the table to the precast segment. Transverse prestressing was introduced to control tensile stresses by service loadings. Structural performance of the proposed modular system was evaluated by static tests. Design requirements of the composite pier cap were satisfied by continuous reinforcing bars and prestressing tendons. Standardized modular substructures can be effectively utilized for the fast replacement or construction of bridges.

• Journal of the Korea Concrete Institute
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• v.28 no.3
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• pp.279-288
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• 2016

The present study simplified the moment-curvature relationship to straightforwardly determine the flexural behavior of reinforced concrete (RC) columns. For the idealized column section, moments and neutral axis depths at different stages(first flexural crack, yielding of tensile reinforcing bar, maximum strength, and 80% of the maximum strength at the descending branch) were derived on the basis of the equilibrium condition of forces and compatibility condition. Concrete strains at the extreme compression fiber beyond the maximum strength were determined using the stress-strain relationship of confined concrete, proposed by Kim et al. The lateral load-displacement curves converted from the simplified moment-curvature relationship of columns are well consistent with test results obtained from column specimens under various parameters. The moments and the corresponding neutral axis depth at different stages were formulated as a function of longitudinal reinforcement and transverse reinforcement indices and/or applied axial load index. Overall, curvature ductility of columns was significantly affected by the axial load level as well as concrete compressive strength and the amount of longitudinal and transverse reinforcing bars.

• Journal of the Microelectronics and Packaging Society
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• v.15 no.2
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• pp.55-61
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• 2008

This paper shows quantitative reliability evaluations of a Bluetooth module through extending previous qualitative methods limited to structure reliability tests and solder joint reliability tests for Bluetooth modules. Accelerated Life Testing (ALT) of the modules using temperature difference in temperature cycling as an accelerated stress was conducted for quantitative reliability evaluation under field environment conditions. Lifetime distribution parameters were estimated using the failure times obtained through the ALT, and then Coffin-Manson model was implemented. Results of the ALT showed that the failure mode of the modules was open and the failure mechanisms are both crack and delamination. The ALT reproduced the failure mode and mechanisms of failed Bluetooth modules collected from the field. Further, a quantitative reliability evaluation method with respect to various temperature differences in temperature cycling was proposed in this paper. $B_{10}$ lifetime of the module for the temperature difference $70^{\circ}C$ using the proposed method would be estimated as about 4 years.

• Composites Research
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• v.29 no.2
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• pp.85-89
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• 2016

This paper aims at estimating the fracture behavior at the bonded part of composite material. CFRP is manufactured as the type of TDCB. The static analysis of Mode 1 due to the configuartion factor of m is carried out. Four kinds of specimens have the configuartion factor(m) of 2, 2.5, 3 and 3.5. As the study result, the displacements at specimens are shown to be similar each other in these four cases. At m of 3.5, the reaction force becomes highest as 412 N and is shown to be improved as much as 14% by comparing m of 2. The data on defection of the bonded interface and reaction force are thought to be contributed to the structural design of CFRP and the safe design.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.10
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• pp.1273-1279
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• 2011

The variable-swash-plate compressor has recently been adopted as a vehicle compressor to improve fuel efficiency. The rotation torque in the variable-swash-plate compressor and the pressure-affected piston have a great influence on the swash-plate design and deformation. This paper suggests the optimal configuration design by using Chebyshev orthogonal polynomial and optimization techniques. The orthogonal array (OA) and analysis of variance (ANOVA) techniques and response surface optimization, are employed to determine the main effects and their optimal design variables. According to the optimal design, we confirm an effective design variable in swash plate and explain the optimal solution, the usefulness for satisfying the constraints of maximum stress and deformation.

• Journal of Korea Foundry Society
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• v.40 no.3
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• pp.85-96
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• 2020

The effect of an aluminum scrap addition ratio on the tensile and solidification cracking properties of the AC4A aluminum alloy in the as-cast state and heat-treated state were investigated in this study. Generally, the expected problem of using scrap in aluminum casting is an increase of hydrogen and Fe element inside the aluminum melt. Another issue is an oxide film which has a weak interface with the molten aluminum and acts as potent nucleation sites for internal porosity and crack initiation. Solidification cracking is one of the critical defects that must be resolved to produce high quality castings. A conventional evaluation method for solidification cracking is a relative and qualitative analysis method which does not provide quantitative data on the thermal stress in the solidification process. Therefore, a newly designed solidification cracking test apparatus was used in this study, and the device can provide quantitative data. As a result, after conducting experiments with different scrap addition ratios (0%, 20%, 35%, 50%), the tensile strengths and elongations in the as-cast state were 214, 187.7, 182.1 and 170.4MPa and 4.6%, 3.4%, 3.1% and 2.3%, respectively. In the case of the T6 heat-treated state, the tensile strengths and elongations were 314.9, 294.6, 293.1 and 271.1MPa and 5.4%, 4.6%, 3.8% and 3.1%, respectively. The strength of the solidification cracking was 3.1, 2.4, 2.2and 1.6MPa as the scrap addition ratio increases.

• The Journal of Korean Physical Therapy
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• v.22 no.3
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• pp.61-69
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• 2010

Purpose: This study was designed to investigate correlations between physical fitness, antioxidant enzymes (SOD, CAT, GPX), lipid peroxidation levels (MDA), lipid profiles, lactate levels and cardiovascular variables in an exercising group and a control group. Methods: Twelve healthy young males (Exercise group: 6, Controls: 6). All subjects took physical fitness tests and blood samples were collected while subjects were resting. Results: In the exercise group, there were several significant correlations: between back strength and SOD enzyme levels (r=0.82, p=0.04), back strength and MDA (r=0.94, p=0.00), agility and GPX (r=0.81, p=0.04), and balance and GPX (r=0.81, p=0.04). In the control group, there were significant correlations between: dominant grip strength and MDA (r=-0.84, p=0.03), and agility and GPX (r= -0.82, p=0.04). In the exercise group, there were no significant correlations between physical fitness factors, TC, TG, HDL-C and lactate levels. In the control group, there were significant correlations between: back strength and TG (r=0.88, p=0.01), and agility and HDL-C (r= -0.84, p=0.03). In the exercise group, there were significant correlations between: non-dominant grip strength and SBP (r=0.94, p=0.00), dominant grip strength and SBP (r=0.85, p=0.03), and power and SBP (r=0.82, p=0.04). In controls, there were significant correlations between: dominant grip strength and DBP (r=-0.85, p=0.03), muscular endurance and ST level (r=-0.93, p=0.00), and muscular endurance and HR (r=-0.88, p=0.01). Conclusion: That cardiovascular patients and controls who participated in regular exercise maintained their antioxidant capacity suggests that long-term physical activity can counteract the negative dysfunction that characterizes sedentary lifestyle, probably by maintaining plasma antioxidant defenses and thereby preventing oxidative stress.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.7
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• pp.911-917
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• 2010

In this study, we performed structural and fatigue analyses of the engine exhaust manifold that was subjected to thermo-mechanical cyclic loading. The methodologies used in this study are based on an approach in which the techniques for modeling the exhaust system, the temperature-dependent properties of the material, and thermal cyclic loading are taken into consideration and a reliable strategy is adopted for failure prediction. An application example shows that at an elevated temperature, considerable compressive plastic deformation is observed and that at a low temperature, tensile stresses remain in those parts of the test exhaust manifold where failure is observed. In order to predict fatigue life, mechanical damage is determined on the basis of the stress.strain hysteresis loops by using the classical Coffin.Manson equation and by adopting a method in which the dissipated plastic energy is taken into consideration.

• Journal of Life Science
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• v.21 no.8
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• pp.1100-1108
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• 2011

The immunomodulating effects of moxifloxacin seem to be effective in downregulating inflammatory reactions. This presumed effect was tested in endotoxin (ETX)-induced acute lung injury (ALI) in rats. After moxifloxacin treatment (10 mg/kg) of ETX-given rats, lung myeloperoxidase (MPO) activity, bronchoalveolar-lavage (BAL) protein, and the number of neutrophils in the BAL cells were measured. Light and electron microscopic structures were also examined. Electron microscopic $CeCl_3$ histochemistry for the detection of hydrogen peroxide in the lungs and immunohistochemistry of cytosolic phospholipase A2 (cPLA2) in the lung tissues and BAL cells were performed. To examine the expression of TNF${\alpha}$ in the lungs, western blotting was carried out with the lung tissues. ETX had accumulated neutrophils in the lungs, which was followed by lung leak. Oxidative stress occurred, and increased expression of cPLA2 in the lung tissues and BAL cells was observed in the ETX-given rats. Simultaneously, the expression of TNF${\alpha}$ was enhanced by ETX. Moxifloxacin, however, decreased all these parameters, indicating that ALI may have been ameliorated. Moxifloxacin appears to ameliorate ETX-induced ALI partially through the suppression of cPLA2 in the lungs of rats.

• Korean Journal of Food Science and Technology
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• v.31 no.5
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• pp.1254-1261
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• 1999

The influence of addition of arrow(Pueraria hirsuta Matsum) root flour and its fractions by ultrafiltration on the flow properties of the rice flour-water systems were investigated. The flow properties of rice flour pastes during cold storage$(5^{\circ}C)$ were measured and the components from arrow root flour responsible for changes of flow properties were screened. Addition of arrow root flour significantly changed the flow properties of rice flour pastes. Permeate fractions by ultrafiltration, representing low molecular weight component fraction, significantly affected the flow property of rice flour paste stored at $5^{\circ}C$. Addition of permeate fraction to rice flour pastes rapidly decreased the consistency index, yield stress and pseudoplasticity, and showed a stability of flow property during storage suggesting the retardation of rice starch retrogradation. Permeate fractions of ultrafiltration were identified as puerarin, daidzein and daidzin known to representive isoflavonoid from arrow root.