• Korea-Australia Rheology Journal
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• v.20 no.2
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• pp.59-63
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• 2008

A theoretical model was developed to describe the flow behavior of a filled polymer in the packing stage of reaction injection molding and predict the residual stress distribution of thin injection-molded parts. The model predictions were compared with experiments performed for phenol-formaldehyde resin filled with wood dust and cured by urotropine. The packing stage of reaction injection molding process presents a typical example of complex non-isothermal flow combined with chemical reaction. It is shown that the time evolution of pressure distribution along the mold cavity that determines the residual stress in the final product can be described by a single 1D partial differential equation (PDE) if the rheological behavior of reacting liquid is simplistically described by the power-law approach with some approximations made for describing cure reaction and non-isothermality. In the formulation, the dimensionless time variable is defined in such a way that it includes all necessary information on the cure reaction history. Employing the routine separation of variables made possible to obtain the analytical solution for the nonlinear PDE under specific initial condition. It is shown that direct numerical solution of the PDE exactly coincides with the analytical solution. With the use of the power-law approximation that describes highly shear thinning behavior, the theoretical calculations significantly deviate from the experimental data. Bearing in mind that in the packing stage the flow is extremely slow, we employed in our theory the Newtonian law for flow of reacting liquid and described well enough the experimental data on evolution of pressure.

• Structural Engineering and Mechanics
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• v.64 no.6
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• pp.793-802
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• 2017

The damage of concrete due to the expansion of alkali-aggregate reaction (AAR) and thermal-chemical reactions affecting the strength of concrete is studied. The empirical equations for the variations of expansion of AAR, compressive strength and degradation of the modulus of elasticity with time, and compressive strength with degradation of the modulus of elasticity are proposed by analysing numerous experimental data. It is revealed that the expansion of AAR and compressive strength increase with time. The proposed combination of the time variations of chemical and mechanical parameters provides a satisfactory prediction of the concrete strength. Seismic analysis of the aged Koyna dam is conceded for two different long-term experimental data of concrete incorporating the proposed AAR based properties. The responses of aged Koyna dam reveal that the crest displacement of the Koyna dam significantly increases with time while the contour plots show that major principal stress at neck level reduces with time. As the modulus of elasticity decreases with ages the stress generated in the concrete structure get reduces. On the other hand with lesser value of modulus of elasticity the structure becomes more flexible and the crest displacement becomes very high that cause the seismic safety of the dam reduce.

• The Korea Journal of Herbology
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• v.21 no.2
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• pp.63-75
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• 2006

Objectives : We investigated the effects of Liriopis Tuber on the nervous protection. Methods : We measured the reaction behavior with EPM(Elevated Plus Maxe) and MWM(Morris Water Maze) after applying restraint stress to rats. Also, the degrees of AchE generation were measured with immunohistochemical method in the regions of hippocampus, and the degree of TH generation in the regions of VTA and LC, respectively. Results : 1. As the results of measuring how long EPM which reflects anxiety reaction stayed in the open arm, there was the trend which can suppress anxiety reaction in the MMD+stress group(Liriopis Tuber+stress) but no statistical significance. The counting results how many EPM passed between opened and closed arm showed suppression trend against a physical activity in the saline+stress group but there was no statistical significance. 2. According to the result of MWM, the saline+stress group showed the learning retardation which means increased time arriving at goal compared to ti1e normal group at the second and third day of measurement. On the contrary, a learning retardation was significantly decreased in the MMD+stress group. Among the probe trial test a memory loss occurred in the saline+stress group, meanwhile memory ability was notably increased in the saline-stress group. 3. The degree of TH generation was investigated at the VTA and LC respectively after test animals treated with drug. In the saline+stress group, TH-immunoreactive cells were significantly increased, and these stress-induced TH increases were suppressed in the saline+stress group at the VTA region. However, the saline+stress group did not show any significant difference. 4. the degree of AchE generation was investigated at the CA3 of hippocampus. The saline+stress group showed that AchE-immunoreactive cells were significantly decreased. Those stress-induced reductions of AchE cells were meaningfully recovered in the saline+stress group. Although the cells showed recovery trend in the region of CA1 of hippocampus, statistical significance was not observed. Conclusion : The results of our study indicate that Liriopis Tuber can improve spatial memory ability of rats applied a restraint stress. This improvement of the spatial memory ability is considered to have an efficacy of nervous protection that Liriopis Tuber suppresses the generation of AchE in the hippocampus region and enhances the generation of TH in the VTA.

• Tribology and Lubricants
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• v.11 no.2
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• pp.24-33
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• 1995

This paper presents the contact stress distributions between the multi-contact bodies and the total reaction forces for various types of contact geometry for multi-load slewing ring bearings. The FEM results indicate that the slope of the roller type of slewing ring bearing has slightly steeper than that of the ball type. This is because the roller type wire race bearings is stiffer than the ball type bearing. The total reaction force of ball type slewing bearing shows much higher than that of wire race slewing bearings.

• Journal of Biomedical Engineering Research
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• v.21 no.3 s.61
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• pp.285-293
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• 2000

Age-related changes in the geometry of human lumbar spine would lead to changes of its mechanical behaviors. To investigate the effects of the geometric changes, no age-related changes in the material/mechanical properties were considered. Using the finite element method. two age-related models of lumbar spine segments (L3-L4) were constructed. The annulus of the models was modeled as laminate composite elements with 16 layers and 6 materials. The spinal stiffness and facet reaction of the lumbar spine increased with the age-related geometric changes in various combined loadings. Fiber and transverse tensile strains of the inner annulus. cancellous bone stress and end-plate stress decreased with the age-related geometric changes whereas fiber/layer compressive strains of the annulus. facet reaction. ligament reaction and end-plate rigidity increased. Consequently, it appears that in the normal age-related deterioration of discs, the age-related geometric change contributes to the increase of spinal stiffness (the decrease in range of the motion segment), preventing an excessive deformation of the disc.

• Safety and Health at Work
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• v.1 no.1
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• pp.87-97
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• 2010

Objectives: This study was conducted to investigate the effect of trust on work stress. Trust can be classified into three dimensions; social trust, institutional trust, and trust in others. The relationship between work stress and trust is regarded as having three components. First, trust has an influence on work stressors as an antecedent variable; secondly, trust modifies the effect of the various stressors, and finally, trust is one of the stressors. Methods: Data for this study was collected by interviews and self-administered structured questionnaires from 376 Korean and 77 Japanese workers in small businesses. Subjects were selected by two stage stratified random sampling from the working population of manufacturing industries. Results: Three different positions of trust are significantly related with the stress causation web. Social trust, institutional trust and trust in others significantly influence different work stressors in both Korean and Japanese workers. Three different kinds of trust influence work stressors among Korean workers, but institutional trust has no impact on work stressors among Japanese workers. As a moderating variable for perceived stress, distrust in an employer is statistically significant in both groups. However, stress symptom prevalence among Korean workers is modified by caution, trust in career development, and distrust in co-workers, but that of Japanese workers is modified only by distrust in employer. Job satisfaction of Korean workers is affected by general trust, utility of relation, institutional trust and trust in employer, but among Japanese workers, caution, reputation and trust in employer have influence on job satisfaction. Conclusion: The effect of trust on work stress, perceived stress, stress reaction and job satisfaction are different among Korean workers and Japanese workers. Three dimensions of trust have three different positions as antecedent, moderating and mediating factors in stress causation.

• Korean Journal of Veterinary Research
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• v.13 no.2
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• pp.119-129
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• 1973

A hypothesis that is a stress condition in animal may cause either enhancement or reduction of the host resistance against microbial infection was experimentally studied. Among of many processes for stress formation an experimental electrization in mice was devised, on the bases of blood picture analysis, and studied the effect of experimental electrization of mice on E. coll infection. The results obtained were as follows. 1. Electrization with ordinary current, A. C. 60 cps., on the path of symmetrical line of both posterior limbs at 20 to 100 volts (less than 10 mA) for 15 to 30 seconds was able to induce a stress reaction in blood pattern without showing any dangers of electrocution, electric burns and other residual signs, and no correlation between blood pattern of the reaction and an amount of current between 20 to 100 volts was observed. As the electrodes, two of 21 gauge hypodermic needles were used, when the electrization each of them were inserted into the center of toe tissue of the both legs. 2. Serum protein fractions following the experimental electrization showed a tendency of a low A/G ratio and a high value of ${\alpha}$-globulin. 3. In the studies on the effect of electrical stress on the pathogenesis of E. coli in mice, a group in which a simultaneous electrization and infection, and a group infected two hours after electrization showed 80 per cent mortality. On the other hand, infection after 20 hours electrization and control groups showed their mortality of 40 and 60 per cent respectively.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.21 no.4
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• pp.245-275
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• 2017

The present investigation deals, Dufour and heat source effects on radiative MHD slip flow of a viscous fluid in a parallel porous plate channel in presence of chemical reaction. The non-linear coupled partial differential equations are solved by using two term perturbation technique subject to physically appropriate boundary conditions. The numerical values of the fluid velocity, temperature and concentration are displayed graphically whereas those of shear stress, rate of heat transfer and rate of mass transfer at the plate are presented in tabular form for various values of pertinent flow parameters. By increasing the slip parameter at the cold wall the velocity increases whereas the effect is totally reversed in the case of shear stress at the cold wall. It is observed that the effect of Dufour and heat source parameters decreases the velocity and temperature profiles.

• Computers and Concrete
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• v.19 no.2
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• pp.143-152
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• 2017

This paper has numerically investigated the changes of loading-induced stress in concrete with the corrosion time in the sulfate-containing environment. Firstly, based on Fick's law and reaction kinetics, a diffusion-reaction equation of sulfate ion in concrete is proposed, and it is numerically solved to obtain the spatial and temporal distribution of sulfate ion concentration in concrete by the finite difference method. Secondly, by fitting the existed experimental data of concrete in sodium sulfate solutions, the chemical damage of concrete associated with sulfate ion concentration and corrosion time is quantitatively presented. Thirdly, depending on the plastic-damage mechanics, while considering the influence of sulfate attack on concrete properties, a simplified chemo-mechanical damage model, with stress-based plasticity and strain-driven damage, for concrete under axial loading and sulfate attack is determined by introducing the chemical damage degree. Finally, an axially compressed concrete prism immersed into the sodium sulfate solution is regarded as an object to investigate the time-varying stress in concrete subjected to the couplings of axial loading and sulfate attack.

• Journal of Microbiology and Biotechnology
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• v.17 no.1
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• pp.176-179
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• 2007

An electron paramagnetic resonance (EPR) signal characteristic of the 5,5'-dimethyl-l-pyrroline-N-oxide (DMPO)-OH spin adduct, which is formed from the reaction of DMPO with superoxide radicals generated by xanthine oxidasemediated reaction, was significantly reduced by the cadaverine or Escherichia coli Mn-containing superoxide dismutase (MnSOD). Likewise, cytochrome c reduction by superoxide was inhibited by cadaverine, and the inhibition level increased in proportion to the level of cadaverine. The cadA mutant of Vibrio vulnificus, which does not produce cadaverine because of the lack of lysine decarboxylase, exhibits less tolerance to superoxide stress in comparison with wild type. The results indicate that cadaverine scavenges superoxide radicals, and protects cells from oxidative stress.