• Journal of applied mathematics & informatics
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• v.8 no.1
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• pp.59-69
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• 2001

The paper deals with the interaction between three Griffith cracks propagating under antiplane shear stress at the interface of two dissimilar infinite elastic half-spaces. The Fourier transform technique is used to reduce the elastodynamic problem to the solution of a set of integral equations which has been solved by using the finite Hilbert transform technique and Cooke’s result. The analytical expressions for the stress intensity factors at the crack tips are obtained. Numerical values of the interaction efect have been computed for and results show that interaction effects are either shielding or amplification depending on the location of each crack with respect to other and crack tip spacing. AMS Mathematics Subject Classification : 73M25.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.2 no.3
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• pp.48-55
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• 2003

This study investigates the effect of temperature and electric field strength on the Bingham characteristics of Electro-Rheological(ER) fluids which change their Yield shear stress and viscosity by temperature and electric field strength. It is found that under constant temperature the Yield sheal stress and viscosity of ER fluids proportionally increase with the applied electric field strength, and under constant applied electric field strength the Yield shear stress and viscosity of ER fluids decrease with the increasing temperature. These results are considered to be applied to the fluid and pneumatic power industry.

• Journal of the Korean Society for Heat Treatment
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• v.5 no.3
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• pp.157-164
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• 1992

Barkhausen noise (BN) is created by the abrupt changes in the magnetization of materials under applied AC magnetizing field. These changes are known to be sensitive to residual and applied stresses. In this study, BN theory was reviewed and it was examined how BN intensity was affected by simultaneous stress, hardness and microstructural changes. Also, magnetoelastic effect was used to evaluate residual stresses through carrying out the cantilever beam test. An increase in BN intensity was observed when applied and residual stress changes from compression into tension. Microstructural softening by tempering also increased the amount of BN. Therefore, the quantitative evaluation of residual stress and microstructural changes will be possible, provided BN method is more studied about various materials through comparing with different stress measuring techniques.

• Tribology and Lubricants
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• v.10 no.3
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• pp.62-70
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• 1994

An analytical model of the stress field caused by sliding indentation of brittle materials is developed. The complete stress field is treated as the superposition of applied normal and tangential forces with a sliding blister approximation of the localized inelastic deformation occuring just underneath the indenter. It is shown that lateral cracking is produced by the sliding blister stress field and that median cracking is caused by the applied contact forces. The model is combined with an experimental volume change measurements to show that the relative magnitude of tensile stresses governing lateral crack and median crack growth varies with the magnitude of the applied load. This prediction is consistent with the different regimes of experimentally observed cracking in soda-lime glass.

• Journal of the Korean Society of Safety
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• v.3 no.2
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• pp.35-48
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• 1988

Modern technological progress demands the use of materials at high temperature and high pressure. One of the most critical factors in considering such applications - perhaps the most critical one - is creep behavior. In this study the stress exponents n were determined during creep over the temperature range of $90^{\circ}C\;to\;500^{\circ}C$ (0.4 - 0.85 Tm) and stress range of 0.64 kgt/$mm^2$ in order to investigate the creep hehavior. The stress dependence of rapture time (n') were determined over the temperature range of $200^{\circ}C\;to\;240^{\circ}C$ and stress range of 8.13 kgt/$mm^2$ to 9.55 kgt/$mm^2$ in order to investigate to creep rupture property. And the stress transient dip tests were also carried out for the internal stress ${\sigma}i$ over the temperature range of $90^{\circ}C\;to\;500^{\circ}C$ and stress range of 0.64kgt/$mm^2$ to 17.2 kgt/$mm^2$. The creep tests for constant temperature and stress transient dip tests were conducted in air with Al 7075 alloy under constant tensile load. At around the temperature range $200^[\circ}C\;-\;230^{\circ}C$ and the stress level 8.13 - 9.55 (kgt/$mm^2$), the temperature range $280^{\circ}C\;-\;310^{\circ}C$ and the stress level 1.85 - 2.55 (kgt/$mm^2$), the temperature range $380^{\circ}C\;-\;410^{\circ}C$ and the stress 1.53 - 0.91 (kgt/$mm^2$), the stress exponent in had the value of 6.2 - 6.65 but at around the temperature range $90^{\circ}C\;-\;120^{\circ}C$ and the stress level 10 - 17.2(kgt/$mm^2$), the value of 1.3, and at around the temperature range $470^{\circ}C\;-\;500^{\circ}C$, the stress level 0.62 - 1.02 (kgt/$mm^2$) the value of 1-1. Besides these results, at around the temperature $200^{\circ}C\;-\;240^{\circ}C$ the stress dependence of rupture time (n') had the value of 6.3. Finally, it was found that the value n calculated by considering the applied stress dependence of the internal stress were in good agreement with those obtained for the creep test. Then, it was concluded that the change in n was mainly attributed to the difference of the applied stress dependence of the internal stress and the ratio of the internal stress to the applied stress, and the creep rupture life may be represented as.

• Journal of Korean Society for Atmospheric Environment
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• v.26 no.3
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• pp.253-264
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• 2010

This study investigates the relationship between daily mortality and heat stress in Seoul, using perceived temperatures (PT) derived from a heat budget model. During the summer season, observed PT intensity showed the biggest magnitude of summer heat stress from the middle 10 days of July to the first 10 days of August. The elderly (65 and above) were found to be the most vulnerable to heat stress. The threshold PT, with a significant increase in excess mortality, was $38^{\circ}C$. No time lagged effect was observed with summer heat stress, while a high correlation was observed between anomalies in PT and relative deviation of mortality. A comparison of the heat index and the discomfort index with excess mortality revealed that the discomfort index underestimated excess mortality, whereas the heat index could not appropriately explain the increase in excess mortality correlated with the increase in excess heat. In contrast, PT was found to be the weather element that best represents excess mortality due to heat stress, and is thus expected to serve as a more reliable forecast index of human biometeorology.

• Journal of Plant Biotechnology
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• v.30 no.2
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• pp.201-206
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• 2003

Differential responses of red pepper plant and cultured cells to enhanced ${\gamma}$-ray($^{60}$ Co) and ultraviolet(UV) stress were investigated. In seed treatment, 1 Gy of ${\gamma}$-ray increased seedling dry weight up to 19.1%, but 50 Gy treatment markedly ingibited seed germination and subsequent growth of seedling. UV treatment to seed did not change the germination ability of seeds and the growth of seedlings regardless of duration of UV treatment until 24 hrs. In case of UV treatment to seedlings, plant injury was seriously progressed even after the seedlings were returned to no UV condition, and eventually all the leaves showed chlorosis by the stress. However, progress of plant injury by ${\gamma}$-ray stress slower than that caused by UV stress, and even at the high dose of ${\gamma}$-ray 50 Gy, did not caused the cholrosis of stressed plant leaf. Amount of electrolytes leakage from plant leaf by UV treatment for 24hrs was increased up to 28.8 folds in comparison with untreated control, whereas that of 50 Gy of ${\gamma}$-ray was increased only 1.2 folds. UV stress induced the production of capsidiol, antimicrobial phytoalexin, by activation of gene expression involved in capsidiol biosynthesis, such as sesquiterpene cyclase and cyclase and cytochrome P450 hydroxylase in the leaf and cultured cell, but ${\gamma}$-ray stress induced neither the production of capsidiol nor expression of the genes.

• Journal of The Korean Society of Grassland and Forage Science
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• v.42 no.4
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• pp.222-228
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• 2022

This study was conducted to investigate the effect of waterlogging stress on the physiological response and growth characteristics of the five Italian ryegrass varieties. For all varieties, the germination rate of seed decreased by 10-15% as the waterlogging period increased, but the waterlogging stress treatment after the early seedling stage increased the growth of shoot and root length. Photosynthetic activity (Fv/Fm) according to waterlogging stress treatment decreased in all vareity, and Florida 80 showed the least decrease with 1.5%. Waterlogging stress treatment was found to reduce the accumulation of reactive oxygen species (malondialdehyde, MDA) and the activities of antioxidant enzymes. These results suggest that other mechanisms may be involved in the defense mechanism of Italian ryegrass against waterlogging stress, such as promoting root growth to escape from waterlogging stress, in addition to the antioxidant enzyme system.

• Proceedings of the Korean Society of Crop Science Conference
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• 2022.10a
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• pp.284-284
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• 2022

The overall effects of gibberellic acid (GA3) with NaCl on different rice genotypes are inadequately understood. The present study determines the effect of different GA3 concentrations on the morphophysiological, molecular and biochemical effects of 120 mM NaCl salt stress in rice seedlings. Salt stress reduced germination percentages and seedling growth and decreased bioactive GA content. It also downregulated the relative expression of a-amylase-related genes - OsAmy1A, OsAmy1C, and OsAmy3C in the salt-sensitive IR28 cultivar. Salt stress differentially regulated the expression of GA biosynthetic genes. Salt stress increased antioxidant activity in all rice genotypes tested, except in IR28. GA3 (50 and 100 µM) mitigates the effect of salt stress, rescuing seed germination and growth attributes. GA3 significantly increased bioactive GA content in Nagdong and pokkali (50 µM) and Cheongcheong and IR28 (100 µM) cultivars. The a-amylase genes were also significantly upregulated by GA3. Similarly, GA3 upregulated OsGA2oxl and OsGA2ox9 expression in the Cheongcheong and salt-sensitive IR28 cultivars. The present study demonstrated that salt stress inactivates bioactive GA - inhibiting germination and seedlings growth - and decreases bioactive GA content and GSH activity in IR28 and Pokkali cultivars. Further, GA3 significantly reversed the effects of 120 mM NaCl salt stress in different rice genotypes. The current study also suggests if we know the coastal area water NaCl concentration we can apply the exogenous GA3 accordingly. Thus, we would be able to grow rice cultivars near the coastal area and reduce the rice damage by salinity.

• Proceedings of the Korean Society of Plant Biotechnology Conference
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• 2003.04a
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• pp.103-103
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• 2003