• Geomechanics and Engineering
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• v.21 no.4
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• pp.357-369
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• 2020

Different from the conventional planar fracture and simplified Newton model, for power-law slurries with a lower water-cement ratio commonly used in grouting engineering, flow model in geological rough fractures is built based on ten standard profiles from Barton (1977) in this study. The numerical algorithm is validated by experimental results. The flow mechanism, grout superiority, and water plugging of pseudo plastic slurry are revealed. The representations of hydraulic grouting properties for JRCs are obtained. The results show that effective plugging is based on the mechanical mechanisms of the fluctuant structural surface and higher viscosity at the middle of the fissure. The formulas of grouting parameters are always variable with the roughness and shear movement, which play a key role in grouting. The roughness can only be neglected after reaching a threshold. Grouting pressure increases with increasing roughness and has variable responses for different apertures within standard profiles. The whole process can be divided into three stationary zones and three transition zones, and there is a mutation region (10 < JRCs < 14) in smaller geological fractures. The fitting equations of different JRCs are obtained of power-law models satisfying the condition of -2 < coefficient < 0. The effects of small apertures and moderate to larger roughness (JRCs > 10.8) on the permeability of surfaces cannot be underestimated. The determination of grouting parameters depends on the slurry groutability in terms of its weakest link with discontinuous streamlines. For grouting water plugging, the water-cement ratio, grouting pressure and grouting additives should be determined by combining the flow conditions and the apparent widths of the main fracture and rough surface. This study provides a calculation method of grouting parameters for variable cement-based slurries. And the findings can help for better understanding of fluid flow and diffusion in geological fractures.

• Polymer(Korea)
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• v.36 no.1
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• pp.88-92
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• 2012

Long-term performance of polymer under constant sustained load has been the main research focus, which created a need for the accelerated test method providing proper lifetime assessment. Cycling fatigue loading is one of the accelerated test method and has been of great interest. Microstructure change of high density polyethylene under cyclic fatigue loading and creep was examined utilizing a tensile device specially designed for creep and fatigue test and also can be attachable to the X-ray diffractometer. In this way, the crystal morphology change of polyethylene under creep and cyclic fatigue load was successfully monitored and compared. Despite the marked differences in macroscopic deformation between the creep and cyclic fatigue tests, crystal morphology such as crystallinity, crystal size, and $d$-spacing was as nearly identical between the two test cases. Specimens pre-deformed to different strains, i.e., before yield point (BYP), at yield point (YP) and after yield point (AYP), however, showed markedly different changes in crystal morphology, especially between AYP and the other two specimens.

• Journal of The Geomorphological Association of Korea
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• v.19 no.1
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• pp.83-97
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• 2012

Slopes of Seoseokdea~ Jangbuljae, at Mt. Moodeung, appears repeatedly the cliffs are mostly greater than $70^{\circ}$, and the planations maintain around $5^{\circ}$ in general. They studied the creation of development environments, cryoplanation are mainly facing the southwest. It is assumed that rock falling had been wostly occurred under a periglacial environment through jointing due to repeated freezing and thawing. Planation at the bottom of Columnar joint are described structural benches. Movement precesses of planation matrix are solifluction or jelifluction. The result of age determination of the slopes in Jangbuljae tells that the upper part of Ibseokdae has been remaining exposed to the land surface from 110,000 year ago. The blocks in the bottom part has been exposed to the surface around 10,000 year ago while Jangbuljae has been exposed to the surface about 50,000 year ago. It was assumed that they moved to the current location since being separated from columnar joint after exposure to the surface.

• Biomolecules & Therapeutics
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• v.27 no.6
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• pp.530-539
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• 2019

Brain aging is an inevitable process characterized by structural and functional changes and is a major risk factor for neurodegenerative diseases. Most brain aging studies are focused on neurons and less on astrocytes which are the most abundant cells in the brain known to be in charge of various functions including the maintenance of brain physical formation, ion homeostasis, and secretion of various extracellular matrix proteins. Altered mitochondrial dynamics, defective mitophagy or mitochondrial damages are causative factors of mitochondrial dysfunction, which is linked to age-related disorders. Etoposide is an anti-cancer reagent which can induce DNA stress and cellular senescence of cancer cell lines. In this study, we investigated whether etoposide induces senescence and functional alterations in cultured rat astrocytes. Senescence-associated ${\beta}$-galactosidase (SA-${\beta}$-gal) activity was used as a cellular senescence marker. The results indicated that etoposide-treated astrocytes showed cellular senescence phenotypes including increased SA-${\beta}$-gal-positive cells number, increased nuclear size and increased senescence-associated secretory phenotypes (SASP) such as IL-6. We also observed a decreased expression of cell cycle markers, including PhosphoHistone H3/Histone H3 and CDK2, and dysregulation of cellular functions based on wound-healing, neuronal protection, and phagocytosis assays. Finally, mitochondrial dysfunction was noted through the determination of mitochondrial membrane potential using tetramethylrhodamine methyl ester (TMRM) and the measurement of mitochondrial oxygen consumption rate (OCR). These data suggest that etoposide can induce cellular senescence and mitochondrial dysfunction in astrocytes which may have implications in brain aging and neurodegenerative conditions.

• Structural Engineering and Mechanics
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• v.72 no.2
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• pp.245-256
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• 2019

The experimentally determined mechanical behavior of the material under the prescribed service conditions is the basis of advanced engineering optimum design. To allow experimental data on the behavior of the material considered, uniaxial stress tests were made. The aforementioned tests have enabled the determination of mechanical properties of material at different temperatures, then, the material's resistance to creep at various temperatures and stress levels, and finally, insight into the uniaxial high cyclic fatigue of the material under different applied stresses for prescribed stress ratio. Based on fatigue tests, using modified staircase method, fatigue limit was determined. All these data contributes the reliability of the use of material in mechanical structures. Data representing mechanical properties are shown in the form of engineering stress-strain diagrams; creep behavior is displayed in the form of creep curves while fatigue of the material is presented in the form of S-N (maximum applied stress versus number of the cycles to failure) curve. Material under consideration was 18CrNi8 (1.5920) steel. Ultimate tensile strength and yield strength at room temperature and at temperature of $600^{\circ}C$: [${\sigma}_{m,20/600}=(613/156)MPa$; ${\sigma}_{0.2,20/600}=(458/141)MPa$], as well as endurance (fatigue) limit at room temperature and stress ratio of R = -1 : (${\sigma}_{f,20,R=-1}=285.1MPa$).

• Steel and Composite Structures
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• v.29 no.5
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• pp.603-622
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• 2018

Precast concrete structures are erected from individual prefabricated components, which are assembled on-site using different types of connections. In the present design of these structures, beam-to-column connections are assumed pin jointed. Bolted billet beam to-column connections have been used in the precast concrete industry for many years. They have many advantages over other jointing methods in component production, quality control, transportation and assembly. However, there is currently limited information concerning their detailed structural behaviour under vertical loadings. The experimental work has involved the determination of moment-relative rotation relationships for semi-rigid precast concrete connections in full-scale connection tests. The study reported in this paper was undertaken to clarify the behaviour of such connections under symmetrical vertical loadings. A series of full-scale tests was performed on sample column for which the column geometry and bolt arrangements conformed to successful commercial practice. Proprietary hollow core floor slabs were tied to the beams by 2T25 tensile reinforcing bars, which also provide the in-plane continuity across the connections. The contribution of the floor strength and stiffness to the flexural capacity of the joint is currently neglected in the design process for precast concrete frames. The flexural strength of the connections in the double-sided tests was at least 0.93 times the predicted moment of resistance of the composite beam and slab. The secant stiffness of the connections ranged from 0.94 to 1.94 times the flexural stiffness of the attached beam. In general, the double-sided connections were found to be more suited to a semi-rigid design approach than the single sided ones. The behaviour of double sided bolted billet connection test results are presented in this paper. The behaviour of single sided bolted billet connection test results is the subject of another paper.

• Korean Journal of Occupational Health Nursing
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• v.28 no.4
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• pp.271-284
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• 2019

Purpose: This study aimed to examine the process from occurrence of a hospital nurse's suicide to workers' compensation approval, responses of the parties involved, issues debated during approval deliberations, and significant policy changes resulting from the incident. Methods: We conducted in-depth interviews with involved parties and collected various documents, including newspaper articles, forum proceedings, and the agency report on determination of workers' compensation. Content analysis was performed on the collected data. Results: A Joint Task Force continuously reported its progress and findings through mass media such as newspaper, radio, and TV. These activities exerted pressure on a government agency to conduct an occupational disease review and significantly impacted the workers' compensation approval. The agency recognized associations between the hospital's inadequate nurse training and the suicide but did not confirm the excessive overtime and workplace harassment experienced by the nurse as causes of the suicide. This case's media coverage and impact resulted in a law prohibiting workplace harassment and a hospital system dedicating at least one nurse to training activities. Conclusions: This incident had a significant social impact as the first case of workers' compensation approval for a hospital nurse's suicide. However, the case produced no structural changes in nurses' working conditions such as heavy workloads.

• The Journal of the Korea Contents Association
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• v.20 no.12
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• pp.482-491
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• 2020

This study proposed a research model based on self-determination theory and unified theory of acceptance and use of technology to explain the factors influencing intention to use sharing economy services. A total of 392 responses were collected, and structural equation analysis was performed with AMOS 22.0. The results are summarized as follows. First, self-technological aptness and trust had a positive effect on intention to use sharing economy services. Second, access bigger market and environmental friendliness had a positive effect on intention to use sharing economy services. Third, intention to use sharing economy services had a positive effect on actual usage of sharing economy services. Finally, benefits was found to strengthen the relationship between intention to use sharing economy services and actual usage of sharing economy services. The findings of this study would provide a theoretical framework for sharing economy services and important information for understanding individuals using the sharing economy services.

• Journal of Ginseng Research
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• v.45 no.2
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• pp.246-253
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• 2021

Background: Ginseng is one of the most valuable herbal supplements. It is challenging to perform quality control of ginseng products due to the diversity of bioactive saponins in their composition. Acid or alkaline hydrolysis is often used for the structural elucidation of these saponins and sugars in their side chains. Complete transformation of the original ginsenosides into their aglycones during the hydrolysis is one of the ways to determine a total saponin group content. The main hurdle of this approach is the formation of various by-products that was reported by many authors. Methods: Separate HPLC assessment of the total protopanaxadiol, protopanaxatriol and ocotillol ginsenoside contents is a viable alternative to the determination of characteristic biomarkers of these saponin groups, such as ginsenoside Rf and pseudoginsenoside F₁₁, which are commonly used for authentication of P. ginseng Meyer and P. quinquefolius L. samples respectively. Moreover, total ginsenoside content is an ideal aggregated parameter for standardization and quality control of ginseng-based medicines, because it can be directly applied for saponin dosage calculation. Results: Different hydrolysis conditions were tested to develop accurate quantification method for the elucidation of total ginsenoside contents in herbal products. Linearity, limits of quantification, limits of detection, accuracy and precision were evaluated for the developed HPLC-MS method. Conclusion: Alkaline hydrolysis results in fewer by-products than sugar elimination in acidic conditions. An equimolar response, as a key parameter for quantification, was established for several major ginsenosides. The developed approach has shown acceptable results in the analysis of several different herbal products.

• Advances in aircraft and spacecraft science
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• v.8 no.4
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• pp.345-372
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• 2021

The analysis of nonlinear vibrations, buckling, post-buckling, flutter boundary determination and post-flutter behavior of a homogeneous curved plate assuming cylindrical bending is conducted in this article. Other assumptions include simply-supported boundary conditions, supersonic aerodynamic flow at the top of the plate, constant pressure conditions below the plate, non-viscous flow model (using first- and third-order piston theory), nonlinear structural model with large deformations, and application of mechanical and thermal loads on the curved plate. The analysis is performed with constant environmental indicators (flow density, heat, Reynolds number and Mach number). The material properties (i.e., coefficient of thermal expansion and modulus of elasticity) are temperature-dependent. The equations are derived using the principle of virtual displacement. Furthermore, based on the definitions of virtual work, the potential and kinetic energy of the final relations in the integral form, and the governing nonlinear differential equations are obtained after fractional integration. This problem is solved using two approaches. The frequency analysis and flutter are studied in the first approach by transferring the handle of ordinary differential equations to the state space, calculating the system Jacobin matrix and analyzing the eigenvalue to determine the instability conditions. The second approach discusses the nonlinear frequency analysis and nonlinear flutter using the semi-analytical solution of governing differential equations based on the weighted residual method. The partial differential equations are converted to ordinary differential equations, after which they are solved based on the Runge-Kutta fourth- and fifth-order methods. The comparison between the results of frequency and flutter analysis of curved plate is linearly and nonlinearly performed for the first time. The results show that the plate curvature has a profound impact on the instability boundary of the plate under supersonic aerodynamic loading. The flutter boundary decreases with growing thermal load and increases with growing curvature.