• Journal of Welding and Joining
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• v.22 no.2
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• pp.59-68
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• 2004

Plasma transferred arc welding (PTAW) has been taken into consideration for repairing Ni-based superalloy components used gas turbine blades. Various cracks has been generally reported to be found in the base metal heat affected zone(HAZ) along grain boundary. Thus, hot cracking susceptibility of Ni-based superalloys was evaluated according to heat treatments. Hot ductility test was conducted on specimens with solution treated at 112$0^{\circ}C$ for 2 hours and aging treated at 845$^{\circ}C$ for 24hours after solution treatment. The results of the hot ductility test appeared that solution treated specimens were the highest ductility recovery rate among three conditions. The loss of ductility at high temperature in Ni-based superalloy was mainly controlled by the degree of pain boundary wetting due to constitutional liquation of MC carbide precipitates. Meanwhile, the highest ductility recovery rate in solution-treated alloys seems to be lack of M23C6, which can be dissolved during heating and then result in the local enrichment of Cr in the vicinity of the grain boundary.

• Journal of Korea Foundry Society
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• v.18 no.4
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• pp.364-372
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• 1998

Effects of Si and Ca additions on the mechanical properties of AM60 based Mg alloys have been investigated. Hardness of the AM60 based Mg alloys reached a maximum value after aging for approximately 33 hours but the amount of hardness increase was negligible. The poor age hardening response of the alloys was due to low Al content, which implies that Al content must be >6 wt.% to observe age hardening effect. The tensile and yield strength increased with increasing Al, Si, and Ca content but elongation decreased with increasing Al and Si content. The best mechanical properties obtained in AM 40-2.5Si-0.2Ca alloy after T4 heat treatment were as follows; tensile strength 193.4 MPa, yield strength 79.2 MPa, and elongation 11.2%. High temperature property obtained from creep test was also improved by introducing $Mg_2Si$ which has high hardness, high melting temperature and low thermal expansion coefficient.

• Bulletin of the Korean Chemical Society
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• v.34 no.8
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• pp.2271-2275
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• 2013

We report on the photoelectrochemical properties of partially reduced mesoporous titania thin films. The fabrication is achieved by synthesizing mesoporous titania thin films through the self-assembly of a titania precursor and a block copolymer, followed by aging and calcination, and heat-treatment under a $H_2$ (1 torr) environment. Depending on the temperature used for the reaction with $H_2$, the degree of the reduction (generation of oxygen vacancies) of the titania is controlled. The oxygen vacancies induce visible light absorption, and decrease of resistance while the mesoporosity is practically unaltered. The photoelectrochemical activity data on these films, by measuring their photocurrent-potential behavior in 1 M NaOH electrolyte under AM 1.5G 100 mW $cm^{-2}$ illumination, show that the three effects of the oxygen vacancies contribute to the enhancement of the photoelectrochemical properties of the mesoporous titania thin films. The results show that these oxygen deficient $TiO_2$ mesoporous thin films hold great promise for a solar hydrogen generation. Suggestions for the materials design for improved photoelectrochemical properties are made.

• The Journal of Asian Finance, Economics and Business
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• v.8 no.4
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• pp.369-379
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• 2021

This paper investigated the relationship between corporate governance mechanisms and firm performance in Vietnam. Based on a dataset of 101 HOSE-listed manufacturing firms, the results showed that CEOs' knowledge capability, gender diversity, and board size are positively associated with firm performance, whereas firm age is negatively associated. These findings suggested that firms should consider enlarging the boardrooms, but to a certain extent to avoid an inverse-U-shaped decline of performance; furthermore, firms should promote women executives' presence in a boardroom for it brings greater cultural-diversity benefits and inhibits information asymmetry. Contrary, the aging process impedes firms' growth. It depreciates their values in terms of total assets, so managers must review their assets' net value after each working year to avoid such a hardship. However, the thesis constrains itself since it did not treat the TMTs' knowledge capability equally as the CEOs' and completely excluded their treatment. Besides, it did not regard the effect of external governance mechanisms such as the supply-demand relationship, customer behavior, market imperfections, and market concentration due to data unavailability. Based on the main findings, several suggestions are set forth for firms and managers to enhance performance and minimize a poor governance mechanism's adverse consequence.

• Journal of Powder Materials
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• v.13 no.3 s.56
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• pp.178-186
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• 2006

The effect of use of $H_2O$ as PCA(process control agent) to prevent the carbon contamination during mechanical alloying process and the precipitation behavior in Ni-20Cr-20Fe-5Nb bulk alloy after aging were investigated. NbC and $Cr_2O_3$ were formed during mechanical alloying and consolidation processes in the Ni-20Cr-20Fe-5Nb alloy in which methanol($CH_3OH$) was added as PCA. Formation of NbC in this alloy decreased the amount of Nb dissolved in the Ni matrix. The use of $H_2O$ as PCA in Ni-20Cr-20Fe-5Nb alloy prevented the formation of NbC and increased the hardness. The increase of hardness in this alloy was attributed to the increased amount of Nb dissolved in the Ni matrix. After aging treatment for 20 hours at $600^{\circ}C\;and\;720^{\circ}C$ of Ni-20Cr-20Fe-5Nb bulk alloy in which $H_2O$ added as PCA, ${\gamma}"$$(Ni_3Nb,\;tetragonal)\;and\;{\delta}\;(Ni_3Nb,\;orthorhombic)$ precipitates were formed, respectively. The precipitation temperatures of ${\gamma}"$ and ${\delta}$ in this bulk alloy were lower than those in commercial IN 718 alloy. It seemed that the lower precipitation temperatures for ${\gamma}"$ and ${\delta}$ in this bulk alloy than in commercial IN 718 alloy were due to severe plastic deformation during mechanical alloying.

• Journal of Welding and Joining
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• v.31 no.3
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• pp.31-38
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• 2013

The transition of serrated grain boundary and its effect on liquation behavior in the simulated weld heat-affected zone (HAZ) have been investigated in a wrought Ni-based superalloy Alloy 263. Recently, the present authors have found that grain boundary serration occurs in the absence of adjacent coarse ${\gamma}^{\prime}$ particles or $M_{23}C_6$ carbides when a specimen is direct-aged with a combination of slow cooling from solution treatment temperature to aging temperature. The present study was initiated to determine the interdependence of the serration and HAZ property with a consideration of this serration as a potential for the use of a hot-cracking resistant microstructure. A crystallographic study indicated that the serration led to a change in grain boundary character as special boundary with a lower interfacial energy as those terminated by low-index {111} boundary planes. It was found that the serrated grain boundaries are highly resistant to boron enrichment, and suppress effectively grain coarsening in HAZ. Furthermore, the serrated grain boundaries showed a higher resistance to susceptibility of liquation cracking. These results was discussed in terms of a significant decrease in interfacial energy of grain boundary by the serration.

• Korean Journal of Food Science and Technology
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• v.36 no.6
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• pp.974-978
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• 2004

Brown-alga-derived natural agent NX42, mainly composed of algal polysaccharides and phlorotannins, showed mild but dose-dependent inhibition of acetylcholinesterase with $IC_{50}=600-700\;{\mu}g/mL$. Phlorotannin-rich fraction of NX42 showed substantial increase of the activity by more than one order of magnitude ($IC_{50}=54\;{\mu}g/mL$) and significant protection of SK-N-SH cells from oxidative stress by $H_2O_2$. Learning trials of mice for 5 consecutive days revealed electric-shock treatment during learning period significantly retarded learning process, whereas NX42-treated mice showed significant resistance against leaning deficiency possibly mainly due to anticholinesterase and neuroprotective activities of phlorotannin.

• Journal of Physiology & Pathology in Korean Medicine
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• v.35 no.3
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• pp.104-116
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• 2021

In order to reduce the social and economic costs due to the increase in dementia patients, which is a representative senile disease in an aging society, it will be important to prevent dementia and to detect and treat early in high-risk groups. This study reported the results of treatment for the elderly with high risk of dementia and depression who received Korean medicine (KM) treatment in 9 KM clinics. Medical charts were surveyed on 116 patients with high risk of dementia and depression who received KM treatment at 9 KM clinics in Gangseo-gu from September 1, 2020 to December 31, 2020. The majority of the patients were female(76.72%), the average age was 71.66±7.18 years old, and the average education level was 8.96±3.91 years. The average treatment period was 61.47±10.30 days, the average number of treatments was 15.38±1.06 times, and both acupuncture and herbal medicine were administered. After receiving KM treatment, cognitive assessment scores such as MMSE-DS and MoCA-K, depression-related GDSSF-K score, dementia knowledge, attitude, and preventive behavior, blood debilitation scale, and GQOL-D score were improved compared to before. There was no specific adverse reaction except that one patient with elevated AST and ALT levels was observed. This study showed improvement in cognitive function, depression, dementia-related scale, and quality of life in high-risk groups for dementia and depression over 60 years old who received KM treatment. More systematic and large-scale planned clinical studies will be needed.

• Journal of the Korean Institute of Gas
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• v.2 no.4
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• pp.42-46
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• 1998

Miniaturized specimen technology Permits mechanical behavior to be determined using a minimum volume of material. The technology is useful in case of not collecting a large amount of materials from industrial equipments. Five kinds of accelerated degradation materials were prepared by isothermal aging heat treatment at $630^{\circ}C$. Three kinds of specimens were prepared for impact testing. In order to increase plastic constraint of subsize specimen, side-groove was introduced. Results between subsize and full size impact testing were compared. Size effects correlations were developed for the impact properties of turbine rotor material. These correlations successfully predict the ductile brittle transition temperature (DBTT) of full size Charpy impact specimens based on subsize specimen data.

• Journal of Physiology & Pathology in Korean Medicine
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• v.34 no.2
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• pp.81-87
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• 2020

Cognitive impairment is symptoms of dementia, a degenerative brain disease that is drawing attention in a rapidly aging society. This study was conducted to investigate the improvement of cognitive function of Leonurus japonicus on scopolamine-induced memory impairment in mice and the effect and mechanism of memory recovery. In vivo studies were conducted on mice orally pretreated with L. japonicus in doses of 50, 100 and 200 mg/kg (p.o.) and scopolamine (1 mg/kg, i.p.) were injected 30 min before the behavioral task. Antioxidant activity was assessed by 2,2-diphenyl-1-picryl hydrazyl (DPPH) assay and 2,2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assay, and acetylcholinesterase (AChE) inhibition activity evaluated by Ellman's method. In behavior studies showed that L. japonicus has an improved the memory of scopolamine-treated mice in Y-maze, passive avoidance and Morris water maze test. In addition, L. japonicus was also exerted free radical scavenging activity and inhibited acetyl cholinesterase activity. These results suggest that L. japonicus improves short-term and long-term memory in scopolamine-induced memory decline model and prevents scopolamine-induced memory impairments through in reduced oxidative stress and acetyl cholinesterase inhibition effect. Thus, L. japonicus is related to functional medicinal materials for prevention and treatment of human dementia patients.