• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.10
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• pp.1832-1838
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• 2010

Aging of transformer insulating material in natural ester insulating oil is compared to that in conventional transformer oil. Aging of insulating paper and insulating oil have been studied by performing accelerated thermal aging test. Sealed aging test vessels containing cooper, laminated core, Kraft paper and insulating oil(natural oil or mineral oil) were aged at $140^{\circ}C$ for 500, 1000, 1500 and 2000 hours. Insulating oils after aging are investigated with total acid number, breakdown voltage and viscosity. Also, degradation of insulating paper after aging is determined using breakdown voltage and mechanical strength. Accelerated aging studies demonstrate a slower aging rate for natural ester insulating oil compared to the rate for conventional mineral oil.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.1216-1216
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• 2015

In this study, the author apply the VLF(Very Low Frequency) tan-delta data that has been measured at each office of the KEPCO 2012 to the Weibull distribution which is the statistical analysis as previous studies for the remaining life prediction through the improvement of the sensitivity and reliability of the degradation state assessment of underground distribution power cables. Also, in this paper, UCD(Used Cable Diagnosis) Matrix proposed by KEPCO was applied to the hierarchy of assessment prioritization. it suggests Aging Index for condition assessment and high reliability of proper economic replacement cycle using the weight according to the assessment prioritization.

• BMB Reports
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• v.49 no.9
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• pp.459-473
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• 2016

Neurodegenerative diseases (NDs) often involve the formation of abnormal and toxic protein aggregates, which are thought to be the primary factor in ND occurrence and progression. Aged neurons exhibit marked increases in aggregated protein levels, which can lead to increased cell death in specific brain regions. As no specific drugs/therapies for treating the symptoms or/and progression of NDs are available, obtaining a complete understanding of the mechanism underlying the formation of protein aggregates is needed for designing a novel and efficient removal strategy. Intracellular proteolysis generally involves either the lysosomal or ubiquitin-proteasome system. In this review, we focus on the structure and assembly of the proteasome, proteasome-mediated protein degradation, and the multiple dynamic regulatory mechanisms governing proteasome activity. We also discuss the plausibility of the correlation between changes in proteasome activity and the occurrence of NDs.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.424-429
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• 2003

Hot gas path components, which are made of nickel based superalloys, are subject to periodic replacement due to degradation of thermomechanical properties that might bring catastrophic failure during normal operation of gas turbine units. In order to rejuvenate the metallurgical condition of the serviced components, heat treating techniques such as solution annealing and aging heat treatments have widely been employed. However, the effectiveness of those typical heat treatments is not apparent enough in terms of quantitative grounds. On the other hand the demand of the rejuvenation heat treatment and hot isostatic pressing (HIP) have constantly been raised by the end users. Therefore it is necessary to verify how the typical heat treating techniques affect to the aged and degraded material. As the result of experimental work in this study, GTD-111 and GTD-222 Ni-based superalloys were collected and analyzed quantitatively through microscopic observation, microhardness evaluation and creep test.

• Proceedings of the KIEE Conference
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• 2005.07e
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• pp.73-75
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• 2005

In present measurement of moisture contents is used as one of method for estimating degradation of transformer. Most of people use Karl-Fischer titration method for detection moisture contents but this measurement is inconvenient method because we must analyze transformer oil-paper after dismounting transformer and sampling in field. Therefore we don't directly investigate them in field. In this paper we will introduce Recovery Voltage Method(RVM) that is new method for estimating measurement in field though dismounting facility. For measure of moisture contents using RVM in accordance with accelerated thermal aging we have made experimental test cell and aged at a temperature up to 140$^{\circ}C$ for 300 hours. And we have been measured at intervals of 100 hours using RVM 5462 made in fetter company.

• Journal of the Korean institute of surface engineering
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• v.50 no.6
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• pp.492-497
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• 2017

In this study, we investigated the effect of thermal aging on mechanical characteristics of Inconel 600 nickel-based alloy. The thermal aging was conducted up to 1000 hours at an atmosphere of $650^{\circ}C$. The microstructure of thermally aged specimens was investigated by an optical microscope (OM), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). In addition, tensile test (strain rate: 2 mm/min) and micro Vickers hardness test were conducted to evaluate mechanical properties with time. As a result of the experiment, Cr-rich carbide continuously precipitated during thermal aging, leading to the change of the mechanical characteristics and fracture mode. With the increase of aging time, tensile strength, yield strength, and hardness gradually decreased. The fracture mode changed from ductile to brittle with the increase of grain boundary carbide.

• Asian-Australasian Journal of Animal Sciences
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• v.31 no.8
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• pp.1336-1344
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• 2018

Objective: This study aimed to observe whether high-pressure processing (HPP) affected aroma development and the degradation rate of umami taste-related ATP breakdown products, specifically inosinic acid in grass-fed beef during vacuum aging. Methods: Strip loin (longissimus lumborum) cuts obtained from six grass-fed Friesian Holstein steers (32 months old) on day 4 post slaughter were vacuum-packed and subjected to pressurization at 300 and 500 MPa for 180 s at $15^{\circ}C{\pm}2^{\circ}C$. The samples were then stored for 4 weeks at $5^{\circ}C{\pm}0.5^{\circ}C$ under vacuum and compared with the control (0.1 MPa). Results: HPP increased the shear force value, promoted moisture loss and lipid oxidation, induced surface paleness, stabilized pH during aging, and reduced bacterial load and growth. The shear force value of 500 MPa-treated samples remained higher than the control after aging, while no significant differences were found between the control and 300 MPa-treated samples. Degradation of inosinic acid and inosine occurred during pressurization, resulting in an increase in hypoxanthine content. However, the degradation rate in HPP-treated samples during aging was slower; therefore, inosinic acid and inosine content remained higher than in control samples. No significant differences were found in hypoxanthine content at the end of aging. HPP intensified the levels of hexanal, octanal, 2-methylbutanal, 3-methylbutanal, benzaldehyde, and 2,5-dimethylpyrazine in cooked-aged beef samples. Conclusion: HPP induced aroma development and delayed the degradation of inosinic acid. However, it also reduced the postmortem tenderization rate.

• Journal of Preventive Medicine and Public Health
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• v.44 no.1
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• pp.9-13
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• 2011

Objectives: Although increased reactive oxygen species (ROS) is caused by stress accelerates collagen degradation, there was no data on the relationship between stress and urinary hydroxyproline (Hyp) and proline (Pro), a good marker of collagen degradation. The purpose of this study was to evaluate the relationship between depression, anxiety, and stress (DAS) and concentrations of urinary Hyp and Pro. Methods: 97 hospital employees aged 20 to 58 were asked to fill out comprehensive self-administrated questionnaires containing information about their medical history, lifestyle, length of the work year, shit-work and DAS. Depression Anxiety Stress Scale (DASS) was applied to evaluate chronic mental disorders. Urine samples were analyzed using High Performance Liquid Chromatography (HPLC) with double derivatization for the assay of hydroxyproline and proline. Results: The mean value of Hyp and Pro concenturation in all subjects was $194.1{\pm}113.4\;{\mu}mol/g$ and $568.2{\pm}310.7\;{\mu}mol/g$. DASS values and urinary Pro concentrations were differentiated by sex (female > male, p < 0.05) and type of job (nurse > others, p < 0.05). In the stepwise multiple linear regressions, urinary Hyp and Pro concentrations were influenced by stress (Adjusted $r^2$ = 0.051) and anxiety and job (Adjusted $r^2$ = 0.199), respectively. Conclusions: We found that stress and anxiety were correlated with urinary Hyp and Pro concentrations. To identifying a definite correlation, further study in large populations will be needed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.3
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• pp.681-686
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• 2017

Degradation is commonly observed in field-aged PV modules due to corrosion of the photovoltaic ribbon. The reduced performance is caused by a loss of fill factor due to the high series resistance in the PV ribbon. This study aimed to mitigate the degradation by corrosion using five sacrificial anodes - Al, Zn and their alloys - to identify the most effective material to mitigate the corrosion of the PV ribbon. The corrosion behavior of the five sacrificial anode materials were examined by open circuit potential measurements, potentiodynamic polarization tests, and galvanic current density and potential measurements using a zero resistance ammeter. Immersion tests for 120 hours were also conducted using materials and damp heat test tests were performed for 1500 hours using 4 cell mini modules. The Al-3Mg and Al-3Zn-1Mg sacrificial anodes had a low corrosion rate and reduced drop in power, making then suitable for long-term use.

• Smart Structures and Systems
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• v.19 no.3
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• pp.335-340
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• 2017

Fiber Bragg grating (FBG) sensors are applied to structural health monitoring (SHM) in many areas due to their unique advantages such as ease of multiplexing and capability of absolute measurement. However, they are exposed to cyclic thermal load, generally in the temperature range of $-20^{\circ}C$ to $60^{\circ}C$, in railways during a long-term SHM and the cyclic thermal load can affect the mechanical strength of FBGs. In this paper, the effects of both cyclic thermal load and the reflectivity of FBGs on the mechanical strength are investigated though tension tests of FBG specimens after they are aged in a thermal chamber with temperature changes in a range from $-20^{\circ}C$ to $60^{\circ}C$ for 300 cycles. Results from tension tests reveal that the mechanical strength of FBGs decreases about 8% as the thermal cycle increases to 100 cycles; the mechanical strength then remains steady until 300 cycles. Otherwise, the mechanical strength of FBGs with reflectivity of 6dB (70%) and 10dB (90%) exhibits degradation values of about 6% and 12%, respectively, compared to that with reflectivity of 3dB (50%) at 300 cycles. SEM photos of the Bragg grating parts also show defects that cause their strength degradation. Consequently, it should be considered that mechanical strength of FBGs can be degraded by both thermal cycles and the reflectivity if the FBGs are exposed to repetitive thermal load during a long-term SHM.