• Restorative Dentistry and Endodontics
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• v.43 no.2
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• pp.26.1-26.12
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• 2018

Objective: The purpose of this study was to investigate the degree of conversion (DC) and mechanical properties of a microhybrid Filtek Z250 (3M ESPE) resin composite after aging. Method: The specimens were fabricated using circular molds to investigate Vickers microhardness (Vickers hardness number [VHN]) and DC, and were prepared according to ISO 4049 for flexural strength testing. The initial DC (%) of discs was recorded using attenuated total reflectance-Fourier transforming infrared spectroscopy. The initial VHN of the specimens was measured using a microhardness tester under a load of 300 g for 15 seconds and the flexural strength test was carried out with a universal testing machine (crosshead speed, 0.5 mm/min). The specimens were then subjected to thermocycling in $5^{\circ}C$ and $55^{\circ}C$ water baths. Properties were assessed after 1,000-10,000 cycles of thermocycling. The surfaces were evaluated using scanning electron microscopy (SEM). Data were analyzed using 1-way analysis of variance followed by the Tukey honest significant difference post hoc test. Results: Statistical analysis showed that DC tended to increase up to 4,000 cycles, with no significant changes. VHN and flexural strength values significantly decreased upon thermal cycling when compared to baseline (p < 0.05). However, there was no significant difference between initial and post-thermocycling VHN results at 1,000 cycles. SEM images after aging showed deteriorative changes in the resin composite surfaces. Conclusions: The Z250 microhybrid resin composite showed reduced surface microhardness and flexural strength and increased DC after thermocycling.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.6
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• pp.490-495
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• 2019

This study performs the thermal aging of chlorosulfonated polyethylene (CSPE) for 807.36 and 1,614.48 hours at $110^{\circ}C$, which is equivalent to 40 and 80 years of aging at $50^{\circ}C$ in nuclear power plants, respectively. Flat-type CSPEs were soaked in seawater for five days and then dried for five days at room temperature. Furthermore, the soaked CSPEs were cleaned for 5 days with fresh water and dried for 1,100 days at room temperature. Through this process, the log IV of the CSPEs decreases, whereas the dissipation factor of the CSPEs increases as thermally accelerated aged years increase at the measured frequency. Although the phase degree of the response voltage versus excitation voltage of the CSPEs increases, that of the response current versus excitation voltage decreases with the thermally accelerated aging. The thermal conductivity of the CSPEs increases slightly, but the thermal diffusivity does not vary with the thermally accelerated aged year increase. The displacement of the compressive strength of the CSPEs decreases gradually as the thermally accelerated aged years increase.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.5
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• pp.319-329
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• 2020

Among the bridges used in Korea, those that are more than 30 years old account for approximately 11% of the total bridges. Therefore, developing a seismic performance-evaluation method is necessary by considering the bridge age. Three composite steel-concrete box girder bridges with port, elastic-rubber, and lead-rubber bearings were selected, and a structural analysis model was developed using the OpenSEESs program. In this study, pier aging was reflected by the reduction in the area of the longitudinal and transverse rebars. Four conditions of 5%, 10%, 25%, and 50% in the degree of pier aging were used. As input earthquakes, 40 near-fault and far-field earthquakes were used, and the maximum displacement and maximum shear-force responses of the piers were obtained and compared. The result shows that as the aging degree increases, the pier strength decreases. Therefore, the pier displacement response increases. To analyze the effects of displacement response and shear resistance, displacement ratio D_ratio and shear-force ratio F_ratio were evaluated. The older the sample bridge is, the greater is the tendency of D_ratio to increase and the smaller is the tendency of F_ratio to decrease.

• Journal of the Korean Society for Heat Treatment
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• v.4 no.2
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• pp.47-53
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• 1991

Recrystallization behaviors of ordered and disordered structures in $Ll_2$ type $Ni_3Fe$ alloy were studied through hardness measurement and differential thermal analysis. When the disordered structure was isothermally aged at $480^{\circ}C$ below order-disorder transition temperature, the hardness of the structure was increased due to progressive ordering with increasing aging time. The hardness of the disordered structure was increased rapidly with increasing deformation degree up to 10%, and then gradually increased with further deformation degree. while the hardness of the ordered structure was increased rapidly with increasing deformation degree up to 10%, showing a constant hardness value up to 50% and gradually decreased with further deformation degree. The hardness of the ordered structure was higher than that of the disordered structure at all same deformation degrees. The recrystallization temperature of the ordered and disordered structures were decreased with increasing deformation degree. At the same deformation degrees, the recrystallization temperature of the ordered structure was lower than that of the desordered structure.

• Journal of the Korea Society of Computer and Information
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• v.25 no.1
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• pp.29-36
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• 2020

Wear-leveling techniques and Error Correction Codes (ECCs) are essential for the improvement of the reliability and durability of flash memories. Low-Density Parity-Check (LDPC) codes have higher error correction capabilities than conventional ECCs and have been applied to various flash memory-based storage devices. Conventional wear-leveling schemes using only the number of Program/Erase (P/E) cycles are not enough to reflect the actual aging differences of flash memory components. This paper introduces an actual aging measurement scheme for flash memory wear-leveling using LDPC decoding information. Our analysis, using error-rates obtained from an flash memory module, shows that LDPC decoding information can represent the aging degree of each block. We also show the effectiveness of the wear-leveling based on the proposed scheme through wear-leveling simulation experiments.

• Journal of Adhesion and Interface
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• v.3 no.2
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• pp.30-39
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• 2002

The effect of cure accelerator content on the change in crosslink density by thermal aging was studied for silica-filled natural rubber (NR) vulcanizates. Influence of silane coupling agent was also investigated. N-tert-Butyl-2-benzothiazole sulfenamide (TBBS) and bis-(3-(triethoxysilyl)-propyl)-tetrasulfide (TESPT) were used as a cure accelerator and a silane coupling agent, respectively. The crosslink density increased by thermal aging and the increasing level became larger as the aging temperature increased. The degree of crosslink density change of the vulcanizates without the silane coupling agent was larger than that of the vulcanizates containing the silane coupling agent. For the vulcanizates silane coupling agent, the activation energy for the crosslink density change decreased with increase of the cure accelerator content in the vulvanizate.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.3
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• pp.149-158
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• 2022

As a bridge ages, its mechanical properties and structural performance deteriorate, degrading its seismic performance during a strong earthquake. In this study, the aging of piers and bridge bearings was quantified in several stages and reflected in the analysis model, enabling the evaluation of the member-level seismic fragility of these bearings. Moreover, by assuming that the failure mechanism of a bridge system is a series system, a method for evaluating the system-level seismic fragility based on the member-level seismic fragility analysis result is formulated and proposed. For piers with rubber and lead-rubber bearings (members vulnerable to aging effects), five quantitative degrees of aging (0, 5, 10, 25, and 40%) are assumed to evaluate the member-level seismic fragility. Then, based on the result, the system-level seismic fragility evaluation was implemented. The pier rather than the bridge bearing is observed to have a dominant effect on the system-level seismic fragility. This means that the seismic fragility of more vulnerable structural members has a dominant influence on the seismic fragility of the entire bridge system.

• The Research Journal of the Costume Culture
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• v.20 no.5
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• pp.725-735
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• 2012

This study investigated the demand for functional clothing that compensates for the physical deformation of women due to aging. For this, the degree of perception of physical deformation at the new silver generation was examined. The demand for functional clothing that corrects body shape and posture according to differences in age and degree of perception was analyzed. Study participants(n=138) were women who ranged from 55 to 65 in age. Perception of physical deformation was investigated in the categories of deformation of body posture, cognition of joint pain, and deformation of body shape. Analysis results showed that cognition of joint pain was the largest of the three elements of body deformation, and each element had a high correlation between each other. Perception for degree of body deformation for women in their 50's and 60's was similar. These results show that changes in posture or body shape occur severely from the late 50's, and this appears as joint pain. The group with a high perception of posture deformation showed an especially high demand for functional clothing that corrects body shape and posture. The group with a high perception of body shape deformation had high demand for functional clothing that corrects body shape by lifting the hips and the breasts, and making the abdomen and waist slimmer. The results of this study show that women of the new silver generation are attuned to deformations in body shape and posture as well as joint pain beginning in their mid-fifties. There is a need to develop functional clothing to correct posture and body shape for the new silver generation women.

• Journal of the Korean Society of Tobacco Science
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• v.23 no.2
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• pp.149-155
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• 2001

This study was carried out to evaluate the correlations among degree of carbonization, chemical components and chromatic characteristics, and to establish the criterion of carbonizaion in leaf tobacco during aging storage. The flue-cured (B2O) and burley (B2T) leaf tobaccos were redried with conventional practices for each other type, and moisture contents of leaf tobaccos were adjusted to 13, 15, 17 and 19% after redrying. The leaf tobaccos were packed in carton box and stored for 8 months in the controlled-environment rooms($35^{\circ}C$, 65% R.H. and $40^{\circ}C$, 80% R.H.). Degree of carbonization, chemical components, and chromatic characteristics(L ; black-white, a ; red to green, b ; yellow to blue) were invetigated every month. Carbonization Index (C.I.) was established as (equation omitted) in accordance with degree of carbonization in two types. The C.I. value of flue-cured leaf(56.5) for slight carbonization was higher than that of burley leaf(48.0). C.I. and rate of usable leaf, L and b were positively correlated in two types. C.I. was significantly shown positive correlation with pH in two types. The correlations between the predicted and the observed values of slight carbonizating times(month after storage) using C.I. and pH were positive significant in two types. The results suggest that cabonization index may be useful to forecast and prevent the carbonization, and pH may be useful to estimate cabonization indirectly for flue-cured and burley leaves during aging storage.

• Journal of dental hygiene science
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• v.22 no.3
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• pp.164-170
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• 2022

Background: When cells are damaged by nicotine, cellular senescence due to oxidative stress accelerates. In addition, stress-induced inflammatory response and cellular senescence cause the accumulation of damaged organelles in cells, and autophagy appears to remove them. Conversely, when autophagy is reduced, harmful cell components accumulate, and aging is accelerated. This study aimed to determine the association between nicotine-induced cellular senescence and autophagy expression patterns in human gingival fibroblasts. Methods: Cells were treated with various concentrations of nicotine (0, 0.1, 0.5, 1, 2, and 5 mM) and 10 nM rapamycin was added to 1 mM nicotine to investigate the relationship between autophagy and cellular senescence. Cell viability was confirmed using WST-8 and the degree of cellular senescence was measured by SA-β-gal staining. The expression of the inflammatory proteins (COX-2 and iNOS) and autophagy markers (LC3-II, p62, and Beclin-1) was analyzed by western blotting. Results: The cell viability tended to decrease in a concentration-dependent manner. COX-2 showed no concentration-dependent expression and iNOS increased in the 0.5 mM nicotine treated group. The degree of cellular senescence was the highest in the 1 mM nicotine treatment group. In the group treated with rapamycin and nicotine, the conversion ratio of LC3-II to LC3-I was the highest, that of p62 was the lowest, and the level of Beclin-1 proteins was significantly increased. Furthermore, the degree of cellular senescence was reduced in the group in which rapamycin was added to nicotine compared to that in the group treated with nicotine alone. Conclusion: This study provides evidence that autophagy activated in an aging environment reduces cellular senescence to a certain some extent.