• Title/Summary/Keyword: Aging

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Aging of Length-Extensional Vibration Modes in PZT Ceramics (PZT 세라믹스에 있어서 길이진동모드의 경시변화)

  • 이개명;김병효;황충구;강찬호;현덕수
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.15 no.10
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    • pp.858-864
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    • 2002
  • Aging stabilities of the operating frequency of piezoelectric devices such as filter, oscillator and discriminator are very important. In this study it was studied aging stabilities of the length-extensional vibration mode of Pb(Zr$\^$y/O$_3$+ x[wt%]Cr$_2$Co$_3$ ceramics. PZT ceramics in morphotropic phase boundary have higher aging rates of k$\_$31/ and resonance frequency than those in tetragonal phase or rhombohedral phase. Thermal aging moves the composition with maximum aging rate to Zr-rich side in Cr$_2$O$_3$ not added PZT system. In the PZT system, aging rates of k$\_$31/ and resonance frequency for first 30 days are bigger than those for the following 90 days. Thermal aging decrease those for first 30 days. Aging rate of resonance frequency of the ceramics with x=0.1, y=0.53 and x=0.3, y=0.53 increased by thermal aging.

Changes in free amino acids and hardness in round of Okinawan delivered cow beef during dry- and wet-aging processes

  • Hanagasaki, Takashi;Asato, Naokazu
    • Journal of Animal Science and Technology
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    • v.60 no.9
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    • pp.23.1-23.9
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    • 2018
  • Background: Aging trials are conducted to determine characteristics associated with dry- and wet-aging processes of beef from delivered cows grown in Okinawa, i.e., dams that have finished giving birth (Okinawan delivered cow beef). Changes in free amino acids, hardness, and other factors were analyzed in round of Okinawan delivered cow beef during dry- and wet-aging processes along with a comparison with characteristics of beef imported from Australia. Results: Functional amino acids did not increase during both dry- and wet-aging processes. However, proteinogenic amino acids increased significantly (P < 0.05) and hardness tended to decrease during both dry- and wet-aging processes. On comparison between dry- and wet-aging processes by analysis of variance, drip and cooking losses were significantly lower during the dry-aging process than during the wet-aging process. However, there was no significant difference in free amino acids or hardness in this comparison. Conclusion: There was no significant difference between dry- and wet-aging methods for all studied variables related to free amino acids or hardness in this study.

Analysis of Insulation Aging Mechanism in Generator Stator Windings (발전기 고정자 권선의 절연열화 메카니즘 분석)

  • 김희동
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.15 no.2
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    • pp.119-126
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    • 2002
  • The mica/epoxy composite used in generator(rated 22 kV and 500 MW) stator windings was aged at 180$\^{C}$ for up to 1000 hours in air and hydrogen. The degradation mechanism was investigated through the defect of evolution and microstructural analysis by performing SEM(Scanning Electron Microscope). As the thermal aging time increases, the number of voids per unit volume increases at the mica/epoxy interface of generator stator windings. The aged specimens in hydrogen showed retarded generation and growth of voids. Accelerated aging tests were conducted using the combination of thermal and electrical aging in air and hydrogen. The aging was carried out at a combined stress such as thermal aging at 110$\^{C}$, electrical aging at 5.5 kV/mm and frequencies 420 Hz in air, and electrical aging at 5.5 kV/mm and frequencies 420 Hz in hydrogen (pressure 4 kg/㎠). Thermal and electrical aging generates large voids at the mica/epoxy interface in air. Electrical aging in hydrogen also generates small voids, delaminations and cracks in mica tapes.

Influence of the Cure Systems on Long Time Thermal Aging Behaviors of NR Composites

  • Choi, Sung-Seen;Kim, Jong-Chul;Lee, Seung-Goo;Joo, Yong-L.
    • Macromolecular Research
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    • v.16 no.6
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    • pp.561-566
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    • 2008
  • NR composites with different curing systems were aged thermally at 60, 70, 80, and $90^{\circ}C$ for 2-185 days in a convection oven, and the changes in the crosslink density were investigated as a function of the accelerated thermal aging. The overall crosslink densities increased with increasing aging time irrespective of the aging temperatures and curing systems. The changes in crosslink density were enhanced by increasing the aging temperature. The degree of the increased crosslink density was in the following order: "the conventional cure system > the semi-EV system > the EV system". For short term thermal aging, the change in crosslink density with the aging time was complicated, particularly for low temperature aging. The activation energies of the change in crosslink density with thermal aging using the conventional and semi-EV cure systems increased and then remained relatively constant with increasing aging time, whereas that of the specimen with an EV cure system tended to increase linearly. The experimental results were explained by the dissociation of the existing polysulfidic linkages and the formation of new cross links through the crosslinking-related chemicals remaining in the sample.

Effects of Asymmetric Rolling and Aging Sequence on Microstructure and Mechanical Properties of Al-Zn-Mg-Cu Aluminum Alloys (비대칭 압연과 시효 시퀀스가 Al-Zn-Mg-Cu합금의 미세조직과 기계적 특성에 미치는 영향)

  • Minkyung Jeong;Jongbeom Lee;Su Hyeon Kim;Jun Hyun Han
    • Journal of the Korean Society for Heat Treatment
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    • v.36 no.5
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    • pp.285-297
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    • 2023
  • The effects of aging treatment sequence, specifically pre-aging and post-aging, on the microstructure and mechanical properties of Al-Zn-Mg-Cu aluminum alloys has been studied in comparison to symmetrically rolled specimens. In symmetrically rolled specimens, a straight-band precipitation distribution was observed, whereas asymmetrically rolled specimens exhibited a curved-band microstructure of fine precipitates. Notably, the asymmetrically rolled specimens displayed higher strengths. In the case of post-aging, the aging process occurred after rolling, and the dislocations generated during rolling acted as nucleation sites for precipitates during aging. This resulted in the formation of fine precipitates, contributing to improved mechanical properties compared to symmetric rolling. To enhance strength of the Al-Zn-Mg-Cu aluminum alloys, asymmetric rolling proves to be more effective than symmetric rolling, with post-aging showing greater efficacy than pre-aging.

The effect of aging on the quality of Semimembranosus muscle from Hanwoo

  • Kim, Sun Hyo;Kim, Hyun Joo;Lee, Hyun Jung;Yong, Hae In;Jo, Cheorun;Nam, Ki Chang;Jung, Samooel
    • Korean Journal of Agricultural Science
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    • v.43 no.1
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    • pp.61-71
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    • 2016
  • The effect of postmortem aging on the quality of Semimembranosus muscle (SM) from Hanwoo was investigated. The quality of SM was compared with that of Longissimus dorsi muscle (LD). SM contained higher moisture, protein, and ash, and lower fat than LD (p<0.05). The $a^*$ and $b^*$ values of SM were significantly decreased after 21 days of aging. SM showed higher $a^*$ values than LD at 1 and 7 day of aging (p<0.05). The cooking loss of SM was not affect by aging. SM had higher cooking loss than that of LD throughout the aging period. Although the shear force of SM was significantly decreased by aging, SM showed high shear force compared to LD during aging period (p<0.05). Aging increased lipid oxidation in both muscles (p<0.05). However, TBARS value of SM was significantly lower than that of LD throughout the aging period (p<0.05). There was no effect of aging on the betaine and L-carnitine contents of SM. SM contained higher betaine and L-carnitine than LD in all aging days (p<0.05). Therefore, we concluded that consumer acceptability of SM could be increased by aging based on the increase of tenderness in addition to its high nutritional properties.

Aging and Wisdom: An Integrated Conceptualization of Successful Aging (나이듦과 지혜: 성공적 노화의 통합적 개념화)

  • Su-Lim Lee;Seong-Ho Cho
    • Korean Journal of Culture and Social Issue
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    • v.13 no.3
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    • pp.65-87
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    • 2007
  • The objective of the study was to cast a frame for the integrating concept of successful aging together with for understanding both elderly problems and aging, which was one of the major issues in aging society. For this, the author reviewed the meaning of aging and also made a general survey of both affirmative change such as growth and development and negative change with regard to aging. Particularly, it was observed that wisdom is a key factor for successful aging. The existing theory of successful aging and major study results were reviewed. As a result, the author proposed an integrated conceptualization of successful aging under the general discussion of the limits of existing theory and also explained the characteristics and implications of an integrated conceptualization of successful aging in line with the discussion on the definition of the integrated concept of successful aging.

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Dry aging of beef; Review

  • Dashdorj, Dashmaa;Tripathi, Vinay Kumar;Cho, Soohyun;Kim, Younghoon;Hwang, Inho
    • Journal of Animal Science and Technology
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    • v.58 no.5
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    • pp.20.1-20.11
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    • 2016
  • The present review has mainly focused on the specific parameters including aging (aging days, temperature, relative humidity, and air flow), eating quality (flavor, tenderness and juiciness), microbiological quality and economic (shrinkage, retail yields and cost) involved beef dry aging process. Dry aging is the process where beef carcasses or primal cuts are hanged and aged for 28 to 55 d under controlling environment conditions in a refrigerated room with $0^{\circ}$ to $4^{\circ}C$ and with relative humidity of 75 to 80 %. However there are various opinions on dry aging procedures and purveyors of such products are passionate about their programs. Recently, there has been an increased interest in dry aging process by a wider array of purveyors and retailers in the many countries. Dry aging process is very costly because of high aging shrinkage (6 to 15 %), trims loss (3 to 24 %), risk of contamination and the requirement of highest grades meat with. The packaging in highly moisture-permeable bag may positively impact on safety, quality and shelf stability of dry aged beef. The key effect of dry aging is the concentration of the flavor that can only be described as "dry-aged beef". But the contribution of flavor compounds of proteolysis and lipolysis to the cooked dry aged beef flavor is not fully known. Also there are limited scientific studies of aging parameters on the quality and palatability of dry aged beef.

Electric Field Induced Super-cooling System for Long Term Dry-aged Beef Loin

  • Park, Sin-Young;Kim, Hack-Youn
    • Food Science of Animal Resources
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    • v.40 no.2
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    • pp.286-296
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    • 2020
  • This study investigates the utilization of an electric-field-induced super cooling system in long-term dry aging of beef loin. Analyzed quality properties of dry-aged beef loin applied with electric field refrigeration (EFR) versus commercial refrigeration (CR). Quality properties was including aging loss, pH, water holding capacity (WHC), cooking loss, color, warner-bractzler shear force (WBSF), total plate count (TPC), and thiobarbituric acid reactive substances (TBARS). Aging loss of wk 1 EFR was significantly lower than CR (p<0.05). pH of EFR was slow change tendency compared CR. WHC of both aging methods were higher with increase in aging duration. Cooking loss of wk 1, 2, 4, and 10 EFR were significantly lower than CR (p<0.05). Lightness and redness of EFR was slow change tendency compared CR. However, yellowness of EFR was increased until wk 2, 3, and significantly decreased at wk 10 (p<0.05), but yellowness of CR was decreased until wk 3 and significantly increased with an increasing aging weeks (p<0.05). Both aging methods of WBSF was decreased with increase in aging weeks; however, wk 10 of CR was significantly lower than EFR (p<0.05). TPC after wk 3 EFR groups were significantly lower than CR groups (p<0.05), and TBARS of EFR groups were significantly lower than CR (p<0.05). The present results show that application of the EFR system for dry aging beef loin can extends its shelf life and induce changes of several aging properties in similar to commercial aging.

Characteristics of Undrained Static Shear Behavior for Sand Due to Aging Effect (Aging 효과에 따른 모래의 비배수 정적전단거동 특성)

  • 김영수;김대만
    • Journal of the Korean Geotechnical Society
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    • v.20 no.6
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    • pp.137-150
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    • 2004
  • Aging effect of sands showed insignificant result in comparison with that of clay, so that it has not been studied so far. But, as penetration resistance increase has been observed with the lapse of time after deposition and disturbance, aging effect of sands has been actively investigated by field tests, and recently many researchers are performing not oかy field tests but also laboratory tests on sands, so aging effects of sands have been also examined by laboratory tests. In this study, to observe the aging effect of undrained static shear behavior for Nak-Dong River sand, undrained static triaxial tests were performed with changing relative density$(D_r)$, consolidation stress ratio$(K_c)$, and consolidation time. These tests showed that modulus within elastic section increased as consolidation time increased, and in addition, phase transformation point strength$(S_{PT})$ and critical stress ratio point strength $(S_{CSR})$ also increased. But pore water pressure ratio$(u/{p_c}')$ decreased as consolidation time increased, so with this various result, aging effect of static shear for sands can be observed as well.