• 제목/요약/키워드: aging variation

검색결과 252건 처리시간 0.026초

이종금속 용접부의 경도변화에 대한 장시간 인공열화의 영향 (Effects of Long-term Artificial-Aging on the Hardness Variation of Dissimilar Metal Weldments)

  • 김정석
    • 한국기계가공학회지
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    • 제18권1호
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    • pp.31-37
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    • 2019
  • This study investigates the effects of long-term artificial-aging on hardness variation in the dissimilar metal weldments for nuclear power plant facilities. These dissimilar welds are inevitably required to join the components in nozzle parts of pressurized vessels, such as austenitic stainless steels and ferritic steels. A artificial thermal aging was conducted in an electrical furnace to simulate material degradation at high temperatures. The test materials were held at the temperature of $600^{\circ}C$ for 10000 hours and interrupted at various levels of degraded specimens. The degradation of hardness is a well-known phenomenon resulting from long-term aging or high-temperature degradation of structural materials. In this study, the variation of hardness at each position was different, and complicated in relation to microstructures such as twins, grains, precipitates, phase transformations, and residual stresses in dissimilar weldments. We discussed the variation of hardness in terms of microstructural changes during long-term aging.

Effects of Channel Aging in Massive MIMO Systems

  • Truong, Kien T.;Heath, Robert W. Jr.
    • Journal of Communications and Networks
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    • 제15권4호
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    • pp.338-351
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    • 2013
  • Multiple-input multiple-output (MIMO) communication may provide high spectral efficiency through the deployment of a very large number of antenna elements at the base stations. The gains from massive MIMO communication come from the use of multi-user MIMO on the uplink and downlink, but with a large excess of antennas at the base station compared to the number of served users. Initial work on massive MIMO did not fully address several practical issues associated with its deployment. This paper considers the impact of channel aging on the performance of massive MIMO systems. The effects of channel variation are characterized as a function of different system parameters assuming a simple model for the channel time variations at the transmitter. Channel prediction is proposed to overcome channel aging effects. The analytical results on aging show how capacity is lost due to time variation in the channel. Numerical results in a multicell network show that massive MIMO works even with some channel variation and that channel prediction could partially overcome channel aging effects.

여성복의 사이즈체계에 관한 연구 : - 미국인 성인여성의 신체만족도 및 기성복 맞음새만족도 - (Sizing System of Women's Ready-to-Wear - Satisfaction with the Somatotype & Fit of American Women's Ready-to-Wear -)

  • 김희숙
    • 한국의류산업학회지
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    • 제6권5호
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    • pp.655-659
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    • 2004
  • The purpose of this study is to investigate the somatotype variation & satisfaction with the fit of ready-to-wear for American women. For this study, questionnaires were administered to 192 American women in Louisiana State areas. Employing a sample of 127 data were analyzed by using F-test. The results were as follows: In the satisfaction with the somatotype variation of American women, height items were increased and width items were decreased with aging. At neck, bust, waist, hip and sleeve circumferences, in the satisfaction with the fit of ready-to-wear, were decreased with aging, Correlation for somatotype variation & satisfaction with the fit of ready-to-wear was significantly positive. With aging, the satisfaction with the somatotype & fit of American women's ready-to-wear for sizing system was generally decreased.

Timing Analysis Techniques Review for sub-30 nm Circuit Designs

  • Kim, Ju-Ho;Han, Sang-Woo;Jewell, Roy
    • JSTS:Journal of Semiconductor Technology and Science
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    • 제10권4호
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    • pp.292-299
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    • 2010
  • With scaled technology, timing analysis of circuits becomes more and more difficult. In this paper, we review recently developed circuit simulation techniques created to deal with the cost issues of transistor-level simulations. Various techniques for fast SPICE simulations and Monte Carlo simulations are introduced. Moreover, process and aging variation issues are mentioned, along with promising methodologies.

Study on Aging Characteristics and Chemical Composition of Hydrogenated Transformer Oil

  • Qian, Yi-Hua;Huang, Yi-Bin;Fu, Qiang;Zhong, Zhen-Sheng
    • Journal of Electrical Engineering and Technology
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    • 제8권3호
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    • pp.588-594
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    • 2013
  • Under the condition of Baader aging, the chemical composition variation and the influence of transformer oil aging on electrical properties such as dielectric loss factor and physic-chemical properties such as interfacial tension were studied in the aging precess. Moreover, the correlation between hydrogenated transformer oil electrical and physic-chemical properties and its chemical composition variation were also investigated. The results show that these parameters of physic-chemical and electrical properties of hydrogenated transformer oil relate to each other and have closed correlation with chemical composition.

Characteristic of High Voltage Aging in AC PDPs

  • Lee, Yong-Han;Kim, Oe-Dong;Ahn, Byoung-Nam;Choi, Kwang-Yeol;Kim, Sung-Tae
    • 한국정보디스플레이학회:학술대회논문집
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    • 한국정보디스플레이학회 2006년도 6th International Meeting on Information Display
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    • pp.932-934
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    • 2006
  • A relationship between discharge delay time and the aging method were investigated: A-Y (Address electrode - Scan electrode) aging and conventional X-Y(Common electrode - Scan electrode) aging with the variation of sustain voltage beyond self-erasing discharge. Although A-Y aging decreases discharge delay time, it has several drawbacks like non-uniformity of discharge, degradation of luminous efficiency and a color temperature. In a conventional aging condition which is carried out near the mid-margin voltage, discharge delay time is short in low voltage and high frequency condition. As an alternative to conventional voltage aging, high voltage aging is suggested which is carried out at self-erasing sustain voltage region. High voltage aging shows lower discharge delay time and fast aging speed than conventional voltage aging.

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The Investigation on Thermal Aging Characteristics of Oil-Paper Insulation in Bushing

  • Liao, Rui-jin;Hu, En-de;Yang, Li-jun;Xu, Zuo-ming
    • Journal of Electrical Engineering and Technology
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    • 제10권3호
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    • pp.1114-1123
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    • 2015
  • Bushing is the key link to connect outer and inner insulating systems and also the essential electric accessory in electric power system, especially in the high voltage engineering (AC 1000kV, DC 800kV). This paper presented the experimental research of thermal aging characteristic of oil-paper insulation used in bushing. A thermally accelerated aging experiment at 90℃ was performed. The bushing models containing five layers of paper were sealed into the aging vessels and further aged for 250 days. Then several important parameters associated with the aging were observed and evaluated. The results showed that the degree of polymerization (DP) of papers gradually decreased. The DP values of outermost layer and middle layer fit well into the second-order kinematic model and first-order kinematic model, respectively. Less deterioration speed of the inter-layer paper than outer layer was confirmed by the variation of DP. Hydrolysis was considered as the main cause to this phenomenon. In addition, the logarithm of the furfural concentrations in insulation oil was found to have good linear relationship with DP of papers. Interestingly, when the aging time is about 250 days and DP is 419, the aging process reaches an inflection point at which the DP approaches the leveling off degree of polymerization (LODP) value. Both tanδ and acid number of oils increased, while surface and volume resistivity of papers decreased. The obtained results demonstrated that thermal aging and moisture absorbed in papers brought great influence to the degradation of insulating paper, leading to rapid decrease of DP and increase of the tanδ. Thus, the bushing should be avoided from damp and real-time monitoring to the variation of tanδ and DP values of paper is an effective way to evaluate the insulation status of bushing.

의복설계를 위한 농촌지역 노년기 여성의 체험 및 기성복 만족도 (Satisfaction with the Somatotype & Fit of Ready-to-Wear for Farm Elderly Women)

  • 김희숙
    • 한국의류산업학회지
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    • 제4권2호
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    • pp.169-175
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    • 2002
  • The purpose of this study is to investigate the somatotype variation & satisfaction with the fit of ready-to-wear for farm elderly women. For this study, questionnaires were administered to 320 farm elderly women in Andong, Eusung and Kunwe areas. Employing a sample of 258 data were analyzed by using F-test. The results were as follows: In somatotype variation of farm elderly women, height decreased and width increased with aging. At neck, bust, waist, hip and sleeve circumferences, satisfaction with the fit of ready-to-wear decreased with aging. Correlation for somatotype variation & satisfaction with the fit of ready-to-wear was significantly positive.

가교 폴리에틸렌의 열노화에 따른 구조와 물성의 변화 (The Variation of Structure and Physical Properties of XLPE during Thermal Aging Process)

  • 이미영;김철환;구철수;김복렬;이영관
    • 폴리머
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    • 제27권3호
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    • pp.249-254
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    • 2003
  • 가교 폴리에틸렌을 열을 가하여 노화시킨 후 구조 및 물성의 변화를 조사하였다. 가교 폴리에틸렌의 열적 산화 반응으로 카보닐 그룹이 형성됨을 X-선 광전자 분광법과 근적외선 분광법을 이용하여 확인하였다. 노화 시간이 길어질수록 1715 nm에서 관찰되는 카보닐 피이크가 정량적으로 증가하는 것을 근적외선 분광법을 이용하여 관찰하였다. 열화 시간에 따른 흡수 피이크의 선형적인 관계로부터 근적외선 분광법이 고분자 재료의 열화 과정을 감시하는데 적합한 방법임을 확인할 수 있었다. 또한 노화에 의한 가교 결합의 발생과 그에 따른 물리적 성질의 변화를 TMA, 응력-변형 시험, 쇼어 경도 측정 방법을 이용하여 관찰하였다. 노화가 진행됨에 따라 유리 전이 온도가 110에서 132$^{\circ}C$로 증가함을 관찰하였으며, 인장률은 265에서 110%로 점차 감소하고 쇼어 D 경도는 32에서 50으로 크게 증가하는 것을 관찰할 수 있었다.

CuAINi 형상기억합금의 시효처리에 따른 상변태 거동 (Phase Transformation Behavior on Aging Treatment in CuAINi Shape Memory Alloy)

  • 앙권승;강조원
    • 열처리공학회지
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    • 제6권4호
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    • pp.213-222
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    • 1993
  • This research was performed to investigate the transformation behavior and shape memory effect of Cu-13.5Al-4.5Ni(wt%) alloy with various aging temperature and time. The results obtained in this study are as follows: Transformation temperature was very increased when aging temperature is at $250^{\circ}C$. The variation of transformation temperature in first reverse transformation cycle and second was very significant, but there was little difference in case of 2nd and 3rd. Transformation temperature at various aging temperature was increased with increasing of aging temperature and time. Microvickers hardness was increased with increasing of aging temperature and time. It was found that ${\alpha}$ and ${\gamma}_2$ phase were created by aging of long time at high temperature.

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