• 제목/요약/키워드: temperature cycles

검색결과 881건 처리시간 0.026초

Effects of atmospheric environmental changes on annual ring growth of Cryptomeria japonica in Southern Korea

  • Luong, Thi-Hoan;Jang, Kyoung-Soo;Choi, Woo-Jung;Lee, Kye-Han
    • Journal of Ecology and Environment
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    • 제36권1호
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    • pp.31-38
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    • 2013
  • Annual ring formation is considered a source of information to investigate the effects of environmental changes caused by temperature, air pollution, and acid rain on tree growth. A comparative investigation of annual ring growth of Cryptomeria japonica in relation to environmental changes was conducted at two sites in southern Korea (Haenam and Jangseong). Three wood disks from each site were collected from stems at breast height and annual ring growth was analyzed. Annual ring area at two sites increased over time (p > 0.05). Tree ring growth rate in Jangseong was higher than that in Haenam. Annual ring area increment in Jangseong was more strongly correlated with environmental variables than that in Haenam; annual ring growth increased with increasing temperature (p < 0.01) and a positive effect of $NO_2$ concentration on annual ring area (p < 0.05) could be attributed to nitrogen deposition in Jangseong. The correlation of annual ring growth increased with decreasing $SO_2$ and $CO_2$ concentrations (p < 0.01) in Jangseong. Variation in annual growth rings in Jangseong could be associated with temperature changes and N deposition. In Haenam, annual ring growth was correlated with $SO_2$ concentration (p < 0.01), and there was a negative relationship between precipitation pH and annual ring area (p < 0.01) which may reflect changes in nutrient cycles due to the acid rain. Therefore, the combined effects of increased $CO_2$, N deposition, and temperature on tree ring growth in Jangseong may be linked to soil acidification in this forest ecosystem. The interactions between air pollution ($SO_2$) and precipitation pH in Haenam may affect tree growth and may change nutrient cycles in this site. These results suggested that annual tree ring growth in Jangseong was more correlated with environmental variables than that in Haenam. However, the further growth of C. japonica forest at two sites is at risk from the long-term effects of acid deposition from fossil fuel combustion.

기후변화의 위험헷지와 기온파생상품

  • 손동희;임형준;전용일
    • 자원ㆍ환경경제연구
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    • 제21권3호
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    • pp.465-491
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    • 2012
  • 지구온난화에 대처하기 위한 한 가지 방안으로, 최근 녹색성장과 녹색금융이 활성화되고 있다. 특히, 금융시장을 통하여 기온상승에 대한 적응을 가능케 하는 기온파생상품은 녹색금융의 능동적 형태로서 주목받고 있다. 본 논문에서는 서울의 일별평균기온에 대한 특성을 파악하여 계절성, 주기성 등을 포함한 일별평균기온 예측모형을 설정한 후, 기온옵션의 일종인 CDD 옵션가격과 HDD 옵션가격을 시뮬레이션을 통해 분석한다. 오차항의 주기성 모형여부에 따라 구분하여 분석을 진행한 결과, CDD 콜옵션과 HDD 풋옵션의 위험중립가치가 시간이 지남에 따라 상승한 것으로 나타나 기온상승의 추세를 금융시장에서 정량적으로 파악할 수 있는 것으로 나타났다. 기존 모형과는 달리, Vasicek 모형에 기반한 CDD 콜옵션가치분석시, 특정 행사가격 이상에서 옵션의 가치가 존재하여, 기온상승위험회피를 위한 금융상품으로서 활용이 가능하다.

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플립 칩 패키지 솔더의 탄소성 거동과 크립 해석 (Elastoplastic Behavior and Creep Analysis of Solder in a FC-PBGA Package)

  • 최남진;이봉희;주진원
    • 마이크로전자및패키징학회지
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    • 제17권2호
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    • pp.21-28
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    • 2010
  • 본 논문에서는 온도 사이클이 진행되는 동안 비선형 거동과 크립 거동을 보이는 FC-PBGA 패키지 솔더볼의 변형거동을 알아보기 위하여 시간에 종속하는 거동을 적용 시킬 수 있는 점소성 모델과 크립 모델에 대하여 유한요소해석을 수행하였다. 유한요소해석 결과의 신뢰성을 평가하기 위하여 무아레 간섭계를 이용하여 온도변화에 따른 열변형 실험을 수행하였다. 전체적인 굽힘변위는 Anand 모델과 변형률 분리 모델 모두 실험결과와 잘 일치하였으나 솔더볼의 변형률은 Anand 모델의 경우 큰 차이를 보이고 변형률 분리 모델의 경우 상당히 일치하는 계산결과를 얻었다. 따라서 본 논문에서는 변형률 분리 모델을 이용하여 시간에 종속하는 FC-PBGA 패키지 솔더볼의 크립 거동을 검토하였다. 솔더를 포함한 패키지에 온도변화가 생길 때 고온에서는 시간이 지남에 따라 크립 거동에 의해 솔더의 응력이 점차 완화되는 현상을 나타내고 있음을 알 수 있었다.

광섬유센서를 이용한 우주환경하에서 복합재료 적층시편의 노화에 따른 열팽창계수변화 측정 (Measurement of CTE Change in a Composite Laminate with Aging under Space Environment using Fiber Optic Sensors)

  • 강상국;강동훈;김천곤;홍창선
    • 한국항공우주학회지
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    • 제31권10호
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    • pp.21-26
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    • 2003
  • 본 논문에서는 광섬유 센서를 사용하여 우주환경하에 노출된 그래파이트/에폭시 복합재 적층판의 열팽창계수의 변화를 측정하였다. 열변형률과 온도를 동시에 측정하기 위해서 두개의 FBG 센서를 사용하였다. 또한 열-진공 챔버를 사용하여 고진공, 자외선, 열적 사이클 등의 인자를 가지는 저궤도(LEO) 우주환경을 모사하였다. 예비실험으로써, 본 실험에서 사용되는 온도범위에 대해 FBG 온도센서를 기준온도계로부터 보정하였고 알루미늄 시편에 부착된 FBG 변형률 센서와 변형률 게이지(ESG)의 비교실험을 통해 FBG 변형률 센서의 사용가능성을 검증하였다. 검증된 FBG센서가 삽입된 그래파이트/에폭시 복합재 평판을 모사된 우주환경에 노출하여 일정한 노화간격마다 열팽창계수 변화를 실시간으로 측정하였다. 실험결과 1000 사이클 노화후의 열팽창계수는 노화전에 비해 대체적으로 큰 변화는 없었지만 전 온도구간에서 약간 감소하는 경향을 보였다. 이러한 현상은 가스방출(outgassing), 수분방출, 모재균열 등에 기인한다.

Membrane용 오스테나이트계 304 스테인리스강 판재의 3점 굽힘피로 특성 (Three-Point Bending Fatigue Properties of Austenitic 304 Stainless Steel Sheets for Membrane)

  • 이태호;김성준;김형식;김철만;홍성호
    • 한국가스학회지
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    • 제3권3호
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    • pp.1-8
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    • 1999
  • Membrane용 오스테나이트계 304 스테인리스강 판재의 3점 굽힘피로 특성에 관한 연구를 상온 및 LNG 온도인 $-162^{\circ}C$, 변형량 $0.43{\~}1.70\%$ 범위에서 수행하였다. 저온에서의 굽힘피로 특성이 상온보다 우수한 것으로 나타났고, 이는 변형유기 마르텐사이트 변태에 필요한 구동력이 적어서 보다 많은 양의 마르텐사이트를 함유했기 때문으로 판단된다. 상온 및 저온 모두에서 반복경화 현상이 관찰되었으며, 이러한 반복경화는 상온의 경우 피로주기가 반복됨에 따라 점진적으로 증가되지만 저온의 경우 초기 피로주기에서 급격히 증가된 후 점차로 감소하거나 일정한 값을 나타내었는데 이러한 차이는 저온의 경우 초기에 급격히 변형유기 마르텐사이트가 생성되지만 상온의 경우 변형유기 마르텐사이트 생성에는 일정한 소성변형의 축적이 필요하기 때문으로 생각된다. 기존의 JGA 연구결과와 비교해 볼 때 본 연구에서 사용된 국산소재의 굽힘피로 특성이 우수한 것으로 나타났다.

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Enhancement of Electrochemical Activity of Ni-rich LiNi0.8Mn0.1Co0.1O2 by Precisely Controlled Al2O3 Nanocoatings via Atomic Layer Deposition

  • Ramasamy, Hari Vignesh;Sinha, Soumyadeep;Park, Jooyeon;Gong, Minkyung;Aravindan, Vanchiappan;Heo, Jaeyeong;Lee, Yun-Sung
    • Journal of Electrochemical Science and Technology
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    • 제10권2호
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    • pp.196-205
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    • 2019
  • Ni-rich layered oxides $Li(Ni_xCo_yMn_z)O_2$ (x + y + z = 1) have been extensively studied in recent times owing to their high capacity and low cost and can possibly replace $LiCoO_2$ in the near future. However, these layered oxides suffer from problems related to the capacity fading, thermal stability, and safety at high voltages. In this study, we use surface coating as a strategy to improve the thermal stability at higher voltages. The uniform and conformal $Al_2O_3$ coating on prefabricated electrodes using atomic layer deposition significantly prevented surface degradation over prolonged cycling. Initial capacity of 190, 199, 188 and $166mAh\;g^{-1}$ is obtained for pristine, 2, 5 and 10 cycles of ALD coated samples at 0.2C and maintains 145, 158, 151 and $130mAh\;g^{-1}$ for high current rate of 2C in room temperature. The two-cycle $Al_2O_3$ modified cathode retained 75% of its capacity after 500 cycles at 5C with 0.05% capacity decay per cycle, compared with 46.5% retention for a pristine electrode, at an elevated temperature. Despite the insulating nature of the $Al_2O_3$ coating, a thin layer is sufficient to improve the capacity retention at a high temperature. The $Al_2O_3$ coating can prevent the detrimental surface reactions at a high temperature. Thus, the morphology of the active material is well-maintained even after extensive cycling, whereas the bare electrode undergoes severe degradation.

데이터센터의 급기온도 변화가 서버 냉각 성능에 미치는 영향에 대한 연구 (A Study on the Effects of Supply Air Temperature on the Server Cooling Performance in a Data Center)

  • 장현재
    • 설비공학논문집
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    • 제30권2호
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    • pp.83-91
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    • 2018
  • A datacenter is a high energy consuming facility whose cooling energy consumption rate is 10~20 times larger than general office buildings. The higher the temperature of supply air from a CRAC (computer room air-conditioner) is supplied, the more energy efficient cooling is possible because of improving the COP of a chiller and advanced range of outdoor air temperature available for the economizer cycles. However, because the temperature of cold air flowing into server computers varies depending on air mixing configurations in a computer room, the proper supply air temperature must be considered based on the investigation of air mixing and heat dissipation. By these, this study aims to understand the effects of variation of the supply air temperature on the air flow distributions, temperature distributions and rack cooling efficiencies. Computational fluid dynamics (CFD) aided in conducting the investigation. As a result, the variation of the supply air temperature does not affect the air flow distributions. However, it mainly affects the temperature distribution. From the results of CFD simulations, Rack cooling indices (RCIHI and RCILO) were evaluated and showed the ideal state set at $19^{\circ}C$ of the supply air temperature.

누적압연접합에 의한 5052 Al 합금의 결정립 미세화와 기계적 특성 연구 (An Investigation of Microstructural Evolution and Sliding Wear Behavior of Ultra-Fine Grained 5052 Aluminum Alloy Fabricated by a Accumulative Roll-Bonding Process)

  • 하종수;강석하;김용석
    • 한국소성가공학회:학술대회논문집
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    • 한국소성가공학회 2003년도 춘계학술대회논문집
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    • pp.84-87
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    • 2003
  • Microstructural evolution and dry sliding wear behavior of ultra-fine grained 5052 Al alloy obtained by an accumulative roll-bonding process have been investigated. After 7 ARB cycles, ultra-fine grains with large misorientations between neighboring grains were obtained. The grain size was about 0.2$\mu\textrm{m}$. The hardness, tensile and yield strengths of the ultra-fine grained alloy increased as the amount of accumulated strain increased with the ARB cycles. Sliding wear teats of the ultra-fine grained 5052 Al alloy were conducted at room temperature. Wear rate of the ultra-fine grained alloy increased in spite of the increase of hardness. Surfaces of the worn specimens were examined with SEM to investigate wear mechanism of the ultra-fine grained alloy.

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골재종류가 콘크리트의 열팽창계수에 미치는 영향 (Influencing Factor on Thermal Coefficient of Concrete due to Aggregate Types)

  • 김진철;양성철;김남호
    • 한국콘크리트학회:학술대회논문집
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    • 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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    • pp.249-254
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    • 2003
  • The thermal coefficient of concrete is measured using dilatometer (AASHTO TP60) and strain gage. Testing parameters such as six different coarse aggregate types, cycles of warming and cooling, specimen shape and measurement types were investigated to evaluate the influencing factors for thermal coefficient of concrete. According to experimental results, the thermal coefficient of concrete made with crushed aggregate showed 9.2 -10.$\mu\varepsilon/^{\circ}C$, , however recycled coarse aggregate classified type II showed a little increasing in comparison with crushed aggregate. The thermal coefficient of concrete made with recycled aggregate was reduced 0.2-0.4$\mu\varepsilon/^{\circ}C$, under temperature cycles. However, specimen shapes were revealed as mainly affecting factors on the thermal coefficient of concrete. Finally the thermal coefficient value determined by the dilatometer device was shown to be similar to the value from PML 60.

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철도차량 견인전동기의 가속열화수명평가 기술현황 (A technology State of Accelerating Degradation and Life Estimation on the Traction Motor for Railway Rolling Stock)

  • 왕종배;김기준;최영찬
    • 한국전기전자재료학회:학술대회논문집
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    • 한국전기전자재료학회 2000년도 제2회 학술대회 논문집 일렉트렛트 및 응용기술전문연구회
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    • pp.25-28
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    • 2000
  • In this paper, the technology for accelerating degradation & life estimation on the traction motor was introduced with the stator form-winding sample coils of the 200 Class insulation system The accelerative degradation was performed in 10 cycles, which were composed of thermal stress, fast rising surge voltage, vibration, water immersion and overvoltage applying. After aging of 10 cycles, condition diagnosis test such as insulation resistance & polarization index, capacitance & dielectric loss and partial discharge properties were investigated in the temperature range of $20{\sim}160^{\circ}C$. Relationship between degradation conditions and diagnosis results were analyzed to find an dominative degradation factor at the end-life point

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