• Ocean and Polar Research
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• 제44권2호
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• pp.179-190
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• 2022

Data missing in optical satellite images caused by natural variations have been a crucial barrier in observing the status of marine surfaces. Although there have been many attempts to fill the gaps of non-observation, there is little research to analyze the ratio of missing grids to overall sea grids and their seasonal patterns. This report introduces the method of quantifying the distribution of missing points and then shows how the missing points have spatial correlation and seasonal trends. Both temporal and spatial integration methods are compared to assess the effectiveness of reducing missing data. The temporal integration shows more outstanding performance than the spatial integration. Moran's I and K-function with statistical hypothesis testing show that missing grids are clustered and there is a non-random distribution from daily integration. The result of the seasonality test for Moran's I through a periodogram shows dependency on full-year, half-year, and quarter-year periods respectively. These analysis results can be used to deduce appropriate integration periods with permissible estimation errors.

• 대한전자공학회논문지SD
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• 제45권4호
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• pp.57-63
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• 2008

본 논문에서는 Contact Etch Stop Layer (CESL)인 nitride film의 mechanical stress에 의해 인가되는 channel stress가 소자 특성에 미치는 영향에 대해 분석하였다. 잘 알려진 바와 같이 NMOS는 tensile stress와 PMOS에서는 compressive stress가 인가되었을 경우 drain current가 증가하였으며 그 원인을 체계적으로 분석하였다. NMOS의 경우 tensile stress가 인가됨으로써 back scattering ratio ($\tau_{sat}$)의 감소와 thermal injection velocity ($V_{inj}$)의 증가로 인해 mobility가 개선됨을 확인하였다. 또한 $\tau_{sat}$, 의 감소는 온도에 따른 mobility의 감소율이 작고, 그에 따른 mean free path ($\lambda_O$)의 감소율이 작기 때문인 것으로 확인되었다. 한편 PMOS의 compressive stress 경우에는 tensile stress에 비해 온도에 따른 mobility의 감소율이 크기 때문에 channel back scattering 현상은 심해지지만 source에서의 $V_{inj}$가 큰 폭으로 증가함으로써 mobility가 개선됨을 확인 할 수 있었다. 따라서 CES-Layer에 의해 인가된 channel stress에 따른 소자 특성의 변화는 inversion layer에서의 channel back scattering 현상과 source에서의 thermal injection velocity에 매우 의존함을 알 수 있다.

• 한국건설순환자원학회논문집
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• 제4권1호
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• pp.74-80
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• 2009

본 연구는 BS를 다량 치환한 콘크리트의 양생온도에 따른 초기품질특성을 검토하여, 온도의존성을 분석한 것으로, 그 결과를 요약하면 다음과 같다. 먼저, 굳지않은 콘크리트의 특성으로 BS 치환율이 증가할수록 유동성은 증가하고, 공기량은 미세하게 감소하는 것으로 나타났다. 응결시간은 전반적으로 BS 치환율이 증가할수록 양생온도가 낮을수록 지연되는 것으로 나타났는데, 단, 양생온도 $35^{\circ}C$의 경우 BS 치환율 80%의 경우라도 $5^{\circ}C$, $20^{\circ}C$의 Plain에 비해 응결시간이 크게 촉진되는 것으로 나타나, 온도의존성이 매우 큰 것을 알 수 있었다. 경화 콘크리트의 특성으로 압축강도는 전반적으로 BS 치환율이 증가하고 양생온도가 낮아질수록 초기 압축강도는 비례적으로 저하하였는데, 양생온도가 높을수록 BS 치환율 증가에 따른 강도 저하폭이 상당부분 감소하여, 역시 온도의존성이 매우 중요함을 알 수 있었다.

• Journal of Mechanical Science and Technology
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• 제18권8호
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• pp.1479-1489
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• 2004

The effect of fluctuation of Equivalence Ratio (ER) in a turbulent reactive field has been studied in order to check the global combustion characteristics induced by the local fluctuation. When the flow is premixed on a large scale, closer examination on a small scale reveals that local fluctuations of ER exist in an imperfectly premixed mixture, and that these fluctuations must be considered to correctly estimate the mean reaction rate. The fluctuation effect is analyzed with DNS by considering the joint PDF of reactive scalar and ER, followed by modeling study where an extension of stochastic mixing models accounting for the ER fluctuation is reviewed and tested. It was found that models prediction capability as well as its potential is in favor to this case accounting the local ER fluctuation. However, the effect of local fluctuation did not show any notable changes on the mean global characteristics of combustion when statistical independence between the reactive scalar and ER field is imposed, though it greatly influenced the joint PDF distribution. The importance of taking into account the statistical dependency between ER and combustible at the initial phase is demonstrated by testing the modeled reaction rate.

• 동력기계공학회지
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• 제17권6호
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• pp.47-53
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• 2013

The article focuses on the Temperature characteristics inside single loop oscillating heat pipe (OHPs). In this paper, heat pipe is experimentally studied thereby providing vital information on the parameter dependency of their thermal performance. The impact depiction has been done for the variation of tube model of the device. OHPs are made of copper capillary tubes of outer diameter 6.25 mm, inner diameter 4 mm heated by constant temperature water bath cooled by ambient temperature. Using four types of OHPs of copper capillary tubes length of 1500mm and HP length 650mm inside tubes working fluid is R-22 Pressure 8 bar and mass 34g,32g,28g,16g. The results indicate a strong influence of filling ratio on the performance.

• 한국추진공학회지
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• 제19권4호
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• pp.45-51
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• 2015

정상초음파의 영향을 받는 메탄-공기 예혼합화염의 주파수-당량비 상관도 분석을 위한 실험적 연구가 수행되었다. 슐리렌가시화기법을 이용하여 예혼합화염의 전파영상을 획득하였으며, 영상 후처리를 통해 화염의 구조변이 및 전파거동을 면밀히 관찰하였다. 정상초음파가 개재할 때, 화염선단과 기연부에서 구조적 변이와 연소반응 촉진으로 인한 화염의 전파속도의 증가를 가져온다는 사실에 더하여, 초음파 구동주파수와 당량비에 대한 화염거동의 종속성을 확인하였다.

• 설비공학논문집
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• 제21권8호
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• pp.448-455
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• 2009

A performance analysis of the regenerative gas turbine system with afterfogging is carried out. Because of the high temperature at the outlet of air compressor, afterfogging has a potential of improved recuperation of exhaust heat than inlet fogging. Thermodynamic analysis model of the gas turbine system is developed by using an ideal gas assumption. Using the model, the effects of pressure ratio, water injection ratio, and ambient temperature are investigated parametrically on thermal efficiency and specific power of the cycle. The dependency of pressure ratio giving peak thermal efficiency is also investigated. The results of numerical computation for the typical cases show that the regenerative gas turbine system with afterfogging can make a notable enhancement of thermal efficiency and specific power. In addition, the peak thermal efficiency is shown to decrease almost linearly with ambient temperature.

• 보건교육건강증진학회지
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• 제6권2호
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• pp.58-65
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• 1989

This study analyzes the structural characteristics of rapid changes in Korean population, using the data of a census and other data on the changes in the population. Major findings are : 1. During 1950~1955, annual increase rate of population was about 1.02%, about 2.88% during 1955~1960, and 1.36% during 1980~1985. It is expected to decrease to 0.07% during 2015~2020. 2. Major Age Composition 0~14 is expected to reduce to 16.5% in 2020 from 41.2% in 1955, while the ratio of population aged 15~64 is expected to increase to 72.1% from 55.5%. Furthermore, for the population group of age 65 and over is expected to increase from a mere 3.3% to 11.4%. 3. The aging index of population is expected to increase to 69.5 in 2020 from 8.0 in 1955 and so the old dependency ratio is expected to 15.9 from 6.0 4. The median age is expected to 40.2 in 2020 from 19.0 in 1955. 5. In 2020 the child-woman ratio is expected to reduce to 22.3 from 64.7 in 1955. 6. In 2020 the age index of 0~4 is expected to 57.4 from 169.4 in 1955, and the age index of 65~69 to 261.7 from 95.6 on the contrary.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 춘계학술대회 논문집
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• pp.451-454
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• 2009

Production and application of biodiesel are expected to grow steadily in the coming years and thus output of its by-product, crude glycerin, will accordingly increase as well. In the present study, gasification of biodiesel by-product as a renewable energy was performed in an entrained flow gasifier to investigate the gasification performance with the operating conditions. Crude glycerin shows a high heating value of 6,000 kcal/kg and low ash and sulphur content. Gasification was conducted in a temperature range of $950\;{\sim}\;1500\;^{\circ}C$. The variation of syngas composition with excess air ratio of 0.17 ~ 0.7 for air or oxygen as a gasification agent was investigated. From the results, syngas heating value, carbon conversion and cold gas efficiency of more than $2500\;kcal/Nm^3$, 95% and 65% were achieved, respectively. The temperature dependency of syngas composition, carbon conversion, and cold gas efficiency shows a similar tendency to excess air ratio at the temperature corresponding to the excess air ratio. The $H_2/CO$ ratio of the product gas was varied from 1.25 to 0.7 with the excess air ratio and this gas composition was favorable for DME synthesis. The optimum excess air ratio for gasification of biodiesel by-product was evaluated to be an approximately 0.35 to 0.4. The present results indicate that crude glycerin can be utilized as a feedstock for gasification to make syngas.

• 한국추진공학회지
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• 제26권6호
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• pp.34-42
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• 2022

기체메탄-액체산소 소형로켓엔진에서 추진제 공급조건과 연소실 압력 사이의 상관관계를 조사하고, 고정된 연소실 압력에서 당량비 변화에 따른 성능특성을 분석하기 위해 지상연소시험이 수행되었다. 상관관계 조사를 통해 연소실 압력은 산화제 공급압력에 선형적으로 비례함이 확인되었다. 연소시험 결과, 당량비가 연료희박 조건으로부터 화학양론비에 가까워질수록 로켓엔진의 주요 성능인자인 추력, 비추력 및 특성속도는 증가하는 경향을 보였으나, 특성속도 효율 및 비추력 효율의 당량비에 대한 종속성은 그 반대의 경향을 보였다.