• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 가을 학술발표회 논문집
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• pp.391-396
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• 2002

The so called setting is defined as the onset of rigidity in fresh concrete. In the analysis of the early-age concrete behavior, we consider fresh concrete as a structural element immediately after mixing. But for the activation of real structural behavior of fresh concrete, it takes some time after the beginning of hydration reaction. So, the very early age deformations due to hydration heat and shrinkage which occur before the setting do not produce restraint stresses. In this paper, we propose a setting characteristic model based on the so called percolation theory. From the analysis using the model, the influence of curing temperature is investigated and analytical results are compared with experimental results. From the comparison, the validity of proposed model is verified. This model is also applied to evaluate stress development in a temperature-stress test machine (TSTM) specimen and then the effect of setting time on the stress development is discussed.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2003년도 총회 및 춘계학술발표회
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• pp.43-46
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• 2003

We consider influences of the aperture variation and the ambient groundwater flow on the migration of DNAPL within a fracture network. In context of a modified invasion percolation (MIP) growth algorithm, we formulate a mechanistic model that includes capillary and gravity forces as well as viscous forces within the DNAPL and the ambient groundwater. The MIP model is verified against laboratory experiments, which is conducted using a two-dimensional random fracture network model. The results show that the aperture variation and ambient groundwater flow can be significant factors controlling DNAPL migration path within fracture networks.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.490-493
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• 2004

In the analysis of early-age concrete behavior, the fresh concrete is considered as a structural element immediately after mixing. But for the activation of real structural behavior in the fresh concrete, the so-called setting time is necessary a few hours after the beginning of hydration reaction. In this paper, analysis on the setting behavior is carried out by proposing an analytical model based on the percolation theory as well as the expanding cluster model by defining the setting as a microstructure formation in fresh concrete. An experimental investigation is also carried out to show the influences of curing temperature, mineral admixtures and chemical admixture on setting behavior of fresh concrete. Finally, the analytical results using proposed model are compared with the experimental results for the sake of verification.

• 대한기계학회논문집B
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• 제33권12호
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• pp.1000-1006
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• 2009

Integrated Coal Gasification Combined Cycle (IGCC) power plants have been developed to reduce carbon dioxide emissions and to increase the efficiency of electricity generation. A devolatilization process of entrained coal gasification is predicted by CPD model which could describe the devolatilization behavior of rapidly heated coal based on the chemical structure of the coal. This paper is intended to compare the mass release behavior of char, tar and gas(CO, $CO_2,\;H_2O,\;CH_4$) for three different coals. The influence of coal structure on gas evolution is examined over the pressure range of 10${\sim}$30atm.

• 농촌계획
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• 제8권1호
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• pp.60-68
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• 2002

A Modified CREAMS model, CREAMS-PADDY was developed to simulate the hydrology and nutrient transport at an irrigated rice paddy. The hydrology at a paddy was simulated by a daily water balance routine which reflects daily inflow, outflow, and water level changes. The soil erosion was simulated using modified USLE. The nutrient transport for total nitrogen and phosphorus were depicted for various phases of each constitute such as extraction, percolation, mineralization, and plant uptakes. Field monitoring was conducted to investigate the water quality changes at a paddy field at three times a week during the growing season of 1996. The proposed model simulates the water quality of the paddy reasonably well, and is found to be applicable to field conditions.

• 방사성폐기물학회지
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• 제4권4호
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• pp.365-372
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• 2006

[ $^{137}C_s$ ]의 토양침적으로 인한 농작물 오염 평가를 위한 동적격실모델이 제시되었다 토양침투(percolation), 쟁기질에 의한 토양혼합(soil mixing), 뿌리흡수(plant uptake), 용출(leaching to a deep soil), 토양고착(fixation to a clay mineral)이 모델에서 고려된 $^{137}C_s$의 주요 이동경로이며 $^{137}C_s$의 토양이동에 대한 토양특성(pH, 점토함량, 유기물함량, 이온교환성 K 농도)의 영향을 반영하기 위하여 Absalom 모델을 적용하였다. 모델의 검증을 위해 다른 토양특성을 가진 17종류의 논토양에서 2년 연속 벼를 재배하면서 수행한 $^{137}C_s$ 모의침적실험으로부터 구한 벼에 대한 $^{137}C_s$ 전이계수를 모델에 의한 예측치와 비교하였다. 측정된 벼의 $^{137}C_s$ 전이계수는 pH와 점토함량 변화에는 뚜렷한 경향을 보여주지 않았으나, 유기물함량의 증가 또는 이온교환성 K 농도의 감소에 따라 다소 증가하는 경향을 보여주었다. 측정된 전이계수는 모델에 의한 예측치와 대체적으로 유사한 값을 가졌다.

• 대한토목학회논문집
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• 제31권3B호
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• pp.211-220
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• 2011

본 연구에서는 유역 물수지 모의를 위한 개념적인 토양수분모형이 제안된다. 모형은 지표면에 떨어지는 강수량이 지표면 유출, 습윤, 기화, 침루 등으로 분할되는 과정을 모의한다. 경험식으로 추정된 연별 기화량, NRCS-CN 방법으로 추정된 월별 습윤량 및 이 두 가지가 모두 주어진 경우를 구분하여 모형의 매개변수가 각각 추정되어 모형의 성능을 평가한다. 연별 기화량과 월별 습윤량 자료 모두가 모형 보정에 적용될 경우만이 보다 합리적인 강수분할이 모의될 수 있음이 분석된다.

• 한국자기학회지
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• 제22권1호
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• pp.6-10
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• 2012

본 연구에서는 인산 용액 하에서 2차 양극 산화 기법에 의해 제작된 양극 산화 알루미나 기판 상에 최대 13 nm 두께의 얇은 니켈 박막을 증착하며 증착 시 박막 두께에 따라 감소하는 박막의 저항 변화를 살펴보았다. 양극 산화 알루미나 막 표면에 존재하는 미세 기공 구조를 따라 증착된 니켈 박막 역시 다공 구조의 박막으로 성장하게 되며 증착된 박막의 두께 범위 내에서 박막의 저항은 $150k{\Omega}$ 이상의 값을 보이면서 박막 두께에 따른 저항의 감소가 매우 천천히 일어나는 것을 확인할 수 있었다. 측정된 저항 값은 기존에 보고된 균일한 기판 상에 증착된 동일 두께의 니켈 박막에 비해 매우 큼을 볼 수 있었으며 기판 표면에 존재하는 기공 구조에 의해 핵자가 형성될 수 있는 표면 면적 비가 박막 성장을 설명하는 스미기(percolation) 현상이론에서 예측하는 임계 값보다 매우 적어 미세 기공에 의해 박막의 성장과 함께 나타나는 전자 전도 채널의 형성이 저해됨으로 이해될 수 있다. 이와 함께 기존의 박막 두께에 따른 비저항 모델과 비교해 보았을 때 미세 기공의 경계에서 나타나는 전자 산란 현상 역시 박막저항의 증가에 기여함을 알 수 있다.

• Nano
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• 제13권11호
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• pp.1850126.1-1850126.10
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• 2018

Flexible strain sensors, as the core member of the family of smart electronic devices, along with reasonable sensing range and sensitivity plus low cost, have rose a huge consumer market and also immense interests in fundamental studies and technological applications, especially in the field of biomimetic robots movement detection and human health condition monitoring. In this paper, we propose a new flexible strain sensor based on thick CVD graphene film and its low-cost fabrication strategy by using the commercial adhesive tape as flexible substrate. The tensile tests in a strain range of ~30% were implemented, and a gage factor of 30 was achieved under high strain condition. The optical microscopic observation with different strains showed the evolution of cracks in graphene film. Together with commonly used platelet overlap theory and percolation network theory for sensor resistance modeling, we established an overlap destructive resistance model to analyze the sensing mechanism of our devices, which fitted the experimental data very well. The finding of difference of fitting parameters in small and large strain ranges revealed the multiple stage feature of graphene crack evolution. The resistance fallback phenomenon due to the viscoelasticity of flexible substrate was analyzed. Our flexible strain sensor with low cost and simple fabrication process exhibits great potential for commercial applications.

• 대한기계학회논문집B
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• 제33권8호
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• pp.613-621
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• 2009

Coal is the energy resource which is important with the new remarking energy resource. Coal combustion produces more NOx per unit of energy than any other major combustion technology. Pollutant emission associated with coal combustion will have a huge impact on the environment. Coal conversion has three processes which are drying, coal devolatilization and char oxidation. Coal devolatilization process is important because it has been shown that HCN which is converted from volatile N contributes 60 to 80% of the total NOx produced. This paper addresses mass release behavior of char, tar, gas and HCN in an experiment of Laminar Flow Reactor with two coals such as Roto middle coal (Sub-bituminous) and Anglo coal (Bituminous). The experiment is compared with the data predicted by CPD model for mass release of HCN about Roto south, Indominco, Weris creek and China orch coals. The results show that HCN increases as a function of decreasing the ratio of fixed carbon(FC)/ volatile matter(VM of the coals contain.)