• 한국대기환경학회지
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• 제26권1호
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• pp.77-84
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• 2010

The diffusion and partition coefficients of polyurethane foam (PUF) are estimated using a microbalance experiment and small chamber test. The microbalance is used to measure sorption/desorption kinetics and equilibrium data. When the diffusion condition is controlled in the chamber of the sample, interactions between volatile organic compounds (VOCs) and PUF can lead to the estimation of a relatively homogenous rate of mass transfer in the interiors and surfaces of PUF. The estimates of the material/air partition coefficient (K) and the material-phase diffusion coefficient (D) are shown to be independent of the concentrations of VOCs. This approach, if applied to a diffusion-controlled or physically-based model, can facilitate more precise prediction of their source/sink behavior. Although further research and more rigorous validation is needed, an emission model applied with the diffusion and partition coefficients from this research holds promise for the improvement of reliability in predicting the behavior of VOCs emitted from porous building materials by D and K.

• Computers and Concrete
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• 제13권2호
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• pp.187-207
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• 2014

This paper mainly discusses the influence of the aggregate properties including grading, shape, content and distribution on the chloride diffusion coefficient, as well as the initiation time of steel corrosion from a probabilistic point of view. Towards this goal, a simulation method of random aggregate structure (RAS) based on elliptical particles and a procedure of finite element analysis (FEA) at meso-scale are firstly developed to perform the analysis. Next, the chloride diffusion coefficient ratio between concrete and cement paste $D_{app}/D_{cp}$ is chosen as the index to represent the effect of aggregates on the chloride diffusion process. Identification of the random distribution of this index demonstrates that it can be viewed as actually having a normal distribution. After that, the effect of aggregates on $D_{app}/D_{cp}$ is comprehensively studied, showing that the appropriate properties of aggregates should be decided by both of the average and the deviation of $D_{app}/D_{cp}$. Finally, a case study is conducted to demonstrate the application of this mesoscopic method in predicting the initiation time of steel corrosion in reinforced concrete (RC) structures. The mesoscopic probabilistic method developed in this paper can not only provide more reliable evidences on the proper grading and shape of aggregates, but also play an important role in the probability-based design method.

• 분석과학
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• 제9권3호
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• pp.292-301
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• 1996

산화환원반응 탐침제로, poly ether 꼬리가 결합된 Cobalt(II)bipyridine 착물을 합성 하였고, 이들 화합물의 느린 확산계수와 불균일 전자이동을 설명하였다. $Co(bpy(ppgm)_2)_{3^-}(ClO_4)_2$에 전해질 $LiClO_4$가 혼합된 neat 상태의 산화반응에 대한 확산계수는 $1.5{\times}10^{-15}cm^2/s$ 였다. 이 화합물들의 불균일 전자이동 속도상수들은 확산계수와 관련이 있었다. 확산계수의 감소에 따라 속도상수(k)의 감소가 일어났다. 강한 이온쌍을 형성하는 $ClO{_4}^-$의 화합물은 약한 이온 쌍을 형성하는 $CF_3COO^-$ 화합물보다 확산계수가 훨씬 작았다.

• Bulletin of the Korean Chemical Society
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• 제4권5호
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• pp.223-227
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• 1983

A molecular dynamic computer experiment was performed on a system of 108 particles composed of a single polymer chain and solvent molecules. The state considered was in the immediate neighborhood of the triple point of the system. The polymer itself is an analog of a freely jointed chain. The Lennard-Jones potential was used to represent the interactions between all particles except for that between the chain elements forming a bond in the polymer chain, for which the interaction was expressed by a harmonic potential. The self-diffusion coefficient and velocity autocorrelation function (VACF) of a polymer were calculated at various chain lengths $N_p$, and various interaction strengths between solvent molecules and a polymer chain element. For self-diffusion coefficients D, the Einstein relation holds good; as chain length $N_p$ increases the D value decreases, and D also decreases as ${\varepsilon}_{cs}$ (the interaction parameter between the chain element and solvent molecules) increases. The relaxation time of velocity autocorrelation decreases as ${\varepsilon}_{cs}$ increases, and it is constant for various chain lengths. The diffusion coefficients in various conditions reveal that our systems are in a free draining limit as is well known from the behavior of low molecular weight polymers, this also agrees with the Kirkwood-Riesman theory.

• 천문학회지
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• 제24권1호
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• pp.95-105
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• 1991

In the presence of synchrotron losses, diffusion of an ensembel of relativistic particles in an intraculster medium is investigated. The diffusion coefficient in the medium is found to be constrained by $28.8\;{\pm}\;0.4\;{\leq}\;Log\;D\;{\leq}\;30.5\;{\pm}\;0.4\;cm^2s^{-1}$ with the energy dependency of $D_0{\varepsilon}^{\mu}$ of ${\mu}=0.4{\pm}0.2$ as the previous observations suggested. As an important implication of the result, the brightest head-tail radio source NGC 4869, whose radio tail structure is indicative for its orbit within the cluster core, is considered to be the major contributor of particles for the formation of the Coma radio halo.

• 한국전기전자재료학회논문지
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• 제14권2호
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• pp.169-174
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• 2001

The electron transport coefficients(the electron drift velocity, W, and the longitudinal and transverse diffusion coefficient, D$_{L}$ and D$_{T}$) in SiH$_4$-Ar mixtures containing 0.5% and 5.0% monosilane were calculated over the E/N range from 0.01 to 300 Td and over the gas pressure range 0.5, 1.0 and 1.5 Torr by the time-of-flight(TOF) method of the Boltzmann equation(BE.) and Monte-Carlo simulation(MCS). The electron energy distribution function in each SiH$_4$-Ar mixtures at E/N=10 Td and L=0.2 cm, which in equilibrium region in the mean electron enregy were compared.red.

• 대한의용생체공학회:의공학회지
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• 제27권5호
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• pp.203-209
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• 2006

The aim of this study is to investigate the feasibility of ex vivo MR diffusion tensor imaging technique in order to observe the diffusion-contrast characteristics of human gastric tissues. On normal and pathologic gastric tissues, which have been fixed in a polycarbonate plastic tube filled with 10% formalin solution, laboratory made 3D diffusion tensor Turbo FLASH pulse sequence was used to obtain high resolution MR images with voxel size of $0.5{\times}0.5{\times}0.5mm^3\;using\;64{\times}32{\times}32mm^3$ field of view in conjunction with an acquisition matrix of $128{\times}64{\times}64$. Diffusion weighted- gradient pulses were employed with b values of 0 and $600s/mm^2$ in 6 orientations. The sequence was implemented on a clinical 3.0-T MRI scanner(Siemens, Erlangen, Germany) with a home-made quadrature-typed birdcage Tx/Rx rf coil for small specimen. Diffusion tensor values in each pixel were calculated using linear algebra and singular value decomposition(SVD) algorithm. Apparent diffusion coefficient(ADC) and fractional anisotropy(FA) map were also obtained from diffusion tensor data to compare pixel intensities between normal and abnormal gastric tissues. The processing software was developed by authors using Visual C++(Microsoft, WA, U.S.A.) and mathematical/statistical library of GNUwin32(Free Software Foundation). This study shows that 3D diffusion tensor Turbo FLASH sequence is useful to resolve fine micro-structures of gastric tissue and both ADC and FA values in normal gastric tissue are higher than those in abnormal tissue. Authors expect that this study also represents another possibility of gastric carcinoma detection by visualizing diffusion characteristics of proton spins in the gastric tissues.

• 한국구조물진단유지관리공학회 논문집
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• 제19권5호
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• pp.83-91
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• 2015

콘크리트 표면의 상태에 따라 염화물은 증가 또는 감소하게 되며 이는 철근부식 및 내구수명에 매우 중요한 인자가 된다. 콘크리트의 내구성 저하를 방지하기 위해 표면함침과 같이 많은 표면강화 기술이 개발되었으나 이중 콘크리트 구조와 확산계수의 시간의존성을 고려한 염화물 해석방법은 매우 제한적이다. 본 논문에서는 표면 강화된 이중구조 콘크리트에 대해 시간의존성 확산계수를 도입하여 염화물 해석기법을 제안하였으며, 역해석을 통하여 기존의 실험결과와 비교하였다. 2년간 비말대, 해수중, 조석대 상태에 노출된 표면 함침된 콘크리트 시편에 대해 표면염화물량과 확산계수를 도출하고 Life-365에서 제안한 확산계수 식과 비교 분석하였다. 시간의존성을 고려한 결과 비말대 시편의 오차는 0.28에서 0.20 수준으로, 조석대 시편은 0.29에서 0.11 수준으로, 해수중에서는 0.54에서 0.40 수준으로 오차가 감소함을 알 수 있었다. 또한 Life365에서 사용되는 확산계수식을 사용할 경우, 과다한 확산계수로 인해 상대오차가 커지고 높은 침투깊이(e)와 낮은 확산계수비($D_1/D_2$)를 필요로 함을 알 수 있다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.681-686
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• 2003

One of the major degradation processes of reinforced concrete (RC) structure is corrosion of reinforced steel due to chloride attack. Severe environments, such as marine environment and exposure to de-icing salts, could accelerate the steel corrosion of RC structures through the chloride ion intrusion into concrete. In order to delay this degradation process, several kinds of admixtures have been used in concrete mix. In this study, effective diffusion coefficient of chloride ion ($D_{eff}$) and total passed charge of concrete with and without fly ash were measured using electrical method. It is found that fly ash concrete has much less chloride ion coefficient than ordinary concrete at later age. By analyzing the test results, $D_{eff}$ at 28 and 90 days was obtained as a function of water-binder ratio (W/B) and an equation for predicting $D_{eff}$ with age was proposed considering the decreasing rate of $D_{eff}$.

• 한국습지학회지
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• 제13권3호
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• pp.385-394
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• 2011

본 연구에서는 유역의 배수구조를 지표면과 하천으로 구분하여 확산-유추 지형학적 순간단위도의 최적 매개변수를 산정하였다. 모형의 매개변수는 지표면과 하천 각각의 유속($u_c$, $u_h$) 및 확산계수($D_c$, $D_h$)로 구성하였다. 대상유역은 보청천 유역의 탄부 소유역을 선정하였으며, 대상유역의 하천망은 Strahler 차수법칙에 의해 4차 하천으로 분류되었다. 최적화 기법은 SCE-UA을 적용하였으며, 추정된 최적 매개변수는 다음과 같다; $u_c$ : 0.589 m/s, $u_h$ : 0.021 m/s, $D_c$ : $34.469m^2/s$, $D_h$ : $0.1333m^2/s$. 추정된 매개변수의 검증결과 평균 첨두유량 오차는 약 11 %, 첨두시간 오차는 0.3 hr로 양호하게 나타났다. 또한 매개변수들의 변동성을 살펴본 결과 하천확산계수($D_c$)는 수문응답함수에 큰 영향을 미치지 못함을 알 수 있었으며, 향후에는 이러한 결과들을 고려함으로서 모형을 좀 더 간편화할 수 있을 것으로 기대된다.