• 산업식품공학
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• 제14권4호
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• pp.354-358
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• 2010

The methods for determining the diffusion parameters for the diffusion of d-limonene, a major volatile compound of orange juice, through a multi-layered food packaging material and predicting its absorption into the packaging material have been investigated. The packaging material used was the 1.5-mm thick multi-layered packaging material composed of high impact polystyrene (HIPS), polyvinylidene chloride (PVDC), and low density polyethylene (LDPE). Orange juice was placed in a cell where volatiles were absorbed in the sample package and kept at $23{\pm}2^{\circ}C$ for 72 hr. The d-limonene absorbed in a 1.5-mm thick multi-layered food packaging material was analyzed by a solid phase micro-extraction (SPME). The absorption parameters for the absorption of d-limonene in the packaging material were determined and absorption of d-limonene into the packaging material was predicted using absorption storage data. The SPME desorption at $60^{\circ}C$ for 1 hr resulted in the most sensitive and reproducible results. The diffusion coefficients of d-limonene in the packaging material and the partition coefficient at $23{\pm}2^{\circ}C$ were approximately $1-2{\times}10^{12}m^2$/s and 0.03, respectively. The absorption profile no earlier than 30 hr was fit well by a model derived from the Fick's law.

• Computers and Concrete
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• 제3권6호
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• pp.401-422
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• 2006

A multi-species model based on the Nernst-Planck equation has been developed by using a finite volume method. The model makes it possible to simulate transport due to an electrical field or by diffusion and to predict chloride penetration through water saturated concrete. The model is used in this paper to assess and analyse chloride diffusion coefficients and chloride binding isotherms. The experimental assessment of the effective chloride diffusion coefficient consists in measuring the chloride penetration depth by using a colorimetric method. The effective diffusion coefficient determined numerically allows to correctly reproduce the chloride penetration depth measured experimentally. Then, a new approach for the determination of chloride binding, based on non-steady state diffusion tests, is proposed. The binding isotherm is identified by a numerical inverse method from a single experimental total chloride concentration profile obtained at a given exposure time and from Freundlich's formula. In order to determine the initial pore solution composition (required as initial conditions for the model), the method of Taylor that describes the release of alkalis from cement and alkali sorption by the hydration products is used here. Finally, with these input data, prediction of total and water-soluble chloride concentration profiles has been performed. The method is validated by comparing the results of numerical simulations to experimental results obtained on various types of concretes and under different exposure conditions.

• 한국전자거래학회지
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• 제17권2호
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• pp.63-72
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• 2012

2000년대 초반부터 한국의 이동통신시장은 급속하게 팽창해 왔으며, 최근 들어 그 성장 속도가 둔화되고 있으나 성장은 계속 진행 중에 있다. 이와 같은 환경에서 4세대 이동통신 서비스가 2011년 10월부터 시작되어 3세대 서비스와 4세대 서비스가 함께 존재하고 이를 통해 이동통신시장의 경쟁구도가 더욱 복잡하고 치열한 상황이 되었다. 본 연구는 다세대 확산 모형을 활용하여 3세대 및 4세대 이동통신 서비스 가입자 규모를 예측하는데 목적이 있다. 이를 위해 세 개의 파라미터, 즉 Norton and Bass 모형[11]에서 사용되는 혁신계수, 모방계수 및 포화수준계수의 값을 추정하기 위해 3세대에서 4세대로 대체되는 서비스 대체의 유사 사례를 역추적하는 방법을 사용하였다. 시뮬레이션 결과, 다세대 확산모형과 유사사례 추론을 통해 신규서비스인 4세대 이동통신서비스 시장규모를 성공적으로 예측할 수 있었다는 결론을 얻었다.

• Journal of applied mathematics & informatics
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• 제13권1_2호
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• pp.393-404
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• 2003

In general, a differential operator can be used as a tool of treating the local properties of given function. However, when the given function is varied with high frequency and has irregular form with non-stationary evolution it may not act its role sufficiently as in case of nowhere differentiable curves. In this paper we introduce a multi-scale derivative as a form of weakened global derivative so that it may explain its semi global diffusion properties as well as local ones for the various irregular diffusion phenomena.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1136-1141
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• 2004

In recent years, demands on microelectrode have been greatly enhanced because of its potential applications and mass production of microelectrodes is needed. An electrochemical fabrication is used as an method for the simple and cheap fabrication of multi microelectrodes. In this paper, one dimensional microelectrode array is used for fabricating of multi electrodes. A diffusion layer which is formed near the electrode surface has an effect on the shape error of multi microelectrodes. The optimal distance between electrodes to minimize shape errors of multi electrodes is investigated. Multi microelectrodes which has several tens of and hundreds of micrometer in diameter are fabricated at a time.

• 소성∙가공
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• 제28권1호
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• pp.15-20
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• 2019

The superplastic forming/diffusion bonding process has been developed to fabricate a core frame structure with joint nodes out of tubes, for the development of a titanium high performance bicycle. The hydroforming process has been applied for bulging of a tube in the superplastic condition before, and during the diffusion bonding process. In this experiment, a commercial Ti-3Al-2.5V tube was selected as raw material for the study. The forming experiment has been performed using a servo-hydraulic press with a capacity of 200 ton. Next, nitrogen gas was used to acquire necessary pressure for the bulging and bonding of the tubes to fabricate the joint nodes. The pertinent processing temperature was $870^{\circ}C$ for the superplastic hydroforming/diffusion bonding (SHF/DB) process, using the Ti-3Al-2.5V tube. The bonding quality and the progress of bulging and diffusion bonding have been observed by the investigation of the joining interfaces at the cross section of the joint structure. The control of the nitrogen pressure throughout the SHF/DB process, was an important factor to avoid any significant defects in the joint structure. The whole progress stage of the diffusion bonding could be observed at a joint interface. A core structure with 5 joint nodes to manufacture a titanium bicycle could be obtained in a SHF/DB process.

• 한국콘텐츠학회논문지
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• 제16권4호
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• pp.114-122
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• 2016

콘크리트는 경제적이며 고내구성 건설재료이지만, 염해에 노출된 경우 매립된 철근의 부식으로 인해 내구성에 대한 문제가 발생한다. 최근 들어 동절기에 제설제가 많이 사용되고 있는데, 제설제의 사용은 콘크리트 표면에 미세균열과 박리를 증가시키고 용해된 제설제는 매립된 철근의 부식을 야기한다. 기존의 염화물 지배방정식인 Fick's 2nd Law의 해석기법은 표면이 열화된 콘크리트의 염해특성을 평가하지 못하므로 이에 대한 고려가 필요하다. 본 연구에서는 콘크리트 다층구조 확산 모델과 시간의존성 염화물 확산을 이용하여 제설제에 노출된 콘크리트의 염화물 해석기법을 제안하였다. 이를 위해 18년 경과된 콘크리트 도로교의 염해실태를 분석하였으며, 역해석을 통하여 표면열화깊이 및 열화된 콘크리트 층의 증가된 염화물 확산성을 평가하였다. 제안된 기법은 30MPa 콘크리트에서 12.5~15.0mm 열화깊이와 2배 증가된 열화층의 염화물 확산성을 나타내었다. 본 해석기법은 표면열화 및 표면 강화 등 2개의 다른 확산성을 가진 콘크리트의 염화물 거동을 평가하는데 효과적으로 적용될 수 있다.

• 대한산업공학회지
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• 제14권1호
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• pp.103-117
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• 1988

Replacement demand plays an important role to forecast the total demand of durable goods, while most of the diffusion models deal with only adoption data, namely initial purchase demand. This paper presents replacement demand forecasting models incorporating repurchase rate, multi-ownership, and dynamic product life to complement the existing diffusion models. The performance of replacement demand forecasting models are analyzed and practical guidelines for the application of the models are suggested when life distribution data or adoption data are not available.

• Computers and Concrete
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• 제13권2호
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• pp.149-171
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• 2014

This study presents the mathematical model for predicting chloride penetration into saturated concrete under non-isothermal condition. The model considers not only diffusion mechanism but also migration process of chloride ions and other chemical species in concrete pore solution such as sodium, potassium, and hydroxyl ions. The coupled multi-ionic transport in concrete is described by the Nernst-Planck equation associated with electro-neutrality condition. The coupling parameter taken into account the effect of temperature on ion diffusion obtained from available test data is proposed and explicitly incorporated in the governing equations. The coupled transport equations are solved using the finite element method. The numerical results are validated with available experimental data and the comparison shows a good agreement.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 1999년도 정기총회 및 춘계 공동 학술발표회
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• pp.6-7
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• 1999