• 멤브레인
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• 제12권4호
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• pp.207-215
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• 2002

한정된 미세공간에서의 제한확산(hindered diffusion)은 멤브레인 기공(pore)에서 입자들의 운동에 의해 결정되는 여과 메카니즘을 매우 미세한 수준에서 이해하는데 중요한 현상이다. 구형(spherical) 콜로이드 입자에 비해 보다 복잡한 형태(conformation)인 고분자사슬 구조를 갖는 다가전해질(polyelectrolyte)의 제한확산 거동에는 다양한 인자들이 관련되어 있기 때문에, 이론 접근은 물론 실험적 접근도 한층 어려운 것이 사실이다. 본 연구에서는, 슬릿형 미세기공에 한정되어 있는 단일한 다가전해질(single polyelectrolyte)에 coarse-grained bead spring model과 먼거리(long-range) 정전상호작용(electrostatic interaction)인 Debye-Huckel potential을 적용하여 분자시뮬레이션 기법인 브라운 동력학 모사를 수행하였다. 기공과 다가전해질 사슬(Polyelectrolyte chain)의 주어진 크기에서, 용액의 전해질 이온농도가 감소함에 따른 사슬의 신장(extension)효과는 제한확산계수를 감소시켰고, 기공 벽면의 하전성은 제한확산계수를 더욱 감소시켰다. 이는, 다가전해질 사슬(polyelectrolyte chain)의 입체적 장애(steric hindrance)와 함께 정전반발력이 미세기공에서의 확산이동을 억제함을 의미한다.

• 한국막학회:학술대회논문집
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• 한국막학회 1997년도 추계 총회 및 학술발표회
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• pp.139-140
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• 1997

1. 서론 : 한외 및 정밀여과의 분리메카니즘에 연관된 물리적 현상에 대해 현재까지 진행된 많은 연구들은, 막기공이 갖는 복잡하고 불규칙한 구조를 단순하고 규칙적인 well-defined 구조인 실린더형이나 슬릿형 기공으로 가정하여 문제를 전개하고 있다. 본래, 다공성 매질(porous media)에서의 유체흐름을 다루는 이론 및 실험연구자들에 의해 제안된 섬유상 매질(fibrous media)에 대한 해석은 계의 미세구조(microstructure)에 추계적 개념을 적용시키려는 최근의 추세에 따라 점차 관심이 높아가고 있다.(생략)

• 대한토목학회논문집
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• 제4권4호
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• pp.13-23
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• 1984

본(本) 연구(硏究)의 목적(目的)은 조류(潮流)에 의한 부유사(浮遊砂)의 확산(擴散)현상에 대하여 2차원 비정상확산(非定常擴散)방정식을 유한차분법(有限差分法)을 이용하여 부유사의 농도분포(分布)를 계산할 수 있는 수치모형(數値模型)을 개발하는데 있다. 바닥으로부터 부상량(浮上量)의 계산은 개수로에서 얻어진 공식(公式) 이용하였으며, 확산계수는 Coleman의 경험공식(公式)을 사용하였다. 특히, 침강속도 감쇠효과와 연직유속이 고려되었다. 여러 가지 경우의 계산예(計算例) 통하여, 유속조차, 연직유속, 침강속도의 감쇠효과 같은 각(各) 변수(變數)들이 부유사의 농도분에 미치는 영향이 검토 되었다.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2004년도 Proceedings of 2004 Korea-Japan Joint Seminar on Particle Image Velocimetry
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• pp.91-110
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• 2004

A comprehensive three-dimensional nano-particle tracking technique in micro- and nano-scale spatial resolution using the Total Internal Reflection Fluorescence Microscope (TIRFM) is discussed. Evanescent waves from the total internal reflection of a 488nm argon-ion laser are used to measure the hindered Brownian diffusion within few hundred nanometers of a glass-water interface. 200-nm fluorescence-coated polystyrene spheres are used as tracers to achieve three-dimensional tracking within the near-wall penetration depth. A novel ratiometric imaging technique coupled with a neural network model is used to tag and track the tracer particles. This technique allows for the determination of the relative depth wise locations of the particles. This analysis, to our knowledge is the first such three-dimensional ratiometric nano-particle tracking velocimetry technique to be applied for measuring Brownian diffusion close to the wall.

• 한국가시화정보학회지
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• 제6권2호
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• pp.45-50
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• 2008

It has been found that the colony size of bacteria grown on an agar plate decreases with increasing agar gel concentration. Evidenc from recent studies suggests that the bacterial colony dynamics is closely related with the mechanical properties of the substrate. We investigate whether bacterial growth on the agar substrate is controlled mostly by the nutrients' diffusion which is hindered more in porous medium than in solution. The number of bacterial cells in single colonies is found to be inversely correlated with agar concentration. High-resolution live cell imaging at the single bacterium level confirms that the bacterial growth rate is reduced with increasing agar concentration. There is a strong correlation between the slowed diffusion and the reduced number of cells in a high concentration of agar medium.

• 기술혁신학회지
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• 제1권1호
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• pp.69-82
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• 1998

As a new medium for knowledge diffusion, E-Journal is expected to be a general type of scholarly communication. However, the techno - economic problems have hindered the advancement of the E-Journal. For the technical aspects, there are problems such as the standardization of document format, automatization of the document preparation, forward and backward link between documents. Also there are necessities for the support of the information infrastructure of digital library and information superhighway. For the economic domain, reengineering of total publishing cycle is considered and the new paradigm of peer review is analyzed. We pointed out that the main difficulties in the diffusion of E-Journal are on the promotion of service and technological advance, not the price and marketing strategy.

• 한국해양공학회지
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• 제4권2호
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• pp.262-262
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• 1990

In order to check the effect of dislocation behavior on creep rate in 12% Chromium steel, 14 samples of different compositions were examined by creep rupture test, and subgrain sizes, distribution of dislocations and precipitates were checked. And, authors reviewed the behaviors of dislocations, the formation and growth of subgrains and precipitates during creep. The results are as the following: 1) Creep rates calculated by .epsilon. over dot = .rho.bv show 10-15% higher values than actual data measured. However, authors conclude that the density and velocity of dislocations together with subgrain size are important factors governing deformation during creep in 12% chromium steel. 2) The values of the strength of obstacles in the mobility of dislocations are more clearly depended on the effective stress in the range of $10{\pm}5kgf/mm^{2}$ and increase with the increase of temperature. 3) Creep rates decrease with the smaller sizes of subgrains formed and can result in the longer creep rupture lives(hours). The smaller subgrains can be made by forming shorter free gliding distances of dislocations with very fine precipitates formed in the matrix during creep by applying proper alloy design. 4) Dislocation mobility gets hindered by precipitates occurring, which are coarsened by the softening process governed by diffusion during long time creep.

• 한국해양공학회지
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• 제4권2호
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• pp.112-120
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• 1990

In order to check the effect of dislocation behavior on creep rate in 12% Chromium steel, 14 samples of different compositions were examined by creep rupture test, and subgrain sizes, distribution of dislocations and precipitates were checked. And, authors reviewed the behaviors of dislocations, the formation and growth of subgrains and precipitates during creep. The results are as the following: 1) Creep rates calculated by .epsilon. over dot = .rho.bv show 10-15% higher values than actual data measured. However, authors conclude that the density and velocity of dislocations together with subgrain size are important factors governing deformation during creep in 12% chromium steel. 2) The values of the strength of obstacles in the mobility of dislocations are more clearly depended on the effective stress in the range of $10{\pm}5kgf/mm^{2}$ and increase with the increase of temperature. 3) Creep rates decrease with the smaller sizes of subgrains formed and can result in the longer creep rupture lives(hours). The smaller subgrains can be made by forming shorter free gliding distances of dislocations with very fine precipitates formed in the matrix during creep by applying proper alloy design. 4) Dislocation mobility gets hindered by precipitates occurring, which are coarsened by the softening process governed by diffusion during long time creep.

• Korean Membrane Journal
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• 제3권1호
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• pp.39-50
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• 2001

The counter-diffusion of two gaseous substances permeating a polymeric membrane has been investigated both experimentally and theoretically. The aim of the study was to find mutual effects, if any, that could influence the permeability and diffusivity data. The experimental data were obtained with an isostatic permeameter operating at ambient pressure and 303 K: helium, nitrogen, carbon dioxide methane were used as permeating gas at different partial pressure; helium or nitrogen as equilibrating or carrier gas. No evident mutual effect of the counter-diffusing gas was observed. The theoretical analysis gave some insight into the phenomena and it was concluded that at near-atmospheric pressures, and in the absence of swelling phenomena no mutual interaction exists. On a theoretical basis any mutual interaction between diffusing and counter-diffusing gases could only occur: i) at high pressures , when the free movement of permeating gas molecules within the polymer is hindered by the counter-diffusing gas; ii) when a large part of the free volume fraction is occupied by the counter--diffusing gas; iii) swelling phenomena modify the structure and free volume fraction of the polymer.

• 전자공학회논문지A
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• 제28A권11호
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• pp.887-893
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• 1991

To take advantage of Ti-polycide, when it is contacted with both n+ and p+ active area of silicon, the effects of BF$_2$ on the formation of Ti-silicide were investigated with RTA temperature and dopant concentration. The intermediate phase C49 TiSi$_2$ appeared at $650^{\circ}C$ and the stable phase C54 TiSi2 was formed at $700^{\circ}C$. And the formation of Ti-silicide was hindered by BF$_2$ doping and this trend was decreased with increasing temperature. The out-diffusion phenomena of BF$_2$ into Ti silicide were not observed. And significantly, the native oxide was a chief factor preventing the formation of Ti-silicides.