• Bulletin of the Korean Chemical Society
• /
• 제22권12호
• /
• pp.1375-1379
• /
• 2001

Monte Carlo simulations of hard-spheres confined in parallel hard walls have been carried out extensively at various densities and for various wall distances. The compressibility factors in the directions parallel and normal to the wall have been calculated from the radial free space distribution function (RFSDF) with the results showing that the compressibility factors normal to the wall are smaller than those in parallel direction and that a solid phase is formed in the direction normal to the wall while a fluid phase remains in the parallel direction. An order parameter is found to classify the phases whether a system (or a molecule) is in a fluid or a solid state. The compressibility factors of narrow wall are very small compared to those when the wall is put away. A plausible mechanism of the rise of sap in xylem vessel has been proposed.

• 대한화학회지
• /
• 제56권2호
• /
• pp.207-211
• /
• 2012

강체구형입자에 대한 Carnahan-Starling식과 인력 포텐셜을 갖는 격자 모델을 이용하여 새로운 2-매개변수 상태식을 유도하였다. 이 식을 이용하여 압축인자를 계산하고 Nelson-Obert 압축인자도표와 비교하여 보았다. 그 결과 이 식은 Redlich-Kwong식과 평균적으로 비슷한 정도로 실험적인 압축인자도표와 일치한다는 것을 알 수 있다. 그런데 새 상태식에서 나타나는 매개변수와 항들은 Redlich-Kwong equation의 경우보다 분명한 물리적 의미를 갖고 있다.

• Korean Chemical Engineering Research
• /
• 제50권1호
• /
• pp.66-71
• /
• 2012

본 연구에서는 크기가 다른 두 종류의 단단한 구형 입자들로 충전된 이분산(二分散) 충전층을 지나는 비압축성 유체 흐름의 투과도를 실험적으로 측정하고 이론적으로 예측하는 문제를 다룬다. 작은 입자에 대한 큰 입자의 크기 비 ${\lambda}$가 1.25와 2인 두 가지 경우에 대해 여러 가지 입자 혼합 비율로 충전층을 만들고 그 공극률과 유체 흐름의 투과도를 측정하였다. 이분산 충전은 입자 크기가 일정한 단분산 충전에 비해 공극률이 감소하고 투과율이 감소하나 입자들의 크기 비 ${\lambda}$나 혼합 비율 ${\gamma}$에 따라 다르게 나타난다. 두 가지 입자의 혼합 비율에 따른 공극률의 변화와 투과율의 변화 형태는 서로 일치하지 않는다. 개별 충전 입자에 걸리는 항력 계산에 기초한 모델을 고안하여 투과도를 예측하는 간단한 이론식을 유도하였고 이 식을 이용한 예측값을 실험 결과 및 선행 연구 결과들과 비교한 결과, 이 이론식에 의한 투과도 예측값이나 입자 혼합 비율에 따른 투과도 변화 경향이 실험값에 가장 근사하였다. 이 이론식을 이용해 이분산 충전층을 지나는 유체 흐름의 투과도를 간단하고 정확하게 예측할 수 있음을 보였다.

• Korea-Australia Rheology Journal
• /
• 제17권4호
• /
• pp.191-198
• /
• 2005

The static and dynamic rheological behavior of concentrated sodium dodecylsulfate (SDS) stabilized, deformability controllable polydimethylsiloxane (PDMS) emulsions is reported and comparisons made with silica (hard sphere) suspensions. Steady-mode measurements indicate 'hard' (viscoelastic) droplets behave as hard spheres, while 'soft' (viscous) droplets induce structural flexibility of the emulsion against shear. Dynamic-mode measurements reveal that viscoelasticity of droplets provides the great magnitude of elasticity for the 'hard' emulsion, while formation of planar films between droplets is the origin of the elasticity of 'soft' emulsions. Combination of steady and dynamic rheological behavior has enabled depiction of droplet structure evolution in relation to the shear stress applied, especially by taking advantage of the normal force that reflects the transient deformation of droplets.

• 대한기계학회논문집B
• /
• 제20권9호
• /
• pp.3015-3029
• /
• 1996

The notion of effective transport property of a heterogeneous medium implies that the medium is large enough that the ergodic theorem holds and local fluctuation of the property can be neglected. In case that the medium is not large enough compared to its characteristic microstructure length scale, the effective property fluctuates and differs from the value of the medium being large enough. As a representative transport phenomenon, diffusion was considered and the fluctuation of varying effective diffusion property, diffusion coarseness $C_k$, was defined as a quantifying parameter. Scaled effective diffusion property, $^*$>/k$_1$ and $C_k$ were computed for the two phase random media consisting of matrix of diffusion coefficient k$_1$ and spheres of diffusion coefficient k$_2$. Numerical simulations were performed by use of the so-called first passage time technique and data were collected for existing microstructure models of hard spheres(HS), overlapping spheres(OS) and penetrable concentric shells(PCS).

• Structural Engineering and Mechanics
• /
• 제55권2호
• /
• pp.263-280
• /
• 2015

This paper describes a study of the collision of hard steel spheres against aluminium thin circular plates at speeds up to 140 m/s. The tests were monitored by a high speed camera and a chronoscope, which allowed the determination of the ballistic limit and the plate deformation pattern. Quasi-static material parameters were obtained from tests on a universal testing machine and dynamic mechanical characterization of two aluminium alloys were conducted in a split Hopkinson pressure bar. Using a damage model, the perforation of the plates was simulated by finite element analysis. Axisymmetric, shell and solid elements were employed with various parameters of the numerical analysis being thoroughly discussed, in special, the dynamic model parameters. A good agreement between experiments and the numerical analysis was obtained.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
• /
• pp.21-22
• /
• 2003

We perform two kinds of computer simulations on polydisperse hard-sphere systems; a molecular-dynamics simulation on atomic systems and a Brownian-dynamics simulation on colloidal suspensions. Analyses of the mean square displacement, the radial distribution function, and the pressure suggest that there exist three phase regions, a liquid phase region, a metastable phase region, and a crystal phase region, where the freezing and melting points are shifted to the values higher than in monodisperse case. It is also shown that the long-time behavior of colloidal suspensions is exactly the same as that of atomic systems.

• 대한세포병리학회지
• /
• 제9권2호
• /
• pp.181-185
• /
• 1998

Polymorphous low grade adenocarcinoma(PLGA) is a rare malignant tumor of the salivary gland. It is characterized by diverse histology, bland-locking cytology indolent behavior and favorable prognosis. The fine needle aspiration cytologic features of PLGA are described. The aspirates from the hard palate in a 33-year-old woman showed cellular smear composed of monotonous small round to oval cells with scanty cytoplasm. Papillary, tubular and cell ball arrangements with characteristic dense stromal spheres were recognized. PLGA could be suggested by fine needle aspiration cytology, if one encountered cellular smear with various architectures and uniform bland-locking cytologic feature.

• 대한수학교육학회지:수학교육학연구
• /
• 제15권4호
• /
• pp.461-488
• /
• 2005

수학적 오류를 인지구조의 수행 변화와 관련 있는 정신용량으로 설명할 수 있다면, 다양한 과제에 따라 여러 유형으로 발생하는 수학적 오류를 분류할 수 있는 공통적인 기준도 학습자의 인지체계와 정신용량을 관련하여 설명할 수 있다고 볼 수 있다. 본 연구에서는 수학적 오류를 Demetrious et al.(1987, 1993)의 경험적 구조주의를 바탕으로 학생들의 인지구조 및 과제상황에 근거하여 설명하고 다양한 내용과 맥락에 공통적으로 적용이 가능한 오류 분류 기준을 제안하고 실제에의 적용가능성을 탐색한다. 그 결과, 오류 분류 기준은 6가지 자발적 정신용량과 그 요소능력 및 양식적 특성으로 요약될 수 있다 제안한 경험적 구조주의에 기반한 오류 분류 기준을 일차함수과제를 예측과제, 번역과제, 해석과제, 척도과제로 세분화하여 적용한 결과, 오류의 재분류가 가능하였다.

• 한국가시화정보학회지
• /
• 제20권3호
• /
• pp.67-73
• /
• 2022

Underwater environmental pollution caused by microplastic particles is considered to be one of the most serious problems in many oceans and countries nearby. Previous academic studies or field technologies tried to remove the micro-sized particles are often energy-consuming and costly, so it is hard to be employed for the actual uses. In this study, the mechanism of removal of micro-sized polyethylene spheres (size in order of 100㎛) using a rising bubble is experimentally investigated. It is found that the particles are either affected by bubble wake, thus translocated close to the water surface, or pushed far away by the surrounding fluid flow, depending on their initial position relative to the bubble. By scrutinizing the visualized behaviors of bubble-particle interaction, we draw the governing parameter, i.e., the polar angle between the particle and the bubble, to determine the effective capturing of the particles with a rising bubble.