• Bulletin of the Korean Chemical Society
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• v.22 no.12
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• pp.1375-1379
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• 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.

• Journal of the Korean Chemical Society
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• v.56 no.2
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• pp.207-211
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• 2012

Using Carnahan-Starling equation for hard spheres and a lattice model with an attractive potential, a new twoparameter equation of state for pure gases is derived. Using this equation, compressibility factors are calculated and compared with Nelson-Obert generalized compressibility factor charts. The results show that the agreement of this equation with the experimental Nelson-Obert charts is similar to that of Redlich-Kwong equation in the average. But parameters and terms of the new equation have physical meanings which are more definite than those of Redlich-Kwong equation.

• Korean Chemical Engineering Research
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• v.50 no.1
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• pp.66-71
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• 2012

We deal with a problem to determine experimentally as well as theoretically permeability of incompressible viscous flow through packed bed of bidisperse hard spheres in size. For the size ratios of large to small spheres ${\lambda}$=1.25 and 2, we set up bidisperse packing and measured porosity and permeability at various volumetric ratios of small to large spheres ${\gamma}$. Bidisperse packing shows lower porosity and permeability than monodisperse packing does. Variation of porosity as a function of ${\gamma}$ does not match with that of permeability. A theoretical expression for predicting permeability of a viscous flow for packed bed of bidisperse packing is derived based on calculation of drag force acting on each sphere and its predictions are compared with the experimental data and those from some relations previously suggested. It is found that our theory shows better agreement with experimental results than the previous studies and is proved to be quite simple and accurate in estimating the permeability.

• Korea-Australia Rheology Journal
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• v.17 no.4
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• pp.191-198
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• 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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.9
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• pp.3015-3029
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• 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
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• v.55 no.2
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• pp.263-280
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• 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
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• 2003.10a
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• pp.21-22
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• 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.

• The Korean Journal of Cytopathology
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• v.9 no.2
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• pp.181-185
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• 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.

• Journal of Educational Research in Mathematics
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• v.15 no.4
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• pp.461-488
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• 2005

This article presents new perspectives for classification of students' mathematical errors on the basis of experiential structuralism. Experiential structuralism's mechanism gives us new insights on mathematical errors. The hard core of mechanism is consist of 6 autonomous capacity spheres that are responsible for the representation and processing of different reality domains. There are specific forces that are responsible for this organization of mind. There are expressed in terms of a set of five organizational principles. Classification of mathematical errors is ascribed by the theory to the interaction between the 6 autonomous capacity spheres. Different types of classification require different autonomous capacity spheres. We can classify mathematical errors in the domain of linear function problem solving comparing cognitive psychological mechanism of experiential structuralism.

• Journal of the Korean Society of Visualization
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• v.20 no.3
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• pp.67-73
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• 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.