• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.3197-3202
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• 2007

An analysis program for pedestrian flow has been developed to investigate the flow patterns of passenger in railway stations. Analysis algorithms for pedestrian flow based on DEM(Discrete Element Method) are newly developed. There are lots of similarity between particle-laden two phase flow and passenger flow. The velocity component of 1st phase corresponds to the unit vector of calculation cell, each particle to passenger, volume fraction to population density and the particle velocity to the walking velocity, etc. And, the walking velocity of passenger is also represented by the function of population density. Key algorithms are developed to determine the position of passenger, population density and numbering to each passenger. By using the developed program, we compared the simulation results of the effects of the location and size of exit and elapsed time.

• 한국자기공명학회논문지
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• 제6권1호
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• pp.38-44
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• 2002

60% Pt on Vulcan XC-72 with similar Pt sizes to fuel cell grade Pt black was investigated by $\^$13/C nuclear magnetic resonance spectroscopy (NMR), cyclic voltammery (CV), transmission electron microscopy (TEM). Experiments were carried out on electrochemically cleaned samples as well as as-received. The TEM and CV results showed that the average particle sizes were changed by cleaning. However, the chemical shift （$\delta$$\_$G/） of $\^$13/C of $\^$13/CO absorbed on Pt surfaces did not show any appreciable variation with particle size change as did in Pt black. These results indicate that a combination of different analytic techniques is essential to understand the properties of the metal particle catalysts and that the presence of carbon black support strongly influences the NMR data, probably through metal-support interaction.

• 한국전기전자재료학회논문지
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• 제22권1호
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• pp.86-92
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• 2009

We fabricated the charged particle type display using opposite-charged two toner particles. The particles were composed of polymer, colorant($TiO_2$, carbon black) and external additives(nano-sized silica and so on). In fabrication process we controlled the putting layers of this toner particles on the inner panel. To get the effect of number of layers ($1{\sim}3$), we measured the threshold, driving and breakdown voltages, reflectivity, viewing angle, and color characteristics using RT-300 anisotropic scattering system. We ascertained that these voltages are increased with increasing of layers of particles. Cell gap between electrodes must be enlarged with increment of layers and the size of particles. The lumping phenomena of particles at near of the rib observed by optical system with same CIE values.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2006년도 추계학술대회 논문집
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• pp.387-391
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• 2006

Insight into behaviour of pedestrians as well as tools to assess passenger flow conditions are important in for instance planning and geometric design of railway station under regular and safety-critical circumstances. Algorithm for passenger flow analysis based on DEM(Discrete Element Method) is newly developed. There are lots of similarity between particle-laden two phase flow and passenger flow. The velocity component of 1st phase corresponds to the unit vector of calculation cell, each particle to passenger, volume fraction to population density and the particle velocity to the walking velocity, etc. And, the walking velocity of passenger is also represented by the function of population density. Key algorithms are developed to determine the position of passenger, population density and numbering to each passenger. To verify the effectiveness of new algorithm, passenger flow analysis for the basic models of railway station is conducted.

• 대한환경공학회지
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• 제22권4호
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• pp.713-722
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• 2000

본 연구는 입자크기를 분석하기 위한 장치인 레이저회절 분광계의 측정오차 및 재현성을 분석한 것이다. 레이저회절 spectrometers는 입자크기를 분석하기 위한 장치 중에서 가장 대표적이고 중요성을 가진다. 이 측정장치는 운전이 간단하며, 입자분석에 있어서 재현성이 우수하고, 빠른 속도로 분석이 가능한 형태이다. 입자크기를 분석하는 과정에 있어서 공급되는 분산형태와 흐름율에 따라서 측정오차가 미세하게 발생되었고, 흐름율은 분산형태가 건식인 경우 0.1~23 g/min로 공급하였고, 습식인 경우는 분산되는 용매에 따라서 1.4~35 %가 되도록 조절하여 측정결과에 따라서 발생되는 측정오차를 분석하였다. 흐름을 변화에 따라서 발생되는 측정 오차는 측정 cell 내의 입자에 입사되는 레이저 회절패턴이 변화함으로서 측정오차가 다양하게 발생하였다. 본 연구에서 측정오차를 분석하기 위해서는 입자모양, 크기, 분산형태와 용매, 흐름율과 농도의 변화에 따라서 실험을 실행하였고, 분석장치의 시스템에 따른 측정오차를 나타내기 위해서는 장치내의 역학적인 공정, 측정시간, 초점거리, 주입압력, 전처리과정인 ultrasonic이나 혼합에 의한 분산효과에 따라 측정오차 및 재현성을 분석하였다.

• Asian-Australasian Journal of Animal Sciences
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• 제20권11호
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• pp.1738-1745
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• 2007

A growth trial and a digestibility trial were conducted to examine the effect of feed particle size on the performance, nutrient digestibility, gastric ulceration and intestinal morphology in pigs fed barley-based diets. Barley was processed through a hammer mill to achieve four diets varying in particle size (average particle $size{\pm}standard $deviation): coarse ($1,100{\pm}2.19\;{\mu}m$), medium ($785{\pm}2.23\;{\mu}m$), fine ($434{\pm}1.70\;{\mu}m$) and mixed (1/3 of coarse, medium and fine) ($789{\pm}2.45\;{\mu}m$). Sixty-four entire male pigs were used in the growth trial and the diets were fed ad libitum between 31 kg and 87 kg live weight. Following slaughter, stomach and ileal tissues were scored for integrity (ulceration or damage) and histological measurements taken. Twenty-four entire male pigs were used in the digestibility trial, which involved total faecal collection. Over the entire growth phase, there were no differences (p>0.05) in average daily gain and feed conversion ratio between pigs fed diets of different particle size. Pigs fed the coarse and medium diets had lower (p<0.05) stomach ulceration scores (0.20 and 0.25, respectively, on a scale from 0 to 3) than those fed the mixed (0.69) or the fine diets (1.87). The stomachs of all animals fed the fine diet had lesions and stomach ulcerations were present only in this group. Pigs fed the fine diet had thicker (p<0.001) ileal epithelial cell layer with no differences (p>0.05) being observed for villous height or crypt depth. Faecal digestibility coefficients of neutral and acid detergent fibre were the highest (p<0.05) for the mixed diet, intermediate for the fine and coarse diets and the lowest for the medium diet. A similar numerical trend (p = 0.103) was observed for the apparent faecal energy digestibility coefficient. It is concluded that, with barley based diets, a variation in average particle size between $400{\mu}m$ and $1,100{\mu}m$ had no effect on pig performance but the fine dietary particle size affected the integrity of the stomach, as well as the structure of the small intestine, thus compromising overall gut health. Our data also demonstrate that changes in particle size distribution during the digestion process, rather than average particle size or particle size variation, are related to apparent faecal digestibility.

• The Korean Journal of Ceramics
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• 제2권3호
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• pp.142-146
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• 1996

The molten carbonate fuel cell matrices, which are usually made of high surface, fine particle size ${\gamma}-LiAlO_2$ are reinforced with coarse particles of the same material and alumina fibers. An the effects of reinforcing materials on pore characteristics, sintering properties and mechanical properties of the matrices are examined.Among the matrices examined, the highest mechanical reinforcement has been achieved in the one containing 10 wt.% coarse particles and 20 wt.% alumina fibers.

• Interaction and multiscale mechanics
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• 제2권2호
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• pp.129-151
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• 2009

This paper presents a meshfree procedure using a convex generalized meshfree (GMF) approximation for the large deformation analysis of particle-reinforced rubber compounds on microscopic level. The convex GMF approximation possesses the weak-Kronecker-delta property that guarantees the continuity of displacement across the material interface in the rubber compounds. The convex approximation also ensures the positive mass in the discrete system and is less sensitive to the meshfree nodal support size and integration order effects. In this study, the convex approximation is generated in the GMF method by choosing the positive and monotonic increasing basis function. In order to impose the periodic boundary condition in the unit cell method for the microscopic analysis, a singular kernel is introduced on the periodic boundary nodes in the construction of GMF approximation. The periodic boundary condition is solved by the transformation method in both explicit and implicit analyses. To simulate the interface de-bonding phenomena in the rubber compound, the cohesive interface element method is employed in corporation with meshfree method in this study. Several numerical examples are presented to demonstrate the effectiveness of the proposed numerical procedure in the large deformation analysis.

• 한국주조공학회지
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• 제10권6호
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• pp.528-537
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• 1990

7XXX aluminum alloy powders produced by the self-manufactured rotating disc atomizer were investigated to determine the influence of the atomization parameters on the particle size distributions in air atmosphere. The particle size distributions are almost always bimodal with the dominant mode on the large particle size. Average powder size of 7XXX aluminum alloy is $74/{\mu}m~125/{\mu}m$ when melt is poured with the rate of 9g /sec at 730$^{\circ}C$ on a rotating disc of 30㎜ diameter at 6300rad/sec. The mass of finer particle increased when disc diameter, angular velocity, pouring temperature increased and pouring rate decreased. The powder shapes of bimodal change from acicular to tear-drop and from tear-drop to ligament with increasing powder size. Powder shape was determined by the atomization mechanism and oxidation in liquid state. Microstructure of powders appeared to be cell and cellular dendrite. The SDAS of Al-7.9wt%Zn-2.4wt%Mg-1.5wt%Cu-0.9wt%Ni Powders is $0.8{\mu}m~1.0{\mu}m$ for the powders of $size＋44{\mu}m~53{\mu}m$ and $1.6{\mu}m∼1.8{\mu}m$ for the powders of $size＋105{\mu}m~125{\mu}m$, repectively.

• 생태와환경
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• 제33권2호통권90호
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• pp.145-151
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• 2000

부영양 상태의 연못에서 채취한 시료수에 규산질다공체(CellCaSi)를 첨가한 후 미세조류의 제거효과에 대하여 조사하였다. 규산질다공체는 입도의 크기(1, 2, 그리고 4 mm 이하) 및 첨가량(0, 1, 5, 그리고 10 g/l)에 따라서 수질에 미치는 영향을 조사하였다. 엽록소-a 농도는 1 mm 이하의 규산질다공체를 10 g/l로 첨가한 경우 처리 3일에 79%의 제거효율을 나타내었다. 즉, 규산질다공체의 조류제거 효과는 입자의 크기가 작을수록, 첨가량이 많을수록 효과가 높았다. 규산질다공체 첨가구의 우점조류종은 Chlorella ellipsoidea로 대조구와 차이가 없으나, 출현 조류종 및 현존량은 감소하였다. 규산질다공체의 첨가에 의하여 총질소 함량은 영향을 받지 않았으나, 총인 함량은 다소 감소하는 경향을 나타내었다. 규산질다공체의 첨가로 인하여 pH와 turbidity는 크게 영향을 받지 않았으나, conductivity는 첨가량에 따라 비례적으로 증가하는 경향을 보였다. 따라서, 대부분의 원수 및 음용수에 있어서 전기전도도의 상한값으로 알려진 500 ${\mu}$mhos/cm를 유지하기 위해서 규산질다공체의 첨가량은 6.6 g/l 이하로 제한하는 것이 바람직하다고 판단된다.