• Computers and Concrete
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• 제13권4호
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• pp.437-456
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• 2014

This work incorporates newly introduced Lattice Discrete Particle Model (LDPM) to assess the failure mechanism and strength of hollow concrete blocks. Alongside, a method for the graphical representation of cracked surfaces in the LDPM is outlined. A slightly modified calibration procedure is also suggested and used to estimate required model parameters for a tested concrete sample. Next, the model is verified for a compressively loaded hollow block made of the very same concrete. Finally, four geometries commonly used in the production of hollow concrete blocks are selected, numerically simulated, and their failure properties are explored under concentric and eccentric compressions.

• 공업화학
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• 제21권3호
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• pp.353-355
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• 2010

양이온성의 2,2'-azobis(2-methylpropionamidine) (AIBA) 개시제를 이용한 methylmethacrylate (MMA)의 무유화제 에멀전 중합을 통해 polymethylmethacrylate (PMMA) 입자를 합성하였다. 스퇴버 방법을 이용하여 양이온성의 PMMA 입자 표면에 실리카를 코팅하였다. 음전하의 실리카 전구체는 양이온성의 PMMA 입자 표면과의 정전기적 인력에 의해 코팅된다. 실리카 코팅 과정 중에 PMMA 입자가 용해되어 후처리 없이 실리카 중공체를 얻을 수 있었다.

• KSTLE International Journal
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• 제6권1호
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• pp.28-32
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• 2005

The electrorheoloRical (ER) fluids are composed of a colloidal dispersion of polarizable particles in insulating oil, and it's the rheological property changes by the applied electric field. These changed are reversible and occur fast within a fewmilliseconds. The ER properties of the ER fluid such as increment of viscosity and yield stress come from the particle chain structure induced by electric fleld. When formulating the ER fluid for a speciflc application, some requirement must besatisfled, which are high yield stress under electric field, rapid response, and dispersion stability. While this characteristic makes valuable ER fluids in valious industrial applications, their lung term and quiescent application has been limited because ofproblems with particle sedimentation. In an effort to overcome sedimentation problem of ER fluids, the anhydrous ER materials of monodispersed hollow polyaniline (PANI) and adipate derivative respectively with submicron-sized suspension providing wide operating temperature range and other advantage were synthesized in a four-step procedure. The ER fluidswere characterized by FT-lR, TGA, DLS, SEM, and TEM. Stability of the suspensions was examined by an UV spectroscopy.The rheological and electrical properties of the suspension were investigated Couette-type rheometer with a high voltagegenerator, current density, and conductivity. And the behavior of ER suspensions was observed by a video camera attached toan optical microscope under 3kV/mm. The suspensions showed good ER properties, durability, and particle dispersion.

• 청정기술
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• 제12권4호
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• pp.205-210
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• 2006

본 연구에서는 폐 polystyrene을 재활용하기 위한 방법으로, 최적의 정제조건을 확립한 다음, 이를 활용하여 부가가치가 높은 Polystyrene 중공 미세구를 제조하고자 하였다. 회수된 PS를 이용하여 다중유화법($W_1/O/W_2$)에 의해 PS/PVA 두층을 갖는 중공 미세구를 얻을 수 있었다. 1단계 반응인 $W_1/O$ emulsion 생성 시 초음파처리는 입자 크기와 분포를 조절하는데 중요한 인자로 작용하였으며, 20초 처리하였을 때 평균입자크기 $1.35{\mu}m$, 입도분포 $0.8{\mu}m{\sim}2.8{\mu}m$인 고분자 중공 미세구를 제조할 수 있었다. 또한 $W_2$상 계면활성제로 gelatin 또는 Tween 80을 사용하였을 때 상대적으로 입자 크기도 작고 균일한 고분자 중공 미세구를 제조할 수 있었다.

• 한국분무공학회지
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• 제5권2호
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• pp.43-52
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• 2000

Numerical simulation of steady, non-evaporating hollow-cone sprays interacting with concentric annular air jets is performed using the discrete stochastic particle method in KIVA. The spray characteristics such as SMD, mean droplet velocity, liquid volume flux, air/liquid mass ratio, and droplet number density arc obtained and compared with the measurements involving different air flow rates in large and small annuli. Overall satisfactory agreement is achieved between calculation and experiment except for the deviation in the downstream SMD arising from uncertainty in the size distribution function at injection, and inaccuracy in the averaged spray parameters due to the small volumes of axisymmetric 2-D sector meshes close to the axis.

• 전기화학회지
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• 제11권3호
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• pp.154-158
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• 2008

The synthesis of hollow ${Sb_93}{Pt_7}$ nanospheres smaller than 30 nm with a shell consisting of smaller nanoparticles, with an average particle size of ${\sim}$ 3 nm is reported. The formation of this alloy is driven by galvanic replacement reaction involving Sb nanoparticles and ${H_2}{PtCl_6} $ without need for any additional reductants. Further, the reaction proceeds selectively as long as the redox potential between two metals is favorable. The capacities of the hollow samples are 669 and 587mAh/g at rates of 1 and 7C, respectively, while those values for the nanoparticles are 647 and 480mAh/g at rates of 1, 7C, respectively. This result shows the significantly improved capacity retention of the hollow sample at higher C rates, indicating that high surface area of the hollow nanospheres makes the current density more effective than that for the solid counterpart.

• 한국펄프종이공학회:학술대회논문집
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• 한국펄프종이공학회 1999년도 Pre-symposium of the 10th ISWPC Recent Advances in Paper Science and Technology
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• pp.309-314
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• 1999

With a view to seek the influence of hollow sphere pigments of latex upon the printed color on coated paper surface, the hollow sphere pigments were compared with filled ones in a variety of experimental approaches. Colloidal properties of latices were determined by measuring zeta potential and particle size distribution. For the amphoteric filled sphere pigment of latex, the polarity was reversed from the negative side to the positive side with decreasing pH. An extraordinarily high peak in the particle size distribution of the amphoteric filled evidenced aggregation between latex particles near the isoelectric point, depending on the electrolyte concentration and pH of the suspending medium. Coated papers containing the hollow sphere pigment in their coating improved optical properties like gloss and brightness. Optical parameters solely of the coating could account for this finding. An equation derived from the Kubelka-Munk equation calculated them fro twice measurements of reflectance of a coated paper over two substrates of different reflectances. This method permitted to predict brightness of coated paper of which coat weight would be different fro the actual one. The colorimetric parameters of solid-printed surfaces of the coated papers closely related to optical and structural properties of the coated papers. The color of the printed surfaces was dominated by the brightness and the smoothness of the coated papers. The hollow sphere pigments were proved to improve optical properties of coated paper and to control minutely colorimetric parameters of printed surfaces.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.245-250
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• 2004

The discharge current oscillation has been measured for various hollow anode widths and its axial positions using a 1㎾-class anode layer hall thruster. As a result, there were thresholds of magnetic flux density for stable discharge. The plasma structure inside the hollow anode was numerically analyzed using the fully kinetic 2D3V Particle-in-Cell (PIC) and Direct Simulation Monte Carlo (DSMC) methods. The results reproduced both stable and unstable operation modes. In the stable operation case, which corresponds to the case with low magnetic flux, the plasma penetrated into the hollow anode deeper than the case with higher magnetic flux density case. This suggests that comparably large substantial anode area should contribute to stable operation.

• Computers and Concrete
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• 제22권4호
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• pp.373-381
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• 2018

Hollow center cracked disc (HCCD) in Brazilian test was modelled numerically to study the crack propagation in the pre-cracked disc. The pre-existing edge cracks in the disc models were considered to investigate the crack propagation and coalescence paths within the modelled samples. The effect of particle size on the hollow center cracked disc (HCCD) in Brazilian test were considered too. The results shows that Failure pattern is constant by increasing the ball diameter. Tensile cracks are dominant mode of failure. These crack initiates from notch tip, propagate parallel to loading axis and coalescence with upper model boundary. Number of cracks increase by decreasing the ball diameter. Also, tensile fracture toughness was decreased with increasing the particle size. In this research, it is tried to improve the understanding of the crack propagation and crack coalescence phenomena in brittle materials which is of paramount importance in the stability analyses of rock and concrete structures, such as the underground openings, rock slopes and tunnel construction.

• 접착 및 계면
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• 제13권4호
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• pp.151-155
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• 2012

본 연구에서는 중공형 나노 입자의 구조체가 되는 구형 폴리스티렌을 조절된 유화중합법으로 여러 크기의 구형 폴리스티렌을 제조하는 연구를 수행하였다. 유화중합에 사용되는 유화제의 농도를 조절하여 구형 폴리스티렌의 크기를 임의로 조절하였다. 이 폴리스티렌을 구조체로 이용하여 중공형 중간세공 실리카를 합성하였으며, 합성 과정 시 반응속도의 조절을 위해 에탄올을 넣어 실리카 전구체의 가수분해 속도를 조절하고, 실리카 전구체의 투여량을 조절하여 중공형 중간세공 실리카의 벽 두께를 조절하였다.