• Journal of the Korean Ceramic Society
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• v.38 no.9
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• pp.799-805
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• 2001

Two commercial alumina powders having different particle size of $0.5{\mu}m$ and 3${\mu}$m were presintered at 1120$^{\circ}$C for 2h and then lanthanum aluminosilicate glass was infiltrated at 1100$^{\circ}$C for up to 4h to obtain the densified glass-alumina composites. The effect of alumina particle size on packing factor, microstructure, wetting, porosity and pore size, and mechanical properties of the composite was investigated. The optimum mechanical properties and compaction behavior were observed for the 3${\mu}$m alumina particle dispersed composite. The 3${\mu}$m alumina particle size and distribution for he preform were within 0.1 to 48${\mu}$m and bimodal and random orientation. The strength and the fracture toughness of the composite having 3${\mu}$m alumina particles were 519MPa and $4.5MPa{\cdot}m^{1/2}$, respectively.

• The Korean Journal of Rheology
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• v.11 no.2
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• pp.128-134
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• 1999

Rheological characterization was examined for two different types of magenetic particle (rod-like $\gamma$-$Fe_{2}O_{3}$, $CrO_2$ )suspension in this study. The measured suspension viscosity (viscosity vs. concentration or shear rate) is used to obtain the dependence of viscous energy dissipation on the microstructural states of magnetic particle dispersions as well as the microstructural shape effects which are related to magnetic particle orientation. The empirical formulas from mean field theory and the Mooney equation are used to relate suspension viscosity to particle concentration. Intrinsic viscosities of these two different types of rod-like magnetic particle suspensions are found to exceed the prediction of hydrodynamic theory for dilute suspensions and support the existence of flocs containing significant amounts of immobilized suspending medium due to native attraction forces among particles in the microstructures.

• Journal of the Korean institute of surface engineering
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• v.31 no.4
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• pp.217-222
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• 1998

The Facing Targets Sputtering(FTS) system has several advantages for preparing films over a wide range of working gas pressure on plasma-free substrates. Co-Cr thin films seem to be one of the most promising media for perpendicular magnetic recording system. In this study, the capabillities of the system fordepositing C0-Cr films have been investigated. Under various Ar gas pressure, films with morphologically dense microstructure and good c-axis orientation were deposited, even when the incident angle $\psi_x$ of sputtered part icles to the film plane was below abount $50^{\circ}C$. this may imply that the shadowing effect by obique incidence of particle can be compensated by rapid surface diffusion owing to the high kinetic energy of particles arriving at the growing film. It has been confirmed that the FTS system is very useful for perparing Co-Cr thin films recorging media.

• Proceedings of the Korean Fiber Society Conference
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• 2003.10a
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• pp.65-66
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• 2003

Ternary blend fibers (TBFs) based on melt blends of PEN, PET, and TLCP were prepared by melt blending and spinning to achieve high performance fibers. The reinforcement effect and the TLCP fibrillar structure resulted in the improvement of mechanical properties for TBFs. Molecular orientation was an important factor in determining the tensile strength and modulus of TBFs. Another part of this research is silica nano-particle filled PEN composites were melt-blended to improve mechanical and physicalproperties, and processability. The tensile modulus and strength were improved adding silica nano-particles to the PEN. The decreased melt viscosity by the fumed silica resulted in the improvement of the processability. The fumed silica may act as a nucleating agent in the PEN matrix.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.684-685
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• 2006

In the present study, the powder metallurgical fabrication of $Bi_{0.4}Te_3Sb_{1.6}$ thermoelectric materials has been studied with specific interest to control the microstructure by the mechanical grinding process. The $Bi_{0.4}Te_3Sb_{1.6}$ thermoelectric powders with a various particle size distribution were prepared by the combination of the mechanical milling and blending processes. The specific electric resistivity of the $Bi_{0.4}Te_3Sb_{1.6}$ sintered bodies mainly depended on the orientation of the crystal structure rather than the particle size of the raw powders.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.1
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• pp.108-114
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• 2014

This paper proposes a generation method of a navigation guidance direction and a fuzzy controller to achieve the autonomous navigation of a mobile robot using a particle swarm optimization(PSO) scheme in unknown environments. The proposed navigation guidance direction is the direction that leads a mobile robot to arrive a target point simultaneously with avoiding obstacles efficiently according to the surrounding local informations. It is generated by selecting the most suitable direction of the many directions in the surrounding environment using a particle swarm optimization scheme. Also, a robot can reach a target point with avoiding the various obstacles by controlling the robot so that it can move from its current orientation to the navigation guidance direction using the proposed fuzzy controller. Simulation results are presented to show the feasibility and validity of the proposed robot navigation scheme.

• Journal of the Korean Society for Heat Treatment
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• v.10 no.1
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• pp.55-62
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• 1997

The morphology of deformation induced dislocations in polycrystalline $Ni_3$(Al, Cr) containing $M_{23}C_6$ precipitates has been investigated in terms of transmission electron microscopy(TEM). Fine Polyhedral precipitates of $M_{23}C_6$ appeared in the matrix by aging at temperatures around 973 K after solution annealing at 1423 K. TEM examination revealed that the $M_{23}C_6$ phase and the matrix lattices have a cube-cube orientation relationship and keep partial atomic matching at the {111} interface. After deformation at temperature below 973 K, typical Orowan loops were observed surrounding the $M_{23}C_6$ particles. At higher deformation temperatures, the Orowan loops disappeared and the morphology of dislocations at the particle-matrix interfaces suggested the existence of attractive interaction between dislocations and particles. The change of the interaction modes between dislocation and particles with increasing deformation temperature can be considered as a result of strain relaxation at the interface bet ween matrix and particles.

• Communications of the Korean Mathematical Society
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• v.31 no.2
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• pp.263-275
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• 2016

Quantum graph of Sierpinski gasket type with attached leads in an electric eld is considered. We study the dependence of the transmission coecient via the wave number of the quantum particle. It has strongly resonance character. The in uence of the amplitude and the orientation of the electric eld on the coecient is investigated.

• Composites Research
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• v.13 no.1
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• pp.50-60
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• 2000

This paper presents an analytical method considering tensile strength enhancement in hybrid $Al_2O_3$ fiber/particle/aluminum composites(MMCs). The tensile strength and elastic modulus of the hybrid MMCs are even 20% higher than those of the fiber reinforced MMCs with same volume fraction of reinforcements. This phenomenon is explained by the cluster model which is newly proposed in this research, and the strengthening mechanisms by a cluster is analyzed using simple modified rule of mixtures. From the analysis, it is observed that cluster structure in hybrid MMCs increase the fiber efficiency factor for the tensile strength and the orientation factor for the elastic modulus. The present theory is then compared with experimental results which was performed using squeeze infiltrated hybrid MMCs made of hybrid $Al_2O_3$ short fiber/particle preform and AC8A alloy as base metal, and the agreement is found to be satisfactory.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.4
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• pp.235-241
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• 2009

Experimental studies on single-phase toroidal circulation loop(thermosyphon) have been performed in the present study with Ag-nanofluids as a working fluids. The present paper deals with an experimental study on the heat transfer behavior of single-phase toroidal loop. Toroidal loop charged with nanofluid has been constructed and a number of tests have been carried out. Different geometric parameter, e.g., orientation has been investigated. The tests were conducted employing two fluids: distilled water and Ag-nanofluid of various volume concentrations. The experiments at Rayleigh number from $10^5$ to $10^6$ showed a systematic and slight deterioration in natural convective heat transfer. It was observed that the deterioration due to the particle concentration was in the range of 5-10%. At a given particle concentration of 0.05%, abrupt decrease in the Nusselt number and the Raleigh number was observed. The present study with toroidal loop shows that the application of nanofluids for heat transfer intensification should not be decided only by the effective thermal conductivity with increasing particle concentration.