• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.6
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• pp.2046-2056
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• 1996

The constrained melting inside an isothermally heated horizontal cylinder has been repeatedly investigated in many studies only for the moderate Rayleigh numbers. This study extends the range of Rayleigh numbers to systematically investigate the transition during melting processes, especially focusing on the complex multi-cellular flow pattern and thermal instability. The enthalpy-porosity formulation, with appropriate source terms to account for the phase change, is employed. For low Rayleigh numbers, initially developed single-cell base flow keeps the flow stable. For moderate Rayleigh numbers, even small disturbances in balance between thermal buoyance force and viscous force result in branched flow structure. For high Rayleight numbers, Benard type convection is found to develop within a narrow gap between thee wall and the unmelted solid. The marginal Rayleigh number and the corresponding wave number are in excellent agreement with those from linear stability theory.

• Journal of Powder Materials
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• v.17 no.6
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• pp.464-469
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• 2010

The Cu nanofluid in ethylene glycol was prepared by electrical explosion of wire, a novel one-step method. The X-ray diffraction, field emission scanning electron microscope and transmission electron microscope were used to study the properties of Cu nanoparticles. The results showed that the nanoparticles were consisted of pure face-centered cubic structure and near spherical shape with average grain size of 65 nm. Ultraviolet-visible spectroscopy (UV-Vis) confirmed Cu nanoparticles with a single absorbance peak of Cu surface plasmon resonance band at 600 nm. The nanofluid was found to be stable due to high positive zeta potential value, +51 mV. The backscattering level of nanofluid in static stationary was decreased about 2% for 5 days. The thermal conductivity measurement showed that Cu-ethylene glycol nanofluid with low concentration of nanoparticles had higher thermal conductivity than based fluid. The enhancement of thermal conductivity of nanofluid at a volume fraction of 0.1% was approximately 5.2%.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.48.4-48.4
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• 2019

Small-scale shear flows are ubiquitous in the universe, and astrophysical plasmas are often magnetized. We study the thermal condensation instability in magnetized plasmas with shear flows in relation to filamentary structure formation in cool structures in the universe, representatively solar prominences and supernova remnants. A linear stability analysis is extensively performed in the framework of magnetohydrodynamics (MHD) with radiative cooling, plasma heating and anisotropic thermal conduction to find the eigenfrequencies and eigenfunctions for the unstable modes. For a shear velocity less than the Alfven velocity of the background plasma, the eigenvalue with the maximum growth rate is found to correspond to a thermal condensation mode, for which the density and temperature variations are anti-phased (of opposite signs). Only when the shear velocity in the k-direction is near zero, the eigenfunctions for the condensation mode are of smooth sinusoidal forms. Otherwise each eigenfunction for density and temperature is singular and of a discrete form like delta functions. Our results indicate that any non-uniform velocity field with a magnitude larger than a millionth of the Alfven velocity can generate discrete eigenfunctions of the condensation mode. We therefore suggest that condensation at discrete layers or threads should be quite a natural and universal process whenever a thermal instability arises in magnetized plasmas.

• Journal of the Korean Chemical Society
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• v.47 no.6
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• pp.553-558
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• 2003

The crystal structure of $[n-Bu_4N]_2[Mo_6O_{19}]$(TBAM) (n-Bu4N=tetrabutylammonium) has been determined by X-ray crystallography. It crystallizes in the monoclinic system, space group C2/c, with lattice parameters ${\alpha}$=16.314(5), b=17.288(5), c=17.776(4)${\AA}$ ${\beta}$=101.47(3), and Z=4. In $[Mo_6O{19}]^{2-}$ anion, Mo atoms occupy six vertices of octahedron and each Mo atom is coordinated by six oxygen atoms to adopt distorted octahedral coordination geometry. The average bond distance of Mo-Ot (terminal), Mo-Ob (bridged) and Mo-Oc (central) are 1.680 ${\AA}$, 1.931 ${\AA}$ and 2.325 ${\AA}$ respectively. In $[n-Bu_4N]^+$ cation, the N atom possesses a slightly distorted tetrahedral geometry. There are some potential extensive C-H ${\cdots}$ O hydrogen bonds in the lattice, by which connecte molecules and stabilize the crystal structure. Thermogravimetric analysis suggests that thermal decomposition of the title compound includes two transitions and it loses weight at 356.0 and 803.5 $^{\circ}$, respectively, and the residue presumable be $Mo_2O_2$. Accordingly, the title compound has high thermal stability.

• The Research Journal of the Costume Culture
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• v.7 no.5
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• pp.165-176
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• 1999

The purpose of this study was to evaluate the effect of various knitted fabrics of sports socks on their properties of hygiene and stability. Seventeen men\`s sports socks to represent five groups with different fiber content, knit structure, yarn fineness, and finishing were used. Properties of hygiene and stability of socks were determined. The results were as follows ; 1. Evaluation of Water, vapor and heat transport properties in socks with varing fiber content showed that cotton 100% socks had the highest drop absorbency, wickability, water absorbency and water retention. Polypropylene 100% socks had an excellent wickability and moisture permeability. Acrylic blend socks had the highest thermal resistance. 2. The greatest knit stretch and knit growth of socks having lower power were found to be with cotton 100% socks had the lowest stretch. Acrylic blend socks had a excellent stretch but low fabric growth, which could give a good fir sensation during wear. 3. The commerical antimicrobial finished socks showed excellent durability after repeated cycles of laundering. 4. Length and width shrinkages were found in all laundered samples during initial cycles due to rearrangement by mechanical relaxation. Shrinkages showed no further changes and reached equilibriums after 5 cycles. Cotton 100% or cotton blend socks showed lower dimensional stability than other socks during fabric care.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.251-251
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• 2009

The generation of energy and the cooling of system using thermoelectric semiconductor material have been in spotlight. Thermoelectric effect increases with the decrease of the thermal conductivity. In the thermoelectric devices, thermal conductivity is related to phonon scattering. Therefore, few studies have been conducted in the thermoelectric materials dispersed nano oxide particle for increasing the phonon scattering. However, core-shell structure which nano particle disperses in solvents and then which thermoelectric materials coated on the nano oxide particles has not been reported. In this study, we selected commercial nano powder such as $Al_2O_3$. This nano particle was about 20nm and was crushed aggregate by mechanical treatment. We have developed the effect of the dispersant and the solvent. The properties of particles were evaluated by SEM, TEM, particle size analysis, and BET. Dispersion and dispersion stability were evaluated by electronic microscope and turbidity.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.13 no.1
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• pp.1-4
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• 2003

In the present work we consider morphological structure of the faces of BGO crystals grown by Czochralski technique under the conditions of low temperature gradient (0.1~1 deg/cm) and interconnection between the morphological features of faces at the crystallization front and the formation of defects within the crystal volume. It is demonstrated that the {112} faces retain stability while the growing surface deviates from the crystallographic (112) plane up to 1 degree. At larger deviation, the region of the stable facet growth passes either to the region of macrosteps or to the region of normal growth. depending on conditions.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.1
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• pp.41-46
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• 1997

The change of flow field and the effects of convective heat transfer on the shape and location of melt/crystal interface has been studied during the crystal growth by the heat exchanger method. Although the thermal structure is stable in the crucible, the flow due to the natural convection driven by radial temperature gradient is significant, because the thermal stability is broken by the hemispherical melt/crystal interface shape. The maximum interface deflection with convection is smaller than without and the convective heat transfer should be considered to simulate the heat transfer process of heat exchanger method rigorously.

• Macromolecular Research
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• v.8 no.5
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• pp.209-214
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• 2000

Polyenaminonitriles containing cycloaliphatic and aliphatic units were prepared by interfacial or solution polymerization reaction of p-bis(1-chloro-2,2-dicyanovinyl) benzene (1) with 4-aminobenzyl-amine, 1-(2-aminoethyl)piperazine, 2-(aminomethyl)pyrrolidine and 4-(aminomethyl)piperidine. The chemical structure of the polymers was confirmed through a syntheses of the model compound. The resulting polymers possessed inherent viscosities of 0.29∼0.62 dL/g and they were easily soluble in polar aprotic solvents and common organic solvents. Thermal properties of the polymers such as curability and stability were studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and infrared spectroscopy. The polymers exhibited a large exotherm in DSC analyses and underwent a curing reaction around 340-370$\^{C}$ to form insoluble materials. The polymers showed 70-80% residual weight at 600 $\^{C}$ under nitrogen.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.533-536
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• 2008

The anthracene derivatives were synthesized by Suzuki coupling reaction. The thermal, optical and electronic properties of MNAn and BIPAn were investigated by thermogravimetric analysis (TGA), differential scanning calorimetry(DSC), UV-vis absorption, photoluminescen ce spectroscopies, and cyclic voltammetry. The materials exhibit high thermal stability and high per formance in EL devices.