• Journal of Korea Foundry Society
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• v.33 no.3
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• pp.122-126
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• 2013

Recently, heat-resistant aluminum alloy has been re-focused as a downsizing materials for the internal combustion engines. Heat-resistant Al alloy development and many researches are still ongoing for the purpose of improving thermal stability, high-temperature mechanical strength and fatigue properties. The conventional principle of heat-resistant Al alloy is the precipitation of intermetallic compounds by adding a variety of elements is generally used to improve the mechanical properties of Al alloys. Heat resistant aluminum alloys have been produced by CrW homogeneous solid solution to overcome the limit of conventional heat resistant aluminum alloy. From EPMA, it is found that CrW homogeneous soild solution phases with the size of $50-100{\mu}m$ have been dispersed uniformly, and there is no reaction between aluminum and CrW alloy. In addition, after maintaining at high temperature of 573 K, there is no growth of hardening phase, nor desolved, but CrW still exists as a homogeneous solid solution.

• Structural Engineering and Mechanics
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• v.19 no.3
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• pp.281-295
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• 2005

An analytical method is presented to solve the elastodynamic problem of finitely long hollow cylinder subjected to torsional impact often occurs in engineering mechanics. The analytical solution is composed of a solution of quasi-static equation satisfied with the non-homogeneous boundary condition and a solution of dynamic equation satisfied with homogeneous boundary condition. The quasi-static solution is obtained directly by solving the quasi-static equation satisfied with the non-homogeneous boundary condition. The solution of the non-homogeneous dynamic equation is obtained by means of finite Hankel transform on the radial variable, r, Laplace transform on time variable, t, and finite Fourier transform on axial variable, z. Thus, the solution for finitely long, hollow cylinder subjected to torsion impact is obtained. In the calculating examples, the response histories and distributions of shear stress in the finitely long hollow cylinder subjected to an exponential decay torsion load are obtained, and the results have been analyzed and discussed. Finally, a dynamic finite element for the same problem is carried out by using ABAQUS finite element analysis. Comparing the analytical solution with the finite element solution, it can be found that two kinds of results obtained by means of two different methods agree well. Therefore, it is further concluded that the analytical method and computing process presented in the paper are effective and accurate.

• Progress in Superconductivity and Cryogenics
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• v.4 no.1
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• pp.114-118
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• 2002

We introduce a design technique for homogeneous magnets using evolution strategy. The method has several advantages over existing techniques including: it allows complete flexibility in geometric constraints on the shape of both the coil and the homogeneous volume; it guarantees a globally optimal solution, and it automatically searches the minimum number of coils that satisfies given constraints.

• Journal of the Korean Chemical Society
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• v.6 no.2
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• pp.122-124
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• 1962

The silver halide precipitate tends to separate in curdy form of flocculated colloid when it is precipitated by direct mixing of reactant solutions. This type of precipitate has a great tendency to adsorb or occlude foreign ions in the solution.When silver halide in precipitated from homogeneous solution using the slow hydrolysis of Alkyl halide or Ally halide, the precipitate becomes dense, filterable and uniform in particle size which is very advantageous in gravimetric analysis.We found that silver halide precipitates obtained from homogeneous solution with hydrogen halide formed by the hydrolysis of alkyl halide do not give the color change with fluorescein as adsorption indicater, while silver halide precipitates obtained by direct mixing method give sharply pink color which appear to be uniformly distributed through the solution in silver ion excess.

• Fibers and Polymers
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• v.1 no.1
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• pp.6-11
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• 2000

In the polycondensation reaction of polyethyleneterephthalate(PET), $Sb_2$$O_3$, can react effectively as a catalyst, if physically transformed. $Sb_2$$O_3$ powder is transformed into liquid solution by dissolving in ethylene glycol(EG). Homogeneous catalyst is made by mixing this liquid solution with glycols having different solubility. The efficient reaction of PET polymerization is expected by using homogeneous catalyst. PET was synthesized using homogeneous catalysts of 4 wt.% $Sb_2$$O_3$ solution dissolved in glycol[EG, 2,2-bis(4-(2-hydroxyethoxy)phenol)propane(BHPP), neopentyl glycol(NPO), and 1,3-propandiol(PD)]. PET using EG-BHPP($Sb_2$$O_3$) catalysts shows the highest I.V. within a reaction time of 120 min. In the p-d analysis, PET using EG-BHPP($Sb_2$$O_3$) catalysts has the fastest propagation rate and slowest degradation rate. EG-BHPP($Sb_2$$O_3$) catalysts are more efficient than EG($Sb_2$$O_3$) catalysts and $Sb_2$$O_3$ powder catalysts.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.34 no.1
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• pp.38-43
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• 1985

Since the superconductor type II with high critical current and high critical magnetic field was discovered in 1961, there were many studies on the superconducting coil for high field and highly homogeneous field. The graphical method and the numerical method by Newton Raphson technique have been studied as the method for design of homogeneous superconducting coil. It is comparatively easy to get a compensating coil for any given main coil by the above methods, but it is too laborious to get a general solution for main coil dimension. This paper studies the optimal design method for minimum volume of superconducting coil under certain central field and highly homogeneous field. The present method makes use of the nonlinear programming for optimization. The optimal solution of NMR superconducting coils by this method are demonstrated very well.

• Journal of the Korean Ceramic Society
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• v.36 no.9
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• pp.991-996
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• 1999

Effect of solution property on the weight varation and microstructural change of film was studied by electrophoretic deposition in order to obtain a homogeneous and dense zirconia film. As a result of weight kinetics of film which obtained in alcohol or aqueous solution having different polarity experimental data showed large deviation from theoretical ones calculated by Zhang's kinetic model. It had been shown that the weight affecting factors was largely dependent on properties other than dielectric constant and viscosity of solvent zeta potential appiled field and time. In initial stage a main factor of the drastic weight increase was the capillary drag of porous substrate. The cause of weight decrease with time in aqueous solution after 300 s was attributed to the defect of film by sagging and electrolytic reaction. The electrolyte film which prepared in alcohol solution with good wetting for substrate had better homogeneous and dense microstructure than one in aqueous solution with high surface tension.

• Communications of the Korean Mathematical Society
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• v.14 no.2
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• pp.301-310
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• 1999

This paper is concerned with the existence of positive solution of a semilinear elliptic equation with homogeneous Dirichlet boundary condition.

• Korean Membrane Journal
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• v.6 no.1
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• pp.61-69
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• 2004

Small angle light scattering (SALS) and field emission scanning electron microscope (FE-SEM) have been used to investigate the effects of alcohol on phase separation of chlorinated poly(vinyl chloride) (CPVC)/tetrahydrofuran (THF)/alcohol (9/61/30 wt%) solution during water vapor induced phase separation. A typical scattering pattern of nucleation & growth (NG) was observed for all casting solutions of CPVC/THF/alcohol. In the case of the phase separation of CPVC dope solution containing 30 wt% ethanol or n-propanol, the demixing with NG was observed to be heterogeneous. Meanwhile, the phase separation of CPVC dope solution with 30 wt% n-butanol was found to be predominantly homogeneous NG. Although the different phase separation behavior of NG was observed with types of alcohol additives, the resultant surface morphology had no remarkable differences. That is, even though the NG process by water vapor is either homogeneous or heterogeneous, this difference does not play a main role on the final surface morphology. However, it was estimated from the result of hydraulic flux that the phase separation by homogeneous NG provided the membrane geometry with lower resistance in comparison with that by heterogeneous one.

• Bulletin of the Korean Chemical Society
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• v.24 no.6
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• pp.797-801
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• 2003

One of the largest challenges for quantum chemistry today is to obtain accurate results for large complex molecular systems, and a variety of approaches have been proposed recently toward this goal. We have developed the ONIOM method, an onion skin-like multi-level method, combining different levels of quantum chemical methods as well as molecular mechanics method. We have been applying the method to many different large systems, including thermochemistry, homogeneous catalysis, stereoselectivity in organic synthesis, solution chemistry, fullerenes and nanochemistry, and biomolecular systems. The method has recently been combined with the polarizable continuum model (ONIOM-PCM), and was also extended for molecular dynamics simulation of solution (ONIOM-XS). In the present article the recent progress in various applications of ONIOM and other electronic structure methods to problems of homogeneous catalyses and nanochemistry is reviewed. Topics include 1. bond energies in large molecular systems, 2. organometallic reactions and homogeneous catalysis, 3. structure, reactivity and bond energies of large organic molecules including fullerenes and nanotubes, and 4. biomolecular structure and enzymatic reaction mechanisms.