• Journal of the Korean Ceramic Society
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• v.27 no.7
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• pp.899-906
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• 1990

The cordierite powders were prepared from Mg(NO3)2.6H2O, Al(NO3)3.9H2O and colloidal silica by the coprecippitation method, and the sintering behavior of the powders were investigated. Two different methods were applied for producing the precursor powders. The one was to added the aqueous solution of Mg(NO3)2.6H2O and Al(NO3)3.9H2O to NH4OH to adjust pH at 10 where the colloidal silica of pH 10 was added. The other wa to add the aqueous solution of Mg(NO3)2.6H2O and Al(NO3)3.9H2O to the colloidal silica with NH4OH to control the final mixture to be at pH 10. It was confirmed that more homogeneous powders were obtained from the latter method. The firing linear shrinkage of the powder compacts fabricated from the calcined powder between 90$0^{\circ}C$ and 110$0^{\circ}C$ was found to be larger as the calcination temperature was low. But all of them stopped shrinking around 120$0^{\circ}C$. The powder compacts, fabricated using the calcined powders at 90$0^{\circ}C$ and 95$0^{\circ}C$ for 2hours and sintered at 142$0^{\circ}C$ for 2hours, showed relative density of 93-96%, 3-point bending strength of 81-83MPa, KIC of 1.9-2.4 MPam1/2 and thermal expansion coefficient of 0.213-0.732$\times$10-6$^{\circ}C$.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.9 no.4
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• pp.103-112
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• 1989

A numerical model for Steady state groundwater flow has been established to understand the groundwater flow phenomena near a radioactive waste repository. The integrated finite difference method based on a network composed of nodes and members was applied to investigate groundwater flow in homogeneous, heterogeneous and layered media. Its numerical solution was in good agreement with analytic solution. Physical phenomena associated in the groundwater flow depending on both hydraulic characteristics and effects of fractured zone were also investigated. A method by which feasible groundwater flow paths can be identified was developed. This method used the composite network for the geologic media near a repository and the direction of computed groudwater velocity. Groundwater velocity and travel time were predicted for the possible pathway form a repository to a biosphere.

• Bulletin of the Korean Chemical Society
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• v.35 no.7
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• pp.2049-2056
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• 2014

A simple method for exfoliating pristine graphite to yield mono-, bi-, and multi-layers of graphene sheets as a highly concentrated (5.25 mg/mL) and yielded solution in an organic solvent was developed. Pre-thermal treatment of pristine graphite at $900^{\circ}C$ in a sealed stainless steel bath under high pressures, followed by sonication in 1-methyl-2-pyrrolidinone solvent at elevated temperatures, produced a homogeneous, well-dispersed, and non-oxidized graphene solution with a low defect density. The electrical conductivities of the graphene sheets were very high, up to 848 S/cm. These graphene sheets were used to fabricate graphene-polyimide nanocomposites, which displayed a higher electrical conductivity (1.37 S/m) with an improved tensile strength (95 MPa). The synthesized graphene sheets and nanocomposites were characterized by transmission electron microscopy, scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy.

• Journal of Ocean Engineering and Technology
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• v.19 no.6 s.67
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• pp.58-63
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• 2005

The estimation of springing responses for recent ships is carried out, and application to a ship design is described. To this aim, springing effects on hull girder were re-evaluated, including non-linear wave excitations and torsional vibrations of the hull. The Timoshenko beam model was used to calculate stress distribution on the hull girder, using the superposition method. The quadratic strip method was employed to calculate the hydrodynamic forces and moments on the hull. In order to remove the irregular frequencies, we adopted 'rigid lid' on the hull free surface level, and addedasymptotic interpolation along the high frequency range. Several applications were carried out on the following existing ships: The Bishop and Price's container ship, S-175 container ship, large container, VLCC, and ore carrier. One of them is compared with the ship measurement result, while another with that of the model test. The comparison between the analytical solution and the numerical solution for a homogeneous beam-type artificial ship shows good agreement. It is found that Most springing energy comesfrom high frequency waves for the ships having low natural frequency and North Atlantic route etc. Therefore, the high frequency tail of the wave spectrum should be increased by $\omega$$\^{-3}$ instead of $\omega$$\^{-4}$ or $\omega$$\^{-5}$ for the springing calculation.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.42 no.6 s.336
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• pp.49-58
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• 2005

In this paper, we propose an optimal ILP scheduling algorithm for multiprocessor design on LDFG(Linear Data-Flow Graph) that can be represented by homogeneous synchronous data-flow. The proposed computation in this paper does not contain data-dependent, all scheduling decisions for such algorithms can be taken at compile time, only fully static overlapped schedules are considered. It means that all linear have the same schedule and the same processor assignment. In this paper, the resource-constrained problem is addressed, for the LDFG optimization for multiprocessor design problem formulating ILP solution available to provide optimal solution. The results show that the scheduling method is able to find good quality schedules in reasonable time.

• Korean Journal of Materials Research
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• v.12 no.12
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• pp.947-954
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• 2002

HCl concentration and reaction time are the decisive factors in determining the structure of precipitates in the process of synthesis of $TiO_2$ particles from aqueous $TiOCl_2$ solution by precipitation and the volumetric proportion of brookite phase in $TiO_2$ particles can be controlled by these two factors. As reaction rate increases with increase of reaction temperature, the reaction time, at which maximum volumetric proportion of brookite phase in $TiO_2$ particles was obtained, was reduced. The brookite was transformed directly to rutile phase with only increase of reaction time. And precipitation was delayed with increase of HCl concentration because the amount of $H_2$O, which is necessary source of oxygen for conversion of $Ti^{+4}$ to $TiO_2$, was relatively reduced with increase of that. Brookite in the mixture phase powder was finally transformed to rutile phase via anatase through heat-treatment.

• Advances in materials Research
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• v.8 no.3
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• pp.155-177
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• 2019

In this paper, a new displacement based high-order shear deformation theory is introduced for the static response of functionally graded sandwich plate with new definition of porosity distribution taking into account composition and the scheme of the sandwich plate. Unlike any other theory, the number of unknown functions involved is only four, as against five in case of other shear deformation theories. The theory presented is variationally consistent, has strong similarity with classical plate theory in many aspects, does not require shear correction factor, and gives rise to transverse shear stress variation such that the transverse shear stresses vary parabolically across the thickness satisfying shear stress free surface conditions. Material properties of FGM layers are assumed to vary continuously across the plate thickness according to either power-law or sigmoid function in terms of the volume fractions of the constituents. The face layers are considered to be FG across each face thickness while the core is made of a ceramic homogeneous layer. Governing equations are derived from the principle of virtual displacements. The closed-form solution of a simply supported rectangular plate subjected to sinusoidal loading has been obtained by using the Navier method. Numerical results are presented to show the effect of the material distribution, the sandwich plate geometry and the porosity on the deflections and stresses of FG sandwich plates. The validity of the present theory is investigated by comparing some of the present results with other published results.

• Journal of the Korean Ceramic Society
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• v.43 no.9 s.292
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• pp.564-568
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• 2006

AlO(OH) nano gel is used in precursor of ceramic material, coating material and catalyst. For use of these, not only physiochemical control for particle morphology, pore characteristic and peptization but also studies of synthetic method for preparation of advanced application products were required. In this study, AlO(OH) nano gel was prepared through the aging and drying process of aluminum hydroxides gel precipitated by the hydrolysis reaction of dilute NaOH solution and aluminum sulfate solution. In this process, optimum synthetic condition of AlO(OH) nano gel having excellent pore volume as studying the effect of water and aluminum sulfate mole ratio on gel precipitates has been studied. Water and aluminum sulfate mole ratio brought about numerous changes on crystal morphology, surface area, pore volume and pore size. Physiochemical properties were investigated as using XRD, TEM, TG/DTA, FT-IR, and $N_2$ BET method.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.5
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• pp.457-460
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• 2006

Y doped zinc oxide (YZO) thin films were deposited on F doped $SnO_2$ (FTO) glass substrate by sol-gel method using the spin-coating system. A homogeneous and stable solution was prepared by dissolving acetate in the solution added diethanolamine as sol-gel stabilizer. YZO films were obtained after preheated on the hot-plate for 5minute before each coating; the number of coating was 3 times. After the coating of last step, annealing of YZO films performed at $450^{\circ}C$ for 30 minute. In order to confirming of a ultraviolet ray interruption and down-conversion effects, optical properties of YZO films, transmission spectrum and fluorescent spectrum were used. Also, for understanding the obtained results by experiment, the elestronic state of YZO was calculated using the density functional theory The results obtained by experiment were compared with calculated structure. The detail of electronic structure was obtained by the discrete variational Xa (DV-Xa) method, which is a sort of molecular orbital full potential method. The density of state and energy levels of dopant element were shown and discussed in association with optical properties.

• Bulletin of the Korean Chemical Society
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• v.20 no.1
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• pp.35-41
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• 1999

Stability characteristics of hyperbolic reaction-diffusion equations with a reversible Brusselator model are investigated as an extension of the previous work. Intensive stability analysis is performed for three important parameters, Nrd, β and Dx, where Nrd is the reaction-diffusion number which is a measure of hyperbolicity, β is a measure of reversibility of autocatalytic reaction and Dx is a diffusion coefficient of intermediate X. Especially, the dependence on Nrd of stability exhibits some interesting features, such as hyperbolicity in the small Nrd region and parabolicity in the large Nrd region. The hyperbolic reaction-diffusion equations are solved numerically by a spectral method which is modified and adjusted to hyperbolic partial differential equations. The numerical method gives good accuracy and efficiency even in a stiff region in the case of small Nrd, and it can be extended to a two-dimensional system. Four types of solution, spatially homogeneous, spatially oscillatory, spatio-temporally oscillatory and chaotic can be obtained. Entropy productions for reaction are also calculated to get some crucial information related to the bifurcation of the system. At the bifurcation point, entropy production changes discontinuously and it shows that different structures of the system have different modes in the dissipative process required to maintain the structure of the system. But it appears that magnitude of entropy production in each structure give no important information related for states of system itself.