• Electrical & Electronic Materials
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• v.10 no.3
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• pp.262-267
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• 1997

In order to improve the brightness and chromaticity of green emitting low voltage phosphor for FED, we examine PL, PLE and CL emission characteristics of ZnGa$_{2}$O$_{4}$:Mn,O prepared in Ar and vacuum. ZnGa$_{2}$O$_{4}$:Mn,O sintered in vacuum shows about 16 times as bright as the one fabricated in Ar and excellent chromaticity. In PL emission spectra of ZnGa$_{2}$O$_{4}$:Mn,O at low temperature of 9 K, two peaks are observed at 504 nm and 513 nm. At room temperature, the two peaks are superimposed due to the lattice thermal vibrational energy, and only one peak is observed at 509 nm. From PLE measurements, it is believed that the energy levels of the host lattice and Mn ions are coexisted. The energy transfer from the host lattice to the emission center of Mn$^{2+}$ ions occurs.s.

• Progress in Superconductivity
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• v.7 no.1
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• pp.64-68
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• 2005

We fabricated Ni-based alloy substrates for YBCO coated conductor using powder metallurgy. Tungsten and copper were selected as alloy elements due to their mutual solubility to the base element of nickel. The alloying elements were mixed with nickel using ball milling and dried in air. The powder mixtures were packed in a rubber mold, cold isostatic pressed 200 MPa and made into rods. The compacted rods were sintered at $1150^{\circ}C$ for 6 hours for densification. It was confirmed by neutron diffraction experiment that W and Cu atoms made complete solid solution with Ni. Lattice constant of nickel alloy increased by $0.004{\AA}$ for 1at. $\%$ W in Ni-W alloy, $0.0006{\AA}$ for 1 at. $\%$ Cu in Ni-W-Cu alloy.

• Journal of the Korean Ceramic Society
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• v.32 no.12
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• pp.1377-1382
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• 1995

A high-resolution transmission electron microscopy study on the lattice defects formed in the high energy P ion implanted silicon was carried out on an atomic level. Results show that Lomer dislocations, 60$^{\circ}$perfect dislocations, 60$^{\circ}$ dislocation dipole and extrinsic stacking fault formed in the near Rp of as-implanted specimen. In the annelaed specimens, interstitial Frank loops, 60$^{\circ}$perfect disolations, 60$^{\circ}$dislocation dipoles, stacking faults, precipitates, perfect dislocation loops and <112> rodlike defects existed exclusively near in the Rp with various annealing temperature and time. From these results, it is concluded that extended secondary defects as well as the point defect clusters could be formed without annealing. Even at low temperature annealing such as 55$0^{\circ}C$, small interstitial Frank loops could be formed and precipitates were also formed by $700^{\circ}C$ annealing. The defect band annealed at 100$0^{\circ}C$ for 1 hr could be divided into two regions depending on the distribution of the secondary defects.

• Korean Journal of Metals and Materials
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• v.50 no.10
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• pp.703-710
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• 2012

The effects of the ordering reaction on high temperature mechanical behavior is investigated by tensile tests at $2{\times}10^{-2}/s-3.3{\times}10^{-5}/s$ up to $745^{\circ}C$. The tensile deformed region is examined by differential scanning calorimeter (DSC), TEM, and high resolution neutron diffraction (HRPD). The results showed that a plateau of tensile strength appeared at $150-500^{\circ}C$ whereas the elongation minimum occurred at about $600^{\circ}C$. This suggests that the occurrence of a plateau does not cause the elongation minimum. The temperature of the elongation minimum decreases with the strain rate. HRPD results show a lattice contraction in the tensile deformed specimen at the temperature of the plateau occurring region. The plateau of tensile strength, the lattice contraction, and the occurrence of serration appeared in the same temperature region.

• Proceedings of the Korean Nuclear Society Conference
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• 2003.10a
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• pp.55.1-55.1
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• 2003

• Journal of Surface Science and Engineering
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• v.29 no.5
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• pp.301-313
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• 1996

The texture of vapor deposits(PVD and CVD) changes from the orientation that places the lowest energy lattice plane parallel to the substrate under the condition of low atom or ion concentration adjacent to the deposit, to the orientation that places the higher energy crystal planes parallel to the substrate as the atom or ion concentration adjacent to the deposit increases. However, in the early stage of deposition, the deposit-substrate interface energy and the surface energy constitute the most important energies of the system. Therefore, if the lattice match is established between the substrate and the deposit without generating much strain energy, the epitaxial growth takes place to reduce the interfacial energy. When the epitaxial growth does not take place, the surface energy is dominant in the early stage of deposition and the lowest energy crystal plane tends to be placed parallel to the substrate up to a critial thickness. The thickness depends on the deposition condition. If the deposition condition does not favor placing the lowest energy crystal plane parallel to the substrate, the initial texture will change to that compatible with the deposition condition as the film thickness increases, and the texture turnover thickness will be short. The microstructure and surface topography of deposits are related to their texture.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1827-1832
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• 2003

In this research, the simulation method for acoustic sounds by a uniform flow around a two-dimensional circular cylinder by using the finite difference lattice Boltzmann model is explained. To begin with, we examine the boundary condition which determined with the distribution function $f_i^{(0)}$ concerning with density, velocity and internal energy at boundary node. Very small acoustic pressure fluctuation, with same frequency as that of Karman vortex street, is compared with the pressure fluctuation around a circular cylinder. The acoustic sound' propagation velocity shows that acoustic approa ching the upstream, due to the Doppler effect in the uniform flow, slowly propagated. For the do wnstream, on the other hand, it quickly propagates. It is also apparently the size of sound pressure was proportional to the central distance $r^{-1/2}$ of the circular cylinder. The lattice BGK model for compressible fluids is shown to be one of powerful tool for simulation of gas flows.

• Journal of Ocean Engineering and Technology
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• v.18 no.2
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• pp.10-17
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• 2004

In this research, a numerical simulation for the acoustic sounds around a two-dimensional circular cylinder in a uniform flaw was developed, using the finite difference lattice Boltzmann model. We examine the boundary condition, which is determined by the distribution function concerning density, velocity, and internal energy at the boundary node. Pressure variation, due to the emission of the acoustic waves, is very small, but we can detect this periodic variation in the region far from the cylinder. Daple-like emission of acoustic waves is seen, and these waves travel with the speed of sound, and are synchronized with the frequency of the lift on the cylinder, due to the Karman vortex street. It is also apparent that the size of the sound pressure is proportional to the central distance to the circular cylinder. The lattice BGK model for compressible fluids is shown to be a powerful tool for the simulation of gas flaws.

• Structural Engineering and Mechanics
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• v.41 no.5
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• pp.645-662
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• 2012

Deteriorative effects of steel corrosion on the structural response of reinforced concrete are simulated for varying degrees of corrosion. The simulation approach is based on a three-dimensional irregular lattice model of the bulk concrete, in which fracture is modeled using a crack band approach that conserves fracture energy. Frame elements and bond link elements represent the reinforcing steel and its interface with the concrete, respectively. Polylinear stress-slip properties of the link elements are determined, for several degrees of corrosion, through comparisons with direct pullout tests reported in the literature. The link properties are then used for the lattice modeling of reinforced concrete beams with similar degrees of corrosion of the main reinforcing steel. The model is successful in simulating several important effects of steel corrosion, including increased deflections, changes in flexural cracking behavior, and reduced yield load of the beam specimens.

• Bulletin of the Korean Chemical Society
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• v.18 no.9
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• pp.965-972
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• 1997

An approximate molecular theory of classical fluids based on the nonrandom lattice statistical-mechanical theory is presented. To obtain configurational Helmholtz free energy and equation of state (EOS), the lattice-hole theory of the Guggenheim combinatorics is approximated by introducing the nonrandom two-fluid theory. The approximate nature in the derivation makes the model possible to unify the classical lattice-hole theory and to describe correctly the configurational properties of real fluids including macromolecules. The theory requires only two molecular parameters for a pure fluid. Results obtained to date have demonstrated that the model correlates quantitatively the first- and second-order thermodynamic properties of real fluids. The basic simplicity of the model can readily be generalized to multicomponent systems. The model is especially relevant to (multi) phase equilibria of systems containing molecularly complex species.