• Journal of KIISE:Software and Applications
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• v.27 no.1
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• pp.41-49
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• 2000

This paper describes a method of generating MPHFs(Minimal Perfect Hash Functions) for large static search key sets. The MOS(Mapping-Ordering-Searching) approach is widely used presently in MPHF generation. In this research, the MOS approach is improved and a SOMS(Selecting-Ordering-Mapping-Searching) approach is proposed, where the Selecting step is newly introduced and the Orderng step is performed before the Mapping step to generate MPHFs more effectively. The MPHF generation algorithm proposed in this research is probabilistic and the expected processing time is linear to the number of keys. Experimental results show that MPHFs are generated fast and the space needed to represent the hash functions is small.

• Journal of the Korean Ceramic Society
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• v.39 no.9
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• pp.863-870
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• 2002

The Single phase $Pb(Fe_{1/2}Ta_{1/2})O_3$ (x=0.0∼1.0) solid solutions were successfully synthesized and their ordering structures as well as dielectric properties were investigated ${{r(Nb^{5+})=r(Ta^{5+})=0.78 {\AA},\;AW(Nb^{5+})=92.91,\;AW(Ta^{5+})=180.95}}$. While $Pb(Fe_{1/2}Ta_{1/2})O_3$ showed typical relaxor ferroelectric characteristics such as dielectric relaxation and diffuse phase transition, the sharpeness of the phase transition increased as $Ta^{5+}$ was replaced by $Nb^{5+}$ and finally $Pb(Fe_{1/2}Nb_{1/2})O_3$ showed normal ferroelectric characteristics with no dielectric relaxation. By using Raman spectroscopy, it was revealed that the $Fe^{3+}\;and\;Ta^{5+}\;of\;Pb(Fe_{1/2}Ta_{1/2})O_3$ were stoichiometrically 1:1 ordered within the short range which can be hardly probed even by TEM. Also, The degree of ordering in $Pb(Fe_{1/2}Ta_{1/2})O_3$ decreased as $Ta^{5+}$ was replaced by $Nb^{5+}$ and finally $Fe^{3+}\;and\;Nb^{5+}\;of\;Pb(Fe_{1/2}Nb_{1/2})O_3$ were completely disordered. The relaxor ferroelectric characteristics of $Pb(Fe_{1/2}Ta_{1/2})O_3$ could be correlated with the stoichiometric 1:1 ordering of B-site cations within the short range which can be hardly probed even by TEM. Also, the decrease of the relaxor ferroelectric characteristics with the replacement of $Ta^{5+}\;by\;Nb^{5+}$ could be correlated with the weakening of the ordering and the normal ferroelectric characteristics of $Pb(Fe_{1/2}Nb_{1/2})O_3$ could be correlated with the complete disordering of B-site cations.

• Korean Journal of Crystallography
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• v.13 no.3_4
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• pp.165-171
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• 2002

Single phase $Pb(Fe_{1/2}Ta_{1/2})O_3$, ceramics were successfully synthesized from the powders prepared by solid state reaction (sintering temperature: $1100^{\circ}C$, density: $9.3g/cm^3$, average grain size: $5.1{\pm}1.2mm$, space group: Pm3m). Their dielectric properties measured at $-150{\sim}50^{\circ}C$ showed the maximum relative dielectric constant of 31000 at $-41^{\circ}C$. 1 kHz, and typical relaxor ferroelectrics characteristics such as diffuse phase transition and dielectric relaxation phenomena. However, the diffuseness of phase transition decreased and the dielectric properties became more normal ferroelectrics as the time of annealing at $1000^{\circ}C$ increased. By using Raman spectroscopy, it was revealed that the $Fe^{3+}$ and $Ta^{5+}$ ions in the as-sintered $Pb(Fe_{1/2}Ta_{1/2})O_3$, are stoichiometrically 1 : 1 ordered within the short-range that can not be probed even by transmission electron microscopy, and this stoichiometric 1 : 1 ordering is enhanced by the annealing. The relaxor ferroelectric characteristics in the as-sintered $Pb(Fe_{1/2}Ta_{1/2})O_3$, could be correlated with the stoichiometric 1 : 1 short-range ordering of B-site cations, and the decrease of relaxor ferroelectric characteristics in the annealed $Pb(Fe_{1/2}Ta_{1/2})O_3$ could be correlated with the enhanced stoichiometric 1 : 1 short-range ordering of B-site cations.

• Journal of the Korean Magnetics Society
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• v.18 no.5
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• pp.190-194
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• 2008

Epitaxial $L1_0$ FePd (001) thin films were successfully manufactured by sputtering deposition method. The structure and magnetic properties of FePd thin films were characterized as a function of Fe compositions. It was found that the long-range ordering parameter had a maximum for the stoichiometric composition, whereas the magnetic anisotropy had a maximum as the Fe content is decreased to slightly above the stoichiometric composition. This indicates that the stoichiometry is directly contributed to the chemical ordering and the magnetic anisotropy. These results imply that nonstoichiometric FePd compositions, with a slight excess of Pd, may in fact be preferred for applications that require high magnetic anisotropy.

• Proceedings of the Materials Research Society of Korea Conference
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• 1996.05a
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• pp.80-81
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• 1996

• Bulletin of the Korean Chemical Society
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• v.18 no.11
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• pp.1210-1213
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• 1997

• Korean Journal of Crystallography
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• v.12 no.2
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• pp.76-80
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• 2001

We have studied the effect of sintering conditions on the long-range order parameter of the 1 : 2 cation ordering in Ba(Mg/sub 1/3/Nb/sub 2/3/)O₃microwave dielectrics prepared through a columbite precursor method. It is found that the order parameter depends strongly on the sintering conditions. As the heat-treatment time increases at 1350℃, the long-range order parameter decreases. When sintered at 1500℃ for 4 hours, BMN shows a high long-range order parameter of 0.94.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.369-369
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• 2010

Adsorption and ordering of methionine molecules on Ge(100) surface have been studied using high resolution photoemission spectroscopy and low-energy electron diffraction (LEED) to investigate the adsorption structure as a function of coverage. Analysis of C 1s, S 2p, N 1s, and O 1s core levels reveals quite different according to methionine coverage. We found that the relative population of the two types of thiolates induces a structural change in the ordering from $2\;{\times}\;1$ to $1\;{\times}\;1$. Such an unusual evolution of the methionine adsorption on the Ge(100) surface is discussed in relation to chemical reactions and possible molecular rearrangement on the surface.

• Applied Microscopy
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• v.32 no.2
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• pp.157-162
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• 2002

Microstructural investigations of $(Na_{1/2}Pr_{1/2})TiO_3$ (NPT) complex perovskite compounds were carried out using X-ray diffractometry and transmission electron microscopy. NPT had not 1:1 chemical ordering of Asite cations but had the antiphase and inphase tilting of oxygen octahedron and the antiparallel shift of cations. Both the antiphase boundaries and the ferroelastic domains were not present in the microstructure. Unidentified second phase was found in the microstructure. The measured dielectric properties were ${\varepsilon}_r=99.6,\;Q\;{\Large f}_o=1124\;GHz,\;{\tau}_{f}=-233.64ppm/^{\circ}C$.

• Corrosion Science and Technology
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• v.22 no.3
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• pp.214-219
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• 2023

Considering the case in the United States where most nuclear power plants with an initial design life of 40 years continue to operate until 60 or 80 years after undergoing material soundness evaluation, it is time to plan a more robust long-term operation strategy for nuclear power plants in Korea. There are some reports that SRO/LRO might be formed when Alloy 690 is heat treated for 10,000 hours to 100,000 hours at 360 to 450 ℃. The possibility of LRO formation in Alloy 690 steam generator tubings of Kori nuclear power plant unit 1 (Kori-1) was investigated using existing research papers. The mechanism in which SRO/LRO occurred was also surveyed. Alloy 690 was found to be more likely to cause ordering than Alloy 600 in terms of alloy composition. The ordering could be evaluated through changes in material properties. However, it is difficult to evaluate it from a microstructural point of view. The likelihood of LRO in Alloy 690 of the Kori-1 plant operated at 320 ℃ for 19 years seemed to be low in terms of time and exposure temperature.