• E2M - 전기 전자와 첨단 소재
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• 제10권2호
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• pp.141-149
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• 1997

L $a_{0.7}$S $r_{0.3}$Mn $O_{3}$ powders were prepared by both GNP(Glycine-Nitrate Process) and solid state reaction method in various of calcination temperature(800-1000.deg. C) and time in air. Also, L $a_{0.7}$S $r_{0.3}$Mn $O_{3}$ cathode contacts on YSZ(Yttria-Stabilized Zirconia) substrate were prepared by screen printing and sintering method as a function of sintering temperature(1100-1450.deg. C) in air. Sintering behaviors have been investigated by SEM(Scanning Electron Microscope) and porosity measurement. Compositional and structural characterization were carried out by X-ray diffractometer and ICP AES(Inductively Coupled Plasma-Atomic Emission Spectrometry) analysis. Electrical characterization was carried out by the electrical conductivity with linear 4 point probe method. As the calcination period increased in solid state reaction method, L $a_{0.7}$S $r_{0.3}$Mn $O_{3}$ phase increased. Although L $a_{0.7}$S $r_{0.3}$Mn $O_{3}$ single phase was obtained only for 48hrs at 1000.deg. C, in GNP method it was easy to get single and ultra-fine L $a_{0.7}$S $r_{0.3}$Mn $O_{3}$ powders with submicron particle size at 650.deg. C for 30min. The particle size and thickness of L $a_{0.7}$S $r_{0.3}$Mn $O_{3}$ cathode contact by solid state reaction method did not change during the heat treatment, while those by GNP method showed good sintering characteristics because initial powder size fabricated from GNP method is smaller than that fabricated from solid state reaction method. Based on enthalpy change from thermodynamic data and ICP-AES analysis, it was suggested to make cathode contact in composition of (L $a_{0.7}$S $r_{0.3}$)$_{0.91}$ Mn $O_{3}$ which have little second phase (L $a_{2}$Z $r_{2}$ $O_{7}$) for high efficient solid oxide fuel cells applications. As (L $a_{0.7}$S $r_{0.3}$)$_{0.91}$Mn $O_{3}$ cathode contact on YSZ substrate was sintering at 1250.deg. C the temperature that liquid phase sintering did not occur. It was possible to obtain proper cathode contacts with electrical conductivity of 150(S/cm) and porosity content of 30-40%.m) and porosity content of 30-40%.

• Journal of Microbiology and Biotechnology
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• 제20권2호
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• pp.271-280
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• 2010

Vibrio alginolyticus, a Gram-negative marine bacterium, is one of the causative agents of fish vibriosis. Its virulence factors and pathogenesis mechanism are barely known, except for some extracellular products (ECPs) that are known to be regulated by quorum sensing system. Therefore, the present study used a microarray to analyze the transcription profiles of the wild-type V. alginolyticus and a deletion mutant of luxO, the pivotal regulator in Vibrio quorum sensing systems, which resulted in the identification of a putative virulence factor, MviN. Quantitative real-time reverse transcription PCR confirmed that the transcription of mviN was upregulated in the luxO mutant when compared with wild-type, and down regulated in a luxO-con complemented strain. Furthermore, Western blotting indicated that MviN was greatly induced during the late-exponential and stationary phases of growth, indicating that the expression of MviN was cell-density dependent and quorum sensing regulated in V. alginolyticus. Meanwhile, the mviN null mutant displayed a much slower growth rate than the wild type, signifying the essential role of MviN in V. alginolyticus. Western blotting also revealed that MviN was present as an extracellular protein in V. alginolyticus. When epithelioma papulosum cyprini (EPC) cells were treated with the ECPs of the mviN mutant, no cytotoxicity was observed, whereas EPC cells treated with the wild type exhibited pathological changes, which increased with the ECPs concentration and treatment time. Therefore, the results demonstrated that MviN is a LuxO-regulated ECPs component and involved in the pathogenicity of V. alginolyticus.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 추계학술대회 논문집 Vol.16
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• pp.148-151
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• 2003

The spin density of ${\beta}-MnO_2$ structure was theoretically investigated by $DV-X_{\alpha}$ (the discrete variation $X{\alpha}$) method, which is a sort of the first principle molecular orbital method using Hatre-Fock-Slater approximation. The used cluster model was $[Mn_{14}O_{56}]^{-52}$. The ${\beta}-MnO_2$ is a paramagnetic oxide semiconductor material having the energy band gap of 0.18 eV and an 3 loan-pair electrons in the 3d orbital of an cation. This material exhibits spin-only magnetism and has the magnetic ordering temperature of 94 K. Below this temperature its magnetism appears as antiferromagnetism. The calculations of electronic state showed that if the initial spin condition of input parameters changed, the magnetic state changed from paramagnetic to antiferromagnetic. When d orbital of all Mn atoms in cluster had same initial spin state as only up spin, paramagnetic spin density distribution appeared by the calculation. On the other way, d orbital had alternately changed spin state along special direction the resulted spin distribution showed antiferromagnetism.

• 한국결정성장학회지
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• 제8권2호
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• pp.332-341
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• 1998

${\alpha}-Al_2O_3$와 비정질 SiO2부터 Mullite를 합성하기 위한 고체상태반응의 반응속도를 1450~$1480^{\circ}C$ 온도 범위에서 연구하였다. 반응속도는 $Al_2O_3$분말을 코팅한 28.16wt%의 $SiO_2$와 일정한 온도에서 여러 시간동안 가열하여 생성된 혼합물에 의하여 결정되었다. MgO안의 반응물과 미반응물의 양은 X-선 회절분석에 의하여 결정되었다. Mullite의 부피율과 peak intensity 비의 자료로부터 $Al_2O_3$와 $SiO_2$의 $3Al_2O_3\;{\cdot}\;2SiO_2$형태로의 반응은 $1450^{\circ}C$와 $1480^{\circ}C$ 사이에서 시작되었다. 고체상태반응 활성화 에너지는 Arrhenius 식에 의하여 결정되었다. 활성화 에너지는 31.9KJ/mol이다.

• Journal of Magnetics
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• 제3권2호
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• pp.39-40
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• 1998

Normal state EPR signals have been studied for the n-type$ high-T_c$ superconductors $Nd_{1.85}Ce_{0.15}CuO_{4-x} and Nd_2CuO_{3.6-x}F_{0.4-y}.$ Since EPR signals were observed only in quenched non-superconducting samples and were absent in furnace-cooled samples, our results suggest that no normal state EPR signals come from pure phase n-type hihg-Tc superconductors. Our observation is consistent with previously reported absence of nomal state EPR signals in the p-type high-Tc superconductors.

• Bulletin of the Korean Chemical Society
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• 제17권9호
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• pp.840-845
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• 1996

Rate constants have been measured spectrophotometrically for the reactions of p-and m-nitrophenyl 2-thiophenecarboxylate (5a and 5b, respectively) with alkali metal ethoxides (EtO-M+) in absolute ethanol at 25.0±0.1 ℃. The reactivity of EtO-M+ exhibits dependence on the size of alkali metal ions, i.e. the reactivity of EtO-M+ toward 5a decreases in the order EtO-K+ ≥ EtO-Na+ > EtO-Li+ > EtO-, while the one toward 5b does in the order EtO-Na+ ≥ EtO-K+ > EtO-Li+ > EtO-. This result indicates that ion paired EtO-M+ is more reactive than dissociated EtO-, and alkali metal ions form complexes with the substrate more strongly at the transition state than at the ground state. The catalytic effect shown by alkali metal ions appears to be less significant in the reaction of 5 than in the corresponding reaction of 4, indicating that complexation of alkali metal ions with 5 is not as strong as the one with 4.

• 자원환경지질
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• 제42권5호
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• pp.479-486
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• 2009

자연환경에서 망간은 +2, +3, +4가의 다양한 산화수로 존재하며 환경적으로 중요한 여러 원소들과 활발한 산화/환원반응을 함으로써 원소의 지화학적 순환에 중요한 역할을 하고 있다. 특히 망간은 다양한 산화물로 존재하며 각각 특징적인 망간의 산화상태를 나타내고 있다. 망간산화물의 지화학적 특성, 즉 망간산화물의 용해도, 흡착력, 산화/환원 능력은 산화물을 구성하는 망간의 산화수에 의해 크게 좌우되는 것으로 알려져 있다. 따라서 망간의 산화수를 결정하는 인자를 밝히는 것이 산화/환원에 민감한 여러 오염원소의 지화학적 거동을 예측하는 데 매우 중요하다. X-선 광전자 분광법(X-ray photoelectron spectroscopy, XPS)은 고체상으로 존재하는 다양한 원소의 산화상태를 밝히는데 매우 유용한 도구이다. 본 연구에서 MnO, $Mn_2O_3$, $MnO_2$에 대한 망간의 산화수를 결정하기 위해 XPS $Mn2p_{3/2}$와 Mn3s 결합에너지 스펙트럼을 측정하여 기존에 보고 된 값들과 비교하였다. 망간산화물에 대한 $Mn2p_{3/2}$ 결합에너지는 MnO, 640.9 eV; $Mn_2O_3$, 641.5 eV; $MnO_2$, 641.8 eV로서, 망간의 산화수가 증가할수록 $Mn2p_{3/2}$ 의 결합에너지가 증가하는 것으로 나타났다. 시료준비 방법 중 하나인 Ar 에칭의 경우 시료 표면의 전자구조를 변화시킬 수 있는 가능성이 확인되었다.

• The Korean Journal of Ceramics
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• 제6권2호
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• pp.150-154
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• 2000

Mobilities of electrons ($\mu_p$) and holes ($\mu_p$) in 2, 5, and 10 mol% $TiO_2$-doped yttria stabilized zirconia (TD-YSZ) have been estimated by a non-steady state gas permeation method using models proposed by Weppner and Maruyama. Values of $\mu_n$ and $\mu_p$ were found to be closed to those in non-doped YSZ reported earlier. The concentration of electrons and holes were calculated from $\mu_n$ and $\mu_p$ values and the partial conductivities of electrons and holes measured by a dc-polarization method. The concentration of electrons at unit oxygen partial pressure increased with increasing $TiO_2$concentration, while the hole concentration was almost independent of $TiO_2$concentration.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1171-1172
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• 2006

Addition of 2.0wt%$Dy_2O_3$ or 0.3wt%Sn proved to be very effective in improving the permanent magnetic properties of NdFeNbB magnets. $Dy_2O_3$ additions result in the increase in the Hci and temperature dependence due to formation of (NdDy)-rich phase and grain refinement of $\Phi$ phase. This improvement of the coercivity stability of the magnets from the addition of Sn is attributed to the smoothing effect of the Sn addition at the grain boundaries. The magnetic properties, the temperature dependence and Curie temperature of NdFeNbB with $Dy_2O_3$ and Sn combined addition were found to be considerably improved.

• 한국재료학회지
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• 제18권3호
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• pp.143-147
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• 2008

Fe compounds in scoria as distributed in the south-western area of Jeju Island were investigated using X-ray fluorescence spectroscopy, X-ray diffractometry, and $^{57}Fe$ $M{\ddot{o}}ssbauer$ spectroscopy. The samples were prepared from four parasite volcanoes. It was found that these samples are typical basalt comprised of $SiO_2$, $Al_2O_3$, Fe, and silicate minerals. The $M{\ddot{o}}ssbauer$ spectra showed doublets for olivine, pyroxene, and ilmenite as well as sextets for hematite and magnetite. The valence state of Fe is chiefly a 3+ charge state with a slight 2+ charge state. It is expected that these results will add to the body of information related to the formation mechanisms of Jeju Island.