• 전기학회논문지
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• 제58권4호
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• pp.770-776
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• 2009

The composites were fabricated by adding 0, 15, 30, 45[vol.%] $ZrB_2$ powders as a second phase to SiC matrix. The physical, mechanical and electrical properties of electroconductive SiC ceramic composites by spark plasma sintering(SPS) were investigated. Reactions between ${\beta}$-SiC and $ZrB_2$ were not observed in the XRD and the phase analysis of the electroconductive SiC ceramic composites. The relative density of mono ${\beta}$-SiC, ${\beta}$-SiC+15[vol.%]$ZrB_2$, ${\beta}$-SiC+30[vol.%]$ZrB_2$ and ${\beta}$-SiC+45[vol.%]$ZrB_2$ composites are respectively 99.24[%], 87.53[%], 96.41[%] and 98.11[%] Phase analysis of the electroconductive SiC ceramic composites by XRD revealed mostly of ${\beta}$-SiC, $ZrB_2$ and weakly of $ZrO_2$ phase. The flexural strength showed the lowest of 114.44[MPa] for ${\beta}$-SiC+15[vol.%]$ZrB_2$ powders and showed the highest of 210.75[MPa] for composite no added with $ZrB_2$ powders at room temperature. The trend of the mechanical properties of the electroconductive SiC ceramic composites is accorded with the trend of the relative density. The electrical resistivity of the electroconductive SiC ceramic composites decreased with increased $ZrB_2$ contents. The electrical resistivity of mono ${\beta}$-SiC, ${\beta}$-SiC+15[vol.%]$ZrB_2$, ${\beta}$-SiC+30[vol.%]$ZrB_2$ and ${\beta}$-SiC+45[vol.%]$ZrB_2$ composites are respectively $4.57{\times}10^{-1},\;2.13{\times}10^{-1},\;2.68{\times}10^{-2}\;and\;1.99{\times}10^{-2}[{\Omega}{\cdot}cm]$ at room temperature. The electrical resistivity of mono ${\beta}$-SiC and ${\beta}$-SiC+15[vol.%]$ZrB_2$ are negative temperature coefficient resistance(NTCR) in temperature ranges from $25[^{\circ}C]\;to\; 100[^{\circ}C]$. The electrical resistivity of ${\beta}$-SiC+30[vol.%]$ZrB_2$ and ${\beta}$-SiC+45[vol.%]ZrB_2$ are positive temperature coefficient resistance(PTCR) in temperature ranges from $25[^{\circ}C]\;to\;100[^{\circ}C]$. It is convinced that ${\beta}$-SiC+30[vol.%]$ZrB_2$ composites by SPS for heater or ignitors can be applied.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.1254_1255
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• 2009

The composites were fabricated by adding 30, 35, 40, 45[vol.%] Zirconium Diboride(hereafter, $ZrB_2$) powders as a second phase to Silicon Carbide(hereafter, SiC) matrix. The physical, mechanical and electrical properties of electroconductive SiC ceramic composites by Spark Plasma Sintering(hereafter, SPS) were examined. Reactions between $\beta$-SiC and $ZrB_2$ were not observed in the XRD analysis. The relative density of SiC+30[vol.%]$ZrB_2$, SiC+35[vol.%]$ZrB_2$, SiC+40[vol.%]$ZrB_2$ and SiC+45[vol.%]$ZrB_2$ composites are 88.64[%], 76.80[%], 79.09[%] and 88.12[%], respectively. The XRD phase analysis of the electroconductive SiC ceramic composites reveals high of SiC and $ZrB_2$ and low of $ZrO_2$ phase. The electrical resistivity of SiC+30[vol.%]$ZrB_2$, SiC+35[vol.%]$ZrB_2$, SiC+40[vol.%]$ZrB_2$ and SiC+45[vol.%]$ZrB_2$ composites are $6.74{\times}10^{-4}$, $4.56{\times}10^{-3}$, $1.92{\times}10^{-3}$ and $4.95{\times}10^{-3}[{\Omega}{\cdot}cm]$ at room temperature, respectively. The electrical resistivity of SiC+30[vol.%]$ZrB_2$, SiC+35[vol.%]$ZrB_2$, SiC+40[vol.%]$ZrB_2$ and SiC+45[vol.%]$ZrB_2$ are Positive Temperature Coefficient Resistance(hereafter, PTCR) in temperature ranges from 25[$^{\circ}C$] to 500[$^{\circ}C$]. It is convinced that SiC+40[vol.%]$ZrB_2$ composite by SPS can be applied for heater or electrode.

• 한국식품영양학회지
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• 제7권2호
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• pp.95-99
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• 1994

In order to investigate the fatty acid composition of Korean pumpkins, this study was designed. Three samples of Korean pumpkins, A(yellowish ripe), B(unripe, 30 days old) and C(unripe, 20 days old) were used for fatty acid analysis by gas chromatography. The results were as follows : Pumkin C, B and A showed 10, 12 and 15 kinds of fatty acids, respectively. In case of palmitic acid(C16:0), pumpkin C, B and A showed 22.5%, 22.9% and 26.6%, respectively. In case of u linolenic acid(C18:3), pumpkin C, B and A showed 22.6%, 23.6% and 44.8%, respectively. In case of palmitoleic acid(Cl6:1), pumpkin C. B and A showed 12.4%, 10.1% and 0.5%, respectively. In case of oleic acid(C18:1), pumpkin C. B and A showed 9.2%, 7.7% and 2.8%, respectively, In case of stearic acid(C18:0), pumpkin C, B and A showed B.S%, 3.7% and 3.5%, respectively. The ratio of P/S was 1.4, 1.6 and 1.9 for sample C, B and A, respectively. The ratio of w-3/w-6 was 1.1, 0.9 and 2.6 for sample C, B and A, respectively. Through this study, the ripe pumpkin(sample A) was thought to be good enough in nutritional aspects of fatty acids, particularly a-linoleic acid, Cl8 : 3(u-3) series.

• 한국세라믹학회지
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• 제34권4호
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• pp.413-419
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• 1997

The specimens which were prepared from cokes with additions of 0~25 wt% B4C were sintered in Ar atmosphere at 220$0^{\circ}C$. The effects of B4C content on graphitization and oxidation resistance of cokes were investigated. B4C accelerates the graphitization of cokes and at 220$0^{\circ}C$ the degree of graphitization increased from 0.33 which is the value of pure carbon to 0.56, which increased bluk density and porosity. Especially bending strength increased as th graphitization temperature increased. Oxidation resistance property was greatly improved when B4C was added more than 10wt% at 80$0^{\circ}C$ and when B4C was added more than 20wt% at 100$0^{\circ}C$. This was because that the thin layer of B2O3 glass phase on the surface of the composite could be identified to increase the oxidation resistance.

• Tuberculosis and Respiratory Diseases
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• 제55권5호
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• pp.488-498
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• 2003

연구배경 : 세포에 방사선을 조사하면 세포사멸과 함께 AP-l, NF-${\kappa}B$와 같은 여러 전사인자가 활성화 되는 것으로 알려져 있다. 이중 염증과 면역반응의 중요한 전사인자인 NF-${\kappa}B$는 항아포프토시스의 기능이 있으며 NF-${\kappa}B$ 활성화를 차단함으로써 TNF-${\alpha}$나 daunorubicine 등에 의 한 항암효과를 상승시킬 수 있음이 밝혀져 있다. NF-${\kappa}B$의 항아포프토시스 기전은 NF-${\kappa}B$ 의존성 단백질인 cIAPI, 2의 전사발현 유도에 의한 것으로 cIAPl, 2는 caspase 3, 7, pro-caspase-9의 활성을 차단함으로써 아포프토시스를 억제하는 것으로 알려져 있다. 이에 저자들은 방사선 유도성 세포사멸에 비교적 내성을 보이는 A549 세포주에서 방사선에 의한 NF-${\kappa}B$ 활성화와 그에 따른 cIAP 발현유도를 조사하고 NF-${\kappa}B$ 활성화를 차단하여 방사선 유도성 세포사멸의 감작효과를 확인하기 위하여 본 연구를 시행하였다. 방 법 : 세포주는 A549 폐암세포주를 이용하였고, 방사선 조사는 Varian사의 Clinac 1800C 선형가속기를 이용하였으며 조사량은 10GY를 사용하였다. 세포독성 검사는 MTT Assay를 이용하였고, NF-${\kappa}B$ 활성화 검사는 luciferase reporter gene assay, electromobility shift assay, $I{\kappa}B-{\alpha}$ degradation에 대한 westem blot을 이용하였다. NF-${\kappa}B$활성을 차단하기 위하여 proteosome inhibitor인 MGI32와 $I{\kappa}B{\alpha}$-superrepressor plasmid를 transfection한 안정적 세포주 A549-$I{\kappa}B{\alpha}$-superrepressor를 이용하였다. cIAP의 발현은 RT-PCR을 이용하였고, cIAP2 promoter 활성은 NF-${\kappa}B$ site를 포함한 cIAP2 유전자 5' f1anking region(1.4kb)을 pGL2-Basic luciferase vector에 cloning 한 construct를 사용하여 transfection 후 luciferase assay를 시행하였다. 결 과 : A549 cell에서 10Gy 방사선 조사에 의한 세포독성은 24hr, 48hr에 각각 $10.82{\pm}.3%$, $17.7{\pm}6.4%$로 비교적 내성이 있음을 확인하였다. 방사선에 의한 NF-${\kappa}B$의 활성은 $I{\kappa}B-{\alpha}$ 분해에 대한 western blot과 EMSA로 확인하였으며 luciferase assay에서도 약 1.6 배 정도의 NF-${\kappa}B$ 활성화가 있었다. NF-${\kappa}B$활성을 차단하기 위해 사용한 MG132는 방사선 유도성 세포사멸에 영향을 주지 않았으며 A549-$I{\kappa}B{\alpha}$-superrepressor 세포주에서도 세포사멸의 감작효과는 없었다. 또한 RT-PCR 결과 방사선에 의한 cIAP1,2 mRNA 발현유도는 관찰되지 않았고 cIAP2 promoter luciferase assay에서도 cIAP2 전사활성 유도는 없었다. 결 론 : A549 폐암세포주에서 방사선에 의해 NF-${\kappa}B$의 활성화는 확인하였으나 활성화 정도가 미약하였고 NF-${\kappa}B$ 의존성 항아포프토시스 유전자인 cIAP가 방사선에 의해 발현유도 되지 않았으며, NF-${\kappa}B$ 활성을 차단함에도 세포독성에 감작효과가 없었으므로 A549 폐암세포주에서 방사선 유도성 세포사멸에 내성을 보이는 기전에는 NF-${\kappa}B$의 역할이 미미하리라고 사료된다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.381-384
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• 2001

The $\beta$-SiC+ZrB$_2$ and $\beta$-SiC+TiB$_2$ceramic electroconductive composites were pressureless-sintered and annealed by adding l2wt% A1$_2$ $O_3$+Y$_2$ $O_3$(6 : 4wt%) powder as a function of sintering temperature. The relative density showed highest value of 84.92% of the theoretical density for SiC-TiB$_2$ at 190$0^{\circ}C$ sintering temperature. The phase analysis of the composites by XRD revealed of $\alpha$-SiC(6H), TiB$_2$, $Al_{5}$Y$_2$ $O_{12}$ and $\beta$-SiC(15R). Flexural strength showed the highest of 230 MPa for SiC-ZrB$_2$ composites sintered at 190$0^{\circ}C$. The vicker's hardness increased with increasing sintering temperature and showed the highest for SiC-ZrB$_2$ composites sintered at 190$0^{\circ}C$. Owing to YAG, the fracture toughness showed the highest of 6.50 MPa . m$^{1}$2/ for SiC-ZrB$_2$ composites at 190$0^{\circ}C$. The electrical resistivity was measured by the Rauw method from $25^{\circ}C$ to $700^{\circ}C$. The electrical resistivity of the composites showed the PTCR(Positive Temperature Coefficient Resistivity).).

• Progress in Superconductivity
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• 제14권1호
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• pp.30-33
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• 2012

We have grown $MgB_2$ superconducting thin films on the SiC buffer layers by means of hybrid physical-chemical vapor deposition (HPCVD) technique. Prior to that, SiC was first deposited on $Al_2O_3$ substrates at various temperatures from room temperature to $600^{\circ}C$ by using the pulsed laser deposition (PLD) method in a vacuum atmosphere of ${\sim}10^{-6}$ Torr pressure. All samples showed a high transition temperature of ~40 K. The grain boundaries of $MgB_2$ samples with SiC layer are greater in amount, compare to that of the pure $MgB_2$ samples. $MgB_2$ with SiC buffer layer samples show interesting change in the critical current density ($J_c$) values. Generally, at both 5 K and 20 K measurements, at lower magnetic field, all $MgB_2$ films deposited on SiC buffer layers have low $J_c$ values, but when they reach higher magnetic fields of nearly 3.5 Tesla, $J_c$ values are enhanced. $MgB_2$ film with SiC grown at $600^{\circ}C$ has the highest $J_c$ enhancement at higher magnetic fields, while all SiC buffer layer samples exhibit higher $J_c$ values than that of the pure $MgB_2$ films. A change in the grain boundary morphologies of $MgB_2$ films due to SiC buffer layer seems to be responsible for $J_c$ enhancements at high magnetic fields.

• 전기학회논문지
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• 제56권9호
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• pp.1602-1608
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• 2007

The composites were fabricated, respectively, using 61[vol.%] SiC-39[vol.%] $TiB_2$ and using 61[vol.%] SiC-39[vol.%] $ZrB_2$ powders with the liquid forming additives of 12[wt%] $Al_2O_3+Y_2O_3$ by hot pressing annealing at $1650[^{\circ}C]$ for 4 hours. Reactions between SiC and transition metal $TiB_2$, $ZrB_2$ were not observed in this microstructure. The result of phase analysis of composites by XRD revealed SiC(6H, 3C), $TiB_2$, $ZrB_2$ and $YAG(Al_5Y_3O_{12})$ crystal phase on the Liquid-Phase-Sintered(LPS) $SiC-TiB_2$, and $SiC-ZrB_2$ composite. $\beta\rightarrow\alpha-SiC$ phase transformation was occurred on the $SiC-TiB_2$ and $SiC-ZrB_2$ composite. The relative density, the flexural strength and Young's modulus showed the highest value of 98.57[%], 249.42[MPa] and 91.64[GPa] in $SiC-ZrB_2$ composite at room temperature respectively. The electrical resistivity showed the lowest value of $7.96{\times}10^{-4}[\Omega{\cdot}cm]$ for $SiC-ZrB_2$ composite at $25[^{\circ}C]$. The electrical resistivity of the $SiC-TiB_2$ and $SiC-ZrB_2$ composite was all positive temperature coefficient resistance (PTCR) in the temperature ranges from $25[^{\circ}C]$ to $700[^{\circ}C]$. The resistance temperature coefficient of composite showed the lowest value of $1.319\times10^{-3}/[^{\circ}C]$ for $SiC-ZrB_2$ composite in the temperature ranges from $100[^{\circ}C]$ to $300[^{\circ}C]$ Compositional design and optimization of processing parameters are key factors for controlling and improving the properties of SiC-based electroconductive ceramic composites.

• 대한수학회보
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• 제30권2호
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• pp.193-199
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• 1993

A hereditary $C^{*}$-subalgebra B of a $C^{*}$-algebra A is said to be full if B is not contained in any proper closed two-sided ideal in A, so each hereditary $C^{*}$-subalgebra of a simple $C^{*}$-algebra is always full. It is well known that every $C^{*}$-algebra is strong Morita equivalent to its full hereditary $C^{*}$-subalgebra, but the strong Morita equivalence of a $C^{*}$-algebra A and its hereditary $C^{*}$-subalgebra B does not imply the fullness of B, ingeneral. We present the following lemma for our computational convenience in the course of the proof of the main theorem. Note that $L_{B}$, $L_{B}$$^{*}$ and $L_{B}$ $L_{B}$$^{*}$ are all .alpha.-invariant whenever B is .alpha.-invariant under the action .alpha. of G.a. of G.a. of G.a. of G.f G.

• 경영과정보연구
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• 제21권
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• pp.271-297
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• 2007

Since B2C EC websites not only become a valuable channel for selling goods to customers and for communicating with the potential clients, but also offer companies an important vehicle for attaining competitive advantages in the new digital economy, the design and content of website must reflect its business goals and customers' needs. However, as little empirical evidence on the effect of B2C EC website contribution of firm performance exist, the functionality of B2C EC website has been decided voluntarily from its business experience. Hence, there has been a call for a rigorous empirical studies to examine the function level of an B2C EC website application. The purpose of this study is to examine the relationship between the function level of B2C EC website and its performance considering the characteristics of B2C EC strategy as moderating variable. 125 questionnaires from internet shopping malls which sell physical goods direct to an individual end consumer were collected. The results showed that four factors(price, product recognition, reliability enhancement, and purchase confidence) affect positive effects on the performance of shopping mall, and the characteristics of B2C EC strategy can be considered as a significant moderating variable between price factor and the performance of shopping mall.