• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제54권12호
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• pp.515-519
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• 2005

We have developed shell type 765kV transformers for generator step-up. Our research and development for shell type 765kV transformers have been continued since 1990. The shell type 765kV transformers of single phase 3MVA for step-up and 500MVA for power transmission were developed in Dec. 1992 and Oct. 1996, respectively. 204MVA 765kV transformer for generator step-up was also developed with the basis of technique and experience to the present. Total 12 phases of 204MVA 765kV transformers will be delivered at Tangjin thermal power plant by 2006. This paper describes electrical and structural features of the shell type 204MVA 765kV transformer.

• 자원리싸이클링
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• 제4권3호
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• pp.2-9
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• 1995

탈황 폐촉매 중에 함유되어 있는 Ni, V 및 Mo을 배소, 암모니아 침출 및 용매추출법을 이용하여 분리.회수하는 프로세스에 대하여 연구하였다. 폐촉매를 $400^{\circ}C$로 3시간 동안 배소한 후, 20mesh 이하로 분쇄하여, 고액비 50g/d㎥의 조건에서 100g/d㎥-(NH$_4$)$_2$CO$_3$를 침출제로 하여 $80^{\circ}C$에서 침출한 결과 Ni, V 및 Mo의 침출율은 각각 81.2%, 65%, 87.5%이었다. 이 침출액을 방냉하면 침출액 중의 74%의 V이 바나듐산 나트륨염의 형태로 침전되어 순도 95.7%의 V을 회수할 수 있었다. 1차 침출 후의 잔사에$ Na_2$$CO_3$를 가하여 $1000^{\circ}C$에서 재차 배소한 후, 온수에 침출하여 잔존된 Mo과 V을 95%이상 침출되었다. 1차 침출액 중의 Ni, V 및 Mo을 용매추출법으로 분리.정제하였다. 용액 중의 Ni는 MSP-8, V은 TOMAC을 추출제로 하여 추출.분리하고 Mo은 raffinate로 분리하였다. Batch 추출에 의하여 Ni은 95%, V은 98%가 유기상에 추출되었으며, 역추출액에 환원제를 첨가하여 순도 99%이상의 V을 회수하였다.

• 한국전기전자재료학회논문지
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• 제17권11호
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• pp.1178-1185
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• 2004

In the atmosphere of $N_2$ gas, BaZ $r_{0.08}$ $Ti_{0.92}$ $O_3$ polycrystal was grown by floating zone technique using BaZ $r_{0.08}$ $Ti_{0.92}$ $O_3$ ceramics as a feed and SrTi $O_3$(1l0) single cystal as a seed. The dielectric constant and loss at 10 kHz, 100 kHz, and 1 MHz for the as-grown sample were measured as a function of temperature in the temperature range between -10$0^{\circ}C$ and 150 $^{\circ}C$ to find a dielectric peak with frequency dispersion at Curie point. The hysteresis loop showed that the grown sample had very small polarization which was 0-0.01 $\mu$C/$\textrm{cm}^2$ for the applied dc-electric fields from -7 kV/cm to +7 kV/cm. However, the normal hysteresis loop was appeared after oxygen annealing. The electric-field dependence of the dielectric constant for both the as-grown and the post-annealed samples was studied by measuring the dielectric constants as a function of the biased-electric fields and their tunability was figured out from it at room temperature(27 $^{\circ}C$) and cryotemperature( -73$^{\circ}C$). Tunability for the as-grown sample was 51 % and the figure of merit 20.4 at 10kHz with the biased electric-field of 12 kV/cm. The tunability for the grown sample may be increased up to 80 % if the electric field of 25 kV/cm is applied. Tunability for the post-annealed sample was 41 % and the figure of merit 10.3 at 10 kHz with the biased electric-field of 12 kV /cm. Post-annealing improved the crystallinity of the as-grown sample but decreased its tunability.ability.

• Advanced Composite Materials
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• 제18권4호
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• pp.339-350
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• 2009

Al-Fe-V-Si alloys reinforced with SiC particles were prepared by multi-layer spray deposition technique. Both microstructures and mechanical properties including hardness and tensile properties development during hot exposure process of Al-8.5Fe-1.3V-1.7Si, Al-8.5Fe-1.3V-1.7Si/15 vol% $SiC_P$ and Al-10.0Fe-1.3V-2Si/15 vol% $SiC_P$ were investigated. The experimental results showed that an amorphous interface of about 3 nm in thickness formed between SiC particles and the matrix. SiC particles injected silicon into the matrix; thus an elevated silicon concentration was found around $\alpha-Al_{12}(Fe,\;V)_3Si$ dispersoids, which subsequently inhibited the coarsening and decomposition of $\alpha-Al_{12}(Fe,\;V)_3Si$ dispersoids and enhanced the thermostability of the alloy matrix. Moreover, the thermostability of microstructure and mechanical properties of Al-10.0Fe-1.3V-2Si/15 vol% $SiC_P$ are of higher quality than those of Al-8.5Fe-1.3V-1.7Si/15 vol% $SiC_P$.

• Nuclear Engineering and Technology
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• 제44권6호
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• pp.663-672
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• 2012

As software based digital I&C (Instrumentation and Control) systems are used more prevalently in nuclear plants, enhancement of software dependability has become an important issue in the area of nuclear I&C systems. Critical attributes of software dependability are safety and reliability. These attributes are tightly related to software failures caused by faults. Software testing and V&V (Verification and Validation) activities are hence important for enhancing software dependability. If the risky modules of safety-critical software can be predicted, it will be possible to focus on testing and V&V activities more efficiently and effectively. It should also make it possible to better allocate resources for regulation activities. We propose a prediction technique to estimate risky software modules by adopting machine learning models based on software complexity metrics. An empirical study with various machine learning algorithms was executed for comparing the prediction performance. Experimental results show SVMs (Support Vector Machines) perform as well or better than the other methods.

• 한국재료학회지
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• 제7권5호
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• pp.381-385
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• 1997

PEMOCVD에 의해서 SrBi$_{2}$Ta$_{2}$O$_{9}$밥막이 낮은 온도에서 성공적으로 Pt/Ti/SiO$_{2}$Si위에 증착되었다. 5$50^{\circ}C$에서 증착된 200nm박막은 치밀하고 작은 결정립을 보였으며 3V의 인가전압하에서 이력곡선은 포화되기 시작하였다. 3V에서 박막은 잔류분극 (P$_{r}$)과 항전계(E$_{c}$)는 각각 15$\mu$/$\textrm{cm}^2$과 50kV/cm이었다. 6V bipolar square pulse의 피로측정에서 박막은 1.0x$10^{11}$cycles까지 피로 현상을 보이지 않았다. PEMOCVD에 의해서 5$50^{\circ}C$에서 증착된 SBT박막은 비휘발성 기억소자에 충분히 활용할 수 있다.다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 C
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• pp.1252-1254
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• 1997

Direct methanol fuel cell based on a proton-exchange membrane electrolyte was investigated. 60% Pt-Ru/C and 60%Pt/C catalysts were employed for methanol oxidation and oxygen reduction, respectively. Morphologies of the catalysts were investigated by x-ray power diffraction, energy dispersive x-ray spectroscopy, and transmission microscopy. Electrochemical characteristics of the catalysts were tested by using cyclic voltametry technique. I-V characteristics of the fuel cell were tested by changing methanol concentration, temperature, and Nafion type as a proton-exchange membrane electrolyte. AC impedance technique was used to investigate the electrochemical performance of the fuel cell. The performance of single cell was enhance with increasing cell temperature. High operation temperature attributed to the combined effects of the reduction of ohmic resistance and polarization. High cell voltage was obtained from the concentration of 205M methanol. With Nafion 112, a current density of $230mA/cm^2$ at 0.55V was obtained from the concentration of 2.5M methanol.

• Restorative Dentistry and Endodontics
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• 제25권1호
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• pp.56-62
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• 2000

The purpose of this study was to assess the effects of restorative materials on the marginal leakage of wedge-shaped class V cavity. The study was performed in vitro in 25 defect-free permanent, extracted teeth. Wedge-shaped class V cavities were prepared and then the teeth were randomly selected and restored according to the following. Group A : restoration with Tetric Ceram(composite resin) Group B : restoration with Tetric flow(flowable resin) Group C : restoration with Compoglass after acid etching(compomer) Group D : restoration with Compoglass(compomer) Group E : restoration with Fuji II LC improved(resin-modified GIC) After thermocycling, the specimens were immersed in 5% basic fuchsin solution for 6 hours and sectioned longitudinally through the center of the restoration. The degree of marginal leakage was measured as the extent of dye penetration under the stereomicroscope. The data were analysed using one-way ANOVA. When significant differences found, multiple comparisons were made using Duncan's Multiple Range Test. The results were as follows: 1. The occlusal margins of all groups except for Fuji II LC improved showed lesser leakage than gingival margins and there was statistically significant difference(p<0.05). 2. At the occlusal margins, group A, B showed same marginal leakage scores, and others were decreased as group C, D, E in that order. There were statistically significant difference between group A, Band group D, E, group C and group E(p<0.05). 3. At the gingival margins, group B, C showed same marginal leakage scores, and others were decreased as group A, D, E in that order. But there was statistically significant difference between group B, C and group E(p<0.05). 4. In the Compoglass restoration, acid-etching technique was beneficial for marginal sealing ability at all of margins. But there was no statistically significant difference (p>0.05). In the restorations for wedge-shaped class V cavities, resin restoration with acid etching technique is recommended.

• 한국자원식물학회지
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• 제19권3호
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• pp.385-391
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• 2006

In vitro-grown axillary buds of Melia aredarach were successfully cryopreserved by vitrification. On the MS medium supplemented with BA 1 mg/L, multiple shoots were developed within $4{\sim}5$ weeks. Plantlets of Melia azedarach were cold-hardened at $10^{\circ}C$ for a 16-hr photo-period for 6 weeks. Excised axillary shoot-tips from hardened plantlets were precultured on a solidified Murashige & Skoog agar medium (MS) supplemented with 0.7 M sucrose for 1 day at $25^{\circ}C$. Axillary shoot-tip meristems wert dehydrated using a highly concentrated vitrification solution (PVS2) for 60 min at $0^{\circ}C$ prior to a direct plunge into liquid nitrogen (LN). The PVS2 vitrification solution consisted of 30% glycerol (w/v), 15% ethylene glycol (w/v), 15% DMSO (w/v) in MS medium containing 0.4M sucrose. After short-term warming in a water bath at $40^{\circ}C$, the meristems were transferred into 2 ml of MS medium containing 1.2M sucrose for 15 min and then planted on solidified MS culture medium. Successfully vitrified and warmed meristems resumed growth within 2 weeks and directly developed shoots without intermediary callus formation. The survival rate of cold-hardened plantlets for 3 and 4 weeks was 90%. We did not find any difference in PCR-band patterns between control and cryopreserved plants. This method appears to be a promising technique for cryopreserving axillary shoot-tips from in vitro-grown plantlets of Medicinal plants.

• 한국결정성장학회지
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• 제12권6호
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• pp.304-310
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• 2002

실리콘 기판 위의 초기 산화막을 NO 열처리 및 재산화 공정방법으로 성장한 재산화된 질화산화막을 게이트 유전막으로 사용한 새로운 전하트랠형 기억소자로의 응용가능성과 계면트랩특성을 조사하였다. 0.35$\mu$m CMOS 공정기술을 사용하여 게이트 유전막은 초기산화막을 $800^{\circ}C$에서 습식 산화하였다 전하트랩영역인 질화막 층을 형성하기 위해 $800^{\circ}C$에서 30분간 NO 열처리를 한 후 터널 산화막을 만들기 위해 $850^{\circ}C$에서 습식 산화방법으로 재산화하였다. 프로그램은 11 V, 500$\mu$s으로 소거는 -l3 V, 1 ms의 조건에서 프로그래밍이 가능하였으며, 최대 기억창은 2.28 V이었다. 또한 11 V, 1 ms와 -l3 V, 1 ms로 프로그램과 소거시 각각 20년 이상과 28시간의 기억유지특성을 보였으며 $3 \times 10^3$회 정도의 전기적 내구성을 나타내었다. 단일접합 전하펌핑 방법으로 소자의 계면트랩 밀도와 기억트랩 밀도의 공간적 분포를 구하였다. 초기상태에서 채널 중심 부근의 계면트랩 및 기억트랩 밀도는 각각 $4.5 \times 10^{10}/{cm}^2$ 와 $3.7\times 10^{1R}/{cm}^3$ 이었다. $1 \times 10^3$프로그램/소거 반복 후, 계면트랩은 $2.3\times 10^{12}/{cm}^2$으로 증가하였으며, 기억트랩에 기억된 전하량은 감소하였다.