• Bulletin of the Korean Chemical Society
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• 제15권6호
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• pp.428-432
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• 1994

The crystals of ${\beta}-and\;{\beta}'-(ET)_2ICl_2$ have a modified structure of organic superconductor ${\beta}(ET)_2I_3$. These salts possess strictly different physical properties : the ${\beta}$ phase is a metal but the ${\beta}'$ phase is a semiconductor. Our band electronic structure calculations show that the ${\beta}$ phase is somewhat anisotropic 2D metal and the ${\beta}'$ phase with the 1D character in electronic structure is magnetic insulating, in good agreement with experimental indications.

• 한국주조공학회지
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• 제18권4호
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• pp.357-363
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• 1998

Microstructure of A356 aluminium alloys cast in a permanent mold was investigated by optical microscope and image analyzer, with particular respect to the shape and size distribution of iron intermetallics known as ${\beta}-phase$ ($Al_5FeSi$). Morphologies of the ${\beta}-phase$ was found to change gradually with the Be:Fe ratio like these. In Be-free alloys, ${\beta}-phase$ with needlelike morphology was well developed, but script phase was appeared when the Be:Fe ratio is above 0.2:1. With the Be:Fe ratios of 0.4:1-1:1, script phase as well as Be-rich phase was also observed. In case of higher Be addition, above 1:1, Be-rich phase was observed on all regions of the specimens, and increasing of the Be:Fe ratios gradually make the Be-rich phase coarse. It was also observed that the ${\beta}-phase$ with needlelike morphology was coarsened with increase of the Fe content in Be-free alloys. However, in Be-added alloys, length and number of these ${\beta}-phases$ were considerably decreased with the increased Be:Fe ratio. It was concluded that Fe impurity element to be crystallized into needlelike intermetallics was tied up by Be addition element, and new phases were crystallized into script or Be-rich intermetallics.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.295-298
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• 2005

High temperature deformation behavior of $\alpha\;and\;\beta$ phase of Ti-6Al-4V was investigated within the framework of a self-consistent approach at various temperature ranges. To examine the flow behavior of u-phase, Ti-7.0Al-1.5V alloy was used, whose chemical composition is close to that of the $\alpha$ phase in Ti-6Al-4V at hot working temperatures. The flow stress of $\beta$ phase was predicted by using self-consistent approach. The flow stress of $\alpha$ phase was higher than that of $\beta$ phase above $750^{\circ}C$, while the $\beta$ phase revealed higher flow stress than a phase at $650^{\circ}C$. It was found that the relative strength and strain rate ratio between $\alpha\;and\;\beta$ phase significantly varied with temperature. From this approach, the mode for grain matrix deformation was proposed as a mixed type of both iso-stress and iso-strain rate modes.

• 한국주조공학회지
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• 제18권5호
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• pp.431-438
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• 1998

Microstructure of A356 aluminum alloys cast in the permanent mold was investigated by optical microscope and image analyzer, with particular respect to the shape and size distribution of iron intermetallics known as ${\beta}-phase$ ($Al_5FeSi$). Morphologies of the ${\beta}-phase$ was found to change gradually with the Be:Fe ratio like these. In Be-free alloys, ${\beta}-phase$ with needlelike morphology was well developed, but script phase was appeared when the Be:Fe ratio is above 0.2:1. With the Be:Fe ratios of 0.4:1-1:1, script phase as well as Be-rich phase was also observed. In case of higher Be addition, above 1:1, Be-rich phase was observed on all regions of the specimens, and increasing of the Be:Fe ratios gradually make the Be-rich phase coarse. It was also observed that the ${\beta}-phase$ with needlelike morphology was coarsened with increase of the Fe content in Be-free alloys. However, in Be-added alloys, length and number of these ${\beta}-phases$ were considerably decreased with the increased Be:Fe ratio. Beryllium addition improved tensile properties and impact toughness of the A356 aluminium alloy, due to the formation of a script phase or a Be-rich phase instead of a needlelike ${\beta}-phase$. The DSC tests indicated that the presence of Be could increase the amount of Mg which is available for $Mg_2Si$ precipitate hardening, and enhance the precipitation kinetics by lowering the ternary eutectic temperature.

• 한국분말재료학회지
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• 제5권1호
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• pp.15-21
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• 1998

The effect of $\alpha$/$\beta$ phase on the mechanical properties and contact damage of silicon nitrides $Si_3N_4$) was investigated. Silicon nitride materials were prepared from two starting powders, at selective increasing hot-pressing temperatures to coarsen the microstructures: (i) from relatively coarse $\alpha$-phase powder, essentially equiaxed $\alpha$-$Si_3N_4$ grains, with limited, slow transformation to $\beta$-$Si_3N_4$ grain; (ii) from relatively fine $\alpha$-phase powder, a more rapid transformation to $\beta$-$Si_3N_4$, with attendant grain elongation. The resulting micro-structure thereby provided a spectrum of $\alpha$/$\beta$ phase ratios, grain sizes, and grain shapes. Fracture strength, hardness, and toughness were measured, and contact damage and strength degradation after indentation were investigated by Hertzian indentation using spherical indenter. A brittle to ductile transition in $Si_3N_4$ depended on $\alpha$/$\beta$ phase ratio as well as grain size. Silicon nitride with elongated $\beta$ grains showed a superior, contact damage resistance.

• 공업화학
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• 제23권6호
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• pp.534-538
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• 2012

$ Na^+$-beta-alumina 고체전해질을 고상반응법을 통해 합성하였으며, 두 종류의 안정화제 $Li_2O$와 MgO가 상 형성 및 소결밀도에 미치는 영향을 비교 분석하였다. 합성온도에 따른 ${\beta}/{\beta}^{{\prime}{\prime}}$-alumina 상 분율 분석을 위해, [$Na_2O$] : [$Al_2O_3$] = 1 : 5의 고정된 몰 비에서 하소온도를 $1200{\sim}1500^{\circ}C$로 변화하여, 각각 2 h동안 하소하였다. $Li_2O$를 안정화제로 사용한 경우에는 $1500^{\circ}C$에서 2차 상 전이가 발생해 ${\beta}^{{\prime}{\prime}}$-alumina 상 분율의 증가가 나타났지만, MgO를 첨가했을 때는 하소온도에 관계없이 상 분율이 유지되었다. 또한 disc 형태의 $Na^+$-beta-alumina 샘플을 $1550{\sim}1650^{\circ}C$의 온도에서 각각 30 min 소결한 후 상대 소결밀도, 상 변화 및 미세구조를 분석하였다. $Li_2O$를 안정화제로 사용하였을 때, 소결온도 $1600^{\circ}C$에서 ${\beta}^{{\prime}{\prime}}$-상 분율과 상대밀도가 각각 94.7%와 98%로 가장 높은 값을 나타냈으며, MgO를 안정화제로 사용하였을 경우, 소결온도의 증가에 따라 상대밀도가 크게 증가하는 결과를 보였다.

• 한국미생물·생명공학회지
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• 제15권2호
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• pp.84-88
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• 1987

Poly(ethylene glycol)/salt가 형성하는 액상 2상계에서 균체내 효소인 $\beta$-galactosidase 분리를 최적화하는 실험을 수행하였다. L. sporogenes에 의해 생산된 $\beta$-galactosidase의 분획은 2상계를 형성하는 PEG 분자량이 작을수록 상층부로 이동하였으며, 상층부 PEG 농도가 증가할 때 salting-out 현상이 나타나서 단백질 뿐아니라 $\beta$-galactosidase는 상층부로 크게 이동하였다. 또한 균체내 효소 정제에서 문제가 되는 세포벽잔사(cell debris)들은 조성이 binodial line에 접근할수록 효소 fraction과 반대방향으로 이동되었다. PEG-salt를 이용한 $\beta$-galactosidase 분리는 조성을 binodial line레 접근시키면서 동시에 상층부의 부피를 줄이는 것이 효과적이었다. PEG1000, 300을 각각 단계적으로 이용한 2단계 추출(two-step extraction)로써 세포벽 잔사, bulk protein, 색소물질 및 핵산 등을 제거할 수 있었으며, 이때 효소의 회수율은 74%, 단백질 회수율 35%로서 정제도는 2 배 이상의 효과를 보였다.

• Journal of Korean Neurosurgical Society
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• 제42권3호
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• pp.200-204
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• 2007

Objective : Radiation therapy is an important treatment for brain tumor. However, serious complications such as radiation necrosis can occur and it may be secondary to the expression of acute phase genes, like cytokines. In particular, inflammatory cytokines (IL-$1{\beta}$, TNF-${\alpha}$) and other immunomodulatory cytokines (TNF-${\alpha}$, TGF-${\beta}1$) might be changed after irradiation (high single dose irradiation). Although it has been reported that IL-1 level is remarkably elevated within 8 week after the irradiation to the rat brain. the change of cytokines levels at acute phase (within 24 hours) has not been reported. In the present study, we examined TNF-${\alpha}$, TGF-${\beta}1$, and IL-$1{\beta}$ levels in acute phase to clarify the early effect of cytokines on the radiation-induced brain damage. Methods : Fifty Sprague-Dawley rats were used and these were divided into irradiation group and control group. After a burr-hole trephination on the right parietal area using a drill, a single 10Gy was irradiated at the trephined site. Their forebrains were extirpated at 30 min, 2 hr, 8 hr, 12 hr and 24 hr, respectively and examined for the expression of TNF-${\alpha}$, TGF-${\beta}1$, and IL-$1{\beta}$. Results : The expression of TNF-${\alpha}$ and TGF-${\beta}1$ were decreased until 12 hr after irradiation but elevated thereafter. The expression of IL-1 was peak at 8 hr and then decreased until 12 hr but elevated after this time window. The present study indicated that expression of cytokines (TNF-${\alpha}$, TGF-${\beta}1$ and IL-$1{\beta}$) were increased at 24 hr after the irradiation to the rat brain. IL-$1{\beta}$ level, on the other hand. reached peak at 8 hr after radiation injury. Conclusion : These findings indicate that IL-1, among various cytokines, may have a more important role in the inflammatory reaction by radiation injury at acute phase and provide some clues for better understanding of the pathogenesis of radiation injury.

• 열처리공학회지
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• 제17권5호
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• pp.271-277
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• 2004

Zr-xNb alloys (x = 0.2, 0.8, 1.5 wt.%) were prepared to study the characteristics of the phase transformation in Zr-Nb system. The samples were heat treated at ${\beta}$-temperature ($1020^{\circ}C$) for 20 min and then cooled with different cooling rate. The microstructures of the specimens having the same compositions were changed with cooling rate and Nb content. The Widmanst$\ddot{a}$tten structure was observed on the furnace-cooled sample. The relationship between ${\alpha}$-Widmanst$\ddot{a}$tten and ${\beta}$-phase was the {0001}${\alpha}$//{110}${\beta}$, <11$\bar{2}$0>//<111>. The ${\beta}$-phase in Widmanst$\ddot{a}$tten structure of Zr-Nb alloys containing Nb more than solubility limit was identified as ${\beta}_{Zr}$ phase which was a stable phase at high temperature. In the water quenched samples, two kinds of martensite structures were observed depending on the Nb-concentration. The lath martensite was formed in Zr-0.2, 0.8 wt.% Nb alloys and the plate martensite having twins was formed in Zr-1.5 wt.% Nb alloy.

• Applied Microscopy
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• 제33권1호
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• pp.49-58
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• 2003

EF-TEM 직접가열 실험을 통하여 titanium의 ${\alpha}-{\beta}$상전이를 연구하였다. 통계적 오차를 줄이기 위해 서로 다른 3군데의 titanium foil의 영역을 관찰하였고, 각각의 영역에 대해 단계별로($RT{\rightarrow}600{\rightarrow}900{\rightarrow}RT$) 회절패턴과 이미지를 기록하였다. 이 연구를 통해 얻은 결과는 다음과 같다. (1) Titanium은 $900^{\circ}C$에서 급격히 상전이가 진행된다. 이 온도에서는 ${\alpha}$와 ${\beta}$-상이 같이 존재한다. (2) 상전이가 일어난 ${\beta}$-상의 영역은 쌍정구조를 가진 plate 형태로 나타나며, 그들은 서로 상호 회전 배열되어 있다. (3) 전자회절도형과 EDS 분석 결과, $600^{\circ}C$ 이상의 가열에서는 열적 산화에 의해 Ti의 산화물이 표면에서 생성되기 시작하며 이들은 냉각 시 Ti의 ${\beta}{\rightarrow}{\alpha}$ 가역 상전이를 저해한다.