• Preventive Nutrition and Food Science
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• 제12권3호
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• pp.131-134
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• 2007

The kinetic analyses for thermal products of alpha-, gamma- and delta-tocopherols during heating as functions of temperature and time were studied. Alpha-, gamma- and delta-tocopherols dissolved in glycerol were heated at $100{\sim}200^{\circ}C$ for $5{\sim}60$ min. The thermal products were separated by hexane extraction and analyzed by HPLC using a reversed phase ${\mu}-Bondapak$ $C_{18}-column$ with two kinds of elution solvents in a gradient mode. The formation kinetics of thermal products of tocopherols followed a first-order kinetic model. The formation rate of thermal products of tocopherols was dependent on heating temperatures and heating times. The activation energy and enthalpy for the thermal products of ${\gamma}-and$ ${\delta}-tocopherols$ were higher than those for ${\alpha}-tocopherol$ as in the case of the oxidative degradation kinetics of tocopherol. The magnitude order of the activation energy was ${\gamma}->{\delta}->{\alpha}-tocopherol$.

• BMB Reports
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• 제31권3호
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• pp.245-248
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• 1998

Human epidermoid carcinoma A431 cells have an extraordinarily large number of epidermal growth factor (EGF) receptors, and their growth is inhibited by EGF, which results in growth arrest at the Gl phase. In order to investigate the EGF-mediated inhibition mechanism, the expression level of DNA topoisomerase (topo) II was analyzed after EGF treatment. As a result, it was shown that EGF treatment lowered the amount of 170 kDa topo II (topo $II{\alpha}$) but not 180 kDa (topo $II{\beta}$). However, the A431 cell variant resistant to EGF was not sensitive to EGF treatment. These results suggest that EGF-induced growth arrest of A431 cells may be closely related to the depletion of topo $II{\alpha}$.

• 미생물학회지
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• 제31권2호
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• pp.175-178
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• 1993

Alkaline .alpha.-amylase expressed in the transformant, Baciollus subtills MB809, containing alkaline amylase gene cloned from alkalophilic Bacillus sp. AL-8, was purified through for step separation processes. The purified alkaline .alpha.-amylase had molecular weight of app[roximately 59, 000 daltons on SDS-PAGE and Sephaex G-100 gel filtration. Amino acid sequence of terminal portion of the enzyme was analyzed with pure amylase eluted form the SDS-PAGE gel. N-terminal amino acid sequence of .alpha.-amylase was determined by the Edman degradation method and resulted in $NH_{2}$-ser-thr-ala-pro-ser-(ile)-lys-ala-gly-thr-(ile)-leu. For C-terminal amino acid sequencing, purified .alpha.-amylase was digested with carboxypuptidase A and B, and reverse-phase HPLC gradient elution system resulted in -thr-trp-pro-lys-COOH.

• 한국결정성장학회지
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• 제5권4호
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• pp.343-350
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• 1995

$\alpha$ - 및 $\beta$-SiC를 출발원료로 하여 일축성형한 후 $1800^{\circ}C$에서 고온가압법으로 소결한 탄화규소에 나타난 우선방위의 정도를 X-ray pole figure analysis로 조사하였다. $\alpha$-SiC를 출발원료로 사용한 경우에 고온 가압소결 후 약한 집합조직을 보인 반면, $\beta$ - SiC를 출발원료로 사용한 경우 고온가압소결 후 강한 집합조직을 보였으며, 이 경우 ${\beta} {\rightarrow} {\alpha}$ 상변태에 기인한 이중미세구조를 나타내었다. 또한, 집합조직의 강도는 고온가압소결 후 행해진 열처리 조건에 따라서도 변화를 보였다.

• 한국세라믹학회지
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• 제37권6호
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• pp.559-563
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• 2000

To decompose carbon dioxide, magnetite was synthesized with 0.2M-FeSO4$.$7H2O and 0.5 M-NaOH by coprecipitation. The deoxidized magnetite was prepared from the magnetite by hydrogen reduction for 1, 1.5, 2 hr. The degree of hydrogen reduction and the decomposition rate of carbon dioxide were investigated with hydrogen reduction time. The crystal structure of the magnetite was identified spinel structute by the X-ray powder diffractions. After magnetite was reduced by hydrogen, magnetite reduced by hydrogen become new phae(${\alpha}$-Fe2O3, ${\alpha}$-Fe) and spinel type simultaneously. After decomposing of carbon dioxide at 350$^{\circ}C$, new phse(${\alpha}$-Fe2O3, ${\alpha}$-Fe) were removed and the spinel type only existed. The specific surface area of the synthesized magnetite was 46.69㎡/g. With the increase of the hydrogen reduction time, the grain size, the hydrogen reduction degree and the decomposition rate of carbon dioxide was increased.

• 한국식품영양학회지
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• 제11권6호
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• pp.635-639
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• 1998

The thermal degradation pattern of $\alpha$-, ${\gamma}$-and $\delta$-tocopherols in glycerol was investigated during heating at 100~25$0^{\circ}C$ for 5-60 min in the absence of oxyge. The tocopherols and thermally decomposed products were separated by HPLC with a reversed phase $\mu$-Bondapak C18-column. The degradation pattern of $\alpha$-tocopherol during the heating in the absence of oxygen was different from those of ${\gamma}$-and $\delta$-tocopherols. But the degradation patterns of ${\gamma}$-and $\delta$-tocopherols were similar to each other. The residual content of $\alpha$-tocopherol during the heating in the absence of oxygen decreased to the range 12~65% and those of ${\gamma}$-and $\delta$-tocopherols decreased to the range 4~96%. The thermal degradation of tocopherols in the absence of oxygen was less than that in the presence of oxygen.

• 한국세라믹학회지
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• 제29권2호
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• pp.143-151
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• 1992

Partially stabilized alpha-sialon composition (X=0.1) powder was hot-pressed at 1800~200$0^{\circ}C$ for 0~90 min with 30 MPa. Sintering behavior, phase changes and mechanical properties for the specimens were studied. As sintering temperature was raised from 1800 to 190$0^{\circ}C$, the relative density tended to increase and reached 99% of theoretical at 190$0^{\circ}C$. However the amount of alpha-sialon decreased because alpha-sialon transformed to beta-Si3N4 and yttrium rich silicate glass. In the case of hot-pressing at 190$0^{\circ}C$ for various times, densification increased with sintering time and full densification above 99% of theoretical was attained by 30 min. The amount of alpha-sialon decreased with sintering time. The maximum strength of 825 MPa was obtained by hot-pressing at 190$0^{\circ}C$ for 60 min.

• 한국식품영양과학회지
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• 제26권6호
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• pp.1028-1032
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• 1997

Low-temperature crystallization method silver nitrate-impregnated silicic acid column chromatography were applied for the isolation of pure $\alpha$-linolenic acid(ALA) from perilla seed oil. ALA or 78% in purity(HALA; yield, 83%) was obtained from the fatty acid mixture(ALA, 65.7%) derived from perilla oil by the low-temperature crystallization method, when the mixture was frozen at -8$0^{\circ}C$ for 210min. ALA over 90% in purity(yield, 71%) was also obtained from HALA ethyl esters(ALA, 78%) by the silver nitrate-impregnated silicic acid column(100cm$\times$10cm, i.d.) chromatography. In addition, the silver nitrate-impregnated silicic acid could be semipermanently used for isolation of ALA, because $Ag^{+}$ ion was not dissociated from the stationary phase.

• 한국자기학회지
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• 제8권1호
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• pp.6-12
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• 1998

플라즈마 이온주입 장치를 이용하여 $\alpha$-Fe foil에 질소 이온을 주입하여 질화철 결정상을 만들었으며, 이때 질소 이온 주입시간을 15분(FEN15)과 30분 (Fe30)으로 처리되었다. 오제 전자 분광법(Auger electron spectroscopy : AES)을 이용하여 측정한 주입된 질소 이온의 깊이는 사편 FeN15와 FeN30에서 각각 12000$\AA$과 40000$\AA$으로 나타난다. 진동 시편 자력계(vibrating sample magnetometer : VSM)측정결과 as-implanted 각각의 시편은 포화자화 값이 순수한 $\alpha$-Fe foil 보다 증가되었으며, 이는 $\alpha$'-Fe8N 또는 $\alpha$'-Fe16N2의 결정구조가 그원인으로 판단된다. 따라서 본 연구는 플라즈마 이온주입 방법으로 제작된 질화철에서 부분적인 $\alpha$'또는 $\alpha$'의 졀정구조 형성 가능성을 확인할 수 있었다.

• Bulletin of the Korean Chemical Society
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• 제14권1호
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• pp.9-11
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• 1993