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Accumulation of 2-Keto-L-Gulonate at 33℃ by a Thermotolerant Gluconobacter Oxydans Mutant Obtained by Ion Beam Implantation

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Plasma Science and Technology 2006年第2期8卷 237-241页

作者：严冰许安张婉周伟王军姚建铭余增亮 Key Laboratory of Ion Beam Bioengineering Institute of Plasma Physics Chinese Academy of Sciences Hefei 230031 China

To obtain thermotolerant mutants of G. oxydans, which can enhance the transformation rate of L-sorbose to 2-Keto-L-gulonate （2-KLG） at 33℃ in a two-step process of vitamin C manufacture, ion beam was used as a mutation source. Gluconobacter oxydans GO and Bacillus megaterium B0 were used in this study. The original strain Gluconobacter oxydans GO was mutated by the heavy ion implantation facility at the Institute of Plasma Physics, Chinese Academy of Sciences. Several mutants including Gluconobacter oxydans GI13 were isolated and cocultured with Bacillus megaterium B0 at 33℃ in shaking flasks. The average transformation rate of the new mixed strain GI13-B0 in per gram-molecule reached 94.4% after seven passages in shaking flasks, which was increased by 7% when compared with the original mixed strain G0-B0 （Gluconobacter oxydans GO and Bacillus megaterium B0）. Moreover, the transformation rate of I13B0 was stable at 94% at temperatures ranging from 25℃ to 33℃, which would be of much value in reducing energy consumption in the manufacture of L-ascorbic acid, especially in the season of summer. To clarify some mechanism of the mutation, the specific activities of L-sorbose dehydrogenase in both GO and GI13 were estimated.

关键词： L-sorbose to 2-keto-L-gulonate transformation rate thermotolerant mutants,ion beam

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MICROSTRUCTURE transformation IN THE WELDING HEAT AFFECTED ZONE OF 800MPa GRADE ULTRA FINE STRUCTURED STEEL

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Acta Metallurgica Sinica(English Letters) 2004年第3期17卷 238-246页

作者： J.B. Liu L.J. Hu Y.T.Wang Z. Q. Liu K. Miao Z.L. Tian Huazhong University of Science and Technology Wuhan 430074 China Technology Center of Wuhan Iron and Steel (Group) Corporation Wuhan 430080 China Central Iron and Steel Research Institute Beijing 100080 China

The transformation behavior and microstructure development in the heat affected zone(HAZ)of 800MPa grade ultra fine structured steel was *** was found that the HAZ has intermediate temperature transformation characteristics in a wide range of cooling rates,with the bainite sheaves consisting of bainite ferrite plates without carbide precipitation and retained austenite in the fast cooling *** relatively high cooling rates,which corresponded to low heat inputs,the hardness of the simulated HAZ was above that of the base *** the cooling rate was below 9C/s,the welding HAZ would have an obvious *** analysis of transformation rates in continuous cooling processes was completed by numerical differential *** result indicated that the microstructure transformation rate of the HAZ in 800MPa grade ultra fine structured steel changed sharply to slow speeds when the cooling time t8/5 is longer than 7s.

关键词： ultra fine structured steel weld heat affected zone transformation rate microstructure

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Effect of Cu on Discontinuous Precipitation of a Symmetrical AlZn Alloy

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Journal of Materials Science & Technology 2005年第2期21卷 215-218页

作者： Shiming HAO, Yuping REN, Dapeng WANG, Danyang DONG and ffongxiao LI College of Materials and Metallurgy, Northeastern University, Shenyang 110004, China Coll. of Mat. and Metall. Northeastern Univ. Shenyang 110004 China

The effect of Cu additions on discontinuous precipitation of AlZn alloy were studied with optical microscopy, scanning electron microscopy and X-ray diffraction. It is found that the effect of addition of 2 at. pct Cu on cellular nucleation site is not remarkable, while the effect of aging temperature on cellular nucleation site of AlZn and AIZn-2Cu alloys is fairly obvious. The cell growth rate of discontinuous precipitation of AlZn alloy is remarkably accelerated with the addition of 2 at. pct Cu. The discontinuous precipitation microstructure of AlZn alloy is not apparently affected with the addition of 2 at. pct Cu and the cellular front is still fine microstructure of spinodal decomposition. The phase constituents consist of a fcc Al-rich phase, a hcp Zn-rich phase and a CuZn4 phase. The transformation rate of discontinuous precipitation of AlZn alloy is remarkably accelerated with the addition of 2 at. pct Cu.

关键词： Al-Zn(-Cu) alloy Spinodal decomposition Discontinuous precipitation transformation rate

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