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Downey Rodney G.; Lempp Steffen; Shore Richard A. 《Journal London Mathematical Society》1996,54(3):417-439
We show that there is a degree a REA in and low over 0' suchthat no minimal degree below 0' jumps to a degree above a. Wealso show that every nonlow recursively enumerable degree boundsa nonlow minimal degree. 相似文献
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Clemens D Vosberg V Hobbs W Breuer U Quadakkers WJ Nickel H 《Analytical and bioanalytical chemistry》1996,355(5-6):703-706
The effect of Si addition on the oxidation behaviour of NiCrAlY alloys in the temperature range 950 bis 1100 degrees C has been investigated. During isothermal oxidation oxide growth rates were practically independent of the Si-content. However during cyclic oxidation Si additions were beneficial. Si additions of 1-2(m)/(0) appeared to shift the onset for spallation to longer times. It was found that Si stabilizes the beta-phase and probably it suppresses the formation of metastable Al(2)O(3) modifications. 相似文献
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Reaction of dicyclopropyl cadmium and phthalic acid monochloride monomethyl ester gives o-carboxyphenyl cyclopropyl ketone (2). Reaction of the methyl ester of 2 with methylamine gives 2 - methyl - 3 - hydroxy-3-cyclopropyl-1-isoindolinone (4b), which is converted by hydrogen halides in chloroform to the rearranged homoallylic halides 5a–c. Thionyl chloride in chloroform converts 2 to 3-(3-chloropropylidene) phthalide (7) which upon reaction with methylamine gives isoshihunine (8). Heating of keto acid 2 with aniline leads to N-phenyl-N-norshihunine (9), while upon heating of 2 with methylamine spiro [(1 - methylpyrrolidine) - 2 - 3′ - (2′ - methyl - 1′ - isoindolinone)] (10) is obtained. 10 is converted to shihunine (1) by 48% HBr solution. The mechanisms of the reactions are discussed. 相似文献
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Iris Reimann Steffen Mergemeier Ingo Ebner Fritz Scholz 《Fresenius' Journal of Analytical Chemistry》1995,353(2):206-210
A determination of ethanol is described, which is based on a purging system in conjunction with a photoionization detector. With that system a fast and reliable determination of ethanol in aqueous solutions is possible. The system has been used for the analysis of wine. The 3-detection limit has been 0.005% ethanol, the relative standard deviation 4.8 to 6.0% and the time constant of the entire analytical system 20 s. The photoionization detector has been also applied to the analysis of artificial and genuine human breath. A comparison with gas-chromatography and non-dispersive IR-detection has been proven the reliability of results. 相似文献
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Hofmann C Boll R Heitmann B Hauser G Dürr C Frerich A Weitnauer G Glaser SJ Bechthold A 《Chemistry & biology》2005,12(10):1137-1143
The oligosaccharide antibiotic avilamycin A is composed of a polyketide-derived dichloroisoeverninic acid moiety attached to a heptasaccharide chain consisting of six hexoses and one unusual pentose moiety. We describe the generation of mutant strains of the avilamycin producer defective in different sugar biosynthetic genes. Inactivation of two genes (aviD and aviE2) resulted in the breakdown of the avilamycin biosynthesis. In contrast, avilamycin production was not influenced in an aviP mutant. Inactivation of aviGT4 resulted in a mutant that accumulated a novel avilamycin derivative lacking the terminal eurekanate residue. Finally, AviE2 was expressed in Escherichia coli and the gene product was characterized biochemically. AviE2 was shown to convert UDP-D-glucuronic acid to UDP-D-xylose, indicating that the pentose residue of avilamycin A is derived from D-glucose and not from D-ribose. Here we report a UDP-D-glucuronic acid decarboxylase in actinomycetes. 相似文献