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1.
We investigate the effects of adding uniformity requirements to concepts in computable structure theory such as computable categoricity (of a structure) and intrinsic computability (of a relation on a computable structure). We consider and compare two different notions of uniformity, previously studied by Kudinov and by Ventsov. We discuss some of their results and establish new ones, while also exploring the connections with the relative computable structure theory of Ash, Knight, Manasse, and Slaman and Chisholm and with previous work of Ash, Knight, and Slaman on uniformity in a general computable structure-theoretical setting. 相似文献
2.
R. G. Downey 《Archive for Mathematical Logic》1987,26(1):127-136
LetA be an r.e. nonrecursive set. We sayA has thestrong antisplitting property if there exists an r.e. setB with 0<
T
B<
T
A such that ifA
1 A
2=A andA
1A
2=0 thenA
1
T
B impliesA
1
T
0 andB
T
A
1 impliesA
1
T
A. It is shown that below any high r.e. degree there exists an r.e. set with the strong antisplitting property. The main ingredient of the proof is a localization of Ambos-Spies' result that the cup or cap theorem fails forW-degrees.Research partially supported by N.U.S. Grant RP 85/83 (Singapore). 相似文献
3.
Differences in the ion flotation properties of palladium(II) and platinum(IV) chloro complexes in aqueous solutions are used to achieve separations of these metals. The anionic chloro complex PtCl2-6 is floated selectively with cationic surfactants of the type, RNR'3Br, from solutions of PdCl2-4 and various concentrations of hydrochloric acid. The palladium(II) does not float from solutions of ? 3.0 M HCl and the platinum(IV) floated from these solutions can be recovered free of palladium. However, the separation is incomplete as much of the platinum(IV) is also unfloated from these solutions. Quantitative separations are obtained by conversion of the palladium(II) to the cationic ammine, Pd(NH3)42+ with aqueous ammonia prior to flotation. The anionic chloro complex of platinum(IV) is unaffected by the presence of ammonia and is floated quantitatively with the surfactant n-hexadecyltri-n-propylammonium bromide from 0.01 M ammonia solutions. 相似文献
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5.
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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9.
Silyl triflate-accelerated additions of catalytically generated zinc acetylides to N-phenyl nitrones
Terminal alkynes readily form zinc acetylides in the presence of iPr2NEt and 20 mol % ZnBr2, then attack N-phenyl nitrones activated by trimethylsilyl trifluoromethanesulfonate. Deprotection with aqueous acid yields N-hydroxyl propargylamine. Yields are generally high for nitrones derived from aromatic aldehydes. Control experiments suggest that silyl triflate has a significant accelerating effect upon the reaction. 相似文献
10.