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11.
James H. Schmerl 《Mathematical Logic Quarterly》1998,44(4):515-521
There is a recursive set of natural numbers which is the difference set of some recursively enumerable set but which is not the difference set of any recursive set. 相似文献
12.
Carlo Carlini Valentina De Luise Anna Maria Raspolli Galletti Glauco Sbrana 《Journal of polymer science. Part A, Polymer chemistry》2006,44(1):200-206
Novel catalytic systems, prepared in situ by the oxidative addition of 8‐hydroxyquinoline ligands to bis(1,5‐cyclooctadiene)nickel(0) and activated by methylaluminoxane, were studied in ethylene polymerization. When 8‐hydroxyquinoline was employed, only oligomeric products were obtained. On the contrary, 5,7‐dinitro‐8‐hydroxyquinoline gave linear polyethylene (PE), but with a modest activity. For the catalyst based on 5‐nitro‐8‐hydroxyquinoline, the productivity was largely dependent on the content of free trimethylaluminum (TMA) present in the commercial aluminoxane. The progressive optimization of the TMA/oligomeric methylaluminoxane ratio increased the productivity, which reached 700 kg of PE/(mol of Ni × h), by an order of magnitude. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 200–206, 2006 相似文献
13.
设G是一个简单连通图,若分离G的余一独立集S的最小点数等于连接S的点之间的内部不相交路的最大个数,则称G是Menger图。我们考虑了图的几种运算并给出了运算后的图是Menger图的条件。 相似文献
14.
In many-valued logic the decision of functional completeness is a basic and important problem, and the thorough solution to this problem depends on determining all maximal closed sets in the set of many-valued logic functions. It includes three famous problems, i.e., to determine all maximal closed sets in the set of the total, of the partial and of the unary many-valued logic functions, respectively. The first two problems have been completely solved ([1], [2], [8]), and the solution to the third problem boils down to determining all maximal subgroups in the k-degree symmetric group Sk, which is an open problem in the finite group theory. In this paper, all maximal closed sets in the set of unary p-valued logic functions are determined, where p is a prime. Mathematics Subject Classification: 03B50, 20B35. 相似文献
15.
The intermolecular interaction energy for reacting systems in singlet, triplet and doublet states was partitioned by the perturbation expansion method into the chemically meaningful five interaction terms: the Coulomb, exchange-repulsion, induction, dispersion, and charge-transfer energies. In the local ZDO approximation, these energy terms were evaluated for the dimerization of methylenes (1,3CH2), the additions of carbenes (1,3CH2 and1,3CF2) as well as amino radicals (2NH2 and2NF2) toward ethylene, and the hydrogen abstractions by methylenes (1,3CH2), nitrene (3NH), and hydroxyl radical (2OH) from methane. It has been found that the reaction path is much influenced by the spinmultiplicity, and that the charge-transfer and exchange-repulsion terms play a dominant role in determining the course of reactions. 相似文献
16.
Summary The results of various quantum chemical calculations, the Hartree-Fock (HF) method, the Møller-Plesset perturbation theory (MP2), and the Hartree-Fock-Slater (HFS) method are compared. Atomic charges, dipole moments, topological properties of the electron density distribution and polarizabilities, and first hyperpolarizabilities are calculated. Atomic charges obtained with the HFS method are found to be very close to those calculated with the MP2 method, from which we conclude that the HFS method describes to some extent electron correlation effects. Performing an MP2 calculation after an HF calculation improves the molecular dipole moments considerably, yielding values close to the experimental ones. HFS calculations are computationally less demanding than MP2 and yield comparable results for the electron density distributions, dipole moments and polarizabilities. 相似文献
17.
Summary The interfering effect of the -radiation of radioactive isotopes of the rare earths on the non-destructive neutron activation analysis of g amounts of uranium, using the 106 KeV--line of 239Np and NaI (Tl). detector, is estimated. The errors introduced by the interfering isotope in the analysis of uranium, are determined as a function of the ratio of the concentration in the sample of the interfering element and uranium. In addition, the possibilities of determining the quantitative effect of these elements are described. The use of the proposed method is demonstrated by the analysis of some geological samples.
Zerstörungsfreie Neutronenaktivierungsanalyse von Uran über die 106 KeV--Strahlung von Neptunium-239II. Einfluß der Seltenen Erden
Zusammenfassung Es wird die Störung bestimmt, die die -Strahlung der radioaktiven Isotope Seltener Erden bei der zerstörungsfreien Neutronenaktivierungsanalyse von Mikrogramm-Mengen Uran über die 106 KeV--Linie des 239Np mit Hilfe eines NaJ(Tl)-Detektors hervorrufen kann. Die Fehler in der Analyse von Uran, die das Störisotop verursachen kann, werden als Funktion des Verhältnisses der Konzentration des Störelements zu der des Urans in der Probe bestimmt. Es werden Möglichkeiten beschrieben, den Einfluß störender Elemente quantitativ zu erfassen. Die Brauchbarkeit der vorgeschlagenen Methode wurde durch Analyse einiger geologischer Objekte bewiesen.
Part I: Z. Anal. Chem. 257, 23 (1971). 相似文献
18.
The parallel between orbital first and second electric moments and statistical first and second central moments is noted. Three measures of orbital spatial distribution in terms of their moments are proposed, and applied to the LMO's in a series of ten-electron hydrides. Consistent differences between bond and lone pair distributions are found. Using the statistical interpretation, for each LMO an effective solid angle around the central atom is postulated. 相似文献
19.
In distinction to Extended Hückel Theory which predicts as the most stable conformation of free zwitterionic GABA a totally extended form, PCILO and SCF ab initio studies show that the intrinsically preferred conformation of the isolated molecule is a highly folded one, resulting from strong interactions between the two charged ends. Computations are also carried out for hydrated GABA in the supermolecule approach allowing moreover for the flexibility of binding of some of the water molecules of the first hydration shell. They predict the coexistence in solution of a large number of conformations showing different degrees of folding (or extension), a result confirmed by recent NMR studies. This and a number of similar results show that we have to adapt our thinking on the role of conformations in pharmacological activity to this situation, which was frequently obscured by the more abundant results of X-ray crystallography yielding a single conformation. 相似文献
20.
Langlet J. Claverie P. Pullman B. Piazzola D. Daudey J. P. 《Theoretical chemistry accounts》1977,46(2):105-116
The effect of water on the conformational preferences of acetylcholine has been studied within the discrete, the continuum and the combined discrete-continuum models described in parts I and II of this series. All the models lead to the conclusion that the trans-gauche form which is, following refined quantum-mechanical computations, the intrinsically preferred one and the one observed in the crystal of acetylcholine and of a number of analogues should remain also the preferred conformation in water. This result agrees with NMR studies. The results of the empirical discrete model used here compare favorably to those obtained by an ab initio super-molecule treatment. The continuum model utilized here represents a net improvement above such models utilized in other works. 相似文献