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481.
Stefania Pragliola Chiara Costabile Mariagrazia Napoli Gaetano Guerra Pasquale Longo 《Macromolecular Symposia》2006,234(1):128-138
Olefin-diene copolymerizations in the presence of C2 symmetric zirconocene rac-[CH2(3-tert-butyl-1-indenyl)2]ZrCl2/MAO catalytic system have been reported and rationalized by experimental and molecular modeling studies. Ethene gives 1,2-cyclopropane and 1,2-cyclopentane, 1,3-cyclobutane, and 1,3-cyclopentane units in copolymerization with 1,3-butadiene, 1,4-pentadiene, and 1,5-hexadiene, respectively. Propene-1,3-butadiene copolymerizations lead to 1,2 and 1,4 butadiene units and to a low amount of 1,2-cyclopropane units. 相似文献
482.
Keppler-type ruthenium(III) complexes exhibit promising antitumor properties. We report here a study of 2-aminothiazolium[trans-tetrachlorobis(2-aminothiazole)ruthenate(III)], both in the solid state and in solution. The crystal structure has been solved and found to exhibit classical features. Important solvatochromic effects were revealed. Notably, we observed that introduction of an amino group in position 2 greatly accelerates chloride hydrolysis compared to the thiazole analogue; this latter finding may be of interest for a fine-tuning of the reactivity of these novel metallodrugs. 相似文献
483.
Pragliola S Milano G Guerra G Longo P 《Journal of the American Chemical Society》2002,124(14):3502-3503
An unprecedented cyclopropanation by cyclopolymerization reaction is presented. In particular, catalytic copolymerization processes of ethene and butadiene lead with high trans selectivity to a complete cyclocopolymerization of butadiene units. Ethene-based copolymers including cyclopropane and cyclopentane rings, which can be relevant to polyolefin applications, are obtained with high yields. Several aspects relative to the mechanism of this cyclocopolymerization reaction, including the high stereoselectivity, are discussed. 相似文献
484.
We consider some properties of countable separation for familiesA andD of subsets of a setX by means of elements of a fixed familyM⊂P(X). We give necessary and sufficient conditions, in terms of measurability of some sets constructed by means of multifunctions,
in order that the familiesA andD satisfy such a property. As an application we derive an implicit function theorem for functions ofCarathéodory-type.
Supported by 60% and 40% research fund of M.P.I. of Italy. 相似文献
485.
[structure: see text] The investigations described introduce a new role for a natural product such as amphotericin B as a potential biophysical reporter group to probe the physical state of a membrane. Specifically, we demonstrated that the K(+) efflux pattern reveals an interesting sterol dependence. This is suggested to be correlated to the physical state of the membrane showing high efflux in a vesicle membrane of intermediate fluidity. 相似文献
486.
487.
Pasquale?AvellaEmail author Maurizio?Boccia Antonio?Sforza Igor?Vasil'Ev 《Computational Optimization and Applications》2005,32(3):215-230
The Median-Path problem consists of locating a st-path on a network, minimizing a function of two parameters: accessibility to the path and total cost of the path. Applications
of this problem can be found in transportation planning, water resource management and fluid transportation.
A problem formulation based on Subtour and Variable Upper Bound (VUB) inequalities was proposed in the seminal paper by (Current,
Revelle and Cohon, 1989).
In this paper we introduce a tighter formulation, based on a new family of valid inequalities, named Lifted Subtour inequalities,
that are proved to be facet-defining. For the class of Lifted Subtour inequalities we propose a polynomial separation algorithm.
Then we introduce more families of valid inequalities derived by investigating the relation to the Asymmetric Traveling Salesman
Problem (ATSP) polytope and to the Stable Set polytope.
These results are used to develop a Branch-and-Cut algorithm that enables us to solve to optimality small and medium size
instances in less than 2 hours of CPU time on a workstation. 相似文献
488.
The transient behavior of a simple Malthus-Verhulst like nonlinear chemical system is analyzed. This model exhibits a nonequilibrium phase transition analogous to the laser instability. We first perform a qualitative analysis of the model in the space of the rate parameters. We show, both with a nonperturbative calculation and a direct computer simulation, that the fluctuations in the transient regime are enhanced above the steady state value. This anomalous behavior occurs in a given range for the rate parameters. 相似文献
489.
The aim of this paper is to prove some results concerning the norm theorem for semisingular quadratic forms, i.e., those which are neither nonsingular nor totally singular. More precisely, we will give necessary conditions in order that an irreducible polynomial, possibly in more than one variable, is a norm ofa semisingular quadratic form, and we prove that our conditions are sufficient if the polynomial is given by a quadratic form which represents 1. As a consequence, we extend the Cassels-Pflster subform theorem to the case of semisingular quadratic forms. 相似文献
490.
Giovanna Barbarella Pasquale Dembech Anna Garbesi Antonino Fava 《Magnetic resonance in chemistry : MRC》1976,8(2):108-114
The 13C NMR spectra have been determined of: (i) aliphatic compounds having at one end a functionalized sulphur atom (? SH, ? S?, ? SMe, ? S(O)Me, ? SO2Me and ? S+Me2) and (ii) saturated sulphur heterocycles variously substituted at the S-atom . The results are discussed in terms of the familiar deshielding effects for α- and β-carbons and shielding effects for γ-carbons, exerted by the sulphur atom itself and/or by the atoms or groups of which the sulphur function is made up. The γ-effect of the S-atom appears to be nearly independent of the nature of the S-function and of comparable magnitude to that of an aliphatic carbon (?2·5 + ?3·0 ppm). Surprisingly, however, a S? CH3 group shields the carbon in γ position with respect to CH3 by an amount (?5·4 ppm) which is more than twice that (?2·5 ppm) exerted by the aliphatic γ-carbon on the S-CH3 carbon itself. As to the cyclic compounds, the shieldings of the α- and β-carbons can be rationalized in terms of the conformational orientation of the substituent at sulphur, and the equilibrium distribution of the conformers. The results confirm the great value of 13C NMR for configurational and conformational assignment of S-heterocycles. 相似文献