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Sans résuméJ'ai mené ce travail à son terme grâce à une année de recherche au Centre de Mathématiques de l'Ecole Polytechnique. Je remercie ceux qui l'ont rendue possible, plus particulièrement Jean-Pierre Kahane, Président de l'Université Paris-Sud, et Laurent Schwartz, Directeur du Centre de Mathématiques. F.L. 相似文献
366.
K. Neumaier D. Steinbinder H. Wipf H. Blank G. Kearley 《Zeitschrift für Physik B Condensed Matter》1989,76(3):359-363
From neutron spectroscopic measurements, we determine a value of (162±4) eV for the tunneling matrix element of trapped H in Nb(CH)0.0002. The matrix element is about 30% smaller than that of (226±4) eV for H trapped by O. The results demonstrate a significant influence of the trapping impurity on the lattice potential of the tunneling H interstitials. 相似文献
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Ya. N. Makarovskaya L. P. Eksperiandova A. B. Blank 《Journal of Analytical Chemistry》2003,58(2):110-113
It was shown that the time dependences of the degree of decomposition of humic substances under exposure to ultrasound and UV radiation exhibit identical maxima. It was found that ultrasonic and ultraviolet treatments enhance the analytical signal even in the absence of humic substances. It was proposed to use the ultrasonic pretreatment before the extraction–X-ray fluorescence analysis of water to eliminate the effect of humic substances on the recovery of elements. 相似文献
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Vadim G. Kessler Gerald I. Spijksma Gulaim A. Seisenbaeva Sebastian Håkansson Dave H. A. Blank Henny J. M. Bouwmeester 《Journal of Sol-Gel Science and Technology》2006,40(2-3):163-179
This paper summarizes recent literature data and presents new experimental data on the mechanisms of chemical modification,
hydrolysis and polycondensation of the alkoxides and demonstrates possibilities to approach new classes of materials, exploiting
these mechanisms. Low reactivity of silicon alkoxides is improved by either basic catalysis exploiting an SN2 mechanism or acidic catalysis facilitating a proton-assisted SN1 mechanism as well as by modification with chelating ligands. Metal alkoxides are much stronger Lewis bases compared to silicon
alkoxides and the acidity of water is strong enough to achieve their rapid hydrolysis via proton-assisted SN1 pathway even in the absence of additional catalysts. Introduction of the modifying chelating ligands is leading generally
to increased charge distribution in the precursor molecules. Modifying chelating ligands are also appreciably smaller than
the alkoxide ligands they replace. The modification with chelating ligands is thus facilitating the kinetics of hydrolysis
and polycondensation. The size and shape of the primary particles formed in sol-gel treatment of metal alkoxides are defined
not by kinetic factors in their hydrolysis and polycondensation but by the interactions on the phase boundary, which is in
its turn directed by the ligand properties. The products of the fast hydrolysis and condensation sequence consist of micelles
templated by self-assembly of ligands (mainly oxo-species). This concept provides explanations for commonly observed material
properties and allows for the development of new strategies for the preparation of materials. We discuss the formation of
inverted micelles, obtained by the appropriate choice of solvents, which allows for the formation of hollow spheres. The modifying
β-diketonate ligands act as the surfactant and form an interface between the hollow sphere and the solvent. Retention of ligands
inside the gel particles is possible only if ligands possessing both chelating and bridging properties are applied. Application
of such ligands, for example, diethanolamine, permits to prepare new transition metal oxide based microporous membranes. 相似文献