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111.
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Mostafa Mimouni Sébastien Perrier Yvon Pointud Jean Juillard 《Journal of solution chemistry》1993,22(9):769-785
Interactions of ionophore monensin with heavy metal monovalent cations, Ag+, Tl+, Hg
2
2+
, were studied in methanol and in various biphasic waterorganic solvent systems to supplement previous data on alkali-metal cations. The species formed were identified and the corresponding formation constants determined. Enthalpies of formation were also obtained in methanol for Ag+ and Tl+ from calorimetric measurements. The results for monovalent cations in general are discussed in terms of cation size and solvation, and structure of the ionophore anion. 相似文献
113.
Hydrogenation of hexagonal Ce2Ni7 was investigated by synchrotron X-ray and neutron powder diffraction. In contrast to the recently investigated lanthanum analogue, which remains hexagonal (La2Ni7D6.5: space group P63/mmc), the cerium compound becomes orthorhombic (Ce2Ni7D approximately 4: space group Pmcn). As in the structurally related CeNi3D2.8, deuterium occupies CeNi2 slabs only, while the bulk of the CeNi5 slabs remains empty. A significant amount of deuterium is bonded in tetrahedral NiD4 units similar to those in nickel-based complex metal hydrides. These findings provide further evidence for directional bonding effects in hydrides that are traditionally considered as "interstitial". Ce2Ni7D approximately 4 displays various orthorhombic lattice distortions, delta = (b/ radical3 - a)/a. Hydrogen pressures of approximately 30 bar stabilize a phase having a negative distortion (delta < 0). Upon a decrease in the pressure, this phase transforms via a two-phase region into another phase having a positive distortion (delta > 0). Both phases are nearly isostructural and have the same space group symmetry and nearly the same composition. This situation is typical for a so-called anti-isostructural phase transition in which delta is considered to be an order parameter. Neither magnetic nor structural transitions have been detected down to 1.5 K. 相似文献
114.
The chemical bonding in the refractory transition metal compounds TiC, TiN, and VN is investigated by experimental and theoretical techniques. High-precision X-ray diffraction is used to determine the electron densities in these three compounds experimentally. The X-ray structure factors and the respective valence electron densities are used twice, once to understand the chemical bonding and once to relate the experimental charge densities to those obtained from band structure calculations. These calculations, which in general are in very good agreement with experimental data, utilize the linearized augmented plane wave (LAPW) method. Theory and experiment lead to a detailed analysis of the chemical bonding in these compounds with 8, 9, and 10 valence electrons. By decomposition of the theoretical charge density into contributions from different states (energy regions), it was possible to show the strong covalent nonmetal p-metal d interaction, which is otherwise apparent only in TiC, but not in TiN or VN. In the latter two compounds the additional electrons occupy mainly metal d states with t2g symmetry, so that in the total valence charge densities the most important bonding feature is covered. In addition to covalent interactions all compounds have a metallic bonding contribution as well as a considerable charge transfer from the metal to the nonmetal site. This mixture in chemical bonding accounts for the unusual combination of properties such as ultrahardness, high melting points, and good conductivity. 相似文献
115.
The parareal in time algorithm is a predictor corrector method that allows to get parallelisation through the time. It consists in segmenting the interval of time integration into slabs, then propose iteratively seed values at the left hand side of each of the slabs. The derivation of the seed values is done sequentially and involves propagator that should mimic the equation to be solved but should be very cheap and parallel accurate propagations of each seed value over each slab. Various approaches have been proposed to get the coarse propagator, in this paper, we use the averaging approach developed by Barenblatt and Chorin for the Korteveg-deVries-Burgers' equations. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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A double-lap, adhesive bonded joint, has been optimized with a fixed thickness of the core, in order to maximize the breaking force, and to obtain reproducible results. The shear profile, longitudinal, corresponds in the central region of the overlapping to classical theory, but is represented empirically, near the extremities, by the transversal shear in outer adherends. This furnishes an abscissa of the shear maximum in the joint, that compares with the location expected in a previous study and indicates also the critical level of shear, at the threshold of microcrack initiation, that compares with the breaking strength of the solid adhesive, in a similar manner for three different adhesives for which we observed a certain length of sheared joint with a cohesive fracture. 相似文献
119.