A new metal oxyhydride; neodymium oxyhydride, NdHO, has been synthesized from a reactant mixture of metal hydride (CaH2 or NdH3) and neodymium oxide (Nd2O3). The unit cell dimensions decrease smoothly in the series from LaHO, CeHO, PrHO to NdHO, in line with the lanthanide contraction. The crystal structure of NdHO is described on the basis of Rietveld refinement on neutron powder diffraction data:
Space group: P4/nmm (no. 129, D4h7).
Axis lengths: a=7.8480(5) Å, c=5.5601(8) Å.
Volume: V=342.46(6) Å3.
The tetragonal structure is derived from the fluorite structure, showing complete ordering of hydride and oxide ions over the anion sublatttice. The formation of NdHO was further substantiated by Raman spectroscopy. 相似文献
An axially chiral dihydroborepine with a binaphthyl backbone and a C(6)F(5) substituent at the boron atom was prepared by transmetalation from the corresponding tin precursor. This novel motif was structurally characterized by X-ray diffraction analysis as its THF and its PhCN Lewis acid/base complex. (1)H NMR measurements at variable temperatures of the former adduct revealed a remarkable dynamic behavior in solution. Several more Lewis pairs with oxygen, nitrogen, carbon, and phosphorus σ-donors were synthesized and analyzed by multinuclear NMR spectroscopy. The determination of the borane's Lewis acidity with the Gutmann-Beckett method attests its substantial Lewis acidity [85% with Et(3) PO as well as 74% with Ph(3) PO relative to the parent B(C(6)F(5))(3)]. Representative examples of Si-H bond activation (carbonyl reduction and dehydrogenative Si-O coupling) are included, demonstrating the chemical stability and the synthetic potential of the new chiral boron-based Lewis acid. 相似文献
New historical aspects of the classification, by Cayley and Cremona, of ruled quartic surfaces and the relation to string
models and plaster models are presented. In a ‘modern’ treatment of the classification of ruled quartic surfaces the classical
one is corrected and completed. The string models of Series XIII of some ruled quartic surfaces (manufactured by L. Brill
and by M. Schilling) are based on a result of Rohn concerning curves in
\mathbbP1×\mathbbP1{\mathbb{P}^1\times \mathbb{P}^1} of bi-degree (2, 2). This is given here a conceptional proof. 相似文献
We consider the three-dimensional motion of a self-propelled deformable structure into a viscous incompressible fluid. The
deformation of the solid is given whereas its position is unknown. Such a system could model the propulsion of fish-like swimmers.
The equations of motion of the fluid are the Navier-Stokes equations and the equations for the structure are deduced from
Newton’s laws. The corresponding system is a free boundary problem and the main result of the paper is the existence of weak
solutions for this problem. 相似文献
We address the global persistence of analyticity and Gevrey-class regularity of solutions to the two and three-dimensional
visco-elastic second-grade fluid equations. We obtain an explicit novel lower bound on the radius of analyticity of the solutions
that does not vanish as t → ∞, and which is independent of the Rivlin–Ericksen material parameter α. Applications to the damped incompressible Euler equations are also given. 相似文献
Chloride avoided! A new chloride‐free method to synthesise ionic liquids (ILs) with mixed borate anions, starting from tetrafluoroborate compounds, has been developed and a number of examples including some new ILs are presented (see scheme; [CAT]+=cation). It is widely applicable and allows access to mixed borates with various types of ligands in a straightforward manner.
We study boundary value problems for the time-harmonic form of the Maxwell equations, as well as for other related systems of equations, on arbitrary Lipschitz domains in the three-dimensional Euclidean space. The main goal is to develop the corresponding theory for Lp-integrable bounday data for optimal values of p’s. We also discuss a number of relevant applications in electromagnetic scattering. 相似文献
We identify the optimal range of coefficients s, p for which differential forms with coefficients in the Sobolev space admit natural Hodge decompositions in arbitrary two and three dimensional Lipschitz domains . To cite this article: D. Mitrea, M. Mitrea, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 109–112 相似文献