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121.
122.
Jean-Louis Gras 《Tetrahedron letters》1978,19(24):2111-2114
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A dilute aqueous solution of neodymium chloride NdCl3 has been taken through two thermodynamic cycles along transformations with varying pressure (between 1 bar and 3.3 kbar) and temperature (between 300 K and 77 K). The characteristic optical line absorption spectrum which shows a Stark splitting of the Nd3+ electronic levels due to a quasi-crystalline surrounding of the ions appears only in that part of the cycles where pure ice Ih phase would be present. In any other part of the cycles where pure ice phases II, III, IX and IC would be present such a phenomenon does not exist. It is shown that ice Ih may constitute a frame for neodymium aquo-ions. 相似文献
126.
In this paper computations in the two dimensional case of a harmonic Navier-Stokes problem with periodic boundary conditions are presented. This study of an incompressible viscous fluid leads to a non-symmetric linear problem (very low Reynolds number). Moreover unknown functions have complex values (monochromatic dynamic behaviour). Numerical treatment of the incompressibility condition is a generalization of the classical treatment of Stokes problem. A mixed formulation, where discrete pressure plays the role of Lagrange multipliers is used (Uzawa algorithm). Two conforming finite element methods are tested on different meshes. The second one uses a classical refinement in the shape function: the so-called bulb function. All computational tests show that the use of a bulb function on each element gives better results than refinement in the mesh without introducing too many degrees of freedom. Finally numerical results are compared to experimental data. 相似文献
127.
In the course of electrophilic cyclisation attempts, o-phenyltellurobenzoyl-chloride did not cyclise to telluroxanthone. but isomerised to 2-chloro tellurobenzophenone through intramolecular carbodetelluration. A breaking of the same Caromatic-Te bond is also realized by protonolysis. This last reaction leads to a preparative method of synthesis of ditellurosalicylic acid, a starting material for synthesis of benzocondensed tellurium heterocycles. 相似文献
128.
Philippe Faury Michel Camplo Anne-Sophie Charvet Nicolas Mourier Philippe Barthelemy Jean-Christophe Graciet Jean-Louis Kraus 《Journal of heterocyclic chemistry》1994,31(6):1465-1471
Synthetic approaches for new 2,5-disubstituted-1,3-thiazolidines are described. Steric and electronic effects of the N-substituent of the thiazolidine ring represent the major parameter in the rearrangement process. The nmr studies demonstrate that N-unsubstituted 2,5-disubstituted-1,3-thiazolidines exist as epimeric mixture, while the corresponding N-acetylated analogues exist as a conformer mixture. 相似文献
129.
Michel F Hamman S Thomas F Philouze C Gautier-Luneau I Pierre JL 《Chemical communications (Cambridge, England)》2006,(39):4122-4124
In copper(ii) complexes of tripodal ligands, the protonation state of the phenol moiety, and its position (axial vs. equatorial), are easily assessed by (19)F NMR. 相似文献
130.
Phase singularities of wave-front-like screw dislocations or vortices possess a well-defined quantity that can only take integer value: the topological charge. In the nonlinear regime, it has been demonstrated that optical or acoustical vortices interact and the topological charge follows a conservation law. Here this facility is used in nonlinear parametric interaction of two vortices shifted in frequency to perform sums and subtractions of the topological charge. Thus, we experimentally demonstrate a new technique to perform wave computation in the group of integer Z. When the two vortices have commensurable frequencies, different combinations give the same frequencies but different tolopological charges may occur. We show that an energy criterion can be used to predict the outcome. A corollary is that a modulation of amplitude of the vortices switches from one result to the other. 相似文献