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1.
We treat here of the question of absorbing boundary conditionsfor nonlinear diffusion equations. We use the conditions designedfor the linear equation, we prove them to be well posed forthe nonlinear problem, and through numerical experiments thatthey are well suited for reactiondiffusion equations. 相似文献
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Wytko JA Michels M Zander L Lex J Schmickler H Vogel E 《The Journal of organic chemistry》2000,65(25):8709-8714
In connection with a study aimed at the evaluation of electronic effects in spiro-dicorrole (1a) and its binuclear Ni(II) complex (1b) we became interested in gem-dimethyl-substituted cyclotetrapyrrole (2a) and the corresponding Ni(II) complex (2b). Attempts to prepare 2a as the 12,13,16,17-tetraethyl-2,3,7, 8-tetramethyl derivative (5) by an acid-catalyzed (1 + 1) condensation of dimethyldipyrrylmethane 3 and diformylbipyrrole 4 resulted in the formation of the (2 + 2) and (3 + 3) condensation products, i.e., the cyclooctapyrrole 6 and the cyclododecapyrrole 7, respectively, rather than in that of the desired gem-dimethyl cyclotetrapyrrole. The cyclododecapyrrole 7, isolated as the major product, is among the largest cyclopolypyrroles known to date. These two new macrocycles have been structurally characterized by variable temperature 1D and 2D NMR experiments, as well as by single-crystal X-ray diffraction analysis. In solution both the cyclooctapyrrole 6 and cyclododecapyrrole 7 exhibit dynamic behavior. At 337 K 6 adopts a D(2)-symmetric conformation, whereas at 196 K two equivalent C(2) conformers that interconvert through the D(2)-symmetric intermediate are observed. The energy barrier for the interconversion process between these two degenerate conformers is found to be 10.6 kcal mol(-)(1). The solution dynamics of 7 could be described in an analogous manner, with the time-averaged conformation at 378 K displaying D(3)(h)() symmetry. X-ray analyses showed that for both macrocycles, 6 and 7, the solid state structures were nearly identical to the low-temperature solution conformers. 相似文献
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Based on the phenomenon of freezing point depression of a solvent byT, experimental evidence is presented to show that the distance between the junction points can be calculated fromT. Direct measurements of the temperature-time-curve of the cooling network and the Differential Scanning Calorimetry offer the determination ofT. Except the mean distances ¯d
c
in dependence on cross-linking density, swelling degree, and other network parameters, the distribution of the distance between the junction pointsH(dc) can be determined, which allows conclusions on the course of cross-linking reaction. This paper attempts to give experimental evidence of influences of the breadth ofH(dc) on application-relevant properties. 相似文献
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The fluorescence of perylene in alcoholic solution is dynamically quenched by AgClO4 resulting in a new emission band with its maximum around 480 nm. Analysis of fluorescence decay curves at various emission wavelengths proves the formation of a perylene/Aa+ ion exciplex in the quenching reaction. 相似文献
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Rate constants of fluorescence quenching by electron acceptors are greater for alternant than for non-alternant hydrocarbons with equal Eoo. The reverse is true for quenching by electron donors. This is consistent with the lowering of the π-orbital energies of non-alternant compared to alternant polycyclic hydrocarbons of equal Eoo. 相似文献
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C. A. Peridier J. L. Matthews M. J. Leitch H. Jeremie M. Irshad B. L. Roberts 《Zeitschrift für Physik A Hadrons and Nuclei》1983,310(4):317-328
The cross section for the3He(γ, 2p) reaction has been measured in a complete kinematics experiment in the energy rangeE γ=80–170 MeV, forθ P1=θ P2=90°. This configuration was selected in order to investigate the role of proton-proton final state interactions in the three-body breakup process. The measured proton spectra are seen to be consistent with a prediction using the Watson-Migdal formalism. The magnitude of the observed cross section clearly indicates an enhancement over phase space, presumably due to the strong proton-proton interaction in the final state. The experimental results agree, within their limited statistical accuracy, with a theoretical calculation which includes this effect. 相似文献