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排序方式: 共有484条查询结果,搜索用时 31 毫秒
71.
72.
A. Lopez M. M. Gauthier R. Martino A. Lattes 《Magnetic resonance in chemistry : MRC》1979,12(7):418-428
Although nitrogen inversion in unsubstituted aziridines has been shown by 1H NMR, it was only possible to study quantitatively the distribution of both invertomers and determine the thermodynamic parameters by a systematic high field NMR study (CAMECA 250 MHz). Thermodynamic parameters have been determined for 32 compounds. In C-aryl aziridines, the steric hindrance of the aromatic group and its variation with other aziridine ring substituents can be studied. These observations are in agreement with a conjugation phenomenon between the aromatic system and the aziridine ring. 相似文献
73.
Exactly soluble two-body two-channel problems are set up with separable potentials. Resonance is defined theoretically then the empirical resonance recognition criteria used in two-body data analyses are tested. Results are summarized in the last section of the paper. 相似文献
74.
During a study of neutralization luminescence following photoionization of aromatic solutes in rigid organic glasses, a new type of long-lived luminescence has been observed simultaneously with the well-known neutralization luminescence following biphotonic ionization. It has been extensively studied for tetramethyl-p-phenylenediamine in methylcyclohexane or ethanol: it is one-photon excited but differs from the ordinary luminescence by the emission spectrum (λmax 430 nm compared to λmax f. 395 nm and λmax ph. 490 nm in ethanol) and by the excitation spectrum, the present luminescence being observed only for short wavelength excitation. Finally the lifetime (of the order of seconds) depends on experimental conditions. Other solid and liquid phase studies suggest that the precursor of this new luminescence is a solute-solvent charge transfer state. 相似文献
75.
R. C. Gauthier 《Optics & Laser Technology》1993,25(5)
In this paper the power coupling expression between two identical axially aligned and spatially separated waveguides is presented. Calculations using the coupling expression for a Gaussian mode profile in the input waveguide produce results that are in excellent agreement with experimental observations. 相似文献
76.
Vanhaelewyn GC Pauwels E Callens FJ Waroquier M Sagstuen E Matthys PF 《The journal of physical chemistry. A》2006,110(6):2147-2156
Beta-D-fructose single crystals were in situ X-irradiated at 80 K and measured using electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR) and ENDOR-induced EPR (EIE) techniques at Q-band (34 GHz) microwave frequencies. The measurements revealed the presence of at least four carbon-centered radicals stable at 80 K. By means of ENDOR angular variations in the three principal crystallographic planes, six proton hyperfine coupling tensors could be determined and were assigned to four different radicals by the aid of EIE. Two of the radicals exhibit only beta-proton hyperfine couplings and reveal almost identical EIE spectra. For the other two radicals, the major hyperfine splitting originates from a single alpha-proton hyperfine coupling and their EIE spectra were also quite similar. The similarity of the EIE spectra and hyperfine tensors led to the assumption that there are only two essentially different radical structures. The radical exhibiting only beta-proton hyperfine couplings was assigned to a C3 centered radical arising from H3 abstraction and the other radical suggested to be an open-ring species with a disrupted C2-C3 bond and a double C2-O2 bond. A possible formation mechanism for the latter open-ring radical is presented. By means of cluster density functional theory (DFT) calculations, the structures of the two radicals were determined and a fairly good agreement between the calculated and experimental hyperfine tensors was found. 相似文献
77.
The Pd8Ni92(1 1 1) surface was studied using low-energy electron diffraction (LEED). IV spectra collected close to normal incidence were analysed by dynamical tensor LEED. Composition and interlayer spacings were determined for first four atomic layers. The surface slab is found to be enriched in Pd (30% in total against 8% in bulk) but this extra palladium is irregularly distributed over the four topmost layers. Contrary to previous reports, the palladium amount, as compared to the bulk, is not significantly changed in the surface layer and it is enriched to 20% only in the third layer. The detected contractions of interlayer spacings are all but one (d34) within the error limits of no contraction at all. We also discuss some aspects of correlations between the fit parameters. 相似文献
78.
Nguyen Vi Cao Emmanuel Fragnière Jacques-Antoine Gauthier Marlène Sapin Eric D. Widmer 《European Journal of Operational Research》2010
Research shows that the success of marriages and other intimate partnerships depends on objective attributes such as differences in age, cultural background, and educational level. This article proposes a mathematical approach to optimizing marriage by allocating spouses in such a way as to reduce the likelihood of divorce or separation. To produce our optimization model, we use the assumption of a central “agency” that would coordinate the matching of couples. Based on a representative and longitudinal sample of 1074 cohabiting and married couples living in Switzerland, we estimate various objective functions corresponding to age, education, ethnicity, and prior divorce concerning every possible combination of men and women. Our results show that the current state of marriages or partnerships is well below the social optimum. We reallocate approximately 68% of individuals (7 out of 10) to a new couple that we posit has a higher likelihood of survival. From this selection of new partners, we obtain our final “optimal” solutions, with a 21% reduction in the objective function. 相似文献
79.
We create optical precursors by propagating a step-modulated optical pulse through a linear resonant dielectric absorber. The field emerging from the dielectric consists of a several-nanosecond-long spike with near 100% transmission, which decays to a constant value expected from Beer's law. This high-transmission spike might be useful for imaging applications requiring penetrating optical radiation. We compare our observations to two different theories, revealing that the spike consists of both the Sommerfeld and Brillouin precursors. 相似文献
80.
Seok Il Yun Lan Cao Tae-Beom Kang Mongyoung Huh Mario Gauthier 《Journal of Macromolecular Science: Physics》2013,52(12):2318-2333
Arborescent (dendrigraft) copolymers with a branched polystyrene (PS) core grafted at the chain termini with deuterated poly(ethylene oxide) segments (PS-dPEO) were characterized in benzene and acetone by small-angle neutron scattering measurements using the contrast matching technique. While copolymers incorporating a G1 (twice-grafted) PS core aggregated to some extent, the portion of the scattering curve corresponding to non-aggregated copolymer molecules could still be analyzed to determine the shape and segment radial density profile for core and shell. These were derived from the pair distance distribution function P(r) and the scattering length density contrast profile Δρ(r) = ρ(r) ? ρ(solvent), obtained by the indirect Fourier transformation and deconvolution methods. The profiles obtained for the G1 copolymer are consistent with a well-defined PS core–dPEO shell morphology, only observed previously for upper generation (G4) polymers with deuterated PS (dPS) chains grafted randomly on arborescent PS substrates. Detailed morphological analysis could not be carried out for an analogous G3 arborescent PS copolymer terminally grafted with dPEO segments due to extensive aggregation in both solvents. 相似文献