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91.
By using pressure to vary the extent of nontetrahedral distortions of the Cr4+ site in Mg2SiO4, we reveal the important influence of the 3T1 state on the emission properties of the 3T2 state. We find that 3T1-3T2 mixing has a pronounced effect on the line shape and radiative decay rate of emission from the 3T2 state and that the extent of mixing depends critically on the magnitude of nontetrahedral distortions. The results provide an explanation for the wide variation of Cr4+ emission properties in different host lattices at ambient pressure and indicate that the tailoring of asymmetric distortions of luminescent centers represents an effective new strategy for tuning the linewidth of spectral transitions. 相似文献
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10B NMR studies have been carried out on lithium borate glasses over the entire glass-forming region of the system. Using the ideas of Krogh-Moe, the relative abundances of the various structural groupings are inferred from the data by fitting computer-simulated lineshapes to the experimental spectra. Structural model are proposed which are consistent with the data: for 0.4 R < 1.0, where R = mol% Li2O/mol% B2O3, the model states that diborate and tetraborate units are proportionately destroyed to form metaborate units and loose BO4 units; for 1.0 < R < 1.86, the model states that metaborate units and loose BO4 units are destroyed linearly but not proportionately to form pyroborate and orthoborate units. These results are compared with earlier 11B NMR studies from this laboratory. 相似文献
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K.H. Bray Mahavir jain K.S. Jayaraman G. LobiancoG.A. Moss W.T.H. Van OersD.O. Wells 《Nuclear Physics A》1972
The elastic and inelastic scattering of protons from 6Li has been studied at incident energies of 25.9, 29.9, 35.0, 40.1 and 45.4 MeV. The 2.18 MeV (3+, T = 0) first excited state of 6Li was found to be strongly excited, but the 3.56 MeV (0+, T = 1) second excited state was quite weakly excited. Angular distributions for excitation of the 2.18 MeV level were measured at all five energies, while angular distributions for excitation of the 3.56 MeV level were extracted only at 25.9 and 45.4 MeV. To test the applicability of the optical model for the scattering of protons from such a light nucleus the elastic scattering angular distributions have been analyzed using the eleven-parameter search code SEEK. Available polarization angular distributions were included in the analysis. Reasonable fits to the data have been obtained with an average geometry potential. Theoretical estimates of the real part of the optical potential and the inelastic scattering differential cross sections have been made using the microscopic model for proton-nucleus scattering. Both phenomenological and realistic forces have been considered and the necessary nuclear transition densities have been extracted from experimental elastic and inelastic electron scattering data. An estimate of a possible spin-spin term in the optical potential has also been made. 相似文献
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Rayleigh and Lamb waves have been excited in scale model railway wheels by an ultrasonic source located on the wheel tread. Simulated flaws in treads and plates have been located. 相似文献
100.
L.S. Smith E. Ehrenfreund A.J. Heeger L.V. Interrante J.W. Bray H.R. Hart I.S. Jacobs 《Solid State Communications》1976,19(4):377-380
Nuclear relaxation studies of the spin-Peierls transition in TTF-BDT are presented. At low temperature, but above Tc, the results agree in magnitude, frequency dependence and temperature dependence with calculations based on the pseudofermion treatment of the , 1-D Heisenberg antiferromagnet. The sharp decrease in the rate below Tc reflects the continuous opening of a magnetic energy gap at the spin-Peierls transition. 相似文献