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排序方式: 共有117条查询结果,搜索用时 46 毫秒
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S. Zaric G. N. Ostojic A. D. Engroff J. Kono J. Shaver V. C. Moore M. S. Strano R. H. Hauge R. E. Smalley X. Wei 《Superlattices and Microstructures》2003,34(3-6):413
We have carried out magneto-absorption and magneto-photoluminescence experiments on micelle-suspended single-walled carbon nanotubes in magnetic fields up to 45 T. Chirality-assigned spectral peaks exhibit significant changes with increasing magnetic field, which can be quantitatively explained in terms of the theoretically predicted splittings and redshifts of the band edge due to the Aharonov–Bohm effect combined with the magnetic-field-induced alignment of the nanotubes. 相似文献
73.
Larry L. Smalley 《Physics letters. A》1977,61(7):436-438
The variation of the field action with the scalar Lagrangian density is calculated with respect to the metric, torsion and non-metricity. When the non-metricity vanishes, the variation reduces to the U4 theory of gravitation when a relativistic matter Lagrangian with minimal coupling is included. 相似文献
74.
The OO band of the B←X visible spectrum of iodine has been observed in spite of its very small Franck-Condon factor. The expected satelite band of the van der Waals molecule HeI2 was not observed, and a mechanism is suggested to account for the absence of the van der Waals spectrum. 相似文献
75.
Friedrich W. Hehl Eric A. Lord Larry L. Smalley 《General Relativity and Gravitation》1981,13(11):1037-1056
We continue our investigation of a variational principle for general relativity in which the metric tensor and the (asymmetric) linear connection are varied independently. As in Part I, the matter Lagrangian is minimally coupled to the connection and the gravitational Lagrangian is taken to be the curvature scalar, but we now relax the Riemannian constraint as far as possible—that is, as far as the projective invariance of the assumed gravitational Lagrangian will allow. The outcome of this procedure is a gravitational theory formulated in a volume-preserving space-time (i.e., with torsion and tracefree nonmetricity). The vanishing of the trace of the nonmetricity is due to the remaining vector constraint. We also discuss the physical significance of the relaxation of the Riemannian constraint, the possible relaxation of the vector constraint, the notion of the hypermomentum current, and its possible relation to elementary particle physics. 相似文献
76.
Larry L. Smalley 《Foundations of Physics》1978,8(1-2):59-68
The parametrized post-Newtonian (PPN) approximation is generalized to accommodate Rastall's modification of Einstein's theory of gravity, which allows nonzero divergence of the energy-momentum tensor. Rastall's theory is then shown to have consistent field equations, gauge conditions, and the correct Newtonian limit of the equations of motion. The PPN parameters are obtained and shown to agree experimentally with those for the Einstein theory. In light of the nonzero divergence condition, integral conservation laws are investigated and shown to yield conserved energy-momentum and angularmomentum. We conclude that the above generalization of metric theories, within the PPN framework, is a natural extension of the concept of metric theories.Recipient of an Alexander von Humboldt Foundation fellowship. 相似文献
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Anderson RE Colorado R Crouse C Ogrin D Maruyama B Pender MJ Edwards CL Whitsitt E Moore VC Koveal D Lupu C Stewart MP Smalley RE Tour JM Barron AR 《Dalton transactions (Cambridge, England : 2003)》2006,(25):3097-3107
The synthetic conditions for the isolation of the iron-molybdenum nanocluster FeMoC [HxPMo12O40 [subset]H4Mo72Fe30(O2CMe)15O254(H2O)98], along with its application as a catalyst precursor for VLS growth of SWNTs have been studied. As-prepared FeMoC is contaminated with the Keplerate cage [H4Mo72Fe30(O2CMe)15O254(H2O)98] without the Keggin [HxPMo12O40]n- template, however, isolation of pure FeMoC may be accomplished by Soxhlet extraction with EtOH. The resulting EtOH solvate is consistent with the replacement of the water ligands coordinated to Fe being substituted by EtOH. FeMoC-EtOH has been characterized by IR, UV-vis spectroscopy, MS, XPS and 31P NMR. The solid-state 31P NMR spectrum for FeMoC-EtOH (delta-5.3 ppm) suggests little effect of the paramagnetic Fe3+ centers in the Keplerate cage on the Keggin ion's phosphorous. The high chemical shift anisotropy, and calculated T1 (35 ms) and T2 (8 ms) values are consistent with a weak magnetic interaction between the Keggin ion's phosphorus symmetrically located within the Keplerate cage. Increasing the FeCl2 concentration and decreasing the pH of the reaction mixture optimizes the yield of FeMoC. The solubility and stability of FeMoC in H2O and MeOH-H2O is investigated. The TGA of FeMoC-EtOH under air, Ar and H2 (in combination with XPS) shows that upon thermolysis the resulting Fe : Mo ratio is highly dependent on the reaction atmosphere: thermolysis in air results in significant loss of volatile molybdenum components. Pure FeMoC-EtOH is found to be essentially inactive as a pre-catalyst for the VLS growth of single-walled carbon nanotubes (SWNTs) irrespective of the substrate or reaction conditions. However, reaction of FeMoC with pyrazine (pyz) results in the formation of aggregates that are found to be active catalysts for the growth of SWNTs. Activation of FeMoC may also be accomplished by the addition of excess iron. The observation of prior work's reported growth of SWNTs from FeMoC is discussed with respect to these results. 相似文献