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991.
研究了链状聚合物的长短键结构呈准周期排列的电子谱。利用紧束缚近似和转移矩阵方法通过理论证明和计算表明:这种准周期排列聚合物的电子谱,当长短键长度相差很小时,具有类似于金属晶体的能带结构;相差很大时,具有无序系统一维能级结构;而对于一般情形,其电子谱与上两者均异,形成所谓的类Cantor集。这3类不同的谱结构反映在链状聚合物的宏观物理性质上也将有所不同,它无疑会影响聚合物的稳定性及相关(超)导电性能,深入研究这方面问题将有助于对有机超导的认识。 相似文献
992.
1. PreliminaryIt is well known that{1] a 8ymPlectic form is invariant along the trajectory of a Hamilto-nian system. Based on this fundamental property, certain techniques have been developed.The purpose of this paper is to extend such an approach to a wider class of dynamic systeIns,namely, genera1ized Hamiltonian systems. Our purpose is to investigate a class of dynaInicsystems, which possess a certain "geometric structure".Deflnition 1.1[1'2]. Let M be a tIlallifo1d. w E fl'(M) is call… 相似文献
993.
The notion of -supplemented modules is a proper generalization of lifting modules. As a proper generalization of -supplemented modules, we introduce (D
12)-modules and obtain some properties, characterizations and decompositions of -supplemented modules and (D
12)-modules. 相似文献
994.
995.
Minzhao Xue Yangang Liu Deyin Huang Bin Gong 《Journal of chemical crystallography》2000,30(11):749-753
p-Formylphenyl, di(p-methylphenyl)amine (1), and p-bromophenyl, di(o-bromo-p-methylphenyl)amine (2) were prepared and characterized by X-ray crystallography. Formyl-substituted triphenylamine(1) crystallizes in the monoclinic space group P21/c with a = 9.068(1), b = 17.115(2), c = 11.297(2) Å, = 106.73(1)°, V = 1679.0(5) Å3 and Z = 4. Bromo-substituted compound 2 crystallizes in the monoclinic space group P21/n with a = 16.170(4), b = 7.9477(8), c = 16.906(4) Å, = 117.67(2)°, V = 1924.1(7) Å3 and Z = 4. The N atoms deviate slightly from the plane of the bonded C atoms and the benzene ring planes are rotated by 25–67° to avoid overlap of the ortho-substituted atoms. The major force of crystal formation comes from the multiple phenyl embraces (MPE). 相似文献
996.
In order to gain insight into the possible Ground State of Quantized Einstein's Gravity, we have derived a variational calculation of the energy of the quantum gravitational field in an open space, as measured by an asymptotic observer living in an asymptotically flat space-time. We find that for Quantum Gravity (QG) it is energetically favourable to perform its quantum fluctuations not upon flat space-time but around a "gas" of wormholes of mass m
p, the Planck mass (m
p 1019 GeV) and average distance l
p, the Planck length a
p(a
p 10–33 cm). As a result, assuming such configuration to be a good approximation to the true Ground State of Quantum Gravity, space-time, the arena of physical reality, turns out to be well described by Wheeler's quantum foam and adequately modeled by a space-time lattice with lattice constant l
p, the Planck lattice. 相似文献
997.
Xue QZ Xue QK Kuwano S Sadowski JT Kelly KF Sakurai T Ohno T 《Physical review letters》2000,84(17):4015
998.
Through quantum-beat spectroscopy collision relaxation of a high vibrational level of SO2 at 44 877.52 cm(-1) is characterized. This is a first measurement of collision relaxation for a single, highly excited vibrational level. The deduced relaxation cross section of this excited level by Ar is 216 A(2), 5 times the area of the hard sphere, and by an ambient temperature SO2 molecule is 969 A(2), almost 20 times the hard sphere. These cross sections indicate that relaxation collisions of highly vibrationally excited molecules have effective distances much longer than van der Waals radii and involve mechanisms qualitatively different from lower excitations. 相似文献
999.
Tong GL Varner GS Wang F Wang LS Wang LZ Wang M Wang P Wang PL Wang SM Wang TJ Wang YY Wei CL Wu N Wu YG Xi DM Xia XM Xie PP Xie Y Xie YH Xu GF Xue ST Yan J Yan WG Yang CM Yang CY Yang HX 《Physical review letters》2000,84(4):594-597
Using the upgraded Beijing Spectrometer, we have measured the total cross section for e(+)e(-) annihilation into hadronic final states at center-of-mass energies of 2.6, 3.2, 3.4, 3.55, 4.6, and 5.0 GeV. Values of R, sigma(e(+)e(-)-->hadrons)/sigma(e(+)e(-)-->&mgr;(+)&mgr;(-)), are determined. 相似文献
1000.
Ab initio molecular orbital calculations (Hartree–Fock, HF and density functional theories, DFTs) have been carried out for SiO2 polymorphs coesite, low cristobalite, and -quartz, in order to investigate the reliability of this method for predicting 29Si and 17O nuclear magnetic resonance (NMR) properties of silicates. Oxygen- and silicon-centered clusters consisting of one (1T) to three tetrahedral (3T) shells (one to four atomic shells), taken from real crystal structure, have been investigated. It is found that for reasonable predication of both the 29Si and 17O chemical shifts (δiSi and δiO), the minimum cluster is one that gives the correct second neighbors to the nucleus of interest. Both the δiSi and δiO have reached convergence with respect to cluster size at the OH-terminated two tetrahedral (2T) shell (three atomic shells around Si and four atomic shells around O) model. At convergence, the calculated δiSi values agree well (within ±1 ppm) with experimental data. The calculated 17O electric field gradient (EFG)-related parameters also agree with experimental data within experimental uncertainties. The calculation also reproduces small differences in δiO for O sites with similar tetrahedral connectivities, but shows deviations up to about 10 ppm in relative difference for O sites with different tetrahedral connectivities. The poor performance for the latter is mainly due to the approximations of the HF method. Our study thus suggests that the ab initio calculation method is a reliable mean for predicting 29Si and 17O NMR parameters for silicates. Such an approach should find application not only to well-ordered crystalline phases, but also to disordered materials, by combining with other techniques, such as the molecular dynamics simulation method. 相似文献