共查询到20条相似文献,搜索用时 15 毫秒
1.
By studying the energy of neutron star matter, we discuss the nuclear symmetry energy at different baryon densities and different coupling constants in the relativistic mean field approximation. The results show that the symmetry energy increases with baryon density at various coupling constants and incompressibilities. Further-more, the symmetry energy at saturation density increases with increasing incompressibility at fixed d, and decreases at fixed c. Specifically, when coupling constants gv and gs are fixed, respectively, the symmetry energy has a little change with increasing incompressibility. It is demonstrated that the NN coupling constants have greater influences on the symmetry energy than the self-coupling constants. 相似文献
2.
In paramagnetic aromatic systems the relation between the hyperfine coupling constants a H for the protons and the spin density ρ on the adjacent carbon atom is usually given by the relation a H = -Qρ (McConnell) in which Q is a constant characteristic for the C-H bond. In the paramagnetic ions of aromatic molecules the carbon atoms have in general besides a non-zero spin density also a non-zero excess charge density. If one takes into account both the effect of the spin density ρ and the excess charge density ε on the C-H bond, the following formula is obtained for the proton hyperfine coupling constant: in which Q and K are predicted to be positive constants of the same order of magnitude. Comparison with experimental data gives Q = 31·2 gauss; K = 17 gauss. 相似文献
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A theoretical study is presented of the effects of solvent molecular motion on nuclear spin-spin coupling constants. Solvent molecules are treated as point dipoles arranged around the solute molecule in a cubic closest packed arrangement. Average dipole moment vectors are given by a rotational Boltzmann average and the resulting perturbation is included in the Fock matrices. Calculations of nuclear spin-spin coupling constants were performed by self-consistent perturbation theory in the INDO (intermediate neglect of differential overlap) approximation of self-consistent-field molecular orbital theory. Calculated results are compared with the experimental data as well as the results of previous models. 相似文献
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Assuming theV-A theory, fully polarized neutrinos, and lepton conservation, best values of the vector and axial vector coupling constants are deduced from all available data on neutron decay and from theft- values of14O,26mAl and34C1. Special consideration is given to the treatment of errors and to radiative corrections. For the determination of the coupling constantratio, radiative corrections are, at present, unimportant. We find ¦GA/GV¦=1.250 + 0.009 with a phase angle φ=(181.1±1.3)0. From the weighted mean ?t-value, including charge dependent and “outer” radiative corrections, we find an effective coupling constant G′V=(1.413±0.002)x 1049erg cm3. The error is mainly due to the uncertainty of charge dependent corrections. 相似文献
6.
The use of ab initio Hartree-Fock electric field gradient calculations to predict nitrogen nuclear quadrupole coupling constants is examined using basis sets of split valence to triple zeta plus polarization size. From results on 20 to 35 molecules for each basis, such calculations are shown to be of predictive value if systematic errors are eliminated by using regression-derived scaling factors, and the reliability of each basis is assessed. For field gradient calculations on larger molecules, a significantly better alternative to a minimal basis which adds little extra computational cost, is proposed. 相似文献
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利用自然杂化轨道,以从头算级别的理论计算方法,选择较小基组STO-3G,研究了C-P(V)键的核自旋偶合常数,并用三种化合物进行验证,理论计算值较好地与文献值相符合. 相似文献
8.
The problem of computing spin-orbit coupling constants from wave-functions of a semi-empirical variety are considered specifically for SCF wavefunctions with intermediate neglect of differential overlap. The incorporation of the 1s electrons into a ‘core’ should result in an effective nuclear charge of Z′ = Z - 2·5846 being used in one-electron terms, but for agreement with experiment the results have to be reduced by some 70 per cent. This reduction factor is different for ions. If the multiplicative factor is included good agreement between observed and calculated spin-orbit coupling constants is given. 相似文献
9.
The scalar-isoscalar term in the two-pion exchange NN potential is abnormally large and does not respect the hierarchy of effects predicted by chiral perturbation theory. We argue that this anomaly is associated with non-perturbative effects, which are also present in the πN scalar form factor. 相似文献
10.
The Pauli principle requires nuclear wavefunctions to be antisymmetrized on the quark level. For a properly antisymmetrized wavefunction compared with a conventional nuclear wavefunction this means the introduction of quark-exchange terms. We included dinucleonic quark-exchange terms in the wavefunctions of p-shell nuclei and calculated observables. In the charge form factor the quark exchanges dominate for high momentum transfer. For heavier nuclei the importance of the quark-exchange contributions decreases. 相似文献
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Calculations of the proton and neutron charge form factors GEp,n(q2) are presented, based on chiral bag as well as confining Dirac potential models with chiral pion-quark coupling. Special emphasis is placed on a detailed treatment of the charged pion cloud contribution to the nucleon current. The role of a finite extension of the pion-quark vertex in truncating the summation over intermediate quark bag states is studied. Quark core radii (including recoil corrections) are constrained by a simultaneous calculation of the nucleon axial form factor. The proton charge form factor is well reproduced for with quark core rms radii between 0.5–0.6 fm. About of the proton charge is carried by the pion cloud in this model. The neutron charge form factor is obtained with the correct sign and overall q2 dependence but needs further refinements, probably at the level of the isoscalar form factor. 相似文献
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The complete world set of parity-violating electron scattering data up to Q2 approximately 0.3 GeV2 is analyzed. We extract the current experimental determination of the strange electric and magnetic form factors of the proton, as well as the weak axial form factors of the proton and neutron, at Q2=0.1 GeV2. Within experimental uncertainties, we find that the strange form factors are consistent with zero, as are the anapole contributions to the axial form factors. Nevertheless, the correlation between the strange and anapole contributions suggest that there is only a small probability that these form factors all vanish simultaneously. 相似文献
15.
Gerald D Fong Robert L Kuczkowski Arthur J Ashe 《Journal of Molecular Spectroscopy》1978,70(2):197-208
The microwave spectrum of 121-SbC5H5, 123-SbC5H5, β-dideutero 121-SbC5H3D2 and 123-SbC5H3D2 has been assigned in the region 26.5–40.0 GHz. The respective rotational constants and uncertainties are: A = 4512.69 ± 0.42, B = 1738.00 ± 0.01, C = 1254.51 ± 0.01; A = 4512.84 ± 0.30, B = 1729.80 ± 0.01, C = 1250.22 ± 0.01; A = 4176.18 ± 0.33, B = 1660.94 ± 0.01, C = 1188.15 ± 0.01; A = 4176.60 ± 0.61, B = 1652.94 ± 0.03, C = 1184.03 ± 0.03 (in MHz units). The structure is found to be planar, C2v in symmetry. The and ∠CSbC = 92.9° ± 1.0°. The nuclear quadrupole coupling constants for the 121 and 123 antimony isotopes are χaa = 456.4 ± 4.1 MHz, η = 0.396 ± 0.008, and χaa = 583.00 ± 5.3 MHz, η = 0.399 ± 0.008, respectively. Several alternate techniques using the coupling constants as data support a σ-donating property for antimony. 相似文献
16.
Deep inelastic scattering data on the F
2 structure function provided by the BCDMS, SLAC, and NMC Collaborations are analyzed in the nonsinglet approximation with
the analytic and “frozen” modifications of the strong-coupling constant featuring no unphysical singularity (the Landau pole).
Improvement of agreement between theory and experiment, with respect to the case of the standard perturbative definition of
α
s
considered recently, is observed and the higher-twist terms are shown to reduce at the next-to-next-to-leading order accuracy
thus confirming earlier studies. 相似文献
17.
The presence of meson exchange currents in the tri-nucleon system is shown to modify significantly the charge form factor of 3He in the region of the dip and the secondary maximum. As a result the form factor is considerably changed at high momentum transfer. 相似文献
18.
R. Yu. Babkin K. V. Lamonova S. M. Orel Yu. G. Pashkevich V. F. Meshcheryakov 《Optics and Spectroscopy》2012,112(3):438-442
We propose a scheme for determining the effective nuclear charge Z
efCF of a 3d ion placed in a crystal field of arbitrary symmetry. As an example, we consider the Co2+ ion in a matrix MCO3 (M = Ca, Cd). We show that the effective nuclear charge Z
efCF correlates with a change in the degree of the bond covalence. 相似文献
19.
K. Jackowski 《Applied magnetic resonance》2003,24(3-4):379-385
Intermolecular interactions modify nuclear magnetic resonance (NMR) chemical shifts and spin-spin coupling constants. The intermolecular effects can be determined if the NMR parameters for an isolated molecule are known. Gas-phase NMR spectroscopy offers such methods which allow one to measure the shielding and spin-spin coupling constants at the zero-density limit where the NMR parameters are free from intermolecular contributions. It is also shown that at present the multinuclear NMR spectra can easily be obtained for gaseous samples containing several micrograms of a solute compound. 相似文献