共查询到20条相似文献,搜索用时 15 毫秒
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The memory structure induced by coherent transitions to the exciton-exciton scattering continuum is shown to have significant influence on spectrally resolved four-wave-mixing signals even under selective excitation of 1s excitons. Comparisons between experiments and calculations that account nonperturbatively for these quantum kinetic Coulomb correlations demonstrate large compensations between mean-field contributions and transitions to the two-pair continuum. Experiments with different polarizations of the laser pulses show that two-pair continuum correlations are responsible for delay-time dependent shifts of the excitonic emission as well as for substantial deformations of the line shape. 相似文献
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The ground-state properties of spherical nuclei over the entire periodic table are investigated by the Skyrme-Hartree-Fock approach with new force parameters SKI4 [P. G. Reinhard and H. Flocard, Nucl. Phys. A584 467 (1995)] plus a density-dependent pairing correlation. By introducing the density-dependent pairing correlation in the Skyrme-Hartree-Fock model with SKI4, both the isospin degree of freedom and the nucleon-nucleon correlation have been suitably included in the theory. The theoretical results agree very well with experimental data of binding energies, single particle energies and radii of spherical nuclei. The isotope shifts of charge radii in Ca, Ni, Sn, and Pb are also well reproduced. 相似文献
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The ground-state properties of spherical nuclei over the entire periodic table are investigated by the Skyrme-Hartree-Fock approach with new force parameters SKI4 [P. G. Reinhard and H. Flocard, Nucl. Phys. A584 467 (1995)] plus a density-dependent pairing correlation. By introducing the density-dependent pairing correlation in the Skyrme-Hartree-Fock model with SKI4, both the isospin degree of freedom and the nucleon-nucleon correlation have been suitably included in the theory. The theoretical results agree very well with experimental data of binding energies, single particle energies and radii of spherical nuclei. The isotope shifts of charge radii in Ca, Ni, Sn, and Pb are also well reproduced. 相似文献
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We define the Jaumann derivative of a tensor field in relativity by a formal generalization of a stress rate in viscoelasticity. A tensor field is said to be Jaumann transported iff its Jaumann derivative vanishes. It is found that the gravitational potentials are Jaumann transported identically. The concept of a complete rotation tensor has been introduced to study the Jaumann derivative with respect to a null vector field. This provides a characterization of the integrability of a hypersurface orthogonal congruence. A perfect fluid collapsing by neutrino emission and undergoing Jaumann transport with respect to the neutrino flow is found to be compatible with that of a catastrophic collapse. The circumstances leading to the existence of ghost neutrinos are cited. The degeneracy of the Kerr-Newman black hole into the Reissner-Nordstrom black hole is expressed in terms of the Jaumann propagation. 相似文献
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A correlation function, the chemical potential, coefficients in a special Bogolyubov transformation, and single-quasiparticle energies were calculatedwith allowance for the effect of the monopole-pairing potential on the energies of single-particle nucleon states in the mean nuclear field. 相似文献
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The properties of the low-energy nuclear spectrum are greatly affected by pairing correlations. We study these effects in the nucleus 210Pb which has two particles moving outside closed shells. The configuration-mixed wave functions describe the motion of particles which are on the average closer together than they would be if the particles were confined to particular orbitals. Since the energy associated with pairing correlations is much smaller than the Fermi energy the width of the associated probability distribution is determined by the wavelength of single particles moving close to the Fermi surface. Despite the fact that the amplitudes associated with high-lying configurations are small, their net effect is important, typically changing the collectivity of the states by a factor of about two. The results of the microscopic calculations compare well with a semiclassical pairing transition density calculated on the basis of the Thomas-Fermi approximation. 相似文献
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A. K. Vlasnikov N. K. Kuzmenko V. M. Mikhailov A. S. Smirnov 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(4):582-586
Weak pairing correlations in aluminum nanograins have been investigated using a symmetrical polynomial method based on the
wave functions projected onto states with a fixed number of electrons. It is shown that this approach does not lead to a sharp
transition from the superconducting to normal state with an increase in temperature, and the intensity of the pairing correlations
exceeds that obtained using traditional BCS theory. 相似文献
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Journal of Applied Spectroscopy - 相似文献
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The quasiparticle resonances are investigated by examining three kinds of quasiparticle spectra, i.e., the density of quasiparticle states, the occupation number density, and the pair number density in the continuum Skyrme Hartree-Fock-Bogoliubov theory with the Green's function method. Taking the weakly bound nucleus ~(66)Ca as an example, the quasiparticle resonant energies and widths extracted from these three kinds of quasiparticle spectra are compared. For the narrow resonances, the extracted resonant energy and the width are consistent with each other. However, it is difficult to use the density of quasiparticle states to identify the broad resonances due to the background of nonresonant continuum. By switching off the pairing potential and/or the Hartree-Fock(HF) potential respectively in the calculation of these quasiparticle spectra, the roles of HF mean-field and pairing correlations in the quasiparticle resonances are demonstrated clearly. It turns out that all the quasiparticle resonances corresponding to the deeply bound, weakly bound and positive-energy single-particle resonant states, are mainly contributed by the HF potential. The pairing potential helps to slightly increase the resonant energy and the width. However, the pairing potential is important to make the nucleons occupy the low-lying nonresonant continuum states near the threshold and take part in the pairing correlations here,especially for the partial waves with small angular momentum ?. 相似文献
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The Kondo lattice model enlarged by an antiferromagnetic coupling J AF between the localized spins is here investigated using computational techniques. Our results suggest the existence of a d-wave superconducting phase close to half-filling mediated by antiferromagnetic fluctuations. This establishes a closer connection between theory and heavy fermion experiments than currently provided by the standard Kondo lattice model with J AF=0. 相似文献
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M. I. Gallardo S. M. Lenzi A. Vitturi 《Zeitschrift für Physik A Hadrons and Nuclei》1993,346(4):269-274
We study pairing correlations in deformed nuclei in the framework of the Nilsson+BCS theory. As in the spherical case, the pairing interaction is found to induce strong spacial correlations between the partners of each paired couple. The presence of the deformed mean field gives rise to a non-spherical pair field, whose deformation is governed by the properties of a few single-particle orbitals around the Fermi surface and does not necessarily follow the shape of the mean field. Multipole expansion of the pair field yields all the pair densities associated with the direct two-particle transfer processes to the members of the g.s. rotational band in the A+2 system. The interplay of the deformations of the mean and the pair fields can lead to different relative magnitudes and phases of these densities and therefore to different excitation patterns of the rotational bands in two-particle transfer reactions. In the case of non-collective twoquasiparticles and bands the associated pair densities display large components with high multipoles and the associated transfer processes may be favoured in heavy-ion collisions by kinematical conditions. Examples corresponding to both prolate and oblate cases are considered. 相似文献
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K. -H. Schmidt H. Delagrange J. P. Dufour N. Cârjan A. Fleury 《Zeitschrift für Physik A Hadrons and Nuclei》1982,308(3):215-225
A microscopic calculation of nuclear state densities was performed starting from realistic single-particle levels. Within this concept, a correspondence between microscopic ground state energy corrections and microscopic effects on state densities was deduced. It is shown that the approximations introduced by a simple analytical expression for the nuclear state density are comparable to the uncertainties of microscopically calculated state densities for nuclei in their ground state configuration. Guidelines for the determination of the parameters of this analytical expression were deduced from the microscopic computations. 相似文献
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《中国物理C(英文版)》2015,(10)
Within the relativistic mean field(RMF) theory, the ground state properties of dysprosium isotopes are studied using the shell-model-like approach(SLAP), in which pairing correlations are treated with particlenumber conservation, and the Pauli blocking effects are taken into account exactly. For comparison, calculations of the Bardeen–Cooper–Schrieffer(BCS) model with the RMF are also performed. It is found that the RMF+SLAP calculation results, as well as the RMF+BCS ones, reproduce the experimental binding energies and one- and twoneutron separation energies quite well. However, the RMF+BCS calculations give larger pairing energies than those obtained by the RMF+SLAP calculations, in particular for nuclei near the proton and neutron drip lines. This deviation is discussed in terms of the BCS particle-number fluctuation, which leads to the sizable deviation of pairing energies between the RMF+BCS and RMF+SLAP models, where the fluctuation of the particle number is eliminated automatically. 相似文献