单极巨共振弛豫过程

用BNV方程讨论了中能重离子反应形成的热核单极巨共振(GMR)的驰豫过程.计算表明,球形热核GMR振荡是各向同性的,共振能与E_GMR=80A^－1/3公式给出的数值基本一致.核子碰撞和粒子逃逸是引起热核GMR阻尼衰减的主要原因.     

雪茄形铷原子玻色-爱因斯坦凝聚中单极子模的朗道阻尼和频移

采用含时哈特里-福克-博戈留波夫近似研究雪茄形铷原子玻色-爱因斯坦凝聚中单极子模的朗道阻尼和频移. 通过考虑元激发的实际弛豫及其各弛豫间的正交关系改进原有方法, 并由此给出计算朗道阻尼和频移的新公式. 此外, 令凝聚体边界处动能密度为零代替令基态能量极小以改进原消除三模耦合矩阵元的方法. 通过这些改进, 同时计算阻尼和频移, 并讨论它们的温度依赖, 所得理论结果都与实验符合. 关键词： 玻色-爱因斯坦凝聚 朗道阻尼和频移 哈特里-福克-博戈留波夫近似 托马斯-费米近似     

Collisional damping of giant monopole and quadrupole resonances

Collisional damping widths of giant monopole and quadrupole excitations for ¹²⁰Sn and ²⁰⁸Pb at zero and finite temperatures are calculated within Thomas-Fermi approximation by employing the microscopic in-medium cross-sections of Li and Machleidt and the phenomenological Skyrme and Gogny forces, and are compared with each other. The results for the collisional widths of giant monopole and quadrupole vibrations at zero temperature as a function of the mass number show that the collisional damping of giant monopole vibrations accounts for about 30 - 40% of the observed widths at zero temperature, while for giant quadrupole vibrations it accounts for only 20 - 30% of the observed widths at zero temperature. Received: 9 January 2001 / Accepted: 29 March 2001     

Finite Temperature Self-Consistent Semiclassical Approach to the Incompressibility of Hot Nuclei

The self-consistent semiclassical approach is extended from zero temperature to finite temperatures. The nucleon densities of a hot nucleus at thermal equilibrium are determined. The centroids of isoscalar giant monopole resonances(GMR) are evaluated by making use of these densities with sum rules. The incompressibility of hot nuclei is studied with these centroids. It is found that the incompressibility decrepes as the temperature increases. A non-self-consistent finite temperature semiclassical approach with a Woods-Saxon mean field is also presented and compared with the self-consistent result.     

Solution of the Vlasov equation for compressed and heated spherical nuclei

The Vlasov equation is solved for spherical nuclei. The properties of the monopole vibrations are studied at zero temperature. A sudden heating of the system is also considered with the sequential deexcitation of the nucleus. A flash temperature higher than in corresponding static calculations is found. Typical evolutions of simultaneously compressed and heated nuclei are sketched.     

The isovector monopole state and the escape width of double analog resonances

An irreducible vector operator is used to generate isovector monopole states with welldefined values of T and T_z in N > Z nuclei. Reduced transition strengths are calculated in two different ways and the results seem compatible. The Wigner-Eckart theorem is used to derive expressions for the mixing of the monopole states with the ground state and its analog states. Expressions for the escape widths of the monopole states are also derived. An application is made to double analog resonances, and it is found, contrary to expectations, that the mixing with the T?1 monopole state is unable to account for the observed elastic partial width of these resonances in medium and heavy nuclei. The reason for this is the small escape width of the monopole state.     

On the vibrational spectrum of a parallel dislocation array

The free vibrations of dislocation arrays of different types (monopole and dipole dislocation walls and a planar dislocation array) have been investigated on the basis of the dispersion equation derived within the self-consistent dynamic theory of dislocations. The relaxation spectrum of a planar dislocation array in the strong damping mode has also been analyzed.     

Landau damping of collective modes in a harmonically trapped Bose--Einstein condensate

This paper proposes a method for calculating the Landau damping of a low-energy collective mode in a harmonically trapped Bose--Einstein condensate. Based on the divergence-free analytical solutions for ground-state wavefunction of the condensate and eigenvalues and eigenfunctions for thermally excited quasiparticles, obtained beyond Thomas--Fermi approximation, this paper calculates the coupling matrix elements describing the interaction between the collective mode and the quasiparticles. With these analytical results this paper evaluates the Landau damping rate of a monopole mode in a spherical trap and discusses its dependence on temperature, particle number and trapping frequency of the system.     

Collisionless Landau damping and stimulated compton scattering

Stimulated scattering by free electrons is first studied within a quantum model due to Schroedinger and subsequently within a classical “hydrodynamical” picture. In the latter case, it can be shown that a method initially introduced by Landau to study the damping of electronic vibrations in plasmas is well suited to this problem and provides a precise analysis of the experimental results recently obtained by a Stanford group.     

Effects of Landau damping and collision on stimulated Raman scattering with various phase-space distributions

Stimulated Raman scattering (SRS) is one of the main instabilities affecting success of fusion ignition. Here, we study the relationship between Raman growth and Landau damping with various distribution functions combining the analytic formulas and Vlasov simulations. The Landau damping obtained by Vlasov-Poisson simulation and Raman growth rate obtained by Vlasov-Maxwell simulation are anti-correlated, which is consistent with our theoretical analysis quantitatively. Maxwellian distribution, flattened distribution, and bi-Maxwellian distribution are studied in detail, which represent three typical stages of SRS. We also demonstrate the effects of plateau width, hot-electron fraction, hot-to-cold electron temperature ratio, and collisional damping on the Landau damping and growth rate. They gives us a deep understanding of SRS and possible ways to mitigate SRS through manipulating distribution functions to a high Landau damping regime.     

Fermi liquid theory and giant resonances in nuclei

Landau's theory of collective motion in Fermi systems is applied to the giant resonances in nuclei. It is shown that the restoring forces associated with these modes can be simply expressed in terms of local Landau parameters. Explicit expressions are given for the energies of the monopole and quadrupole modes. The validity of this approach is briefly discussed.     

“Radius” model of baryon couplings

The systematic predictable effects of self-consistency in particle-hole calculations are examined. It is shown that self-consistent radial wave functions are essential for monopole excitations and that self-consistency in deformation is vital for the quadrupole and other vibrations of deformed nuclei.     

Scaling- and antiscaling-type oscillations in isoscalar and isovector nuclear monopole vibrations

Isoscalar (T = 0) and isovector (T = 1) giant monopole resonances are studied using a localscale version of the ATDHF theory developed on the basis of a rigorous energy-density functional approach. Due to the strong coupling between the bulk and surface density vibrations, the monopole collective motion is split into four normal modes. Two of them, lower in energy, correspond to scaling-type density vibrations. The other two are of antiscaling-type in which the nuclear surface oscillates opposite in phase to the scaling-type vibrations. Excitation energies, transition densities, T = 0 and T = 1 energy weighted sum rules and other properties of breathing even-even nuclei are calculated using different Skyrme-type effective forces. The strong sensitivity of the antiscaling-type vibrations to the particular form of the approximate energy-density functionals is demonstrated.     

球对称铷原子玻色-爱因斯坦凝聚中单极子模的朗道阻尼和频移

采用含时哈特里-福克-博戈留波夫近似研究球对称铷原子玻色-爱因斯坦凝聚中单极子模的朗道阻尼和频移,并用现有实验和数值模拟研究的粒子数和囚禁频率参量,解析计算了阻尼系数和频移大小及其它们的温度依赖。计算中,考虑元激发的实际弛豫及其各弛豫间的正交关系以获得阻尼和频移计算公式,把基态波函数取为高斯分布函数的一级近似以消除三模耦合矩阵元的发散。我们的计算结果与数值模拟结果和实验结果分别进行直接和间接地对比,讨论和说明了我们理论方法的合理性。     

球对称铷原子玻色-爱因斯坦凝聚中单极子模的朗道阻尼和频移

采用含时哈特里-福克-博戈留波夫近似研究球对称铷原子玻色-爱因斯坦凝聚中单极子模的朗道阻尼和频移,并用现有实验和数值模拟研究的粒子数和囚禁频率参量,解析计算了阻尼系数和频移大小及其它们的温度依赖.计算中,考虑元激发的实际弛豫及其各弛豫间的正交关系以获得阻尼和频移计算公式,把基态波函数取为高斯分布函数的一级近似以消除三模耦合矩阵元的发散.我们的计算结果与数值模拟结果和实验结果分别进行直接和间接地对比,讨论和说明了我们理论方法的合理性.     

Nuclear compressibilities

We discuss the relation between the compressibility of nuclear matter and the frequencies of the collective monopole vibrations of nuclei. We analyse some of the problems which arise when one extrapolates from properties of finite nuclei to those of infinite nuclear matter. The best way to perform this extrapolation is to use a theory capable of describing both systems on the same footing. Self-consistent calculations using phenomenological effective interactions realize such a program. The general properties of these effective interactions are discussed. The theory we used is described; we emphasize that it accounts for both the properties of the ground states of nuclei and the small amplitude collective vibrations. Simple models of compression modes in infinite nuclear matter and in nuclei are presented; they illustrate various features of the collective modes in both systems. In particular we discuss the role of the shell structure and the effects of the nuclear surface. Results of extensive self-consistent calculations of the breathing mode of nuclei are presented and many features of the mode are analyzed. The role of the single particle spectrum on the frequencies of the collective modes is studied. Finally we briefly review the experimental situation on the monopole excitations of nuclei.We show that experimental data are compatible with a well defined value of the compression modulus of nuclear matter: K_∞ = 210±30 MeV.