arXiv subjects
Publications and source records attributed to Ning Wang.
We previously proposed a formula for calculating the Coulomb energy of spherical nucleus with Wood-Saxon charge distribution. In this work, the analytical formula is extended for description of the Coulomb energy of nucleus with beta2 deformation.
We propose a semi-empirical nuclear mass formula based on the macroscopic-microscopic method in which the isospin and mass dependence of model parameters are investigated with the Skyrme energy density functional. The number of model parameters is considerably reduced compared with the finite range droplet model. The rms deviation with respect to 2149 measured nuclear masses is reduced by 21%, falls to 0.516 MeV. The new magic number N=16 in light neutron-rich nuclei and the shape coexistence phenomena for some nuclei have been examined with the model. The shell corrections of super-heavy nuclei are also predicted.
An alternative way to constrain the density dependence of the symmetry energy with the slope of the neutron skin thickness of nuclei which shows a linear relation to both the isospin asymmetry and the nuclear charge with a form of Z^{2/3} is proposed. The linear dependence of the neutron skin thickness on the nuclear charge and isospin asymmetry is systematically studied with the data from antiprotonic atom measurement experimentally and the extended Thomas-Fermi approach incorporated the Skyrme energy density functional theoretically. An obviously linear relationship between the slope parameter L of the symmetry energy and the slope of the neutron skin thickness on the isospin asymmetry can be found by adopting 66 Skyrme interactions in the calculation. Combining the available experimental data, the constraint of 16<L<66 MeV on the slope parameter of the symmetry energy is obtained. The Skyrme interactions satisfying the constraint are selected.
The dynamical nucleus-nucleus potentials for fusion reactions 40Ca+40Ca, 48Ca+208Pb and 126Sn+130Te are studied with the improved quantum molecular dynamics (ImQMD) model together with the extended Thomas-Fermi approximation for the kinetic energies of nuclei. The obtained fusion barrier for 40Ca+40Ca is in good agreement with the extracted fusion barrier from the measured fusion excitation function, and the depth of the fusion pockets are close to the results of time-dependent Hartree-Fock calculations. The energy dependence of fusion barrier is also investigated. For heavy fusion system, the fusion pocket becomes shallow and almost disappears for symmetric systems and the obtained potential at short distances is higher than the adiabatic potential.
We report superconducting resistive transition characteristics for array(s) of coupled 4-Angstrom single wall carbon nanotubes embedded in aluminophosphate-five (AFI) zeolite. The transition was observed to initiate at 15K with a slow resistance decrease switching to a sharp, order of magnitude drop between 7.5-6.0K. The transition has strong (anisotropic) magnetic field dependence. Differential resistance versus current (voltage) measurements indicate that the establishment of coherence proceeds in stages as the temperature is lowered below 15K. In particular, the sharp resistance drop and its attendant nonlinear IV characteristics are consistent with the manifestations of a Kosterlitz-Thouless (KT) transition that establishes quasi long range order in the plane transverse to the c-axis of the nanotubes, leading to an inhomogeneous system comprising 3D superconducting regions connected by weak links. Global coherence is established at below 5K with the appearance of a well-defined supercurrent gap at 2K.
Among natural biological flocks/swarms or even mass social activities, when the collective behaviors of the followers has been dominated by the moving direction or opinion of one leader group, it seems very difficult for later-coming leaders to reverse the orientation of the mass followers, especially when they are in quantitative minority. This Letter reports a counter-intuitive phenomenon, Following the Later-coming Minority, provided that the late-comers obey a favorable distribution pattern which enables them to spread their influence to as many followers as possible in a given time and to accumulate enough power to govern these followers. We introduce a discriminant index to quantify the whole group's orientation under competing leadership, which helps to design an economic way for the minority later-coming leaders to defeat the dominating majority leaders solely by optimizing their distribution pattern. Our investigation provides new insights into the effective leadership in biological systems, with meaningful implication to social and industrial applications.
The elastic and large-angle quasi-elastic scattering reactions were studied with the same nucleus-nucleus potential proposed for describing fusion reactions. The elastic scattering angle distributions of some reactions are reasonably well reproduced by the proposed Woods-Saxon potential with fixed parameters at energies much higher than the Coulomb barrier. With an empirical barrier distribution based on the modified Woods-Saxon potential and taking into account the influence of nucleons transfer, the calculated quasi-elastic scattering cross sections of a series of reactions are in good agreement with the experimental data.
A modified Woods-Saxon potential model is proposed for a unified description of the entrance channel fusion barrier and the fission barrier of fusion-fission reactions based on the Skyrme energy-density functional approach. The fusion excitation functions of 120 reactions have been systematically studied. The fusion (capture) cross sections are well described with the calculated potential and an empirical barrier distribution. Incorporating a statistical model (HIVAP code) for describing the decay of the compound nucleus, the evaporation residue (and fission) cross sections of 51 fusion-fission reactions have been systematically investigated. Optimal values of some key parameters of the HIVAP code are obtained based on the experimental data of these reactions. The experimental data are reasonably well reproduced by the calculated results. The upper and lower confidence limits of the systematic errors of the calculated results are given.
Finite size effect on the antiferromagnetic transition temperature, TN, of Co3O4 nanoparticles of 75, 35, and 16 nm in diameter, has been investigated. The AFM transition point, TN, reduces with the decreasing diameter, d. Along with the results from the previous experiments on the Co3O4 nanoparticles of 8 and 4.3 nm, the variation of TN with d appears to follow the finite size relation. According to the scaling behavior, the shift exponent is determined as λ= 1.4 \pm 0.4, the correlation length, \ksi_0 = 3.0 \pm 0.3 nm, and the bulk Neel temperature, TN(\infint) = 38.6 \pm 0.7 K.
The Skyrme energy-density functional approach has been extended to study the massive heavy-ion fusion reactions. Based on the potential barrier obtained and the parameterized barrier distribution the fusion (capture) excitation functions of a lot of heavy-ion fusion reactions are studied systematically. The average deviations of fusion cross sections at energies near and above the barriers from experimental data are less than 0.05 for 92% of 76 fusion reactions with $Z_1Z_2<1200$. For the massive fusion reactions, for example, the $^{238}$U-induced reactions and $^{48}$Ca+$^{208}$Pb the capture excitation functions have been reproduced remarkable well. The influence of structure effects in the reaction partners on the capture cross sections are studied with our parameterized barrier distribution. Through comparing the reactions induced by double-magic nucleus $^{48}$Ca and by $^{32}$S and $^{35}$Cl, the 'threshold-like' behavior in the capture excitation function for $^{48}$Ca induced reactions is explored and an optimal balance between the capture cross section and the excitation energy of the compound nucleus is studied. Finally, the fusion reactions with $^{36}$S, $^{37}$Cl, $^{48}$Ca and $^{50}$Ti bombarding on $^{248}$Cm, $^{247,249}$Bk, $^{250,252,254}$Cf and $^{252,254}$Es, and as well as the reactions lead to the same compound nucleus with Z=120 and N=182 are studied further. The calculation results for these reactions are useful for searching for the optimal fusion configuration and suitable incident energy in the synthesis of superheavy nuclei.
The Skyrme energy density functional has been applied to the study of heavy-ion fusion reactions. The barriers for fusion reactions are calculated by the Skyrme energy density functional with proton and neutron density distributions determined by using restricted density variational (RDV) method within the same energy density functional together with semi-classical approach known as the extended semi-classical Thomas-Fermi method. Based on the fusion barrier obtained, we propose a parametrization of the empirical barrier distribution to take into account the multi-dimensional character of real barrier and then apply it to calculate the fusion excitation functions in terms of barrier penetration concept. A large number of measured fusion excitation functions spanning the fusion barriers can be reproduced well. The competition between suppression and enhancement effects on sub-barrier fusion caused by neutron-shell-closure and excess neutron effects is studied.
By using the improved Quantum Molecular Dynamics model, the $^{244}$Pu+$^{244}$Pu, $^{238}$U+$^{238}$U and $^{197}$Au+$^{197}$Au reactions at the energy range of $E_{c.m.}$=800 $MeV$ to 2000 $MeV$ are studied. We find that the production probability of superheavy fragments(SHF) with $Z \geq$ 114 is much higher for $^{244}$Pu+$^{244}$Pu reaction compared with that of $^{238}$U+$^{238}$U reaction and no product of SHF is found for $^{197}$Au+$^{197}$Au. The production probability of SHF is narrowly peaked in incident energy dependence. The decay mechanism of the composite system of projectile and target and the time scale of decay process are explored. The binding energies of superheavy fragments are found to be broadly distributed and their shapes turn out to be exotic form.
We study the relation between the WDVV equations and the $τ$-function of the noncommutative KP (NCKP) hierarchy. WDVV-like equations (Hirota triple-product relation) in the noncommutative context appear as a consequence of the non-trivial equation for $τ$-function of the NC KP hierarchy, while the prepotential in the Seiberg-Witten (SW) theory has been identified to the $τ$-function of the Whitham hierarchy. We show that the spectral curve for the SW theory is the same as the Toda-chain hierarchy. We also show that Whitham hierarchy includes commutative Toda/KP hierarchy as a construction. Further, we comment on the origin of the Hirota triple-product relation in the context of the SW theory.
The Improved Quantum Molecular Dynamics model is further developed by introducing new parameters in interaction potential energy functional based on Skyrme interaction of SkM$^{*}$ and SLy series. The properties of ground states of selected nuclei can be reproduced very well. The Coulomb barriers for a series of reaction systems are studied and compared with the results of the proximity potential. The fusion excitation functions for a series of fusion reactions are calculated and the results are in good agreement with experimental data.
By using the updated improved Quantum Molecular Dynamics model in which a surface-symmetry potential term has been introduced for the first time, the excitation functions for fusion reactions of $^{40,48}$Ca+$^{90,96}$Zr at energies around the Coulomb barrier have been studied. The experimental data of the fusion cross sections for $^{40}$Ca+$^{90,96}$Zr have been reproduced remarkably well without introducing any new parameters. The fusion cross sections for the neutron-rich fusion reactions of $^{48}$Ca+$^{90,96}$Zr around the Coulomb barrier are predicted to be enhanced compared with a non-neutron-rich fusion reaction. In order to clarify the mechanism of the enhancement of the fusion cross sections for neutron-rich nuclear fusions, we pay a great attention to study the dynamic lowering of the Coulomb barrier during a neck formation. The isospin effect on the barrier lowering is investigated. It is interesting that the effect of the projectile and target nuclear structure on fusion dynamics can be revealed to a certain extent in our approach. The time evolution of the N/Z ratio at the neck region has been firstly illustrated. A large enhancement of the N/Z ratio at neck region for neutron-rich nuclear fusion reactions is found.
An improved Quantum Molecular Dynamics model is proposed. By using this model, the properties of ground state of nuclei from $^{6}$Li to $^{208}$Pb can be described very well with one set of parameters. The fusion reactions for $^{40}$Ca+$^{90}$Zr, $^{40}$Ca+$^{96}$Zr and $^{48}$Ca+$^{90}$Zr at energy near barrier are studied by this model. The experimental data of the fusion cross sections for $^{40}$Ca+$^{90,96}$Zr at the energy near barrier can be reproduced remarkably well without introducing any new parameters. The mechanism for the enhancement of fusion probability for fusion reactions with neutron-rich projectile or target is analyzed.