Competing fusion and quasifission reaction mechanisms in the production of superheavy nuclei

Within the framework of a dinuclear system model, a new master equation is constructed and solved, which includes the relative distance of nuclei as a new dynamical variable in addition to the mass asymmetry variable so that the nucleon transfer, which leads to fusion and the evolution of the relative distance, which leads to quasifission (QF) are treated simultaneously in a consistent way. The QF mass yields and evaporation residual cross sections to produce superheavy nuclei are systematically investigated under this framework. The results fit the experimental data well. It is shown that the Kramers formula gives results of QF, which agree with those by our diffusion treatment, only if the QF barrier is high enough. Otherwise some large discrepancies occur.

Dynamical symmetry of screened Coulomb potential and isotropic harmonic oscillator

It is shown that for the screened Coulomb potential and isotropic harmonic oscillator, there exists an infinite number of closed orbits for suitable angular momentum values. At the aphelion (perihelion) points of classical orbits, an extended Runge-Lenz vector for the screened Coulomb potential and an extended quadrupole tensor for the screened isotropic harmonic oscillator are still conserved. For the screened two-dimensional (2D) Coulomb potential and isotropic harmonic oscillator, the dynamical symmetries SO3 and SU(2) are still preserved at the aphelion (perihelion) points of classical orbits, respectively. For the screened 3D Coulomb potential, the dynamical symmetry SO4 is also preserved at the aphelion (perihelion) points of classical orbits. But for the screened 3D isotropic harmonic oscillator, the dynamical symmetry SU(2) is only preserved at the aphelion (perihelion) points of classical orbits in the eigencoordinate system. For the screened Coulomb potential and isotropic harmonic oscillator, only the energy (but not angular momentum) raising and lowering operators can be constructed from a factorization of the radial Schrodinger equation.

Attractor crisis and bursting in a fluid flow with two no-slip directions

Characteristic burtsing behavior is observed in a driven, two-dimensional viscous flow, confined to a square domain and subject to no-slip boundaries. Passing a critical parameter value, an existing chaotic attractor undergoes a crisis, after which the flow initially enters a transient bursting regime. Bursting is caused by ejections from and return to a limited subdomain of the phase space, whereas the precrisis chaotic set forms the asymptotic attractor of the flow. For increasing values of the control parameter the length of the bursting regime increases progressively. Passing another critical parameter value, a second crisis leads to the appearance of a secondary type of bursting, of very large dynamical range. Within the bursting regime the flow then switches in irregular intervals from the primary to the secondary type of bursting. Peak enstrophy levels for both types of bursting are associated to the collapse of a primary vortex into a quadrupolar state.

Distribution, stability, bifurcations and catastrophe of steady rotation of a symmetrical heavy gyroscope with viscous-liquid-filled cavity

The number, the angles of orientation and the stability in Rumyantsev Movchan's sense of oblique steady rotations of a symmetric heavy gyroscope with a cavity completely filled with a uniform viscous liquid, possessing a fixed point 0 on its symmetric axis. are given for various values of the parameters. By taking the square of the upright component of the angular momentum M2 as a control parameter, three types of bifurcation diagrams of the steady rotations, two types of jumps and two kinds of local catastrophes, one being the symmetric reduced cusp type and the other being of the symmetric reduced butterfly type, are obtained. By taking account of the M2-damping owing to the moment of unavoidable faint friction, two different modes for the gyroscope, initially in a stable quasi-steady upright rotation with a nutation angle theta(s) equal to zero, to topple over are found.

Comment on: Computation of the optical trapping force using an FDTD based technique

In this comment, problems associated with an oversimplified FDTD based model used for trapping force calculation in recent papers "Computation of the optical trapping force using an FDTD based technique" [Opt. Express 13, 3707 (2005)], and "Rigorous time domain simulation of momentum transfer between light and microscopic particles in optical trapping" [Opt. Express 12, 2220 (2004)] are discussed. A more rigorous model using in Poynting vector is also presented.

离子辅助沉积中离子束流密度的作用

测量了End-Hall离子源在不同条件下的离子束流密度，在不同离子束流密度下进行了心离子辅助沉积ZrO2薄膜的实验，研究了离子束流密度对薄膜折射率、晶相的影响．根据动量传递模型分析了离子束流密度对薄膜折射率的作用；根据热尖峰理论证明了一定条件下离子束流密度不会影响薄膜晶体结构。

High laser-induced damage threshold HfO2 films prepared by ion-assisted electron beam evaporation

HfO2 films were deposited by electron beam evaporation with different deposition parameters. The properties such as refractive index, weak absorption, and laser induced damage thresholds (LIDTs) of these films have been investigated. It was found that when pulsed Nd:YAG 1064 nm laser is used to investigate LIDT of films: Metallic character is the main factor that influences LIDTs of films obtained from Hf starting material by ion-assisted reaction, and films prepared with higher momentum transfer parameter P have fewer metallic character; The ion-assisted reaction parameters are key points for preparing high LIDT films and if the parameters are chose properly, high LIDT films can be obtained. (c) 2004 Elsevier B.V. All rights reserved.

Electronic structure and exciton states in the freestanding ZnO nanorods

The electronic structure and exciton states of cylindrical ZnO nanorods with radius from 2 to 6 nm are investigated based on the framework of the effective-mass theory. Using the adiabatic approximation, the exciton binding energies taking account of the dielectric mismatch are solved exactly when the total angular momentum of the exciton states L = 0 and L = +/- 1. We find that the exciton binding energies can be enhanced greatly by the dielectric mismatch and the calculated results are almost consistent with the experimental data. Meanwhile, we obtain the optical transition rule when the small spin-obit splitting Delta(so) of ZnO is neglected. Furthermore, the radiative lifetime and linear optical susceptibilities chi(w) of the exciton states are calculated theoretically. The theoretical results are consistent with the experimental data very well. (C) 2009 American Institute of Physics. [DOI 10.1063/1.3125456]

Anisotropic Zeeman splitting and Stark shift of In1-yMnyAs1-xNx oblate quantum dots

The electronic structure, Zeeman splitting, and Stark shift of In1-yMnyAs1-xNx oblate quantum dots are studied using the ten-band k center dot p model including the sp-d exchange interaction between the carriers and the magnetic ion. The Zeeman splitting of the electron ground states is almost isotropic. The Zeeman splitting of the hole ground states is highly anisotropic, with an anisotropy factor of 918 at B=0.1 T. The Zeeman splittings of some of the electron and hole excited states are also highly anisotropic. It is because of the spin-orbit coupling which couples the spin states with the anisotropic space-wave functions due to the anisotropic shape. It is found that when the magnetic quantum number of total orbital angular momentum is nearly zero, the spin states couple with the space-wave functions very little, and the Zeeman splitting is isotropic. Conversely, if the magnetic quantum number of total orbital angular momentum is not zero, the space-wave functions in the degenerate states are different, and the Zeeman splitting is highly anisotropic. The electron and hole Stark shifts of oblate quantum dots are also highly anisotropic. The decrease of band gap with increasing nitrogen composition is much more obvious in the smaller radius case because the lowest conduction level is increased by the quantum confinement effect and is closer to the nitrogen level. (C) 2007 American Institute of Physics.

Electron g factors and optical properties of InAs quantum ellipsoids

The electronic structure, electron g factors and optical properties of InAs quantum ellipsoids are investigated, in the framework of the eight-band effective-mass approximation. It is found that the light-hole states come down in comparison with the heavy-hole states when the spheres are elongated, and become the lowest states of the valence band. Circularly polarized emissions under circularly polarized excitations may have opposite polarization factors to the exciting light. For InAs ellipsoids the length, which is smaller than 35 nm, is still in a strongly quantum-confined regime. The electron g factors of InAs spheres decrease with increasing radius, and are nearly 2 when the radius is very small. The quantization of the electron states quenches the orbital angular momentum of the states. Actually, as some of the three dimensions increase, the electron g factors decrease. As more dimensions increase, the g factors decrease more. The dimensions perpendicular to the direction of the magnetic field affect the g factors more than the other dimension. The magnetic field along the z axis of the crystal structure causes linearly polarized emissions in the spheres, which emit unpolarized light in the absence of magnetic field.

Electronic structure of coupled vertically stacked self-assembled InAs quantum disks in a vertical electric field

In the framework of the effective-mass and adiabatic approximations, by setting the effective-mass of electron in the quantum disks (QDs) different from that in the potential barrier material, we make some improvements in the calculation of the electronic energy levels of vertically stacked self-assembled InAs QD. Comparing with the results when an empirical value was adopted as the effective-mass of electron of the system, we can see that the higher levels become heightened. Furthermore, the Stark shifts of the system of different methods are compared. The Stark shifts of holes are also studied. The vertical electric field changes the splitting between the symmetric level and the antisymmetric one for the same angular momentum. (C) 2003 Elsevier Ltd. All rights reserved.

Quantum-confined stark effect of vertically stacked self-assembled quantum discs

We study the electronic energy levels and probability distribution of vertically stacked self-assembled InAs quantum discs system in the presence of a vertically applied electric field. This field is found to increase the splitting between the symmetric and antisymmetric levels for the same angular momentum. The field along the direction from one disc to another affects the electronic energy levels similarly as that in the opposite direction because the two discs are identical. It is obvious from our calculation that the probability of finding an electron in one disc becomes larger when the field points from this disc to the other one.

Electronic structure and transport properties of quantum rings in a magnetic field

The electronic structure of quantum rings is studied in the framework of the effective-mass theory and the two dimensional hard wall approximation. In cases of both the absence and presence of a magnetic field the electron momenta of confined states and the Coulomb energies of two electrons are given as functions of the angular momentum, inner radius, and magnetic-field strength. By comparing with experiments it is found that the width of the real confinement potential is 14 nm, much smaller than the phenomenal width. The Coulomb energy of two electrons is calculated as 11.1 meV. The quantum waveguide transport properties of Aharonov-Bohm (AB) rings are studied complementarily, and it is found that the correspondence of the positions of resonant peaks in AB rings and the momentum of confined states in closed rings is good for thin rings, representing a type of resonant tunneling.

Competition in rotation-alignment between high-j neutrons and protons in transfermium nuclei

The study of rotation-alignment of quasiparticles probes sensitively the properties of high-j intruder orbits. The distribution of very-high-j orbits, which are consequences of the fundamental spin-orbit interaction, links with the important question of single-particle levels in superheavy nuclei. With the deformed single-particle states generated by the standard Nilsson potential, we perform Projected Shell Model calculations for transfermium nuclei where detailed spectroscopy experiments are currently possible. Specifically, we study the systematical behavior of rotation-alignment and associated band-crossing phenomenon in Cf, Fm, and No isotopes. Neutrons and protons from the high-j orbits are found to compete strongly in rotation-alignment, which gives rise to testable effects. Observation of these effects will provide direct information on the single-particle states in the heaviest nuclear mass region.

Prolate and oblate shape coexistence in Pt-188

A standard in-beam gamma-spectroscopy experiment for Pt-188 is performed via the Yb-176(O-18, 6n) reaction at beam energies of 88 and 95 MeV, and the level scheme for (188) Pt is established. Prolate and oblate shape coexistence has been demonstrated to occur in Pt-188 by applying the projected shell model. The rotation alignment of i(13/2) neutrons drives the yrast sequence changing suddenly from prolate to oblate shape at angular momentum 10th, indicating likely a new type of shape phase transition along the yrast line in Pt-188.