Inelastic scattering of electrons from inert gas atoms in the eikonal distorted-wave approximation

The excitation of dipole states in neon and argon by electron impact has been calculated in the eikonal distorted-wave approximation. The total and differential cross-sections, the angular distributions of electrons and photons are in good agreement with experiment.     

Electron impact ionization of neon and neonic ions under distorted-wave Born approximation

The （e, 2e） triple differential cross sections of 2s orbitals of neon and neonic ions （Z = 11-14） are calculated using a distorted-wave Born approximation under coplanar asymmetric geometry. The calculated results show that, with the increase in the nuclear charge number Z, the amplitude of triple differential cross sections decreases. The angle difference between the binary peak position and the direction of momentum transfer gradually increases with the increase in the nuclear charge Z, and a new structure appears at an ejected angle 90° 〈 θ2 〈 120°. Three kinds of collision processes are proposed to illustrate the formation mechanism of such collision peaks.     

Field-induced spin-flip and spin-flip transitions in PrGa2

A detailed neutron diffraction study of a single crystal of hexagonal PrGa₂ under an applied field is presented. The field is applied along the easy [100] direction of the hexagonal plane. The compound exhibits several field-induced magnetic structures and, in particular, an uncompensated long period commensurate antiphase structure defined by the propagation vector (4/27, 4/27, 0) at zero field and below T_t = 3.5 K. Concerning the intermediate magnetic structures below T_t, two types of magnetic phase transitions are observed: a spin-flip transition where one moment per magnetic cell turns over, and a spin-slip transition from the low field commensurate propagation vector (4/27, 4/27, 0) to another commensurate vector (1/7, 1/7, 0). Between T_t and T_N = 7.2 K, the structure becomes apmlitude-modulated with a propagation vector (0.148, 0.148, 0.023). Important and original magnetic domain effects are also observed due to the high degeneracy of the easy direction of the hexagonal plane in both T<T_t and T_t<T<T_N regions.     

Damping of the giant spin-flip dipole and spin-flip quadrupole charge exchange modes in 90Zr

The damping of the giant spin-flip dipole (L=1, S=1, T=1, J^π=0⁻, 1⁻, 2⁻) and spin-flip quadrupole (L=2, S=1, T=1, J^π=1⁺, 2⁺, 3⁺) charge exchange resonances in ⁹⁰Zr is calculated in a microscopic nuclear structure model which includes both one-particle-one-hole (1p1h) and two-particle-two-hole (2p2h) configurations in a systematic way. It is shown that the coupling to 2p2h configurations gives rise to a strongly energy dependent spreading width which shifts a large fraction of transition strength to high excitation energies. The implications for the analysis of intermediate energy ⁹⁰Zr(p,n) data is discussed.     

Polarization effects on heavy-ion scattering in the distorted-wave method

On the basis of an exact formalism for DWBA methods we calculate the distorting potentials to be used in a standard distorted-wave Born approximation for systems with strongly coupled channels. We examine for a practically useful model some simple approximate treatments through comparisons of the polarization potentials in the case of elastic and inelastic ¹⁶O + ¹⁶O scattering. The adiabatic approximation omitting the radial kinetic energy in the propagator is found to lead to satisfactory agreement with the exact coupled-channel cross sections.     

On the spin-flip line shape in CdS

The longitudinal relaxation time of Spin-Flip Raman scattering (SFRS) in n-CdS is explained in terms of the Elliott mechanism. The energy dispersion of spectroscopic factors of the conduction electrons and the Hasegawa model yield a transversal relaxation time different from the longitudinal relaxation time, but do not reproduce the experimental value. The diffusion coefficient, responsible for the SFRS line width behavior with temperature in n-CdS, is explained based upon hopping effects in the low temperature region.     

Proton and α-particle impactM-shell ionization of atoms in binary encounter approximation

M-shell ionization cross sections for atoms due to the impact of proton and α-particles have been calculated in the binary encounter approximation. The effects of Coulomb deflection of the incident projectile and increase in binding of the target electron have been investigated. Roothan-Hartree-Fock velocity distribution for the target electrons has been used in the present work. The calculated cross-sections have been compared with experimental results and other theoretical calculations wherever available. The present calculations give a good account of experimental observations.     

Cyclotron spin-flip mode in the extreme quantum limit

In a two-dimensional electron system, the combined excitation (the cyclotron spin-flip mode) associated with changes in both orbital and spin quantum numbers is investigated. The energy of the cyclotron spin-flip mode is studied as a function of the electron filling factor. Comparative dependences of the decay times of the cyclotron spin-flip mode and the magnetoplasmon are measured. It is shown that, as the filling factor increases from v = 0 or decreases from v = 1, the damping of the cyclotron spin-flip mode increases significantly, while the magnetoplasma mode remains undamped.     

A microscopic approximation for sequential decay processes in light nuclear systems

An approximative treatment for sequential decay processes is presented which uses the cluster model reaction formalism. In the case of a dominating sequential decay mechanism, the break-up amplitude is decomposed in two factors which can be obtained from two-particle reaction calculations. This factorization is essentially based on the same idea as the Watson-Migdal formalism. The method is applied to the α + d →⁵He + p → α + n + p break-up. The results are in good agreement with recent experimental data.     

New bound spin-flip transitions in n-InSb

Donor spin - flip transitions with ΔN = 0, ΔM = ?1, and Δλ = 1 are observed in InSb in high magnetic fields using an optically pumped far-infrared laser system. Variational calculations of the donor levels yielded good agreement with previously observed donor transitions energies. As regards the new spin - flip transitions reported in this work, the theoretical treatment has to be revised particularly for obtaining correct selection rules.     

Universal spin-flip transition in itinerant antiferromagnets

We reveal a universal spin-flip (SF) transition as a function of temperature in spin-density-wave (SDW) systems. At low temperatures the antiferromagnetic (AFM) polarization is parallel to the applied field and above a critical temperature the AFM polarization flips perpendicular to the field. This transition occurs in any SDW system and may be considered as a qualitative probe of the itinerant character of AFM in a given material. Our SF transition may provide an explanation to the long-standing puzzle of the SF transition observed in chromium and may be at the origin of the equally puzzling SDW-I to SDW-II transition in Bechgaard salts for which we make experimental predictions.     

Probing spin-flip scattering in ballistic nanosystems

Because spin-flip length is longer than the electron mean-free path in a metal, past studies of spin-flip scattering are limited to the diffusive regime. We propose to use a magnetic double barrier tunnel junction to study spin-flip scattering in the nanometer sized spacer layer near the ballistic limit. We extract the voltage and temperature dependence of the spin-flip conductance Gs in the spacer layer from magnetoresistance measurements. In addition to spin scattering information including the mean-free path (70 nm) and the spin-flip length (1.0-2.6 microm) at 4.2 K, this technique also yields information on the density of states and quantum well resonance in the spacer layer.     

X-ray cross section in helium for electron capture to excited states by C6+ and O8+ ions in the continuum distorted-wave approximation

The projectile X-ray cross sections which are closely related to the total capture cross sections have been calculated in C⁶⁺ + He and O⁸⁺ + He collision processes. The calculated data for K-shell X-ray cross sections for capture to excited states are found to be in good agreement with the recent experimental findings and the existing theoretical calculations.     

A population-level model from the microscopic dynamics in Escherichia coli chemotaxis via Langevin approximation

Recent extensive studies of Escherichia coli (E. coli) chemotaxis have achieved a deep understanding of its mi- croscopic control dynamics. As a result, various quantitatively predictive models have been developed to describe the chemotactic behavior of E. coli motion. However, a population-level partial differential equation (PDE) that rationally incorporates such microscopic dynamics is still insufficient. Apart from the traditional Keller-Segel (K-S) equation, many existing population-level models developed from the microscopic dynamics are integro-PDEs. The difficulty comes mainly from cell tumbles which yield a velocity jumping process. Here, we propose a Langevin approximation method that avoids such a difficulty without appreciable loss of precision. The resulting model not only quantitatively repro- duces the results of pathway-based single-cell simulators, but also provides new inside information on the mechanism of E. coli chemotaxis. Our study demonstrates a possible alternative in establishing a simple population-level model that allows for the complex microscopic mechanisms in bacterial chemotaxis.     

Proton emission from the drip-line nuclei I-Bi using the WKB approximation with relativistic mean-field densities

crucial application to the existence of exotic nuclei. The effective relativistic meanfield formalism(E-RMF), with NL3, FSUGarnet, G3 and IOPB-I interactions, is adopted for analysis of the ground state properties of proton emitters. Furthermore, in the E-RMF background, the Wentzel-Karmers-Brillouin(WKB)barrier penetration method is used for the calculation of proton emission half-lives. It is found that the calculated halflives are in good agreement with the experimental results for all emitters considered in this study.     

Small-angle neutron spin-flip scattering in ferromagnetic films

This paper reports on the results of reflectometric measurements of anisotropic (Co₆₇Fe₃₁V₂) and almost isotropic (Fe) films prepared by magnetron sputtering. Nonspecular reflections and the corresponding peaks of the intensities of refracted neutrons have been observed for the alloy samples in magnetic fields H ≤ 7 Oe applied in the film plane along the easy magnetization axis. For iron films, angular splitting of the reflected neutron beam becomes observable only at H > 100 Oe and increases with an increase in the magnetic field. A general scheme has been proposed for this small-angle scattering with allowance made for different variants of changes in the Zeeman energy of neutrons. This scheme has allowed us to identify the magnetic structures of Co-Fe films. The magnetization of 0.15-μm-thick films with uniaxial and unidirectional textures leads to the formation of unidirectional textures characterized by different intensity distributions, for which the qualitative differences are retained with an increase in the magnetic field from 7 to 800 Oe. It has been revealed that, for 2.5-μm-thick films with the initial unidirectional texture, the oppositely magnetized states are nonequivalent.