Ionization from the outer shell of Ar by proton impact

Recent results for proton-argon total ionization cross sections [Kirchner Phys. Rev. Lett. 79, 1658 (1997)] show large disagreement between theory and experiment for energies below 80 keV. To address this problem we have employed a recently developed theoretical method with a more pragmatic approach to the charge screening both in the initial and final channels. The target is considered as a one-electron atom and the interactions between this active electron and remaining target electrons are treated by a model potential including both short- and long-range effects. In the final channel the usual product of two continuum distorted wave functions each associated with a distinct electron-nucleus interaction is used. New results in the present calculation show good agreement in total cross sections for the energy range 10-300 keV with the measurement of Rudd [Rev. Mod. Phys. 57, 965 (1985)].

Fixed-node diffusion Monte Carlo computations for closed-shell jellium spheres

Fixed-node diffusion Monte Carlo computations are used to determine the ground state energy and electron density for jellium spheres with up to N = 106 electrons and background densities corresponding to the electron gas parameter 1 less than or equal to r(s)less than or equal to5.62. We analyze the density and size dependence of the surface energy, and we extrapolate our data to the thermodynamic limit. The results agree well with the predictions of density functional computations using the local density approximation. In the case of N = 20, we extend our computation to higher densities and identify a transition between atomic- and jelliumlike nodal structures occurring at the background density corresponding to r(s)=0.13. In this case the local density approximation is unable to reproduce the changes in the correlation energy due to the discontinuous transition in the ground state nodal structure. We discuss the relevance of our results for nonlocal approximations to density functional theory.

The rotational molding characteristics of metallocene polyethylene skin/foam structures

This article reports on the results of ongoing work in which the foaming characteristics of metallocene-catalyzed linear low density polyethylenes for rotational molding are investigated. Earlier publications related rheological and thermal parameters to the polymer structure and mechanical properties and found that metallocene polyethylene can be used in rotational foam molding to produce a foam that will perform as well as a Ziegler-Natta catalyzed foam. Through adjustments to molding conditions, the significant processing and physical material parameters, which optimize metallocene catalyzed linear low-density polyethylene foam structure, have been identified. This article details the optimum processing route for the production of two layer skin/foam parts using the drop box method. © SAGE Publications 2007.