Calculations of lowenergy positron-hydrogen and positroniumproton scattering using the close coupling method are reported at eErgkk belowthe ionization threshold. The chanAelspace ir&uded six hydrogen (Is. 2s. 2p, 3s. 3p and 3d) and six positronium (Is, 2s. 2p, 3s. 4s and 3p) states. Comparisons with more accurate calculations demonstrate that this model should give integrated cross sections accurate to 10%. Cross sections are computed with a fine energy mesh and a total of 11 resonances associated with the H(n = 2) and Ps(n = 2) thresholds have been identified and the resonance positions and widths determined.Calculalions of the total cross section and the positronium formation cross section for positronhydrogen scattering are consistent with the available experimental data. Cross sections for elastic scattering in the Ps(ls)-p entrance channel are dominated by a strong polaridion potential and vary from 1000 ro; at threshold to 15 at 1.0 Ryd. Cross sections for the Ps(ls) + p + e+ + H(nl) rean'angement collision are also reporred since these provide baseline data relevant to exp"ments aimed at making antihydrogen atoms. Differential ccoss sections for elastic Ps(ls)-p and e+-H(ls) scattering and for electron transfer to the hydrogen atom ground state are also reported at selected energies.

The authors report new differential cross section measurements (E0=1.5-50 eV) and coupled channel optical model calculations for elastic scattering of electrons from helium. The experimental results, from a crossed electron-atomic beam apparatus are analysed via a complex phaseshift technique with the derived phaseshifts, and their associated errors, then being used to derive total elastic, total reaction, total momentum transfer and grand total cross sections, and their respective errors, in a mathematically rigorous manner. Further, the authors applied fixed-energy inverse scattering techniques to the present data in order to deduce the interaction potential between the colliding particles.

We present a compilation of recommended positron–molecule cross sections for a range of scattering processes including elastic scattering, vibrational excitation, discrete electronic-state excitation, positronium formation, ionization, and also for the grand total cross section. Where possible, in particular for possible application in positron transport simulations for a given molecule, we try and list data for energies in the range 0.1–1000 eV although in practice the actual energy is highly target–molecule and scattering process specific. Aside from being relevant to positron transport studies, through, for example, Monte Carlo simulations, the present compilation should also be germane for benchmarking the validity and accuracy of positron–molecule scattering calculations and, just as importantly, to allow a comparison with corresponding electron scattering results. That latter comparison can shed real light on the projectile–target interactions that underpin the scattering dynamics.

We report results from new positron-argon total cross-section (TCS) measurements. Agreement with the corresponding recent data of Jones et al (2011 Phys. Rev. A 83 032701) is found to be very good, except at the lowest energies of common measurement. Excellent qualitative agreement is also found between our measurements and an improved convergent close-coupling (CCC) calculation which was undertaken as a part of this study. This level of accord between our experimental and theoretical TCSs has enabled us to determine an experimental scattering length (a) of a = −4.9 ± 0.7 au for the positron-argon system. That value is in excellent agreement with the relativistic polarized orbital optical potential approach result of Jones et al (a = −4.7 au) and our CCC result of a = −4.3 au.

The evolution of resistivity versus temperature (ρ (T)) curve for different doping elements, and in the presence of various defects and clustering are explained for both diluted magnetic semiconductors (DMS) and manganites. Here, we provide unambiguous evidence that the concept of ionization energy (EI) which is explicitly associated with the atomic energy levels, can be related quantitatively to transport measurements. The proposed ionization energy model is used to understand how the valence states of ions affect the evolution of ρ (T) curves for different doping elements. We also explain how the ρ (T) curves evolve in the presence of, and in the absence of defects and clustering. The model also complements the results obtained from first‐principles calculations. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)