Positron scattering and annihilation in hydrogenlike ions

Diagrammatic many-body theory is used to calculate the scattering phase shifts, normalized annihilation rates Zeff, and annihilation ? spectra for positron collisions with the hydrogenlike ions He+, Li2+, B4+, and F8+. Short-range electron-positron correlations and longer-range positron-ion correlations are accounted for by evaluating nonlocal corrections to the annihilation vertex and the exact positron self-energy. The numerical calculation of the many-body theory diagrams is performed using B-spline basis sets. To elucidate the role of the positron-ion repulsion, the annihilation rate is also estimated analytically in the Coulomb-Born approximation. It is found that the energy dependence and magnitude of Zeff are governed by the Gamow factor that characterizes the suppression of the positron wave function near the ion. For all of the H-like ions, the correlation enhancement of the annihilation rate is found to be predominantly due to corrections to the annihilation vertex, while the corrections to the positron wave function play only a minor role. Results of the calculations for s-, p-, and d-wave incident positrons of energies up to the positronium-formation threshold are presented. Where comparison is possible, our values are in excellent agreement with the results obtained using other, e.g., variational, methods. The annihilation-vertex enhancement factors obtained in the present calculations are found to scale approximately as 1+(1.6+0.46l)/Zi, where Zi is the net charge of the ion and l is the positron orbital angular momentum. Our results for positron annihilation in H-like ions provide insights into the problem of positron annihilation with core electrons in atoms and condensed matter systems, which have similar binding energies.

X-ray scattering from warm dense iron

We have carried out X-ray scattering experiments on iron foil samples that have been compressed and heated using laser-driven shocks created with the VULCAN laser system at the Rutherford-Appleton Laboratory. This is the highest Z element studied in such experiments so far and the first time scattering from warm dense iron has been reported. Because of the importance of iron in telluric planets, the work is relevant to studies of warm dense matter in planetary interiors. We report scattering results as well as shock breakout results that, in conjunction with hydrodynamic simulations, suggest the target has been compressed to a molten state at several 100 GPa pressure. Initial comparison with modelling suggests more work is needed to understand the structure factor of warm dense iron. (C) 2013 Published by Elsevier B.V.

Spin-wave modes in Ni nanorod arrays studied by Brillouin light scattering

Dynamic magnetic properties of arrays of Ni nanorods with a low aspect ratio have been investigated. It has been shown that the spectra of spin-wave resonances localized on nanorods with a low aspect ratio typically feature the presence of zones with high density of states resulting in a characteristic two-peak pattern of Stokes and anti-Stokes lines of magneto-optical (MO) Brillouin light scattering with pronounced Stokes–anti-Stokes (S-AS) asymmetry. A simple theoretical model based on the analysis of the elliptic character of the polarization of the optical wave interacting with a dipole magnetostatic wave has been proposed. It has been shown that the S-AS asymmetry is due entirely to the asymmetry of the MO interaction efficiency with respect to time reversal of the magnetic precession in a magnon.

Statin Use and Risk of Delirium in the Critically Ill

Rationale: Delirium is common in intensive care unit (ICU) patients and is a predictor of worse outcomes and neuroinflammation is a possible mechanism. The antiinflammatory actions of statins may reduce delirium.

Objectives: To determine whether critically ill patients receiving statin therapy had a reduced risk of delirium than those not on statins.

Methods: A prospective cohort analysis of data from consecutive ICU patients admitted to a UK mixed medical and surgical critical care unit between August 2011 and February 2012; the Confusion Assessment Method for ICU was used to determine the days each patient was assessed as being free of delirium during ICU admission.

Measurements and Main Results: Delirium-free days, daily administration of statins, and serum C-reactive protein (CRP) were recorded. Four hundred and seventy consecutive critical care patients were followed, of whom 151 patients received statins. Using randomeffects multivariable logistic regression, statin administration the previous evening was associated with the patient being assessed as free of delirium (odds ratio, 2.28; confidence interval, 1.01-5.13; P , 0.05) and with lower CRP (b = 20.52; P , 0.01) the following day. When the association between statin and being assessed as free of delirium was controlled for CRP, the effect size became nonsignificant (odds ratio, 1.56; confidence interval, 0.64-3.79; P = 0.32).

Conclusions: Ongoing statin therapy is associated with a lower daily risk of delirium in critically ill patients. An ongoing clinical trial, informed by this study, is investigating if statins are a potential therapy for delirium in the critically ill.Copyright © 2014 by the American Thoracic Society.

Effect of magnetic bias on Gaussian pulse scattering by stacked nonlinear semiconductor layers

The nonlinear scattering of pulses by periodic stacks of semiconductor layers with magnetic bias has been studied in the self-consistent problem formulation, taking into account mobility of carriers. The three-wave mixing technique has been applied to the analysis of the waveform evolution in the stacks illuminated by two Gaussian pulses with different central frequencies and lengths. The effects of external magnetic bias, and stack physical and geometrical parameters on the properties of the scattered waveforms are discussed. © 2013 IEEE.

Low-energy scattering of electrons by caesium atoms

The relativistic R-matrix method is used to calculate elastic and inelastic cross sections for electrons incident on caesium atoms with energies from 0-3 eV. These cross sections reveal a wealth of resonance structure in this energy range. The differential cross sections as well as the spin polarisation function S( theta ) and the left-right asymmetry function S( theta ) are calculated and enable conclusions to be drawn on the importance of spin-dependent interactions.

An investigation of the ((3p)(4s) ) resonances in the elastic scattering of electrons by argon atoms

Initial results are presented on the elastic scattering of electrons by argon atoms in the neighbourhood of the well known ((3p) (4s)) resonances. An R-matrix calculation is employed to investigate how the resonance characteristics change as the spin-orbit interaction is switched on.