Electron-impact excitation of Fe2: a comparison of intermediate coupling frame transformation, Breit-Pauli and Dirac R-matrix calculations

Modeling the spectral emission of low-charge iron group ions enables the diagnostic determination of the local physical conditions of many cool plasma environments such as those found in H II regions, planetary nebulae, active galactic nuclei etc. Electron-impact excitation drives the population of the emitting levels and, hence, their emissivities. By carrying-out Breit-Pauli and intermediate coupling frame transformation (ICFT) R-matrix calculations for the electron-impact excitation of Fe$^{2+}$ which both use the exact same atomic structure and the same close-coupling expansion, we demonstrate the validity of the application of the powerful ICFT method to low-charge iron group ions. This is in contradiction to the finding of Bautista et al. [Ap.J.Lett, 718, L189, (2010)] who carried-out ICFT and Dirac R-matrix calculations for the same ion. We discuss possible reasons.

Electron-impact excitation of Fe 4+ : an intermediate-coupling R -matrix calculation

For a number of years, there has been a major effort to calculate electron-impact excitation data for every ion stage of iron embodied by the ongoing efforts of the IRON project by Hummer et al (1993 Astron. Astrophys. 279 298). Due to the complexity of the targets, calculations for the lower stages of ionization have been limited to either intermediate-coupling calculations within the ground configurations or LS -coupling calculations of the ground and excited configurations. However, accurate excitation data between individual levels within both the ground and excited configurations of the low charge-state ions are urgently required for applications to both astrophysical and laboratory plasmas. Here we report on the results of the first intermediate-coupling R -matrix calculation of electron-impact excitation for Fe 4+ for which the close-coupling (CC) expansion includes not only those levels of the 3d 4 ground configuration, but also the levels of the 3d 3 4s, 3d 3 4p, 3d 3 4d and 3d 2 4s 2 excited configurations. With 359 levels in the CC expansion and over 2400 scattering channels for many of the J Π partial waves, this represents the largest electron–ion scattering calculation to date and it was performed on massively parallel computers using a recently developed set of relativistic parallel R -matrix programs.

Valence-shell photoionization of chlorinelike Ar+ ions

Absolute cross-section measurements for valence-shell photoionization of Ar + ions are reported for photon energies ranging from 27.4 eV to 60.0 eV. The data, taken by merging beams of ions and synchrotron radiation at a photon energy resolution of 10 meV, indicate that the primary ion beam was a statistically weighted mixture of the 2P o3/2 ground state and the 2P o1/2 metastable state of Ar +. Photoionization of this Cell-like ion is characterized by multiple Rydberg series of autoionizing resonances superimposed on a direct photoionization continuum. Observed resonance lineshapes indicate interference between indirect and direct photoionization channels. Resonance features are spectroscopically assigned and their energies and quantum defects are tabulated. The measurements are satisfactorily reproduced by theoretical calculations based on an intermediate coupling semi-relativistic Breit-Pauli approximation.

High-resolution photoionization of Xe + ions: Experiment and theory

High-resolution photoionization measurements of Xe + ions have been performed at the Advanced Light Source in Berkeley, California, USA. The experimental cross sections are compared with results from Dirac-Coulomb R-matrix calculations.

Novel Metabolite Biomarkers of Huntington's Disease As Detected by High-Resolution Mass Spectrometry

Huntington's disease (HD) is a fatal autosomal-dominant neurodegenerative disorder that affects approximately 3-10 people per 100 000 in the Western world. The median age of onset is 40 years, with death typically following 15-20 years later. In this study, we biochemically profiled post-mortem frontal lobe and striatum from HD sufferers (n = 14) and compared their profiles with controls (n = 14). LC-LTQ-Orbitrap-MS detected a total of 5579 and 5880 features for frontal lobe and striatum, respectively. An ROC curve combining two spectral features from frontal lobe had an AUC value of 0.916 (0.794 to 1.000) and following statistical cross-validation had an 83% predictive accuracy for HD. Similarly, two striatum biomarkers gave an ROC AUC of 0.935 (0.806 to 1.000) and after statistical cross-validation predicted HD with 91.8% accuracy. A range of metabolite disturbances were evident including but-2-enoic acid and uric acid, which were altered in both frontal lobe and striatum. A total of seven biochemical pathways (three in frontal lobe and four in striatum) were significantly altered as a result of HD. This study highlights the utility of high-resolution metabolomics for the study of HD. Further characterization of the brain metabolome could lead to the identification of new biomarkers and novel treatment strategies for HD.

High Resolution measurement and mapping of tungstate in waters, soils and sediments using the low-disturbance DGT sampling technique.

Increasing tungsten (W) use for industrial and military applications has resulted in greater W discharge into natural waters, soils and sediments. Risk modeling of W transport and fate in the environment relies on measurement of the release/mobilization flux of W in the bulk media and the interfaces between matrix compartments. Diffusive gradients in thin-films (DGT) is a promising passive sampling technique to acquire such information. DGT devices equipped with the newly developed high-resolution binding gels (precipitated zirconia, PZ, or ferrihydrite, PF, gels) or classic/conventional ferrihydrite slurry gel were comprehensively assessed for measuring W in waters. FerrihydriteDGT can measure W at various ionic strengths (0.001–0.5 mol L−1 NaNO3) and pH (4–8), while PZDGT can operate across slightly wider environmental conditions. The three DGT configurations gave comparable results for soil W measurement, showing that typically W resupply is relatively poorly sustained. 1D and 2D high-resolution W profiling across sediment—water and hotspot—bulk media interfaces from Lake Taihu were obtained using PZDGT coupled with laser ablation ICP–MS measurement, and the apparent diffusion fluxes across the interfaces were calculated using a numerical model.