The Mg isotope composition of presolar silicate grains from red giant stars

We report O and Mg isotope compositions of presolar silicate grains which likely formed around asymptotic giant branch stars. Our grains represent the most abundant Mg-rich presolar grain group and their Mg isotope composition provides thus far missing information about the contribution of isotopically anomalous presolar dust to the Mg isotope inventory of the early Solar System. Presolar silicate grains were identified in situ, using the NanoSIMS, in the matrix of the ungrouped carbonaceous chondrite Acfer 094. O isotope compositions suggest that the presolar grains of the present study formed in the stellar winds of low mass (M <= similar to 2.2 x M-solar) red giant or asymptotic giant branch stars of close-to-solar metallicity and thus belong to the most abundant presolar silicate grain group. In order to minimise matrix contributions during spatially poorly resolved Mg isotope analyses (spatial resolution comparable to average grain size), meteorite matrix in the presolar grains' vicinity was removed using a focussed Ga ion beam. To monitor accuracy, we prepared and analysed O-isotopically regular (Solar System) matrix grains the same way as the presolar grains. The Mg-25/Mg-24 ratios of all seven successfully analysed presolar silicate grains are identical to that of the Solar System at the precision of our measurements. The Mg-26/Mg-24 ratios of five grains are also solar but two grains have significant positive anomalies in Mg-26/Mg-24. On average, however, Mg-25/Mg-24 and Mg-26/Mg-24 ratios are higher than solar by a few %. All grain compositions are consistent with Galactic chemical evolution and, possibly, isotope fractionation caused by interstellar or Solar System processing (sputtering and/or recondensation). The grain with the strongest enrichment in Mg-26 relative to Mg-25 (delta Mg-25 = 34 +/- 25 parts per thousand, delta Mg-26 = 127 +/- 25 parts per thousand; where delta Mg-x = 1000 x [(Mg-x/Mg-24)(grain)/(Mg-x/Mg-24)(meteorite matrix)) - 1] with x = 25 or 26; the reported uncertainty corresponds to 1 sigma), probably incorporated Al-26 during grain condensation. Our and previously reported Mg isotope data on presolar oxide and silicate grains indicate that the isotopically anomalous O-rich dust component of the Solar System's parent molecular cloud was heterogeneous with respect to Mg isotope compositions and probably had a higher Mg-26/Mg-24 ratio on average than that of the present-day Solar System. (C) 2014 Elsevier Ltd. All rights reserved

Focus on radioiodine-131 biokinetics: the influence of methylprednisolone on intratherapeutic effective half-life of 131I during radioiodine therapy of Graves’ disease

Aim!#!Radioiodine therapy (RIT) may trigger the development of Graves' ophthalmopathy (GO) or exacerbate pre-existing subclinical GO. Therefore, glucocorticoid administration is recommended for patients with pre-existing GO. Aim of this study was to analyze the influence of glucocorticoid therapy with methylprednisolone on intratherapeutic effective half-life (EHL) of radioiodine-131 in patients with Graves' disease (GD) as recent studies showed an effect for prednisolone.!##!Methods!#!In a retrospective study, 264 patients with GD who underwent RIT without any additional antithyroid medication were evaluated. Intrathyroidal EHL was determined pre- and intratherapeutically. Patients with co-existing GO (n = 43) received methylprednisolone according to a fixed scheme starting 1 day prior to RIT, patients without GO (n = 221) did not receive any protective glucocorticoid medication. The ratios of EHL during RIT and during radioiodine uptake test (RIUT) were compared.!##!Results!#!Patients receiving methylprednisolone showed a slight decrease of the mean EHL from 5.63 d (RIUT) to 5.39 d (RIT) (p &amp;gt; 0.05). A comparable result was obtained in patients without glucocorticoids (5.71 d (RIUT) to 5.47 d (RIT); p &amp;gt; 0.05). The ratios of the EHL between RIT and RIUT failed to show a significant difference between the two groups. EHL is therefore not significantly influenced by an additional protective treatment with methylprednisolone.!##!Conclusions!#!In the present study a decreased intrathyroidal EHL under glucocorticoid medication with methylprednisolone could not be detected. Therefore, co-medication with methylprednisolone in patients with GO may be preferred to avoid an intratherapeutic decrease of EHL by accompanying protective glucocorticoides

Dependence of phosphorus gettering and hydrogen passivation efficacy on grain boundary type in multicrystalline silicon

This investigation analyzes the dependency of minority charge carrier lifetime values at grain boundaries in multicrystalline silicon on the grain boundary type after P gettering and/or firing of SiNx:H layers deposited by plasma enhanced chemical vapor deposition. To get a broad statistics, a new method to determine the coincidence site lattice grain boundary types on large scale throughout entire 50 × 50 mm2 samples is combined with spatially resolved lifetime-calibrated photoluminescence measurements and mappings of the interstitial iron concentration. As an evaluation of the lifetime data at grain boundaries in comparison to the recombination activity of the bordering grains, lifetime contrast values are calculated. The correlation of this dependency on the grain boundary type with the impurity concentration is analyzed by the investigation of multicrystalline samples from two different ingots grown by directional solidification with different crucible material qual ities. A dependency of the efficacy of all applied processes on the grain boundary type is shown based on broad statistics-higher coincidence site lattice indexes correlate with a decrease of median lifetime values after all processes. Hydrogenation of both grains and grain boundaries is found to be more effective in cleaner samples. Extended getter sinks, as a P emitter, are also beneficial to the efficacy of hydrogenation. The lifetime contrast values are dependent on the degree of contamination of the multicrystalline silicon material. In cleaner samples, they rather decrease after the processes; in standard solar-grade material, they increase after POCl3 diffusion and decrease again after subsequent hydrogenation. No correlation with the interstitial iron concentration is found