The Ti environment in natural hibonite: XANES spectroscopy and computer modelling

The local atomic structure around Ti in Ti-bearing hibonite (CaAl12O19) was studied using X-ray absorption near-edge structure (XANES) spectroscopy and computer modelling. Structural models of the direct substitution of Al by Ti3+, Al by Ti4+ charge balanced by the coupled substitution of Mg2+ for Al, and small Ti clusters were considered. The Ti K-XANES spectra of natural hibonite with different Ti concentration were recorded. Theoretical Ti K- XANES spectra for structural models of hibonite were calculated. It was shown that the theoretical Ti K-XANES spectra for a model with Ti at the five-coordinated M2 site are in agreement with the experimental XANES spectra of hibonite with low concentrations of Ti, while the theoretical spectra for a structural model of clustered Ti are in agreement with the experimental spectra of hibonite with higher Ti contents

Cardiovascular magnetic resonance in acute ST-segment-elevation myocardial infarction: recent advances, controversies, and future directions

Although mortality after ST-segment elevation myocardial infarction (MI) is on the decline, the number of patients developing heart failure as a result of MI is on the rise. Apart from timely reperfusion by primary percutaneous coronary intervention, there is currently no established therapy for reducing MI size. Thus, new cardioprotective therapies are required to improve clinical outcomes after ST-segment-elevation MI. Cardiovascular magnetic resonance has emerged as an important imaging modality for assessing the efficacy of novel therapies for reducing MI size and preventing subsequent adverse left ventricular remodeling. The recent availability of multiparametric mapping cardiovascular magnetic resonance imaging has provided new insights into the pathophysiology underlying myocardial edema, microvascular obstruction, intramyocardial hemorrhage, and changes in the remote myocardial interstitial space after ST-segment-elevation MI. In this article, we provide an overview of the recent advances in cardiovascular magnetic resonance imaging in reperfused patients with ST-segment-elevation MI, discuss the controversies surrounding its use, and explore future applications of cardiovascular magnetic resonance in this setting

Water in the Earth's mantle: A solid-state NMR study of hydrous wadsleyite

Wadsleyite, β-(Mg,Fe)2SiO4, is the main component of the transition zone in the Earth's mantle, at depths of 410-530 km below the surface. This mineral has received considerable interest as a potential reservoir for the vast amount of hydrogen, as hydro

Getting Better (or Worse) All the Time: Support Trajectories and Employee Turnover

As employment relationships develop over time, changes in static perceptions of organizational support (POS) provide the basis for evaluating one’s present and future with an organization. We develop and test hypotheses on how POS and referent POS (RΔPOS) trajectories influence employee turnover intentions. Drawing on a sample of 167 employees, our analysis shows that changes to static POS (ΔPOS) and RΔPOS significantly influence employee turnover intentions. This research extends organizational support theory by shedding light on the dynamic nature of POS and the effects of those changes on employee outcomes, specifically turnover intentions

Getting Better (or Worse) All the Time: Support Trajectories and Employee Turnover

As employment relationships develop over time, changes in static perceptions of organizational support (POS) provide the basis for evaluating one’s present and future with an organization. We develop and test hypotheses on how POS and referent POS (RΔPOS) trajectories influence employee turnover intentions. Drawing on a sample of 167 employees, our analysis shows that changes to static POS (ΔPOS) and RΔPOS significantly influence employee turnover intentions. This research extends organizational support theory by shedding light on the dynamic nature of POS and the effects of those changes on employee outcomes, specifically turnover intentions

OH-bearing planar defects in olivine produced by the breakdown of Ti-rich humite minerals from Dabie Shan (China)

The partial breakdown of Ti-chondrodite and Ti-clinohumite during exhumation from ultra-high pressure to amphibolite facies conditions in garnet-pyroxenites from Dabie Shan (China) produces coronas of olivine coexisting with ilmenite blebs. Fourier transform infrared (FTIR) spectra of this newly formed olivine exhibit absorption bands in the hydroxyl-stretching region. Two intense peaks were observed at 3,564 and 3,394 cm-1, identical in energy to peaks in Ti-clinohumite. Transmission electron microscopy (TEM) of the same olivine domains revealed the presence of a complex (001) planar intergrowth. These interlayers have a 1.35 nm repeat distance, which is characteristic of clinohumite. Such interlayers are also enriched in Ti with respect to the adjacent olivine as shown by energy dispersive spectrometry. The combined evidence from FTIR spectroscopy and TEM indicates that OH is incorporated along Ti-clinohumite planar defects. This study provides evidence that the nominally anhydrous phase olivine may contain OH as a humite-type defect beyond the breakdown of the hydrous humite minerals and confirms earlier suggestions that Ti plays a key role in OH incorporation in mantle olivine. We suggest that olivine containing Ti-clinohumite defects is an important phase for water transport in subduction zones and for the storage of water in cold subcontinental mantle. However, these defects are unlikely to be stable in hotter parts of the oceanic mantle such as where basaltic magmas are generated

Polycrystalline Crusts in Accreting Neutron Stars

The crust of accreting neutron stars plays a central role in many different observational phenomena. In these stars, heavy elements produced by H-He burning in the rapid proton capture (rp-) process continually freeze to form new crust. In this paper, we explore the expected composition of the solid phase. We first demonstrate using molecular dynamics that two distinct types of chemical separation occur, depending on the composition of the rp-process ashes. We then calculate phase diagrams for three-component mixtures and use them to determine the allowed crust compositions. We show that, for the large range of atomic numbers produced in the rp-process ($Z\sim 10$--$50$), the solid that forms has only a small number of available compositions. We conclude that accreting neutron star crusts should be polycrystalline, with domains of distinct composition. Our results motivate further work on the size of the compositional domains, and have implications for crust physics and accreting neutron star phenomenology.Comment: 8 pages, 4 figures, Submitted to ApJ, this article supersedes arXiv:1709.0926

Ice-core Records and Ozone Depletion—Potential for a Proxy Ozone Record

Time-series of the ionic composition in polar ice cores can provide detailed direct and proxy records of seasonal to Millenial scale fluctuations in climate, atmospheric chemistry, and volcanic activity. Even though problems of species-source links and air/snow fractionation have not all been entirely resolved,the fact remains that ice cores currently hold the best hope of retrieving detailed paleo-atmospheric records. While direct links between the chemistry in ice cores and the ozone depletion phenomenon cannot be guaranteed, ice-core records provide the only means by which signals related to the ozone cycle can be produced for pre-measurement periods or for unmonitored sites. We propose that measurements of nitrate and/or chloride in polar snow/ice samples may provide proxy records of ozone depletion because of the role these species play in the ozone cycle (e.g., see summary review by Schoeberl and Krueger 1986). Heterogeneous chemical reactions in the ant-arctic atmosphere involving catalyzing agents such as chlorine monoxide, bromine monoxide, and/or nitrogen oxides are known to be effective in reducing ozone concentrations through their effect on the general reaction: oxygen plus ozone forms 202(e.g., McElroy et al. 1986a). Removal of nitrogen oxides by condensation from polar stratospheric clouds (e.g., Toon et al.1986; McElroy et al. 1986b; Crutzen and Arnold 1986) triggered particularly by cooling in the stratosphere helps set the stage for more efficient removal of ozone by reactions with chlorine monoxide and bromine monoxide (e.g., McElroy et al. 1986a). These reactions may result in increased concentrations of nitrate and chloride in polar snow/ice cores