X-ray-absorption fine-structure study of ZnSexTe1−x alloys

X-ray-absorption fine-structure experiments at different temperatures in ZnSexTe1−x (x=0, 0.1, 0.2, 0.55, 0.81, 0.93, 0.99, and 1.0) have been performed in order to obtain information about the structural relaxation and disorder effects occurring in the alloys. First and second neighbor distance distributions have been characterized at the Se and Zn K edges, using multiple-edge and multiple-scattering data analysis. The first neighbor distance distribution was found to be bimodal. The static disorder associated with the Zn–Te distance variance did not depend appreciably on composition. On the other hand, the static disorder associated with the Zn–Se distance increased as the Se content diminished. Using the bonding angle information provided by our experiments the point of view of the anion has been related to that of the cation. The resulting structural model indicates that Zn tetrahedra surrounding the anions remain essentially undistorted, but forced to tilt from their ideal zincblende orientation to accommodate the minority element. The main origin of structural disorder is [email protected] ; [email protected]

Determination of the high-pressure crystal structure of BaWO4 and PbWO4

We report the results of both angle-dispersive x-ray diffraction and x-ray absorption near-edge structure studies in BaWO4 and PbWO4 at pressures of up to 56 GPa and 24 GPa, respectively. BaWO4 is found to undergo a pressure-driven phase transition at 7.1 GPa from the tetragonal scheelite structure (which is stable under normal conditions) to the monoclinic fergusonite structure whereas the same transition takes place in PbWO4 at 9 GPa. We observe a second transition to another monoclinic structure which we identify as that of the isostructural phases BaWO4-II and PbWO4-III (space group P21/n). We have also performed ab initio total energy calculations which support the stability of this structure at high pressures in both compounds. The theoretical calculations further find that upon increase of pressure the scheelite phases become locally unstable and transform displacively into the fergusonite structure. The fergusonite structure is however metastable and can only occur if the transition to the P21/n phases were kinetically inhibited. Our experiments in BaWO4 indicate that it becomes amorphous beyond 47 GPa.Comment: 46 pages, 11 figures, 3 table

Monazite-type SrCrO4 under compression

We report a high-pressure study of monoclinic monazite-type SrCrO4 up to 26 GPa. Therein we combined x-ray diffraction, Raman, and optical-absorption measurements with ab initio calculations, to find a pressure-induced structural phase transition of SrCrO4 near 8–9 GPa. Evidence of a second phase transition was observed at 10–13 GPa. The crystal structures of the high-pressure phases were assigned to the tetragonal scheelite-type and monoclinic AgMnO4-type structures. Both transitions produce drastic changes in the electronic band gap and phonon spectrum of SrCrO4. We determined the pressure evolution of the band gap for the low- and high-pressure phases as well as the frequencies and pressure dependencies of the Raman-active modes. In all three phases most Raman modes harden under compression, however the presence of low-frequency modes which gradually soften is also detected. In monazite-type SrCrO4, the band gap blueshifts under compression, but the transition to the scheelite phase causes an abrupt decrease of the band gap in SrCrO4. Calculations showed good agreement with experiments and were used to better understand the experimental results. From x-ray-diffraction studies and calculations we determined the pressure dependence of the unit-cell parameters of the different phases and their ambient-temperature equations of state. The results are compared with the high-pressure behavior of other monazites, in particular PbCrO4. A comparison of the high-pressure behavior of the electronic properties of SrCrO4 (SrWO4) and PbCrO4 (PbWO4) will also be made. Finally, the possible occurrence of a third structural phase transition is discussed

Angle-resolved photoemission study and first principles calculation of the electronic structure of GaTe

The electronic band structure of GaTe has been calculated by numerical atomic orbitals density-functional theory, in the local density approximation. In addition, the valence-band dispersion along various directions of the GaTe Brillouin zone has been determined experimentally by angle-resolved photoelectron spectroscopy. Along these directions, the calculated valence-band structure is in good concordance with the valence-band dispersion obtained by these measurements. It has been established that GaTe is a direct-gap semiconductor with the band gap located at the Z point, that is, at Brillouin zone border in the direction perpendicular to the layers. The valence-band maximum shows a marked \textit{p}-like behavior, with a pronounced anion contribution. The conduction band minimum arises from states with a comparable \textit{s}- \textit{p}-cation and \textit{p}-anion orbital contribution. Spin-orbit interaction appears to specially alter dispersion and binding energy of states of the topmost valence bands lying at $\Gamma$. By spin-orbit, it is favored hybridization of the topmost \textit{p}$_z$-valence band with deeper and flatter \textit{p$_x$}-\textit{p$_y$} bands and the valence-band minimum at $\Gamma$ is raised towards the Fermi level since it appears to be determined by the shifted up \textit{p$_x$}-\textit{p$_y$} bands.Comment: 7 text pages, 6 eps figures, submitted to PR

High-pressure structural study of the scheelite tungstates CaWO4 and SrWO4

Angle-dispersive x-ray diffraction (ADXRD) and x-ray absorption near edge structure (XANES) measurements have been performed in the AWO4 tungstates CaWO4 and SrWO4 under high pressure up to approximately 20 GPa. Similar phase transitions and phase transition pressures have been observed for both tungstates using the two techniques in the studied pressure range. Both materials are found to undergo a pressure-induced scheelite-to-fergusonite phase transition under sufficiently hydrostatic conditions. Our results are compared to those found previously in the literature and supported by ab initio total energy calculations. From the total energy calculations we have also predicted a second phase transition from the fergusonite structure to a new structure identified as Cmca. Finally, a linear relationship between the charge density in the AO8 polyhedra of ABO4 scheelite-related structures and the bulk modulus is discussed and used to predict the bulk modulus of other materials, like zircon.Comment: 52 pages, 9 figure, 4 table

New polymorph of InVO4: A high-pressure structure with six-coordinated vanadium

This document is the unedited Author’s version of a Submitted Work that was subsequently accepted for publication in Inorganic Chemestry, copyright © American Chemical Society after peer review. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/ic402043xA new wolframite-type polymorph of InVO4 is identified under compression near 7 GPa by in situ high-pressure (HP) X-ray diffraction (XRD) and Raman spectroscopic investigations on the stable orthorhombic InVO4. The structural transition is accompanied by a large volume collapse (Delta V/V = -14%) and a drastic increase in bulk modulus (from 69 to 168 GPa). Both techniques also show the existence of a third phase coexisting with the low- and high-pressure phases in a limited pressure range close to the transition pressure. XRD studies revealed a highly anisotropic compression in orthorhombic InVO4. In addition, the compressibility becomes nonlinear in the HP polymorph. The volume collapse in the lattice is related to an increase of the polyhedral coordination around the vanadium atoms. The transformation is not fully reversible. The drastic change in the polyhedral arrangement observed at the transition is indicative of a reconstructive phase transformation. The HP phase here found is the only modification of InVO4 reported to date with 6-fold coordinated vanadium atoms. Finally, Raman frequencies and pressure coefficients in the low- and high-pressure phases of InVO4 are reported.This research supported by the Spanish government MINECO under Grant Nos. MAT2010-21270-C04-01/04 and CSD2007-00045. O.G. acknowledges support from Vicerrectorado de Investigacion y Desarrollo of UPV (Grant No. UPV2011-0914 PAID-05-11 and UPV2011-0966 PAID-06-11). S.N.A. acknowledges support provided by Universitat de Valencia during his visit to it. B.G.-D. acknowledges the financial support from MINECO through the FPI program.Errandonea, D.; Gomis Hilario, O.; García-Domene, B.; Pellicer Porres, J.; Katari, V.; Achary, SN.; Tyagi, AK.... (2013). New polymorph of InVO4: A high-pressure structure with six-coordinated vanadium. Inorganic Chemistry. 52(21):12790-12798. https://doi.org/10.1021/ic402043xS1279012798522

Efficacy and Safety of Tunneled Pleural Catheters in Adults with Malignant Pleural Effusions: A Systematic Review

BackgroundMalignant pleural effusions (MPE) are a frequent cause of dyspnea and discomfort at the end of cancer patients' lives. The tunneled indwelling pleural catheter (TIPC) was approved by the FDA in 1997 and has been investigated as a treatment for MPE.ObjectiveTo systematically review published data on the efficacy and safety of the TIPC for treatment of MPE.DesignWe searched the MEDLINE, EMBASE, and ISI Web of Science databases to identify studies published through October 2009 that reported outcomes in adult patients with MPE treated with a TIPC. Data were aggregated using summary statistics when outcomes were described in the same way among multiple primary studies.Main measuresSymptomatic improvement and complications associated with use of the TIPC.Key resultsNineteen studies with a total of 1,370 patients met criteria for inclusion in the review. Only one randomized study directly compared the TIPC with the current gold standard treatment, pleurodesis. All other studies were case series. Symptomatic improvement was reported in 628/657 patients (95.6%). Quality of life measurements were infrequently reported. Spontaneous pleurodesis occurred in 430/943 patients (45.6%). Serious complications were rare and included empyema in 33/1168 patients (2.8%), pneumothorax requiring a chest tube in 3/51 (5.9%), and unspecified pneumothorax in 17/439 (3.9%). Minor complications included cellulitis in 32/935 (3.4%), obstruction/clogging in 33/895 (3.7%) and unspecified malfunction of the catheter in 11/121 (9.1%). The use of the TIPC was without complication in 517/591 patients (87.5%).ConclusionsBased on low-quality evidence in the form of case series, the TIPC may improve symptoms for patients with MPE and does not appear to be associated with major complications. Prospective randomized studies comparing the TIPC to pleurodesis are needed before the TIPC can be definitively recommended as a first-line treatment of MPE

Aerobic interval exercise improves parameters of Non Alcoholic Fatty Liver Disease (NAFLD) and other alterations of metabolic syndrome in obese Zucker rats.

Metabolic syndrome (MS) is a group of metabolic alterations that increase the susceptibility to cardiovascular disease and type 2 diabetes. Nonalcoholic fatty liver disease has been described as the liver manifestation of MS. We aimed to test the beneficial effects of an aerobic interval training (AIT) protocol on different biochemical, microscopic, and functional liver alterations related to the MS in the experimental model of obese Zucker rat. Two groups of lean and obese animals (6 weeks old) followed a protocol of AIT (4 min at 65%-80% of maximal oxygen uptake, followed by 3 min at 50%-65% of maximal oxygen uptake for 45-60 min, 5 days/week, 8 weeks of experimental period), whereas 2 control groups remained sedentary. Obese rats had higher food intake and body weight (P < 0.0001) and suffered significant alterations in plasma lipid profile, area under the curve after oral glucose overload (P < 0.0001), liver histology and functionality, and antioxidant status. The AIT protocol reduced the severity of alterations related to glucose and lipid metabolism and increased the liver protein expression of PPARγ, as well as the gene expression of glutathione peroxidase 4 (P < 0.001). The training protocol also showed significant effects on the activity of hepatic antioxidant enzymes, although this action was greatly influenced by rat phenotype. The present data suggest that AIT protocol is a feasible strategy to improve some of the plasma and liver alterations featured by the MS