90 research outputs found
Structure of strontium tellurite glass, anti-glass and crystalline phases by high-energy X-ray diffraction, reverse Monte Carlo and Rietveld analysis
The structures of xSrO–(100 _ x)TeO2 (x = 5, 7.5, 8.5 and 10 mol.%) glass, antiglass and crystalline samples were studied by high-energy X-ray diffraction (HEXRD), reverse Monte Carlo (RMC) simulations, atomic pair distribution function analysis and Fullprof Rietveld refinement. The atomic pair distributions show the first peak at 1.90 A ˚ due to the Te—O equatorial bonds and the Te—O peak is asymmetrical due to the range of Te—O bond lengths in glass, anti-glass and crystalline samples. The short-range structural properties of glasses such as Te—O bond lengths, Te–O speciation, Te–Te distances and O— Te—O bond angle distributions were determined by RMC simulations. The average Te–O coordination number (NTe–O) for 5SrO–95TeO2 glass is 3.93 which decreases to 3.59 on increasing the SrO concentration to 10 mol.%. The changes in NTe–O revealed that the glass network predominantly contains TeO4 units with a small amount of TeO3 units and there is a structural transformation TeO4 ! TeO3 with an increase in SrO concentration. The O—Te—O bond angle distributions have a peak at 79_ and reveal that the Oequatorial—Te—Oequatorial bonds are the most abundant linkages in the tellurite network. Two glass samples containing 7.5 and 8.5 mol.% of SrO were annealed at 350_C for 1 h to produce anti-glass phases; they were further annealed at 450_C for 4 h to transform them into crystalline phases. The anti-glass samples are disordered cubic SrTe5O11 and the disordered monoclinic SrTeO3 phases, whereas the crystalline samples contain monoclinic SrTeO3 and the orthorhombic TeO2 phases. The unit-cell parameters of the anti-glass and crystalline structures were determined by Fullprof Rietveld refinement. Thermal studies found that the glass transition temperature increases with an increase in SrO mol.% and the results on the short-range structure of glasses from Raman spectroscopy are in agreement with the RMC findings.Funding for this research was provided by: Inter University Accelerator Centre, New Delhi, UGC-DAE Consortium for Scientific Research, University Grants Commission, Mumbai. Financial support by the Department of Science and Technology (Government of India) provided within the framework of the India @DESY collaboration is gratefully acknowledged
Hypoxia‐inducible transcription factor 2α promotes steatohepatitis through augmenting lipid accumulation, inflammation, and fibrosis
Oxygen dynamics in the liver is a central signaling mediator controlling hepatic homeostasis, and dysregulation of cellular oxygen is associated with liver injury. Moreover, the transcription factor relaying changes in cellular oxygen levels, hypoxia‐inducible factor (HIF), is critical in liver metabolism, and sustained increase in HIF signaling can lead to spontaneous steatosis, inflammation, and liver tumorigenesis. However, the direct responses and genetic networks regulated by HIFs in the liver are unclear. To help define the HIF signal‐transduction pathway, an animal model of HIF overexpression was generated and characterized. In this model, overexpression was achieved by Von Hippel‐Lindau ( Vhl ) disruption in a liver‐specific temporal fashion. Acute disruption of Vhl induced hepatic lipid accumulation in an HIF‐2α–dependent manner. In addition, HIF‐2α activation rapidly increased liver inflammation and fibrosis, demonstrating that steatosis and inflammation are primary responses of the liver to hypoxia. To identify downstream effectors, a global microarray expression analysis was performed using livers lacking Vhl for 24 hours and 2 weeks, revealing a time‐dependent effect of HIF on gene expression. Increase in genes involved in fatty acid synthesis were followed by an increase in fatty acid uptake‐associated genes, and an inhibition of fatty acid β‐oxidation. A rapid increase in proinflammatory cytokines and fibrogenic gene expression was also observed. In vivo chromatin immunoprecipitation assays revealed novel direct targets of HIF signaling that may contribute to hypoxia‐mediated steatosis and inflammation. Conclusion: These data suggest that HIF‐2α is a critical mediator in the progression from clinically manageable steatosis to more severe steatohepatitis and liver cancer, and may be a potential therapeutic target. (H EPATOLOGY 2011;)Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/86905/1/24400_ftp.pd
Alkali environments in tellurite glasses
Neutron diffraction measurements are reported for five binary alkali tellurite glasses, xM2O · (100 − x)TeO2 (containing 10 and 20 mol% K2O, 10 and 19 mol% Na2O, and 20 mol% 7Li2O), together with 23Na MAS NMR measurements for the sodium containing glasses. Differences between neutron correlation functions are used to extract information about the local environments of lithium and sodium. The Na–O bond length is 2.37(1) Å and the average Na–O coordination number, nNaO, decreases from 5.2(2) for x = 10 mol% Na2O to 4.6(1) for x = 19 mol% Na2O. The average Li–O coordination number, nLiO, is 3.9(1) for the glass with x = 20 mol% Li2O and the Li–O bond length is 2.078(2) Å. As x increases from 10 to 19 mol% Na2O, the 23Na MAS NMR peak moves downfield, confirming an earlier report of a correlation of peak position with sodium coordination number. The close agreement of the maximum in the Te–O bond distribution for sodium and potassium tellurite glasses of the same composition, coupled with the extraction of reasonable alkali coordination numbers using isostoichiometric differences, gives strong evidence that the tellurium environment in alkali tellurites is independent of the size of the modifier cation used
Effect of Dopants on Zirconia Stabilization—An X-ray Absorption Study: I, Trivalent Dopants
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65562/1/j.1151-2916.1994.tb06964.x.pd
ChemInform Abstract: Effective and Preferential Transformation of Compounds Having 2- Haloethyl Groups on Positive Sulfur into Ethenyl Compounds Under PTC Conditions.
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