X-ray and Neutron Study on the Structure of Hydrous SiO2 Glass up to 10 GPa

The structure of hydrous amorphous SiO2 is fundamental in order to investigate the effects of water on the physicochemical properties of oxide glasses and magma. The hydrous SiO2 glass with 13 wt.% D2O was synthesized under high-pressure and high-temperature conditions and its structure was investigated by small angle X-ray scattering, X-ray diffraction, and neutron diffraction experiments at pressures of up to 10 GPa and room temperature. This hydrous glass is separated into two phases: a major phase rich in SiO2 and a minor phase rich in D2O molecules distributed as small domains with dimensions of less than 100 angstrom. Medium-range order of the hydrous glass shrinks compared to the anhydrous SiO2 glass by disruption of SiO4 linkage due to the formation of Si-OD deuterioxyl, while the response of its structure to pressure is almost the same as that of the anhydrous SiO2 glass. Most of D2O molecules are in the small domains and hardly penetrate into the void space in the ring consisting of SiO4 tetrahedra

Precise determination of phase relations in pyrolite across the 660 km seismic discontinuity by in situ X-ray diffraction and quench experiments

Mineral assemblage changes in a pyrolite composition with increasing pressure were observed by in situ X-ray diffraction and quench experiments at pressures near that of the 660 km seismic discontinuity and at a fixed temperature of 1600 °C. According to results obtained by in situ X-ray diffraction experiments, ringwoodite (Rw) was observed with majorite garnet and CaSiO3-rich perovskite at pressures of about 20–22 GPa. Dissociation of ringwoodite to MgSiO3-rich perovskite and magnesiowüstite (Mw) was completed at 22.0±0.2 GPa according to Matsui et al.'s periclase pressure scale, and at 21.7±0.1 GPa according to Shim et al.'s gold pressure scale. Majorite garnet persisted to about 24 GPa where pyrolite transformed to a lower mantle mineral assemblage, i.e. MgSiO3-perovskite, CaSiO3-rich perovskite, and magnesiowüstite. Thus, majorite garnet coexists with the lower mantle assemblage at pressures of about 22–24 GPa. In the quench experiments, an assemblage of MgSiO3-perovskite, magnesiowüstite, CaSiO3-rich perovskite, and majorite garnet was synthesized at 22.5 GPa and 1600 °C, in which Mg-perovskite contained 2.8 wt.% Al2O3, and was significantly poorer in Fe than coexisting magnesiowüstite. The Fe–Mg partition coefficient between Mg-perovskite and magnesiowüstite including ferric iron (Kapp=0.27±0.06) is very close to that in the Al-free system, which suggests that these P–T conditions are in the vicinity of those of ringwoodite decomposition. Both the results of in situ X-ray diffraction and quench experiments in the present study yield a convergent result that ringwoodite decomposes into Mg-perovskite and magnesiowüstite before the garnet-to-perovskite transition at 1600 °C in pyrolite. The relation between the Al content in Mg-perovskite and Kapp in pyrolite is non-linear, which is consistent with the Fe–Mg partitioning between Mg-perovskite and magnesiowüstite previously reported for a simpler MgO–FeO–Al2O3–SiO2 system

Cobalt protoporphyrin accelerates TFEB activation and lysosome reformation during LPS-induced septic insults in the rat heart.

Lipopolysaccharide (LPS)-induced myocardial dysfunction is caused, at least in part, by mitochondrial dysfunction. Mitochondrial dysfunction and the oxidative damage associated with it are scavenged through various cellular defense systems such as autophagy to prevent harmful effects. Our recent study has demonstrated that cobalt protoporphyrin IX (CoPPIX), a potent inducer of heme oxygenase-1 (HO-1), ameliorates septic liver injuries by enhancing mitochondrial autophagy in rats. In our current study, we show that CoPPIX (5 mg/kg s.c.) not only accelerates the autophagic response but also promotes lysosome reformation in the rat heart treated with LPS (15 mg/kg i.p.). Lysosomal membrane-associated protein-2 (LAMP2), which is essential to the maintenance of lysosomal functions in the heart, is depleted transiently but restored rapidly during LPS administration in the rat. Activation of transcription factor EB (TFEB), a master regulator of lysosomal biogenesis and autophagy, was also observed, indicating a hyper consumption and subsequent reformation of the lysosome to meet the increased demand for autophagosome cleaning. CoPPIX was found to promote these processes and tended to restore the LPS-induced suppression of cardiac performances whilst chloroquine (CQ; 20 mg/kg i.p.), an inhibitor of lysosomes and autophagic protein degradation, abrogates these beneficial effects. The cardioprotective effect of CoPPIX against LPS toxicity was also observed via decreased levels of cardiac releasing enzymes in the plasma. Taken together, our current data indicate that lysosome reformation mediated by TFEB may be involved in cardioprotection against LPS-induced septic insults, and serve as a novel mechanism by which CoPPIX protects the heart against oxidative stress

Structural studies of expanded fluid mercury using synchrotron radiation

The energy-dispersive X-ray diffraction measurements using synchrotron radiation at SPring-8 for expanded fluid Hg were carried out for the first time in the density range from the liquid to the dense vapour region including the metal–nonmetal (M–NM) transition region. Densities ranged from 13.6 to 1.9 g cm-3. We obtained the structure factor, S(k), and the pair distribution functions, g(r). The density variations of the obtained interatomic distance r1 and coordination number N1 were discussed in relation to the M–NM transition in fluid Hg

X-ray diffraction measurements for expanded fluid-Se using synchrotron radiation

X-ray diffraction measurements at temperatures up to 1500C and pressures up to 843 bar have been carried out using synchrotron radiation at SPring-8 to investigate structural change in the semiconductor-to-metal transition in expanded fluid-Se. The signal-to-noise ratio in the intensity spectra was better than the previous one using in-house X-ray source. It is found important to estimate the background from a sapphire cell to deduce a structure factor of fluid Se with greater accuracy from the spectra. The preservation of the twofold coordinated chain structure and the contraction of the covalent bond are reconfirmed in the transition. When metallic properties were increased, the first peak in the pair distribution function became asymmetric towards larger distance and the first minimum became larger. These results may imply the modification on the chain structure in the transition

Hexagonal Close-packed Iron Hydride behind the Conventional Phase Diagram

六方最密充填構造の鉄は幅広い温度圧力領域で安定に存在することが知られている一方で、鉄水素化物ではこれまでに知られている鉄-水素系の温度圧力相図上には六方最密充填構造は存在しない。水素濃度を0.6以下になるように制御した状態において、高温高圧下放射光その場X線回折およびその場中性子回折実験を実施し、六方最密充填構造の鉄水素化物が形成されることを明らかにした。水素は鉄の作る八面体サイトを部分的に、そしてランダムに占有しており、水素による体積膨張率は面心立方構造のものよりも大きいことがわかった

Neutron diffraction study on the deuterium composition of nickel deuteride at high temperatures and high pressures

3.36 GPa, 1073 - 300 Kの高温高圧下でのfcc Ni中の重水素専有サイトを中性子回折その場観察実験により決定した。重水素は主にOサイトを専有しており、サイト占有率は1073から300 Kの冷却で0.4から0.85に増加した。Tサイト専有率は0.02で一定であった。重水素誘起の体積増加は2.09Å3/D原子と算出されたが、この値は過去の報告と一致していた