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151.
The knowledge from the compression behavior of densified SiO2 glass suggests that SiO2 melt may behave as a single phase having a densified network structure (intermediate-range order) at the pressure condition of the Earth’s deep upper mantle, including the transition zone. A simple and easy-to-use equation of state of silicate melts which is applicable to a wide range of chemical composition at the pressure condition of the deep upper mantle is proposed based on the assumption that SiO2 component is in its densified state (or phase). The equation of state proposed in this study is consistent with all the available density data of silicate melts with an SiO2 content of about 35–55 mol% measured with large-volume presses at pressures between 8 and 22 GPa. The equations of state in previous studies differ considerably from each other. The main reason for the discrepancies seems to be that the compression behavior of multiple states (or phases) of silicate melts has been described in most cases with a single equation of state. It is necessary to consider that silicate melts are in their densified states (or phases) in the deep upper mantle. 相似文献
152.
Noriyuki Matsunaga Hinako Fukushi Yoshikazu Nakada Toshihiko Tanabé Michael W. Feast John W. Menzies Yoshifusa Ita Shogo Nishiyama Daisuke Baba Takahiro Naoi Hidehiko Nakaya Takahiro Kawadu Akika Ishihara Daisuke Kato 《Monthly notices of the Royal Astronomical Society》2006,370(4):1979-1990
We report the result of our near-infrared observations ( JHK s ) for type II Cepheids (including possible RV Tau stars) in galactic globular clusters. We detected variations of 46 variables in 26 clusters (10 new discoveries in seven clusters) and present their light curves. Their periods range from 1.2 d to over 80 d. They show a well-defined period–luminosity relation at each wavelength. Two type II Cepheids in NGC 6441 also obey the relation if we assume the horizontal branch stars in NGC 6441 are as bright as those in metal-poor globular clusters in spite of the high metallicity of the cluster. This result supports the high luminosity which has been suggested for the RR Lyr variables in this cluster. The period–luminosity relation can be reproduced using the pulsation equation assuming that all the stars have the same mass. Cluster RR Lyr variables were found to lie on an extrapolation of the period–luminosity relation. These results provide important constraints on the parameters of the variable stars.
Using Two Micron All-Sky Survey (2MASS) data, we show that the type II Cepheids in the Large Magellanic Cloud (LMC) fit our period–luminosity relation within the expected scatter at the shorter periods. However, at long periods ( P > 40 d, i.e. in the RV Tau star range) the LMC field variables are brighter by about one magnitude than those of similar periods in galactic globular clusters. The long-period cluster stars also differ from both these LMC stars and galactic field RV Tau stars in a colour–colour diagram. The reasons for these differences are discussed. 相似文献
Using Two Micron All-Sky Survey (2MASS) data, we show that the type II Cepheids in the Large Magellanic Cloud (LMC) fit our period–luminosity relation within the expected scatter at the shorter periods. However, at long periods ( P > 40 d, i.e. in the RV Tau star range) the LMC field variables are brighter by about one magnitude than those of similar periods in galactic globular clusters. The long-period cluster stars also differ from both these LMC stars and galactic field RV Tau stars in a colour–colour diagram. The reasons for these differences are discussed. 相似文献
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Daisuke Nagaoka Masahito Shigemitsu Masao Minagawa Shinichiro Noriki 《Journal of Oceanography》2010,66(1):117-132
We have investigated Pb concentrations and isotopic compositions in settling particles collected by sediment traps experiments
over a period of two years, from May 2005 to April 2007, at two depths, 770 and 5100 m, at station KNOT in the Northwestern
Pacific Ocean (44°N, 155°E). To the identify provenances of Pb, the samples were separated into two fractions by chemical
leaching techniques, with the leachate expected to contain Pb of anthropogenic origin. Isotopic compositions of Pb and concentrations
of Pb, Sc, Mn, La, Yb, and Th were measured by quadrupole ICP-MS. The isotope ratios of leachable Pb in settling particles
were 207Pb/206Pb = 0.860 ± 0.001; 208Pb/206Pb = 2.116 ± 0.002 (mean ± 95% confidence intervals), which are similar to those of aerosols in China that are greatly affected
by pollution from coal combustion. We estimated the mean contribution from anthropogenic Pb sources to the Pb in settling
particles, using the conventional binary (anthropogenic and natural Pb) mixing equation for Pb isotopes, as 90% in the upper
trap and 78% in the lower trap. Furthermore, we found a significant negative correlation between the isotope ratios of Pb
and concentrations of leachable Mn, normalized to those of leachable Pb, suggesting that manganese oxides play an important
role in transporting Pb from the upper layers of the ocean to the deeper layers. Our results support the speculation published
in a previous study that Pb might be scavenged by Mn oxides in the Northwestern Pacific Ocean. 相似文献
160.
Intermineral oxygen three‐isotope systematics of silicate minerals in equilibrated ordinary chondrites
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David McDougal Daisuke Nakashima Travis J. Tenner Noriko T. Kita John W. Valley Takaaki Noguchi 《Meteoritics & planetary science》2017,52(11):2322-2342
High‐precision oxygen three‐isotope ratios were measured for four mineral phases (olivine, low‐Ca and high‐Ca pyroxene, and plagioclase) in equilibrated ordinary chondrites (EOCs) using a secondary ion mass spectrometer. Eleven EOCs were studied that cover all groups (H, L, LL) and petrologic types (4, 5, 6), including S1–S4 shock stages, as well as unbrecciated and brecciated meteorites. SIMS analyses of multiple minerals were made in close proximity (mostly <100 μm) from several areas in each meteorite thin section, to evaluate isotope exchange among minerals. Oxygen isotope ratios in each mineral become more homogenized as petrologic type increases with the notable exception of brecciated samples. In type 4 chondrites, oxygen isotope ratios of olivine and low‐Ca pyroxene are heterogeneous in both δ18O and Δ17O, showing similar systematics to those in type 3 chondrites. In type 5 and 6 chondrites, oxygen isotope ratios of the four mineral phases plot along mass‐dependent fractionation lines that are consistent with the bulk average Δ17O of each chondrite group. The δ18O of three minerals, low‐Ca and high‐Ca pyroxene and plagioclase, are consistent with equilibrium fractionation at temperatures of 700–1000 °C. In most cases the δ18O values of olivine are higher than those expected from pyroxene and plagioclase, suggesting partial retention of premetamorphic values due to slower oxygen isotope diffusion in olivine than pyroxene during thermal metamorphism in ordinary chondrite parent bodies. 相似文献