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排序方式: 共有261条查询结果,搜索用时 31 毫秒
1.
We report multi-frequency and multi-epoch radio continuum observations with multi-spatial resolution for the low-luminosity active galactic nucleus (LLAGN) NGC 266. In the centimetre regime, we find diffuse components with Very Large Array (VLA) observations, and a variable compact core with a rising spectrum with Very Long Baseline Array (VLBA) observations. Although the spectral index of the rising spectrum is consistent with the prediction of the simple advection-dominated accretion flow (ADAF) model, the observed radio power is slightly high compared with that of the model prediction. A spectral break at centimetre-to-millimetre wavelengths is inferred from the upper limits of flux densities from Nobeyama Millimetre Array (NMA) and James Clerk Maxwell Telescope (JCMT) data at millimetre and submillimetre wavelengths, respectively. More complicated considerations are required for the theoretical model to interpret such observed radio properties. 相似文献
2.
Yusuke Seto Naoya Sakamoto Takashi Kaito Hisayoshi Yurimoto 《Geochimica et cosmochimica acta》2008,72(11):2723-2734
We report the mineral compositions and micro-texture of the isotopically anomalous (δ17,18OSMOW ∼ +180‰) Fe-S-Ni-O material recently discovered in matrix of the primitive carbonaceous chondrite Acfer 094 [Sakamoto N., Seto Y., Itoh S., Kuramoto K., Fujino K., Nagashima K., Krot A. N. and Yurimoto H. (2007) Oxygen isotope evidence for remnants of the early solar system primordial water. Science317, 231-233]. Synchrotron radiation X-ray diffraction and transmission electron microscopy studies indicate that this material consists of the symplectitically intergrown magnetite (Fe3O4) and pentlandite (Fe5.7Ni3.3S8) with magnetite/pentlandite volume ratio of ∼2.3. Magnetite forms column-shaped grains (10-30 nm in diameter and 100-200 nm in length); pentlandite occurs as worm-shaped grains or aggregates of grains 100-300 nm in size between magnetite crystals. Although both the X-ray diffraction and electron energy loss spectra support identification of iron oxide as magnetite, the electron diffraction patterns show that magnetite has a weak 3-fold superstructure, possibly due to ordering of vacancies. We infer that the isotopically anomalous symplectite formed by sulfurization and oxidization of metal grains either in the solar nebula or on an icy planetesimal. The intersite cation distribution of pentlandite suggests that timescale of oxidation was no longer than 1000 years. 相似文献
3.
In situ strength measurements on natural upper-mantle minerals 总被引:1,自引:0,他引:1
Junji Yamamoto Jun-ichi Ando Hiroyuki Kagi Toru Inoue Akihiro Yamada Daisuke Yamazaki Tetsuo Irifune 《Physics and Chemistry of Minerals》2008,35(5):249-257
Using in situ strength measurements at pressures up to 10 GPa and at room temperature, 400, 600, and 700°C, we examined rheological
properties of olivine, orthopyroxene, and chromian-spinel contained in a mantle-derived xenolith. Mineral strengths were estimated
using widths of X-ray diffraction peaks as a function of pressure, temperature, and time. Differential stresses of all minerals
increase with increasing pressure, but they decrease with increasing temperature because of elastic strain on compression
and stress relaxation during heating. During compression at room temperature, all minerals deform plastically at differential
stress of 4–6 GPa. During subsequent heating, thermally induced yielding is observed in olivine at 600°C. Neither orthopyroxene
nor spinel shows complete stress relaxation, but both retain some stress even at 700°C. The strength of the minerals decreases
in the order of chromian-spinel ≈ orthopyroxene > olivine for these conditions. This order of strength is consistent with
the residual pressure of fluid inclusions in mantle xenoliths. 相似文献
4.
Yusuke Okazaki Osamu Seki Takeshi Nakatsuka Tatsuhiko Sakamoto Minoru Ikehara Kozo Takahashi 《Journal of Oceanography》2006,62(5):639-648
Cycladophora davisiana, a radiolarian species dwelling at mesopelagic depths, is known as a representative glacial fauna due to its unique distribution
during glacial periods. In the present ocean, abundant production of C. davisiana is only observed in the Okhotsk Sea, indicating an adaptation of C. davisiana for seasonal sea-ice covered conditions. We found pronounced abundant production of C. davisiana during the early to middle Holocene in the Okhotsk Sea, suggesting more favorable conditions for C. davisiana than the present Okhotsk Sea. In order to clarify the reason, oceanographic conditions during the Holocene were reconstructed
based on biomarkers, lithogenic grains including ice-rafted debris (IRD), biogenic opal, and total organic carbon (TOC) in
two sediment cores from the Okhotsk Sea. These indicators suggest that the pronounced C. davisiana production may be attributed to: 1) a supply to mesopelagic depths under intensified stratification of fine organic particles
derived from coccolithophorids, bacteria, and detrital materials; and 2) cold, well-ventilated intermediate water formation. 相似文献
5.
Tetsuo Yanagi Koji Ishikawa Koh-ichi Inoue Satoshi Susami 《Journal of Oceanography》1995,51(2):225-238
The detailed flow structure around a tical front in Hiuchi-Nada, Japan was observed with the use of ADCP (Acoustic Doppler Current Profiler). The surface convergence region is observed at the transition zone between vertically well mixed area and the stratified area. The surface divergence regions exist next to the surface convergence region. The strong downward current is estimated in the middle layer just below the surface convergence region. The maximum surface convergence and the maximum downward velocity in the middle layer are 1.0×10–4 s–1 and 0.12 cm s–1, respectively. 相似文献
6.
7.
E. M. Chamorro Pérez I. Daniel J.-C. Chervin P. Dumas J. D. Bass T. Inoue 《Physics and Chemistry of Minerals》2006,33(7):502-510
High-pressure synchrotron infrared (IR) absorption spectra were collected between 650 and 4,000 cm−1 at ambient temperature for hydrous Mg-ringwoodite (γ-Mg2SiO4) up to 30 GPa. The main feature in the OH− stretching region is an extremely broad band centred at 3,150 cm−1. The hydrogen bond is strong for most protons and the most probable site for protonation is the tetrahedral edge. With increasing pressure, this band shifts downward while decreasing its integrated intensity until disappearance at a pressure of 25 GPa. Only one band at 2,450 cm−1 and an absorption plateau persist with a maximum wavenumber of 3,800 cm−1. This behaviour is reversible upon pressure release. We interpret this as a second-order phase transition occurring in hydrated Mg-ringwoodite at high pressure (beyond ∼ 25 GPa). This result is compatible with the observation by Kleppe et al. (Phys Chem Miner 29:473–476, 2002a) who suggested the presence of Si–O–Si linkages and/or partial increase in the coordination of Si. Beyond the phase transition, the protons are delocalized and their environment on the ringwoodite structure is probably quite different from that at low pressure. Data obtained in situ at high pressures and temperatures are needed to better understand the effect of protonation on the structure and to better constrain this phase transition. 相似文献
8.
Dynamic damaging potential of ground motions must be evaluated by the response behaviour of structures, and it is necessary to indicate what properties of ground motions are most appropriate for evaluation. For that purpose, the behaviour of energy input process and hysteretic energy dissipation are investigated in this study. It is found that the momentary input energy that is an index for the intensity of input energy is related to the characteristics of earthquakes such as cyclic or impulsive, and to the response displacement of structures immediately. On the basis of these results, a procedure is proposed to predict inelastic response displacement of structures by corresponding earthquake input energy to structural dissipated damping and hysteretic energy. In this procedure the earthquake response of structures is recognized as an input and dissipation process of energy, and therefore structural properties and damaging properties of ground motions can be taken into account more generally. Lastly, the studies of the pseudodynamic loading test of reinforced concrete structure specimens subjected to ground motions with different time duration are shown. The purpose of this test is to estimate the damaging properties of ground motions and the accuracy of the proposed prediction procedure. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
9.
Takashi Ono 《冰川冻土》2004,26(Z1):64-69
Serious failure on the slope of rock ground can be caused by a cyclic action of freezing and thawing in the cold regions. The frost susceptibility and the effect of freezing and thawing onthe rock material, however, have not been well investigated. In order to find out the freezing effect on the rock materials, mortar specimens are frozen as a pseudo-rock material under the constant rate of freezing by means of controlling the temperature of both ends of specimen. The freezing process is given one-dimensionally to the cylindrical samples in the laboratory to simulate the in-situ freezing phenomena in the natural ground. Formation of ice lens, frost heave and water intake during freezing process are observed on the mortar specimen under constant freezing rate, which probably causes cracks or large deformation in the real rock ground. The values of the velocity of elastic wave propagation are compared before and after freezing process to estimate the degree of weathering due to freezing and thawing. 相似文献
10.