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Sanae Koizumi Takehiko Hiraga Chihiro Tachibana Miki Tasaka Tomonori Miyazaki Tamio Kobayashi Asako Takamasa Naoki Ohashi Satoru Sano 《Physics and Chemistry of Minerals》2010,37(8):505-518
Synthesized mineral powders with particle size of <100 nm are vacuum sintered to obtain highly dense and fine-grained polycrystalline
mantle composites: single phase aggregates of forsterite (iron-free), olivine (iron containing), enstatite and diopside; two-phase
composites of forsterite + spinel and forsterite + periclase; and, three-phase composites of forsterite + enstatite + diopside.
Nano-sized powders of colloidal SiO2 and highly dispersed Mg(OH)2 with particle size of ≤50 nm are used as chemical sources for MgO and SiO2, which are common components for all of the aggregates. These powders are mixed with powders of CaCO3, MgAl2O4, and Fe(CO2CH3)2 to introduce mineral phases of diopside, spinel, and olivine to the aggregates, respectively. To synthesize highly dense
composites through pressureless sintering, we find that calcined powders should be composed of particles that have: (1) fully
or partially reacted to the desired minerals, (2) a size of <100 nm and (3) less propensity to coalesce. Such calcined powders
are cold isostatically pressed and then vacuum sintered. The temperature and duration of the sintering process are tuned to
achieve a balance between high density and fine grain size. Highly dense (i.e., porosity ≤1 vol%) polycrystalline mantle mineral
composites with grain size of 0.3–1.1 μm are successfully synthesized with this method. 相似文献
2.
How do we understand national climate change politics in the United States? Using a methodological innovation in network analysis, this paper analyzes discussions about the issue within the US Congress. Through this analysis, the ideological relationships among speakers providing Congressional testimony on the issue of climate change are mapped. For the first time, issue stances of actors are systematically aggregated in order to measure coalitions and consensus among political actors in American climate politics in a relational way. Our findings show how consensus formed around the economic implications of regulating greenhouse gases and the policy instrument that should do the regulating. The paper is separated into three sections. First, we review the ways scholars have looked at climate change policymaking in the United States, paying particular attention to those who have looked at the issue within the US Congress. Next, we present analysis of statements made during Congressional hearings on climate change over a four-year period. Our analysis demonstrates how a polarized ideological actor space in the 109th Congress transforms into a more consensual actor landscape in the 110th Congress, which is significantly less guided by partisan differences. This paper concludes by discussing how these findings help us understand shifting positions within American climate politics and the implications of these findings. 相似文献
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Crustal transect from the North Atlantic Knipovich Ridge to the Svalbard Margin west of Hornsund 总被引：1，自引：0，他引：1
Frode Ljones Asako Kuwano Rolf Mjelde Asbjrn Breivik Hideki Shimamura Yoshio Murai Yuichi Nishimura 《Tectonophysics》2004,378(1-2):17-41
The crustal structure along a 312 km transect, stretching from the axial mountains of the North Atlantic Knipovich Ridge to the continental shelf of Svalbard, has been obtained using seismic reflection data and wide angle OBS data. The resulting seismic Vp and Vs models are further constrained by a 2-D-gravity model. The principal objective of this study is to describe and resolve the physical and compositional properties of the crust in order to understand the processes and creation of oceanic crust in this extremely slow-spreading counterpart of the North Atlantic Ridge Systems. Vp is estimated to be 3.50–6.05 km/s for the upper oceanic crust (oceanic layer 2), with a marked increase away from the ridge. The measured Vp of 6.55–6.95 km/s for oceanic layer 3A and 7.10–7.25 km/s for layer 3B, both with a Vp/Vs ratio of 1.81, except for slightly higher values at the ridge axis, does not allow a clear distinction between gabbro and mantle-derived peridotite (10–40% serpentized). The thickness of the oceanic crust varies a lot along the transect from the minimum of 5.6 km to a maximum of 8.1 km. The mean thickness of 6.7 km for the oceanic crust is well above the average thickness for slow-spreading ridges (<10 mm/year half-spreading rate). The areas of increased thickness could be explained by large magma production-rates found in the zones of axial highs at the ridge axis, which also have generated the off-axial highs adjacent the ridge. We suggest that these axial and off-axial highs along the ridge control the lithological composition of the oceanic crust. This approach suggests normal gabbroic oceanic crust to be found in the areas bound by the active magma segments (the axial and off-axial highs) and mantle-derived peridotite outside these zone. 相似文献
4.
We studied the applicability of two types of existing three-dimensional (3-D) basin velocity structure models of the Osaka
basin, western Japan for long-period ground motion simulations. We synthesized long-period (3–20 s) ground motions in the
Osaka basin during a M6.5 earthquake that occurred near the hypothetical Tonankai earthquake source area, approximately 200 km
from Osaka. The simulations were performed using a 3-D finite-difference method with nonuniform staggered grids using the
two basin velocity structure models. To study the ground motion characteristics inside the basin, we evaluated the wave field
inside the basin using the transfer functions derived from the synthetics at the basin and a reference rock site outside the
basin. The synthetic waveforms at the basin site were obtained by a convolution of the calculated transfer function and the
observed waveform at the reference rock site.
First, we estimated the appropriate Q values for the sediment layers. Assuming that the Q value depends on the S wave velocity V
S and period T, it was set to Q = (1/3V
S)(T
0/T) where V
S is in m/s and the reference period T
0 is 3.0 s. Second, we compared the synthetics and the observations using waveforms and pseudovelocity response spectra, together
with a comparison of the velocity structures of the two basin models. We also introduced a goodness-of-fit factor to the pseudovelocity
response spectra as an objective index. The synthetics of both the models reproduced the observations reasonably well at most
of the stations in the central part the basin. At some stations, however, especially where the bedrock depth varies sharply,
there were noticeable discrepancies in the simulation results of the models, and the synthetics did not accurately reproduce
the observation. Our results indicate that the superiority of one model over the other cannot be determined and that an improvement
in the basin velocity structure models based on simulation studies is required, especially along the basin edges. We also
conclude that our transfer function method can be used to examine the applicability of the basin velocity structure models
for long-period ground motion simulations. 相似文献
5.
Asbjrn Johan Breivik Rolf Mjelde Paul Grogan Hideki Shimamura Yoshio Murai Yuichi Nishimura Asako Kuwano 《Tectonophysics》2002,355(1-4)
The assembly of the crystalline basement of the western Barents Sea is related to the Caledonian orogeny during the Silurian. However, the development southeast of Svalbard is not well understood, as conventional seismic reflection data does not provide reliable mapping below the Permian sequence. A wide-angle seismic survey from 1998, conducted with ocean bottom seismometers in the northwestern Barents Sea, provides data that enables the identification and mapping of the depths to crystalline basement and Moho by ray tracing and inversion. The four profiles modeled show pre-Permian basins and highs with a configuration distinct from later Mesozoic structural elements. Several strong reflections from within the crystalline crust indicate an inhomogeneous basement terrain. Refractions from the top of the basement together with reflections from the Moho constrain the basement velocity to increase from 6.3 km s−1 at the top to 6.6 km s−1 at the base of the crust. On two profiles, the Moho deepens locally into root structures, which are associated with high top mantle velocities of 8.5 km s−1. Combined P- and S-wave data indicate a mixed sand/clay/carbonate lithology for the sedimentary section, and a predominantly felsic to intermediate crystalline crust. In general, the top basement and Moho surfaces exhibit poor correlation with the observed gravity field, and the gravity models required high-density bodies in the basement and upper mantle to account for the positive gravity anomalies in the area. Comparisons with the Ural suture zone suggest that the Barents Sea data may be interpreted in terms of a proto-Caledonian subduction zone dipping to the southeast, with a crustal root representing remnant of the continental collision, and high mantle velocities and densities representing eclogitized oceanic crust. High-density bodies within the crystalline crust may be accreted island arc or oceanic terrain. The mapped trend of the suture resembles a previously published model of the Caledonian orogeny. This model postulates a separate branch extending into central parts of the Barents Sea coupled with the northerly trending Svalbard Caledonides, and a microcontinent consisting of Svalbard and northern parts of the Barents Sea independent of Laurentia and Baltica at the time. Later, compressional faulting within the suture zone apparently formed the Sentralbanken High. 相似文献
6.
Abstract A single layer of widespread tephra deposits possibly can provide an instantaneous record of the past geomagnetic field and potentially can indicate even a small-scale tectonic rotation compared to a range of geomagnetic secular variations. We report paleomagnetic data of the Ebisutoge–Fukuda tephra, which is dated at approximately 1.8 Ma and is distributed in central Japan between the Osaka–Kyoto area and the Boso Peninsula. The Fukuda volcanic ash layer and its correlative ash deposits in the Osaka–Kyoto area, near Lake Biwa and in the Mie and Niigata areas yield identical site mean declinations of approximately −170° after tilt correction, whereas moderate inclination shallowing is observed in the upper unit at several localities. Anisotropy measurements both of low-field magnetic susceptibility and of anhysteretic remanent magnetization suggest that the inclination shallowing results from the biased alignment of magnetic grains, which were deposited in the fluvial environment. The source volcanic unit, Ebisutoge pyroclastic deposits in the Takayama area, yields a mean declination of approximately −155°, showing clockwise deflection from the magnetic directions of the correlative tephra deposits. These results suggest that no significant rotation occurred between the Osaka–Kyoto, Mie and Niigata areas, but that the Takayama area suffered a clockwise rotation in respect to the other areas during the Quaternary. This rotation might have been caused under an east–west stress field associated with the collision of the Okhotsk Plate with the Eurasia Plate. 相似文献
7.
Temporal and spatial variation of infilling processes in a landslide scar in a steep mountainous region,Japan 
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下载免费PDF全文 The duration of the soil‐depth recovery needed for reoccurrence of shallow colluvial landslides at a given site in humid regions is much longer than the return period of rainfall needed to generate sufficient pore water pressure to initiate a landslide. Knowledge of the rate of change in soil depth in landslide scars is therefore necessary to evaluate return intervals of landslides. Spatial variation in sediment transport at the Kumanodaira landslide scar in central Japan was investigated by field observations. Spatial distribution of the rate of change in soil depth was estimated using sediment transport data and geographic information system (GIS) analysis. Observations revealed that the timing of sediment transport differed for shallow and deep soil layers. Near‐surface sediment transport (mostly dry ravel and some shallow soil creep at depths ≤0·05 m) measured in sediment traps was active in winter and early spring and was affected by freezing–thawing; soil creep of subsoil (i.e. >0·05 m), monitored by strain probes, was active in summer and autumn when precipitation was abundant. Near‐surface sediment flux was estimated by a power law function of slope gradient. Deeper soil creep was more affected by relative location to the landslide scar, which influences soil depth, than by slope gradient. Our study indicated that the rate of soil‐depth recovery is high just below the head scarp of the landslide. Abrupt changes in the longitudinal slope topography immediately above, within and just below the head scarp became smoother with time due to degradation proximate to the landslide head scarp and flanks, as well as aggradation just below the head scarp. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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