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261.
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263.
Hiroyuki Tashiro Naoshi Sugiyama 《Monthly notices of the Royal Astronomical Society》2006,368(2):965-970
Early reionization of the intergalactic medium (IGM), which is favoured from the WMAP temperature–polarization cross-correlations, contests the validity of the standard scenario of structure formation in the cold dark matter (CDM) cosmogony. It is difficult to achieve early enough star formation without rather extreme assumptions such as a very high escape fraction of ionizing photons from protogalaxies or a top-heavy initial mass function (IMF). Here, we propose an alternative scenario that additional fluctuations on small scales induced by primordial magnetic fields trigger early structure formation. We found that ionizing photons from Population III stars formed in dark haloes can easily reionize the Universe by z ≃ 15 if the strength of primordial magnetic fields is between 0.7 and 1.5 × 10−9 G . 相似文献
264.
Gerassimos A. Papadopoulos Hiroyuki Matsumoto Athanassios Ganas Vassilis Karastathis Spyros Pavlides 《Journal of Seismology》2004,8(3):381-394
The static displacement field of the Athens 1999 earthquake has been numerically modeled by a BEM method and analysed from SAR interferometry images with compatible results: (a) for a fault that reaches the surface the subsidence field coincides with the hangingwall domain of the Fili neotectonic normal fault with maximum amplitude, d
max, 5.5–7 cm, which is consistent with the possibly co-seismic displacement of 6–10 cm observed in the field, the average fault dislocation of 5–8 cm found by the application of circular source models, and the displacement up to 6 cm predicted by empirical relations between magnitude and displacement; the field of uplift covers the footwall domain of the fault with d
max1.5 cm;d gradually decreases with distance from the fault at a gradient of 0.4 cm/km, (b) for a blind fault d
max is only 1.8 and 0.3 cm in the hangingwall and footwall, respectively, and the decay gradient becomes 0.15 cm/km, (c) the total deformation area is 15 km × 15 km and the Fili fault, with a preferred mean dip of 60°, constitutes the natural boundary between the subsidence and uplift areas. The macroseismic field pattern is similar with that of the static ground deformation. The majority of intensity values VI (MM and EMS-98 scales), are distributed within the hangingwall of the Fili fault, while the highest intensities (VIII and IX) concentrate very close to the Fili fault within its hangingwall domain. A gradual decrease of the intensities with the distance from the Fili fault is evident. Because of the similarity between the intensity distribution pattern and the static ground deformation pattern, we make the hypothesis that the latter predicts well enough the main characteristics of the former although the ground displacement is dominated by relatively low frequency as compared to the ground acceleration. 相似文献
265.
We have obtained a high-resolution sedimentary record covering the last 6500 yr from a maar in Cheju Island, Korea, in order to reconstruct the history of variations in the eolian quartz flux (EQF) and hence Asian dust. The long-term variation of EQF reveals three intervals: a period of high EQF (4000-2000 cal yr B.P.) and two periods of low EQF (6500-4000 cal yr B.P. and 2000 cal yr B.P. to present), which have been affected by the East Asian monsoon due to insolation change and the cold air activity in high latitudes correlated with polar high-pressure systems. This long-term variation is superimposed by millennial- and centennial-scale fluctuations with periodicities of 1137, 739, 214, 162, 137, 127, and 111 yr, implying drier conditions in the source areas in China. The detrended EQF record correlates visually and statistically (cross-spectral analysis) with the atmospheric Δ14C record (solar proxy). The centennial-scale variability in EQF may be affected by the solar activity through the Sun-East Asian monsoon linkage. 相似文献
266.
Frictional discharge at fault asperities: Origin of fractal seismo-electromagnetic radiation 总被引:1,自引:0,他引:1
To investigate the relation between the rock friction and the fractal electromagnetic radiation before the main-shock of earthquakes, we conducted a friction experiment simulating the motion of an asperity on a fault plane, and observed photon emissions due to electric discharge by dielectric breakdown of ambient gases from friction contacts between rock minerals. This indicates that frictional discharges (plasma generations) could occur locally at microscopic asperities on fault surfaces. From concepts on the fractal size-distribution and temporal evolution of fault asperities, the frictional discharge occurring at asperities on the fault plane can be one of origins of the fractal electromagnetic radiation (Benioff electromagnetic radiation) prior to earthquakes. 相似文献
267.
Neogene rift system configuration for the back-arc of southwest Japan, southern rim of the Japan Sea, is argued on the basis of reflection seismic interpretation. Divergent rifting and subsequent contraction provoked by an arc–arc collisional event are manifested by the formation of faulted grabens and their inverted deformation, respectively. We identified the following four Cenozoic tectonic epochs as a decomposition process of the eastern Eurasian margin based on reliable paleomagnetic data: (1) Plate margin rearrangement on a regional left-lateral fault through southwest Japan and Sikhote Alin, which constituted a continuous geologic province before the early Tertiary differential motion; (2) Early Tertiary clockwise rotation (>20°) of the east Tan-Lu block relative to the North China block; (3) Oligocene to early Miocene divergent rifting and spreading of the Japan Sea, which divided southwest Japan from the east Tan-Lu block; (4) Middle Miocene bending and back-arc inversion of southwest Japan caused by collision with the Izu-Bonin arc. According to the estimation of relative motions during these events, a paleogeographic reconstruction is presented through Cenozoic time. 相似文献
268.
A constitutive law for viscoelastic behaviour of rocks is derived from irreversible thermodynamics. To this model, two specific parameters are introduced; one is an internal state variable which is a variable concerning the microstructures such as defects in crystals or microcracks, and the other is a temperature reduced time obtained by normalizing the various temperature behaviours. A large number of internal state variables have the respective relaxation times and show the respective time evolutions, while a set of the time evolutions generates temporal power-law behaviour of rocks. The time evolutions of internal states are regarded as dynamics of elements of the generalized Maxwell model, and the stress–strain relation is represented by a response function following a temporal power-law in terms of linear system theory. This relation is inversely formulated to investigate the source field from output data. This model enables us to explain experimentally-based constitutive laws for transient and steady-state behaviour of rocks (e.g., lherzolite) following a temporal power-law and for attenuation behaviour of polycrystals (e.g., olivine) represented by a relation between the quality factor and frequency. Both laws show power-laws on deformation time or frequency depending on the fractal structure in polycrystals or rocks, and the experimental high-temperature behaviours can be extrapolated to long deformation time or high frequency behaviour. 相似文献
269.
Yuki Matsushi Sachi Wakasa Hiroyuki Matsuzaki Yukinori Matsukura 《Geomorphology》2006,82(3-4):283-294
Depth profiling of in situ-produced cosmogenic 10Be and 26Al was applied to estimate the rate of long-term denudation on actively uplifting hillcrests made of weakly consolidated sandstone in the Boso Peninsula, Japan. The nuclide concentration in the topmost meter of the hillcrest has reached an equilibrium value owing to surface denudation at 90 mm/kyr. This rate is much smaller than the regional uplift rate, and is consistent with the current isolated residual topography of the hillcrest. By considering the epoch of emergence of the sandstone hillcrests, we estimate the summit denudation rate of the adjacent mudstone hill formation to be 720 ± 110 mm/kyr. 相似文献
270.
Resolution dependence of tropical cyclone formation in CMIP3 and finer resolution models 总被引:1,自引:0,他引:1
Kevin Walsh Sally Lavender Enrico Scoccimarro Hiroyuki Murakami 《Climate Dynamics》2013,40(3-4):585-599
Detection of tropical lows is performed in a suite of climate model simulations using objectively-determined detection thresholds that are resolution-dependent. It is found that there is some relationship between model resolution and tropical cyclone formation rate even after the resolution-dependent tropical cyclone detection threshold is applied. The relationship is investigated between model-simulated tropical cyclone formation and a climate-based tropical cyclone Genesis Potential Index (GPI). It is found that coarser-resolution models simulate the GPI better than they simulate formation of tropical cyclones directly. As a result, there appears to be little relationship from model to model between model GPI and the directly-simulated cyclone formation rate. Statistical analysis of the results shows that the main advantage of increasing model resolution is to give a considerably better pattern of cyclone formation. Finer resolution models also simulate a slightly better pattern of GPI, and for these models there is some relationship between the pattern of GPI simulated by each model and that model’s pattern of simulated tropical cyclone formation. 相似文献