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721.
We present numerical modeling of SH-wave propagation for the recently proposed whole Moon model and try to improve our understanding of lunar seismic wave propagation. We use a hybrid PSM/FDM method on staggered grids to solve the wave equations and implement the calculation on a parallel PC cluster to improve the computing efficiency. Features of global SH-wave propagation are firstly discussed for a 100-km shallow and 900-km deep moonquakes, respectively. Effects of frequency range and lateral variation of crust thickness are then investigated with various models. Our synthetic waveforms are finally compared with observed Apollo data to show the features of wave propagation that were produced by our model and those not reproduced by our models. Our numerical modeling show that the low-velocity upper crust plays significant role in the development of reverberating wave trains. Increasing frequency enhances the strength and duration of the reverberations. Surface multiples dominate wavefields for shallow event. Core–mantle reflections can be clearly identified for deep event at low frequency. The layered whole Moon model and the low-velocity upper crust produce the reverberating wave trains following each phases consistent with observation. However, more realistic Moon model should be considered in order to explain the strong and slow decay scattering between various phases shown on observation data. 相似文献
722.
Experimental evaluation of dynamic characteristics of seesaw energy dissipation system for vibration control of structures
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Seesaw energy dissipation system (SEDS), a vibration control system used to provide enhanced seismic protection, has been proposed and investigated numerically. Because of its complicated arrangement, verification experiments are necessary to demonstrate the SEDS damping capacity. This paper presents the results of experimental investigation of the SEDS using fluid viscous dampers. Free vibration tests are conducted to demonstrate the SEDS damping capacity. Results of the free vibration test show that the SEDS has sufficient damping capacity for reduction of the seismic response of the frames. Parametric experimental investigations of the SEDS were conducted, the results of which demonstrate the effects of the system parameter on the damping capacity. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
723.
Lingyu Wang Michael Rowan-Robinson Issei Yamamura Hiroshi Shibai Rich Savage Seb Oliver Matthew Thomson Nurur Rahman Dave Clements Elysandra Figueredo Tomotsugu Goto Sunao Hasegawa Woong-Seob Jeong Shuji Matsuura Thomas G. Müller Takao Nakagawa Chris P. Pearson Stephen Serjeant Mai Shirahata Glenn J. White 《Monthly notices of the Royal Astronomical Society》2008,387(2):601-615
We present a careful analysis of the point-source detection limit of the AKARI All-Sky Survey in the WIDE-S 90-μm band near the North Ecliptic Pole (NEP). Timeline analysis is used to detect IRAS ( Infrared Astronomy Satellite ) sources and then a conversion factor is derived to transform the peak timeline signal to the interpolated 90-μm flux of a source. Combined with a robust noise measurement, the point-source flux detection limit at signal-to-noise ratio (S/N) > 5 for a single detector row is 1.1 ± 0.1 Jy which corresponds to a point-source detection limit of the survey of ∼0.4 Jy.
Wavelet transform offers a multiscale representation of the Time Series Data ( tsd ). We calculate the continuous wavelet transform of the tsd and then search for significant wavelet coefficients considered as potential source detections. To discriminate real sources from spurious or moving objects, only sources with confirmation are selected. In our multiscale analysis, IRAS sources selected above 4σ can be identified as the only real sources at the Point Source Scales. We also investigate the correlation between the non- IRAS sources detected in timeline analysis and cirrus emission using wavelet transform and contour plots of wavelet power spectrum. It is shown that the non- IRAS sources are most likely to be caused by excessive noise over a large range of spatial scales rather than real extended structures such as cirrus clouds. 相似文献
Wavelet transform offers a multiscale representation of the Time Series Data ( tsd ). We calculate the continuous wavelet transform of the tsd and then search for significant wavelet coefficients considered as potential source detections. To discriminate real sources from spurious or moving objects, only sources with confirmation are selected. In our multiscale analysis, IRAS sources selected above 4σ can be identified as the only real sources at the Point Source Scales. We also investigate the correlation between the non- IRAS sources detected in timeline analysis and cirrus emission using wavelet transform and contour plots of wavelet power spectrum. It is shown that the non- IRAS sources are most likely to be caused by excessive noise over a large range of spatial scales rather than real extended structures such as cirrus clouds. 相似文献
724.
725.
By means of a simplified three degrees of freedom model, seismic behavior of reinforced concrete bridge piers and foundations were evaluated based on pseudo‐dynamic (PsD) tests for cases where pier strengthening and foundation strengthening are implemented. In addition, analysis based on PsD test results was conducted to investigate the influence of pier strengthening on seismic damage to the foundation. The PsD tests and the analysis show that the foundation suffers increased hysteretic response when pier strengthening is applied. The results also show that the foundation strengthening can prevent foundation damage. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
726.
Yasuyuki Nakagawa Kazuo Nadaoka Hiroshi Yagi Ryuichi Ariji Haruo Yoneyama Kazuhiro Shirai 《Ocean Dynamics》2012,62(10-12):1535-1544
Tokyo Bay is one of the estuaries in Japan with a high population of almost 26 million people in the basin area. One of the major concerns for the environment in this water area is the decreasing ecosystem functions including the deterioration of water and sediment qualities caused by various anthropogenic activities. Since the bottom sediments around almost the entire area of the inner bay consist of fine materials with a high organic content, which cause the deterioration of water quality through processes such as hypoxia, an understanding of the fine sediment dynamics in the Bay is crucial for an environmental assessment of the water area. This paper proposes a model for the key processes of fine sediment dynamics, which reflects field data about muddy bed structures and their dynamics obtained during the monitoring campaign in 2007. One of the specific features of the sediment in the Bay at present is the persistent existence of fluid mud layers (water content over 300?%) with a thickness of around a few decimeters, which might be caused by deposition of abundant organic particles due to eutrophication. The present study shows that diffusion flux model delivers quite reliable results for estimating erosion flux from the top of fluid mud layers after calibrating the model parameter against the time series data of vertical flux measured by an acoustic Doppler velocimeter system. This study also derives analytical solutions, based on the Bingham fluid concept, of advection flux in the fluid mud layer on which external shear stress force is applied. 相似文献
727.
For the conservation and restoration of river environment,a sediment replenishment technique, which conveys a part of the sediments excavated and/or dredged from reservoirs to the river below dams is developed and has been implemented tentatively in several dams.Sediments placed as replenishment can be flushed out and transported downstream by floodwater or dam releases.The flushed sediments are expected to contribute to the control of degradation and the variation of the low-flow channel.However,this technique is in the development stage because there are many unknown factors.Therefore,systematic investigations are necessary for practical management of the technique.In this study,the effects of the location of replenishment sediment on sediment flushing and on control of degradation were investigated by means of flume experiments.A two-dimensional numerical model was also developed to further investigate the effects of sediment augmentation on river restoration.The numerical model treats bank erosion and sediment transport over fixed beds. The simulation results were verified against the experimental results.The flushing process of replenishment sediment was investigated first,and then its effect as a countermeasure for river bed degradation was analyzed.Results are summarized as follows:(1) Augmentation at upper riffles is effective for flushing of replenishment sediment and variation of low-flow channel.(2) Amelioration of degradation can be found in the cases of two types of placement.The amelioration effect of upper riffle placement was larger than that of lower riffle placement(3) Aggradation rate of the bed near the replenishment site in the fixed bed is large in the lower riffle placement compared with the upper riffle placement.(4) The numerical model was found to be generally successful as a predictive tool. 相似文献
728.
Variation of the southward interior flow of the North Pacific subtropical gyre,as revealed by a repeat hydrographic survey 总被引:2,自引:1,他引:1
Akira Nagano Hiroshi Ichikawa Yasushi Yoshikawa Shoichi Kizu Kimio Hanawa 《Journal of Oceanography》2012,68(2):361-368
Baroclinic variations of the southward flow in the interior region of the North Pacific subtropical gyre are presented with
five hydrographic sections from San Francisco to near Japan during 2004–2006. The volume transport averaged temperature of
the interior flow, which varies vigorously by a maximum of 0.8°C, is negatively correlated with the transport in the layer
of density 24.5–26.5σ
θ, associated with changes in the vertical current structure. Transport variation in this density layer is thus mainly responsible
for the thermal impact of the interior flow on the heat transport of the subtropical gyre. 相似文献
729.
Kenichiro Tani Richard S. Fiske Yoshihiko Tamura Yukari Kido Jiro Naka Hiroshi Shukuno Rika Takeuchi 《Bulletin of Volcanology》2008,70(5):547-562
Sumisu volcano was the site of an eruption during 30–60 ka that introduced ∼48–50 km3 of rhyolite tephra into the open-ocean environment at the front of the Izu-Bonin arc. The resulting caldera is 8 × 10 km
in diameter, has steep inner walls 550–780 m high, and a floor averaging 900 m below sea level. In the course of five research
cruises to the Sumisu area, a manned submersible, two ROVs, a Deep-Tow camera sled, and dredge samples were used to study
the caldera and surrounding areas. These studies were augmented by newly acquired single-channel seismic profiles and multi-beam
seafloor swath-mapping. Caldera-wall traverses show that pre-caldera eruptions built a complex of overlapping dacitic and
basaltic edifices, that eventually grew above sea level to form an island about 200 m high. The caldera-forming eruption began
on the island and probably produced a large eruption column. We interpret that prodigious rates of tephra fallback overwhelmed
the Sumisu area, forming huge rafts of floating pumice, choking the nearby water column with hyperconcentrations of slowly
settling tephra, and generating pyroclastic gravity currents of water-saturated pumice that traveled downslope along the sea
floor. Thick, compositionally similar pumice deposits encountered in ODP Leg 126 cores 70 km to the south could have been
deposited by these gravity currents. The caldera-rim, presently at ocean depths of 100–400 m, is mantled by an extensive layer
of coarse dense lithic clasts, but syn-caldera pumice deposits are only thin and locally preserved. The paucity of syn-caldera
pumice could be due to the combined effects of proximal non-deposition and later erosion by strong ocean currents. Post-caldera
edifice instability resulted in the collapse of a 15° sector of the eastern caldera rim and the formation of bathymetrically
conspicuous wavy slump structures that disturb much of the volcano’s surface. 相似文献
730.
Hiroshi Momiji 《地球表面变化过程与地形》2008,33(14):2297-2299
Barchan dunes are known to maintain their shapes during their downwind migration, and therefore considered to be at equilibrium. Such an equilibrium state may be materialized by multiple stabilizing mechanisms, which have rarely been discussed. As an example, it is shown here how dune size is maintained by employing the kinematics approach based on the balance between incoming and outgoing sand fluxes. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献