Experimental Investigation of Shock Wave Attenuation in Basalt     

S. Nakazawa  S. WatanabeY. Iijima  M. Kato 《Icarus》2002,156(2):539-550

Shock compression experiments on Kinosaki basalt were carried out in the interest of studying collisional phenomena in the solar nebula. Shock waves of 7 and 31 GPa were generated using a thin flyer plate, and a shock wave of 16 GPa was generated using a thick cylindrical projectile. By employing in-material manganin and carbon pressure gauges, the shock wave attenuation was examined and the propagation velocities of the shock wave and rarefaction wave were measured.The attenuation mechanism consists of two effects: the rarefaction wave and geometrical expansion. The rarefaction effect includes the reflected wave and the edge wave. The efficiency of these mechanisms depends on the geometry of the projectile, initially induced pressure, and materials of the target and projectile.As a result of the experiments, a cylindrical impactor created an isobaric region of size almost equal to the projectile radius. The shock wave in the far field was attenuated similarly with the power of −1.7 to −1.8 of the propagation distance under our experimental conditions. The shock wave generated using a thin flyer plate was attenuated by the rarefaction wave generated on the back surface of the flyer plate and by geometrical expansion effects. The shock wave generated using a thick projectile was attenuated by edge-wave and by geometrical expansion effects.According to elastic theory, the rigidity of basalt at 7 and 31 GPa was calculated as 35±7 and 0±3 GPa, respectively, using the measured rarefaction wave velocities. The decayed shock pressure was related to the ejection velocity of the impact fragments, which were obtained in previous disruption experiments. The attenuation rates in previous experiments were consistent with ours. The previous impact scaling parameter called “nondimensional impact stress (PI)” has been improved.  相似文献   

Effects of soil-structure interaction on seismic response of PC cable-stayed bridge     

Jingzhe Zheng  Tetsuo Takeda 《Soil Dynamics and Earthquake Engineering》1995,14(6):427-437

This paper attempts to assess the effects of dynamic soil-structure interaction (SSI) on the seismic behavior of a PC cable-stayed bridge placed on a moderately deep soil stratum overlying rigid bedrock, and to evaluate the applicability of a simple mass-spring model in evaluating SSI. Parametric analysis is performed to investigate the significance of SSI under various stiffness, foundation depth conditions using finite element methods. The applicability of a mass-spring model is discussed by comparison with FEM. The results of analysis reveal the influence of SSI on the seismic behavior of bridge-soil system, and recommendations for aseismic design are provided. The mass-spring model proves to be promising for representing the seismic behavior of the bridge-soil system, and the mechanism is interpreted in detail.  相似文献   

Effects of environmental gradients concerning water qualities on the structure of the phytoplankton community in the coastal sea     

Tetsuo Mukai  Kazuto Takimoto 《Estuarine, Coastal and Shelf Science》1985,20(2):169-181

The effects on the structure of the phytoplankton community of in situ environmental gradients concerning water qualities, formed during the mixing process of coastal with oceanic waters, were investigated on macro scale over a wide area of the Seto Inland Sea, Japan.The community structure of the phytoplankton varied almost constantly along the in situ environmental gradients in the community, which was shown by use of the diversity index rather than a mere listing of the phytoplankton community. These observations were considered to be the result of the direct or indirect response of the phytoplankton community to environmental gradients which occur in situ, which mean a series of variations of the habitat of the phytoplankton community. Their effects were reflected not in biomass but in the structure of the phytoplankton community. It was difficult to establish quantitatively the extent of their effects because of the variability in the degree of the environmental gradients which occur in situ.  相似文献   

Morphological Features of Co-Rich Manganese Deposits and Their Relation to Seabed Slopes     

Tetsuo Yamazaki  Rahul Sharma 《Marine Georesources & Geotechnology》2013,31(1):43-76

Abstract

The morphological features associated with Co-rich manganese deposits, the size variations of nodules, and the occurrence of different substrates have been analyzed, to evaluate the influence of various seabed slope angles on the distribution of these features. The coverage and size of the crusts depend on their surface morphology and seabed topography, resulting in cobble-type, lineated, or step-like outcrops. Small nodules (1–4 cm in diameter) dominate all seabed slopes, with a few locations having nodules ranging from 1 to 8 or 1 to 10 cm. Sediments invariably occur as substrates for nodules and as cover for crusts, their coverage being inversely proportional to that of the nodules and crust outcrops.

Steeper seafloor areas have large crust outcrops exposed with no or few nodules and sediments associated with them. The intermediate slopes have a combination of nodules, sediments, and crusts in various proportions, depending on topography and gradient. Large-scale nodule occurrences, followed by sediment fields and crust outcrops on seabed slopes of < 3°, 3–7°, and > 15°, respectively, represent typical morphological distribution zones of the Co-rich manganese deposits on a seamount in the central Pacific Ocean. A transition zone between nodule-dominated fields and large crust outcrops occurs for slopes from 7° to 15°. This detailed study on distribution of Co-rich deposits gives a better understanding for purposes of their exploitation.  相似文献   

Evaluation of Vector Winds Observed by NSCAT in the Seas around Japan     

Harunobu Masuko  Kohei Arai  Naoto Ebuchi  Masanori Konda  Masahisa Kubota  Kunio Kutsuwada  Teruko Manabe  Akira Mukaida  Tetsuo Nakazawa  Atsushi Nomura  Akira Shibata  Yoshihiko Tahara 《Journal of Oceanography》2000,56(5):495-505

In order to validate wind vectors derived from the NASA Scatterometer (NSCAT), two NSCAT wind products of different spatial resolutions are compared with observations by buoys and research vessels in the seas around Japan. In general, the NSCAT winds agree well with the wind data from the buoys and vessels. It is shown that the root-mean-square (rms) difference between NSCAT-derived wind speeds and the buoy observations is 1.7 ms^–1, which satisfies the mission requirement of accuracy, 2 ms^–1. However, the rms difference of wind directions is slightly larger than the mission requirement, 20°. This result does not agree with those of previous studies on validation of the NSCAT-derived wind vectors using buoy observations, and is considered to be due to differences in the buoy observation systems. It is also shown that there are no significant systematic trends of the NSCAT wind speed and direction depending on the wind speed and incidence angle. Comparison with ship winds shows that the NSCAT wind speeds are lower than those observed by the research vessels by about 0.7 ms^–1 and this bias is twice as large for data observed by moving ships than by stationary ships. This result suggests that the ship winds may be influenced by errors caused by ship's motion, such as pitching and rolling.  相似文献   

Age gap between the intrusion of gneissose granitoids and regional high‐temperature metamorphism in the Ryoke belt (Mikawa area), central Japan          下载免费PDF全文

Kota Takatsuka  Tetsuo Kawakami  Etienne Skrzypek  Shuhei Sakata  Hideyuki Obayashi  Takafumi Hirata 《Island Arc》2018,27(1)

The relationships between the intrusion of gneissose granitoids and the attainment of regional high‐T conditions recorded in metamorphic rocks from the Ryoke belt of the Mikawa area, central Japan, are explored. Seven gneissose granitoid samples (tonalite, granodiorite, granite) were collected from three distinct plutonic bodies that are mapped as the so‐called “Older Ryoke granitoids.” Based on bulk‐rock compositions and U–Pb zircon ages obtained by laser ablation inductively coupled plasma mass spectrometry, the analyzed granitoids can be separated into two groups. Gneissose granitoids from the northern part of the area give weighted mean ²⁰⁶Pb/²³⁸U ages of 99 ±1 Ma (two samples) and 95 ±1 Ma (one sample), whereas those from the southern part yield 81 ±1 Ma (two samples) and 78–77 ±1 Ma (two samples). Regional comparisons allow correlation of the northern granitoids (99–95 Ma) with the Kiyosaki granodiorite, and mostly with the Kamihara tonalite found to the east. The southern granitoids are tentatively renamed as “78–75 Ma (Hbl)?Bt granite” and “81–75 Ma Hbl?Bt tonalite” (Hbl, hornblende; Bt, biotite). and seem to be broadly coeval members of the same magmatic suite. With respect to available age data, no gneissose granitoid from the Mikawa area shows a U–Pb zircon age which matches that of high‐T metamorphism (ca 87 Ma). The southern gneissose granitoids (81–75 Ma), although they occur in the highest‐grade metamorphic zone, do not seem to represent the heat source which produced the metamorphic field gradient with a low dP/dT slope.  相似文献   

Sea level response to wind field fluctuation around the tip of the Izu Peninsula   总被引：1，自引：0，他引：1  

Hirofumi Hinata  Tetsuo Yanagi  Chizuru Satoh 《Journal of Oceanography》2008,64(4):605-620

The mechanism of a characteristic sea level response (barotropic coastal ocean response) to wind field fluctuation around the tip of the Izu Peninsula observed during the middle of December 2000 to the middle of January 2001 was investigated based on three types of numerical experiments using the Princeton Ocean Model with various parameters. The response was characterized by the relaxation of sea level falling (rising) during eastward upwelling (westward downwelling) favorable wind regime. Analyses of quasi-realistic numerical model results in terms of the vertically integrated momentum balances and vorticity balance for the barotropic mode revealed that: 1) development/abatement of two anomalous circulations generated around the tip of the Izu Peninsula controls the sea level response through the acceleration/deceleration of a quasi-geostrophic barotropic coastal current between the circulations; 2) nonlinear vorticity advection by the Kuroshio Current and by the coastal current, coupled with vorticity diffusion, decelerates the quasi-geostrophic coastal current in the latter half of the wind regimes, which induces the relaxation of sea level rise/fall. The results of the quasi-realistic numerical experiment suggest that an analysis of the vorticity balance for the barotropic mode contributes to a better understanding of sea level responses to wind in coastal regions with strong currents and complex topography. In addition, a numerical experiment with idealized spatially uniform density stratification and a quasi-realistic wind field shows that if the Kuroshio Current had been shifted far offshore from the Izu Peninsula during the observation period, westward propagating continental shelf waves would have controlled the coastal sea level response.  相似文献