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21.
Angelika-M. Wulff Toshiyuki Hashida Kimio Watanabe & Hideaki Takahashi 《Geophysical Journal International》1999,139(2):395-409
Laboratory measurements of ultrasonic wave propagation in tuffaceous sandstone (Kimachi, Japan) and granite (Iidate, Japan) were performed during increasing fracturing of the samples. The fracturing was achieved by unconfined uniaxial compression up to and beyond the point of macrofracture of the specimen using a constant low strain rate. The observed variation of wave velocity (up to 40 per cent) due to the development of micro- and macrofractures in the rock is interpreted by rock models relating velocity changes to damage and crack density. The calculated density of the newly formed cracks reaches higher values for the sandstone than for the granite. Using the estimated crack densities, the attenuation behaviour is interpreted in terms of different attenuation mechanisms; that is, friction and scattering. Rayleigh scattering as described by the model of Hudson (1981 ) may explain the attenuation qualitatively if the largest plausible crack dimensions are assumed in modelling. 相似文献
22.
Toshiro Saino Shaoling Shang Yoshihisa Mino Koji Suzuki Hideaki Nomura Sei-ichi Saitoh Hideo Miyake Toshiyuki Masuzawa Koh Harada 《Journal of Oceanography》1998,54(5):583-592
A sediment trap experiment was carried out in conjunction with an over flight of Ocean Color Temperature Scanner (OCTS) on
board Advanced Earth Observing Satellite (ADEOS) at 40°N, 143°E off Sanriku in April to May 1997. Short term variability of
particle fluxes was examined at depths of 450 m and 600 m from April 6 to May 1 with a sampling interval of two days, and
at 450 m with one day interval from 2nd to 10th May. Daily averaged mass flux at 450 m and 600 m was 815 mg m−2d−1 and 862 mg m−2d−1, respectively. A sharp increase in mass flux was observed during the period from April 26 to April 29 with the highest mass
flux of 8 g m−2d−1. About 85% of the total mass flux for the entire duration (26 days) was collected within these 4 days. Trapped material during
the peak flux period was mainly composed of diatoms dominated byThalassiosira spp. and resting spores ofChaetoceros spp. This suggested that the peak flux was the result of (a) diatom bloom(s) in the euphotic column. Current meter records
at 420 m showed that on April 26 and 27, the period when the peak flux was observed, the southwestward current had diminished
in strength and changed its direction northwestward. Low current speeds appeared to have enhanced trap efficiency to help
form the peak flux. A time series of OCTS Intensive-LAC (Local Area Coverage: Region B) images from mid-March to early May
was examined todetect phytoplankton bloom(s). In the March 26th Chl image, high concentration region was restricted to the
southwest off Cape Erimo, but spread around the warm core ring (WCR) 93A by April 10. East of the WCR93A, high Chl concentration
remained steady until May, but to the west of the WCR93A, Chl decreased rapidly before the 19th of April. From this observation
we suspect that the peak flux observed at the end of April originated from a bloom, which ceased on the 17th or 18th of April,
in the region north of 40°N and west of 143°E. Taking the current meter records into account, the source region for the trapped
material is most likely around southwest of the Cape Erimo. 相似文献
23.
Vertical and cross-wind profiles of mean currents were measured systematically in vertical cross-sections of two wind-wave
tanks with aspect ratios of order one to study the secondary flow in the tanks. A pair of Langmuir cells turned out to be
driven by a close combination of the pressure gradient along the tank and the side-wall effects. That is, part of the adverse
pressure gradient produced a parabolic cross-wind profile with the smallest downwind current at the centerline and the largest
current along the two sidewalls. As a result, upwelling occurred in the center zone where the return flow was strongest, probably
because of the entrainment action of the wind-driven current. In order to compensate for this upwelling, downwelling occurred
along the two side-walls from the flow continuity. The resulting vertical circulation formed a pair of Langmuir circulations
across the span and served to maintain the parabolic profile formed by the pressure gradient. A positive feedback mechanism
is thus found between the primary and secondary circulations through upwelling of the return flow in the center zone. Vertical
shears of the span-averaged downwind current measured in two tanks were found to be systematically different from each other.
This difference seems to depend on the magnitude of the advective Reynolds stresses in the two tanks. 相似文献
24.
Teruhisa Komatsu Masahiro Fukuda Atsuko Mikami Shizuha Mizuno Attachai Kantachumpoo Hideaki Tanoue Michio Kawamiya 《Marine pollution bulletin》2014
Global warming effects on seaweed beds are already perceptible. Their geographical distributions greatly depend on water temperatures. To predict future geographical distributions of brown alga, Sargassum horneri, forming large beds in the northwestern Pacific, we referred to future monthly surface water temperatures at about 1.1° of longitude and 0.6° of latitude in February and August in 2050 and 2100 simulated by 12 organizations under an A2 scenario of global warming. The southern limit of S. horneri distribution is expected to keep moving northward such that it may broadly disappear from Honshu Island, the Chinese coast, and Korean Peninsula in 2100, when tropical Sargassum species such as Sargassum tenuifolium may not completely replace S. horneri. Thus, their forests in 2100 do not substitute those of S. horneri in 2000. Fishes using the beds and seaweed rafts consisting of S. horneri in East China Sea suffer these disappearances. 相似文献
25.
Kohsaku Arai Hideaki Machiyama Shun Chiyonobu Hiroki Matsuda Keiichi Sasaki Marc Humblet Yasufumi Iryu 《Island Arc》2014,23(1):1-15
Bathymetric mapping and observations of the seafloor using a remotely operated vehicle (ROV, Hyper‐Dolphin 3K) were carried out on the slopes of the Miyako‐Sone submarine platform, east of Miyako‐jima in the Ryukyu Islands, northwestern Pacific Ocean. The bathymetric map indicates that terraces are present at water depths of approximately 140 m, 330 m, 400 m, and 680 m on the northwestern slope of the platform. A number of NW–SE trending lineaments, probably faults, extend perpendicular to the axis of the Ryukyu Island Arc. Two ROV surveys were conducted at water depths ranging from 519 m (on the slope) to 121 m (shallowest part of the platform). The surveys revealed that well‐indurated carbonate rocks are exposed at terrace margins and on upper slopes, and that the lower slopes are covered with modern sediments consisting of unconsolidated, coarse‐sand‐sized bioclastic carbonates. Calcareous nannofossils from the well‐indurated carbonate rocks indicate a Middle–Late Pleistocene age, which suggests that the rocks correlate with the Quaternary reef and fore‐reef deposits of the Ryukyu Group (Ryukyu Limestone) on the Ryukyu Islands. No siliciclastic deposits corresponding to the upper Miocene–lower Pleistocene Shimajiri Group (as exposed on Okinawa‐jima and Miyako‐jima islands) were recovered during the surveys. Coeval well‐indurated carbonate rocks, all of which formed in a similar sedimentary environment, have been downthrown towards the west due to displacements on the western sides of normal faults. Subsidence of the Miyako‐Sone submarine platform was the result of large vertical displacements on such normal faults. The timing of initial subsidence cannot be tightly constrained, but the presence of the youngest limestone at progressively lower levels towards the west suggests the subsidence continued until after 0.265 Ma. 相似文献
26.
This paper presents an experimental study on the local bed morphology and grain size characteristics around an impermeable spur dyke.A series of experiments are conducted with different types of sedime... 相似文献
27.
Compaction of a Rock Fracture Moderated by Competing Roles of Stress Corrosion and Pressure Solution 总被引:1,自引:0,他引:1
Unusually rapid closure of stressed fractures, observed in the initial stages of loading and at low temperatures, is examined
using models for subcritical crack growth and pressure solution. The model for stress corrosion examines tensile stress concentrations
induced at the Hertzian contact of propping fracture asperities, and mediates fracture growth according to a kinetic rate
law. Conversely, pressure solution is described by the rate-limiting process of dissolution, resulting from the elevated stresses
realized at the propping asperity contact. Both models are capable of following the observed compaction of fractures in novaculite.
However, closure rates predicted for stress corrosion cracking are orders of magnitudes faster than those predicted for pressure
dissolution. For consistent kinetic parameters, predictions from stress corrosion better replicate experimental observations,
especially in the short-term and at low temperature when mechanical effects are anticipated to dominate. Rates and magnitudes
of both stress corrosion and pressure solution are dependent on stresses exerted over propping asperities. Rates of closure
due to stress corrosion cracking are shown to be always higher than for pressure solution, except where stress corrosion ceases
as contact areas grow, and local stresses drop below an activation threshold. A simple rate law is apparent for the progress
of fracture closure, defined in terms of a constant and an exponent applied to the test duration. For current experimental
observations, this rate law is shown to replicate early progress data, and shows promise to define the evolution of transport
properties of fractures over extended durations. 相似文献
28.
Akira Mizuta Hideaki Takabe Jave O. Kane Bruce A. Remington Dmitri D. Ryutov Marc W. Pound 《Astrophysics and Space Science》2005,295(1-2):197-202
A sample of 54 6.7-GHz methanol maser sources was monitored at HartRAO for 4 years, and 11 12.2-GHz methanol masers for 3 years. The majority of the maser features display a significant degree of variability but with a wide range of timescales and behaviors. Some maser features remained unvarying throughout the monitoring programme, while others showed sporadic flares or sudden drops in flux density. Yet another group show quasi-periodic and periodic variations. In some cases the maser features dropped below the detection limit for a significant length of time before increasing in intensity and reappearing. 相似文献
29.
Simulation of the Collection of Catch Crops for the Recovery of Agricultural Resources using Geographic and Statistical Data 下载免费PDF全文
The cultivation of catch crops has great potential in agricultural areas for the recovery of nutrients, mitigation of groundwater contamination, and secondary utilization of harvestry. To estimate the potential volume of catch crops that can be collected at prospective locations, we simulated the cultivation and collection process at a regional scale using geographic and statistical data. Three types of geographic data, namely the locations of greenhouses, collecting stations and road networks, were used in a geographic information system to compute the volume of collected catch crops and carrying distance between greenhouses and collecting stations. Carbon emission from transportation of the catch crop was calculated using an improved ton‐km method, and the results were compared with the carbon content of the catch crop to evaluate the carbon balance. We found that the total fresh weight of the collected catch crops was 67900 t, of which 70% was collected at the top 15 of 73 stations. Carbon emissions from transportation ranged from >1 to 12% of the carbon content of the catch crop. The analytical method used in this study can readily be applied to other environmental studies concerning the collection of agricultural products and other biomass resources. 相似文献
30.
Several numerical experiments were carried out on the formation of water masses and their fronts such as observed in the Kii Channel in winter. Such water masses and fronts may caused by density-induced current system. The phenomenon is assumed to take place in the vertical two-dimensional plane not involving the effect of the earth's rotation. The linear momentum equation and the diffusion-advection equations of salinity and temperature are integrated with respect to time under a vertically hydrostatic condition. The result is that two rolls which correspond to the onshore water mass and the offshore water mass are formed with an accompanying front between them. The apparent diffusion coefficient reaches a relatively great amount inside the water masses and drops down to the eddy diffusivity level at the front. The dependence of the synoptic distributions of the temperature and salinity on several parameters is also examined. Finally another experiment is carried out involving the effect of the earth's rotation, which results in a rather different distribution pattern from that of the non-rotating model. 相似文献