Satellite detection of red tide in Ariake Sound, 1998–2001     

Joji Ishizaka  Yasuhisa Kitaura  Yasuharu Touke  Hiroaki Sasaki  Akihiko Tanaka  Hiroshi Murakami  Toshikazu Suzuki  Kazumi Matsuoka  Hideaki Nakata 《Journal of Oceanography》2006,62(1):37-45

High resolution SeaWiFS data was used to detect red tide events that occurred in the Ariake Sound, Japan, a small embayment known as one of the most productive areas in Japan. SeaWiFS chlorophyll data clearly showed that a large red tide event, which damaged seaweed (Nori) cultures, started early in December 2000 in Isahaya Bay, expanded to the whole sound and persisted to the end of February 2001. The monthly average of SeaWiFS data from May 1998 to December 2001 indicated that the chlorophyll peaks appeared twice a year, in early summer and in fall, after the peaks of rain and river discharge. The SeaWiFS data showed that the red tide event during 2000–2001 winter was part of the fall bloom; however, it started later and continued significantly longer than other years. Satellite ocean color data is useful to detect the red tide; however the algorithms require improvement to accurately estimate chlorophyll in highly turbid water and in red tide areas.  相似文献   

Temporal change of clustered distribution of planktonic ciliates in Toyama Bay in summers of 1989 and 1990     

Toshikazu Suzuki  Akira Taniguchi 《Journal of Oceanography》1997,53(1):35-40

Temporal change of clustered distribution in vertical profiles of three nutritional groups of planktonic ciliates, e.g. heterotrophic naked ciliates, mixotrophic naked ciliates and heterotrophic loricated ciliates, was investigated by following a drifting buoy in Toyama Bay on the Japan Sea coast of central Japan in summers of 1989 and 1990. Clustered distribution, represented as the mode of population density in the vertical plane, occurred mainly in the oligotrophic upper layer (0–50 m depth) above the subsurface chlorophyll-a maximum layer. Its clustered degree was stronger when the mode of population density in the vertical plane was formed at shallower depth, while its longevity was shorter as mentioned above. Vertical distribution of ciliates during summer in Toyama Bay is characterized by ephemeral clustered distribution, or in other wards, by rapid alternations of appearance and disappearance of the clustered distribution.  相似文献   

Wave-induced porewater pressure in a seabed with inhomogeneous permeability     

Toshikazu Kitano  Hajime Mase 《Ocean Engineering》2001,28(3)

We have developed an analytical treatment for the wave-induced response of a seabed with inhomogeneous permeability, by employing the boundary layer approximation. By assuming an exponential function for vertically distributed permeability, the inhomogeneous consolidation equation was formulated as Bessel's differential equation. Subsequently, we proposed some representative quantities for examining the effects of inhomogeneity of permeability. The main effects of inhomogeneity are that the boundary layer becomes thinner and the phase delay in the direction of depth becomes larger as the inhomogeneity becomes significant. In addition, it was shown that the boundary layer is properly evaluated by using the averaged permeability.  相似文献   

The squeezing potential of rock around tunnels: Theory and prediction with examples taken from Japan   总被引：5，自引：2，他引：5  

Prof. Dr. Ö. Aydan  T. Akagi  T. Kawamoto 《Rock Mechanics and Rock Engineering》1996,29(3):125-143

Summary Large deformations of surrounding media around tunnels are often encountered during excavations in rocks with squeezing characteristics. These deformations may sometimes continue for a long period of time. Predictions of deformations of tunnels in such grounds are urgently needed, not because of stability concerns, but also of their sevicability. In the present study, the squeezing phenomenon of rock around tunnels and its mechanism and associated factors are first clarified by carefully studying failures of tunnels, and a survey of tunnels in squeezing rocks in Japan is presented and its results are summarised. Then, a practical method is proposed to predic the squeezing potential and deformation of tunnels in squeezing rock and this method has beeen applied to actual tunnelling projects, where squeezing problems were encountered, to check its applicability and validity. Finally, an extension of this method to the time-dependent behaviour of squeezing rocks is given and an application of this method to an actual tunnel is presented.  相似文献   

The anisotropy of surface morphology characteristics of rock discontinuities   总被引：1，自引：4，他引：1  

Ö. Aydan  Y. Shimizu  T. Kawamoto 《Rock Mechanics and Rock Engineering》1996,29(1):47-59

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Effects of grain morphology on critical state: a computational analysis     

Alex X. Jerves  Reid Y. Kawamoto  José E. Andrade 《Acta Geotechnica》2016,11(3):493-503

We introduce a new DEM scheme (LS-DEM) that takes advantage of level sets to enable the inclusion of real grain shapes into a classical discrete element method. Then, LS-DEM is validated and calibrated with respect to real experimental results. Finally, we exploit part of LS-DEM potentiality by using it to study the dependency of critical state (CS) parameters such as critical state line (CSL) slope \(\lambda \), CSL intercept \(\varGamma \), and CS friction angle \(\varPhi _{\mathrm{CS}}\) on the grain’s morphology, i.e., sphericity, roundness, and regularity. This study is carried out in three steps. First, LS-DEM is used to capture and simulate the shape of five different two-dimensional cross sections of real grains, which have been previously classified according to the aforementioned morphological features. Second, the same LS-DEM simulations are carried out for idealized/simplified grains, which are morphologically equivalent to their real counterparts. Third, the results of real and idealized grains are compared, so the effect of “imperfections” on real particles is isolated. Finally, trends for the CS parameters (CSP) dependency on sphericity, roundness, and regularity are obtained as well as analyzed. The main observations and remarks connecting particle’s morphology, particle’s idealization, and CSP are summarized in a table that is attempted to help in keeping a general picture of the analysis, results, and corresponding implications.  相似文献   

High-reliability zircon separation for hunting the oldest material on Earth: An automatic zircon separator with image-processing/microtweezers-manipulating system and double-step dating     

Yukio Isozaki  Shinji Yamamoto  Shuhei Sakata  Hideyuki Obayashi  Takafumi Hirata  Ken-ichi Obori  Toshinori Maebayashi  Satoshi Takeshima  Toshikazu Ebisuzaki  Shigenori Maruyama 《地学前缘(英文版)》2018,9(4):1073-1083

Despite the recent development in radiometric dating of numerous zircons by LA-ICPMS, mineral separation still remains a major obstacle, particularly in the search for the oldest material on Earth. To improve the efficiency in zircon separation by an order of magnitude, we have designed/developed a new machine-an automatic zircon separator(AZS). This is designed particularly for automatic pick-up of100 μm-sized zircon grains out of a heavy mineral fraction after conventional separation procedures. The AZS operates in three modes:(1) image processing to choose targeted individual zircon grains out of all heavy minerals spread on a tray,(2) automatic capturing of the individual zircon grains with microtweezers, and(3) placing them one-by-one in a coordinated alignment on a receiving tray. The automatic capturing was designed/created for continuous mineral selecting without human presence for many hours. This software also enables the registration of each separated zircon grain for dating, by recording digital photo-image, optical(color) indices, and coordinates on a receiving tray. We developed two new approaches for the dating; i.e.(1) direct dating of zircons selected by LA-ICPMS without conventional resin-mounting/polishing,(2) high speed U-Pb dating, combined with conventional sample preparation procedures using the new equipment with multiple-ion counting detectors(LA-MIC-ICPMS).With the first approach, Pb-Pb ages obtained from the surface of a mineral were crosschecked with the interior of the same grain after resin-mounting/polishing. With the second approach, the amount of time required for dating one zircon grain is ca. 20 s, and a sample throughput of 150 grains per hour can be achieved with sufficient precision(ca. 0.5%).We tested the practical efficiency of the AZS, by analyzing an Archean Jack Hills conglomerate in Western Australia with the known oldest(4.3 Ga) zircon on Earth. Preliminary results are positive; we were able to obtain more than 194 zircons that are over 4.0 Ga out of ca. 3800 checked grains, and 9 grains were over 4300 Ma with the oldest at 4371 ± 7 Ma. This separation system by AZS, combined with the new approaches, guarantees much higher yield in the hunt for old zircons.  相似文献   

The squeezing potential of rocks around tunnels; Theory and prediction   总被引：7，自引：4，他引：7  

Ö. Aydan  T. Akagi  T. Kawamoto 《Rock Mechanics and Rock Engineering》1993,26(2):137-163

Summary The deformational behaviour of tunnels, which underwent large deformations, socalled squeezing, have been recently receiving great attention in the field of rock mechanics and tunnelling. Contrary to rockbursting phenomenon in which the deformation of the medium takes place instantaneously, the deformation of the surrounding rock in squeezing phenomenon takes place slowly and gradually when the resulting stress state following the excavation exceeds the strength of the surrounding medium. Although there are some proposals for the definition of squeezing rocks and prediction of their squeezing potential and deformations of tunnels in literature, it is difficult to say that they are concise and appropriate.In the first half of this paper, the squeezing phenomenon of rock about tunnels and its mechanism and associated factors are clarified by studying carefully observed failures in-situ and laboratory model tests. Then, an extensive survey of tunnels in squeezing rocks in Japan is presented and the results of this survey are summarised. In the second half of the paper, a new method is proposed to predict the squeezing potential and deformations of tunnels in squeezing rock. Then, the method is applied to actual tunnelling projects, where squeezing problems have been encountered, to check its validity and applicability. As a concrete example, an application of the method to predict the squeezing potential and deformations of the rock along a 300 m long section of an actual tunnel was made.  相似文献   

Fate and transport of pollutants through a municipal solid waste landfill leachate in Sri Lanka     

S. S. R. M. D. H. R. Wijesekara  Sonia S. Mayakaduwa  A. R. Siriwardana  Nalin de Silva  B. F. A. Basnayake  Ken Kawamoto  Meththika Vithanage 《Environmental Earth Sciences》2014,72(5):1707-1719

This study focuses on the characterization of leachate generated from Gohagoda dumpsite in Kandy, Sri Lanka, assessment of its spatial and temporal variations, and identification of subsurface canals and perched water bodies in the wetland system affected by the leachate flow. Leachate samples were collected monthly throughout dry and rainy seasons from different points of the leachate drainage channel over a period of 1 year and they were tested for quality parameters: pH, temperature, electrical conductivity, total dissolved soils, alkalinity, hardness, total solids, volatile solids, total suspended solids, volatile suspended solids, biochemical oxygen demand (BOD₅), chemical oxygen demand, nitrate-nitrogen, nitrite-nitrogen, phosphates, ammonium-nitrogen, chloride, dissolved organic carbon, total organic carbon and heavy metals. Sequential soil extraction procedures were performed for the characterization of leachate-affected local soil. A geophysical survey using direct current resistivity technique was conducted at locations downstream of the dumpsite. Leachate characteristics indicated that the leachate is in the methanogenic phase and the results strongly suggest that the leachate may be polluting the river where the leachate is discharged directly. Leachate exceeds the allowable limits of Sri Lankan wastewater discharge standards for many of the parameters. Significant difference (P < 0.05) was observed for most of organic and inorganic parameters among all sampling locations. Many parameters showed a negative correlation with pH. The affected soils showed high heavy metal concentrations. Resistivity study confirmed a confined leachate flow at the near surface with few subsurface canals. However, no separate subsurface plume movement was observed. The results of this research can effectively be used for the establishment of an efficient and effective treatment method for the Gohagoda landfill leachate.  相似文献   

Development of the Global Earthquake Model’s neotectonic fault database   总被引：2，自引：0，他引：2  

Annemarie Christophersen  Nicola Litchfield  Kelvin Berryman  Richard Thomas  Roberto Basili  Laura Wallace  William Ries  Gavin P. Hayes  Kathleen M. Haller  Toshikazu Yoshioka  Richard D. Koehler  Dan Clark  Monica Wolfson-Schwehr  Margaret S. Boettcher  Pilar Villamor  Nick Horspool  Teraphan Ornthammarath  Ramon Zuñiga  Robert M. Langridge  Mark W. Stirling  Tatiana Goded  Carlos Costa  Robert Yeats 《Natural Hazards》2015,79(1):111-135

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