Risk evaluation and warning threshold of unstable slope using tilting sensor array     

Wang  Lin  Seko  Ichiro  Fukuhara  Makoto  Towhata  Ikuo  Uchimura  Taro  Tao  Shangning 《Natural Hazards》2022,114(1):127-156

Slope monitoring and early warning systems are a promising approach toward mitigating landslide-induced disasters. Many large-scale sediment disasters result in the destruction of infrastructure and loss of human life. The mitigation of vulnerability to slope and landslide hazards will benefit significantly from early warning alerts. The authors have been developing monitoring technology that uses a micro-electro-mechanical systems tilt sensor array that detects the precursory movement of vulnerable slopes and informs the issuance of emergency caution and warning alerts. In this regard, the determination of alarm thresholds is very important. Although previous studies have investigated the recording of threshold values by an extensometer which installation of an extensometer at appropriate sites is also difficult. The authors prefer tilt sensors and have proposed a novel threshold for the tilt angle, which was validated in this study. This threshold has an interesting similarity to previously reported viscous models. Additionally, multi-point monitoring has recently emerged and allows for many sensors to be deployed at vulnerable slopes without disregarding the slope’s precursory local behavior. With this new technology, the detailed spatial and temporal variation of the behavior of vulnerable slopes can be determined as the displacement proceeds toward failure.

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Activity Profile of the Sextantid Meteor Shower     

Ohtsuka  Katsuhito  Shimoda  Chikara  Yoshikawa  Makoto  Watanabe  Jun-Ichi 《Earth, Moon, and Planets》1997,77(2):83-91

The detailed activity profile of the Sextandids - one of the day-time meteor showers - is poorly known and still unclear. Using the forward-scatter radio technique we have successfully been able to obtain further detailed overall activity profile of the Sextantids for seven consecutive years: 1991–1997. Analysis confirmed the Sextantid activity duration in solar longitude (J2000) of at least 184–193° and the maximum solar longitude at 188.35 ± 0.10° with a full width at half maximum (FWHM) of 2.0 ± 0.2°. Performing the numerical integrations, we also substantiated a possibility of the association between Apollo-type asteroid (3200) Phaethon and the Sextantids. Furthermore, we roughly estimated relative maximum flux rate of Sextantids : Geminids as 1 : 3 amplitude ratio. Depending upon the flux rates and the time lags of the orbital evolution with Phaethon, we conclude that the Sextantids are at a more progressive stage of orbital evolution than the Geminids if both meteor streams are really associated with Phaethon. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

The nationwide investigation of endocrine disruptors in sediment of harbours   总被引：3，自引：0，他引：3  

Hosokawa Y  Yasui M  Yoshikawa K  Tanaka Y  Suzuki M 《Marine pollution bulletin》2003,47(1-6):132-138

Various types of endocrine disruptors or environmental hormones flow from their sources down into harbours through rivers and other watercourses, and are accumulated in sediment on the sea bottom. Tributyltin, which has been used as paint for ship bottoms, is considered one of the endocrine disruptors.In close cooperation with the other ministries and agencies, the Ports and Harbours Bureau of the Ministry of Land, Infrastructure and Transport carried out an investigation in 1999 to determine the actual condition of 12 endocrine disruptors in the sediment of 39 harbours, in order to gather fundamental data to be used in future examinations of policy. Furthermore, in 2000 the bureau chose seven harbours out of the above 39 harbours as subjects of an additional investigation regarding the surface distribution of endocrine disruptors in the harbour areas and the synchronistic change of accumulation of dioxin and other substances. As the result of the investigation regarding the surface distribution of endocrine disruptors accumulated in seven harbours, relatively high concentrations were measured in the innermost parts of harbours and the mouths of rivers. Synchronistic changes in the amount of dioxin and other substances accumulated in sediments of five harbours were determined. Small amounts of dioxin and other substances, including an especially small amount of coplanar-PCBs, were found in the layers formed before or around 1950. Relatively large amounts of these substances were measured in the upper layers formed during roughly 1960-1990, though no significant yearly differences in concentration could be identified. This result coincides with the facts that, during roughly 1960-1980, PCP and CNP were used as agricultural chemicals and full-scale production of PCBs started in 1960.  相似文献   

Ecology and restoration techniques for Sargassum beds in the Seto Inland Sea,Japan   总被引：7，自引：0，他引：7  

Terawaki T  Yoshikawa K  Yoshida G  Uchimura M  Iseki K 《Marine pollution bulletin》2003,47(1-6):198-201

Due to the reduction and degradation of coastal areas in Japan by land reclamation and anthropogenic perturbations, from the point of view of conservation of the coastal environment, the restoration of Sargassum beds is essential. Between 1978 and 1991, 6400 ha of seagrass and seaweed beds have been lost along the Japanese coast, of which Sargassum beds were 22%. New techniques for Sargassum bed restoration are summarized based on three coastal engineering techniques. (1) Construction of shallow and gentle sloping bottom substrata have been shown to be effective for the reestablishment of 'management-free seagrass and Sargassum beds' on developed coasts. (2) Seeding or transplanting using artificial substratum for extension of nursery and fishing grounds around natural Sargassum beds. (3) Periodic transplanting of Sargassum plants using artificially produced seedlings is effective to produce niches to allow faunal re-colonization in severely polluted and sparsely vegetated area. However, prior to implementation, the suitability and limitations of these three techniques requires to be ascertained for effective Sargassum bed restoration.  相似文献   

Undrained torsional shear tests on gravelly soils   总被引：5，自引：2，他引：3  

Karma?Kuenza  Ikuo?TowhataEmail author  Roland?P.?Orense  Talib?H.?Wassan 《Landslides》2004,1(3):185-194

Slope instability and landslides are frequently triggered during heavy rainfalls in mountainous areas. Geomaterials that are subject to this type of failure normally include coarse grains, which are made by weathering of mother rocks. These materials are called sandy gravel or gravelly sand in soil mechanics, depending upon the amount of gravelly components. This situation suggests a need for laboratory investigations that aim to understand the shear behavior of sand with gravel toward failure. Another feature of this type of failure is a quick rate of slope failure that is reasonably considered as an undrained process of shear distortion. Hence, the present study investigated by means of experiments the undrained shear behavior of sand with gravel. The torsion shear tests on hollow cylindrical specimens concerned the effects of gravel content on the undrained shear behavior. The tests revealed that the effect of gravel content is twofold. When the gravel content is relatively small, the effects of the sandy component are more important. Hence, the relative density of the sandy matrix among gravels has a predominant influence. In this situation, therefore, the overall relative density is a less important index to account for the shear behavior. In contrast, when the gravel content exceeds a threshold value, the amount of gravel comes to have a more predominant influence than the sandy matrix. This is probably because gravel particles start to have contact with each other to form a structural matrix of gravel grains that governs the overall stress–strain behavior. These results were summarized in three-dimensional diagrams that related the strength properties of gravelly sand varying with the density of sand matrix or the density of sand–gravel mixtures as well as the gravel content.  相似文献   

Glass veins in the unequilibrated eucrite Yamato 82202     

Paul C. Buchanan  Takaaki Noguchi  Donald D. Bogard  Ikuo Katayama 《Geochimica et cosmochimica acta》2005,69(7):1883-1898

The unequilibrated eucrite Yamato 82202 (Y82202) contains a network of relatively thick (up to 1 mm in width) glass veins. The host of the meteorite represents a monomict breccia composed of volcanic rock that crystallized > 4.3 Ga ago as a lava flow on the surface of 4 Vesta. The veins formed 3.90 ± 0.04 Ga ago, probably as a result of frictional melting associated with impact, under conditions of low effective oxygen fugacity and higher sulfur fugacity. The glass contains disordered structural elements characteristic of pyroxene and feldspar, reminiscent of the eucritic target lithology. The unequilibrated pyroxenes of the volcanic host and the pristine character of the glass indicate that this meteoritic material did not experience significant thermal metamorphism after initial crystallization of the lava. Hence, it was not affected by regional metamorphism caused by burial to a significant depth or by long-term contact metamorphism associated with a thick lava flow, large intrusion, or hot layer of impact ejecta. The meteorite resided at a shallow depth (though not at the surface) on 4 Vesta or on one of the vestoids until it was ejected and traveled to Earth, probably with other HED materials that have ³⁶Ar exposure ages of ∼13 Ma. These data suggest that the surface of the asteroid 4 Vesta has significant, though probably small, proportions of glass, as well as unequilibrated volcanic rock.  相似文献   

The misorientation index: Development of a new method for calculating the strength of lattice-preferred orientation   总被引：5，自引：4，他引：5  

Philip Skemer  Ikuo Katayama  Zhenting Jiang  Shun-ichiro Karato 《Tectonophysics》2005,411(1-4):157-167

Using orientation data from experimentally deformed olivine, we explore some practical problems with the J-index, a commonly applied measure of fabric strength. We show that the J-index is highly dependent on several factors, including the number of discrete data in the orientation distribution function (ODF), and arbitrary numerical parameters specified for its calculation. Because of this non-uniqueness, we conclude that the J-index is difficult to interpret and should only be applied with caution. As an alternative to the J-index, we propose a new measure of fabric strength that is based on the distribution of uncorrelated misorientation angles. This “M-index” is shown to be insensitive to the parameters specified for its calculation. For typical deformed olivine samples, we show that 150 discrete data are adequate to quantify fabric strength using the M-index technique. The M-index correlates well with seismic anisotropy, particularly for materials of the same fabric type. Therefore, we conclude that the M-index technique is well-suited for the quantification of fabric strength and the comparison of like materials.  相似文献   

STOIC: a study of coupled model climatology and variability in tropical ocean regions   总被引：13，自引：4，他引：13  

M. Davey  M. Huddleston  K. Sperber  P. Braconnot  F. Bryan  D. Chen  R. Colman  C. Cooper  U. Cubasch  P. Delecluse  D. DeWitt  L. Fairhead  G. Flato  C. Gordon  T. Hogan  M. Ji  M. Kimoto  A. Kitoh  T. Knutson  M. Latif  H. Le Treut  T. Li  S. Manabe  C. Mechoso  G. Meehl  S. Power  E. Roeckner  L. Terray  A. Vintzileos  R. Voss  B. Wang  W. Washington  I. Yoshikawa  J. Yu  S. Yukimoto  S. Zebiak 《Climate Dynamics》2002,18(5):403-420

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Unusual Behavior of the Kuroshio Current System from Winter 1996 to Summer 1997 Revealed by ADEOS-OCTS and Other Data (Continued): A Study from Broad External Conditions with Bottom Topography     

Yoshiaki Toba  Junichi Kimura  Hiroshi Murakami  Myoungsun Kim  Yasushi Yoshikawa  Koji Shimada 《Journal of Oceanography》2001,57(2):141-154

In the previous paper (Toba and Murakami, 1998) we reported on an unusual path of the Kuroshio Current System, which occurred in April 1997 (April 1997 event), using the Ocean Color and Temperature Scanner (OCTS) data of the Advanced Earth Observing Satellite (ADEOS). The April 1997 event was characterized by the flow of the Kuroshio along the western slope (northward) and the eastern slope (southward) of the Izu-Ogasawara Ridge, a very southerly turning point at about 32°N, followed by a straight northward path up to 37°N of the Kuroshio Extension along the eastern flank of the Izu-Ogasawara and the Japan Trenches. Overlaying of depth contours on ADEOS-OCTS chlorophyll-a images at the April 1997 event demonstrates the bottom topography effects on the current paths. A new finding based on TOPEX/Poseidon altimeter data is that the sea-surface gradient across the Kuroshio/Kuroshio Extension diminished greatly in the sea area southeast of the central Japan, as a very temporary phenomenon prior to this event. This temporary diminishing of the upper-ocean current velocity might have caused a stronger bottom effect along the Izu-Ogasawara Ridge, and over the Izu-Ogasawara Trench disclosed a weak background, barotropic trench-flank current pattern, which existed otherwise independently of the Kuroshio Extension. The very southerly path of the Kuroshio Extension from winter 1996 to autumn 1998 corresponded, with a time lag of about 1.5 years, to the previous La Niña tendency with weaker North Equatorial Current. The April 1997 event occurred in accordance with its extreme condition.  相似文献   

Circulation of Intermediate and Deep Waters in the Philippine Sea     

Ikuo Kaneko  Yasushi Takatsuki  Hitomi Kamiya 《Journal of Oceanography》2001,57(4):397-420

The circulation of intermediate and deep waters in the Philippine Sea west of the Izu-Ogasawara-Mariana-Yap Ridge is estimated with use of an inverse model applied to the World Ocean Circulation Experiment (WOCE) Hydrographic Program data set. Above 1500 m depth, the subtropical gyre is dominant, but the circulation is split in small cells below the thermocline, causing multiple zonal inflows of intermediate waters toward the western boundary. The inflows along 20°N and 26°N carry the North Pacific Intermediate Water (NPIW) of 11 × 10⁹ kg s⁻¹ in total, at the density range of 26.5σ_θ–36.7σ₂ (approximately 500–1500 m depths), 8 × 10⁹ kg s⁻¹ of the NPIW circulate within the subtropical gyre, whereas the rest is conveyed to the tropics and the South China Sea. The inflow south of 15°N carries the Tropical Salinity Minimum water of 35 × 10⁹ kg s⁻¹, nearly half of which return to the east through a narrow undercurrent at 15–17°N, and the rest is transported into the lower part of the North Equatorial Countercurrent. Below 1500 m depth, the deep circulation regime is anti-cyclonic. At the density range of 36.7σ₂, – 45.845σ₄ (approximately 1500–3500 m depths), deep waters of 17 × 10⁹ kg s⁻¹ flow northward, and three quarters of them return to the east at 16–24°N. The remainder flows further north of 24°N, then turns eastward out of the Philippine Sea, together with a small amount of subarctic-origin North Pacific Deep Water (NPDW) which enters the Philippine Sea through the gap between the Izu Ridge and Ogasawara Ridge. The full-depth structure and transportation of the Kuroshio in total and net are also examined. It is suggested that low potential vorticity of the Subtropical Mode Water is useful for distinguishing the net Kuroshio flow from recirculation flows. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献