Spatial Distributions of Phyllosoma Larvae (Crustacea: Decapoda: Palinuridae and Scyllaridae) in Taiwanese Waters     

Nariaki Inoue  Hideo Sekiguchi  Shinn-Pyng Yeh 《Journal of Oceanography》2001,57(5):535-548

Distributions and taxonomy of phyllosoma larvae were examined in Taiwanese waters, based on ichthyoplankton samples collected from May 1990 to July 1995. Phyllosoma larvae belonged to the two families Scyllaridae and Palinuridae representing 6 genera and 13 species. Of the collected phyllosoma larvae, those of Scyllarus and Panulirus species were most abundant, forming 90% of total numbers. Early stage Scyllarus and Panulirus phyllosoma larvae were abundant in Taiwanese waters. Middle to late stages (except the final stage) of Panulirus phyllosoma larvae were absent from the waters throughout the year, while those of Scyllarus phyllosoma larvae were collected in the waters. This suggests that all stages of Scyllarus phyllosoma larvae may be retained in the northern part of the waters around northern Taiwan while middle to late stages of Panulirus phyllosoma larvae may be flushed out from the waters, the sub-final and final stages then possibly returning to the waters. An anticlockwise eddy existed in the waters off northeastern Taiwan, which may be closely related to flushing out and returning of Panulirus phyllosoma larvae through a much longer planktonic period. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Imaging an asperity of the 2003 Tokachi-oki earthquake using a dense strong-motion seismograph network     

R. Honda  S. Aoi  H. Sekiguchi  H. Fujiwara 《Geophysical Journal International》2008,172(3):1104-1116

The 2003 Tokachi-oki earthquake ruptured a large area of approximately 100 km². The location of the largest asperity was estimated to be several dozen kilometres offshore of Hokkaido, Japan. The magnitude measured 8.0 on the Japan Meteorological Agency scale, and several studies used waveform inversion analysis to estimate the moment-magnitude as M _w 8.0–8.2. Several studies reported that there was a minor asperity at the northeastern edge of the fault plane, and that the rupture velocity towards the minor asperity was less than that towards the main asperity. One of them illustrated that the location and timing of the minor asperity were poorly constrained. In this paper, we introduce a procedure based on semblance analysis to image the location of the minor northeastern asperity with improved resolution. We group 15 strong-motion seismographs into three arrays, and we perform semblance analysis on impulsive waves that were possibly generated from the minor asperity and were conspicuously observed at stations in eastern Hokkaido. By projecting the semblance values onto the fault plane, we estimate the location of the minor asperity. We find it to be shallower and farther from the coast than the previous results indicated. The average rupture velocity towards the asperity is estimated to be 2.5 km s⁻¹, which is slower than the 3.6 km s⁻¹ obtained by waveform inversion analysis.  相似文献   

AMS analysis of I in Japanese soil samples collected from background areas far from nuclear facilities     

Yasuyuki Muramatsu  Yukari Takada  Hiroyuki Matsuzaki  Satoshi Yoshida 《Quaternary Geochronology》2008,3(3):291-297

Analytical procedures in the determination of iodine-129 (half-life: 1.6×10⁷ y) have been studied using accelerator mass spectrometry (AMS), with special references to the separation procedures of iodine from soil samples for the AMS measurement. Iodine was successfully volatilized from soil samples by pyrohydrolysis at 1000 °C and collected in a trap solution. Iodine was purified from the matrix by solvent extraction. Finally, it was precipitated as silver iodide to make a target for AMS. In order to obtain information on the ¹²⁹I/¹²⁷I ratio in a chemical blank (or iodine carrier), we have determined the ratios in several iodine reagents and found that the ratios fell in a narrow range around 1.7×10⁻¹³. The detection limit for soil sample (1 g material) by the present method was about 0.01 mBq/kg or 4×10⁻¹¹ as the ratio of stable iodine (¹²⁹I/¹²⁷I ratio), i.e. these values were much better than that by neutron activation analysis (NAA) used in our previous studies. We have applied this method in the analysis of soil samples collected from different places in Japan. We could successfully determine ¹²⁹I in soil samples with low ¹²⁹I concentrations, which could not be detected by NAA. Sample size necessary for the soil analysis by AMS was only about 0.5 g or less, whereas about 100 g of the sample were required for NAA [Muramatsu, Y., Ohmomo, Y., 1986. Iodine-129 and iodine-127 in environmental samples collected from Tokaimura/ Ibaraki, Japan. Sci. Total Environ. 48, 33-43]. Using this method, new data were obtained for the ¹²⁹I levels in 20 soil samples collected from background areas far from nuclear facilities, and the ranges were 1.4×10⁻⁵−4.5×10⁻³ Bq/kg as ¹²⁹I concentrations and 3.9×10⁻¹¹−2.2×10⁻⁸ as ¹²⁹I/¹²⁷I ratios. These values are useful in understanding the ¹²⁹I levels in Japanese environments. Higher ¹²⁹I concentrations were observed in forest soils than those in field and rice paddy soils should be related to the interception effect of atmospheric ¹²⁹I due to tree canopies. Relatively high ¹²⁹I/¹²⁷I ratios found in rice paddy soils could be explained by their low stable iodine concentrations which were caused by the desorption of stable iodine from the rice paddies during the cultivation.  相似文献   

Experiment and simulation of turbulent flow in local scour around a spur dyke   总被引：6，自引：2，他引：4  

Hajime NAKAGAWA  Kenji KAWAIKE  Yasuyuki BABA 《国际泥沙研究》2009,24(1):33-45

The turbulent flow in the local scour hole around a single non-submerged spur dyke is investigated with both experimental and numerical methods. The experiments are conducted under clear-water scour regime with an impermeable spur dyke. The scour geometry and flow velocities are measured in details with a high-resolution laser displacement meter, electro-magnetic velocimetries and PIV （Particle image velocimetry）. A 3D non-linear k-ε model is developed to simulate the complex local flow field around the scour area. The numerical model is formulated using FVM （Finite volume method） on a collocated unstructured mesh, capable of resolving complex geometries and boundaries. It is found that the simulation results are reasonably consistent with those of the experimental measurements. Based on the study results, the nature of the flow structure around a spur dyke with local scour hole is analyzed.  相似文献   

Intermediate high-pressure exhumation of the northern segment of the Sanbagawa belt, Saruta-gawa area, central Shikoku, Japan     

Yasuyuki Banno 《Lithos》2000,50(4):289-303

The retrograde chemical zonal structure of amphibole in hematite-bearing basic and quartz schists from the higher grade zone in the Saruta-gawa area of the Sanbagawa belt was studied to investigate the relationships between the prograde and retrograde P–T paths of the Sanbagawa metamorphism. This amphibole coexists with chlorite, epidote, muscovite, albite, quartz and hematite, and is composed of Al-rich core and Al-poor mantle. The core is fairly homogeneous and has a barroisitic composition. In the mantle part, ^[B]Na increases with decreasing ^[4]Al towards the margins, which have winchite–magnesioriebeckite compositions. The barroisite–winchite–magnesioriebeckite composite crystal is sometimes rimmed by actinolite and/or winchite with low ^[4]Al and ^[B]Na. The Al-rich core and Al-poor mantle are regarded as prograde and retrograde products, respectively. The retrograde mantle in the Saruta-gawa area: (1) is systematically richer in ^[B]Na [0.40–1.73 per formula unit (pfu; for O=23)] than that from the same grade zone in the Asemi-gawa area (0.19–0.78 pfu), about 8 km south of the studied area; (2) tends to be ^[B]Na-poorer (less than 1.73 pfu) than prograde sodic amphibole (up to 1.93 ^[B]Na pfu) produced in the peak temperature stage from the lower grade zone in the same and other areas; and (3) extends its compositional range towards higher ^[B]Na and lower ^[4]Al than prograde-formed amphibole from the same grade zone in the same area. These zonal characteristics imply that (1) the Saruta-gawa samples experienced retrograde metamorphism under higher P/T conditions than the Asemi-gawa samples, (2) the retrograde P–T path of the Saruta-gawa area passes on the lower pressure side of the metamorphic field gradient, and (3) the Saruta-gawa samples underwent retrograde metamorphism under higher P/T conditions than the prograde metamorphism. The higher P/T conditions of the retrograde metamorphism suggests an increasing dP/dT of the geotherm during exhumation. Retrograde P–T conditions during the formation of magnesioriebeckite can be roughly estimated at 7–8 kbar, 400–450°C based on semi-quantitative phase relations of actinolite–winchite–magnesioriebeckite–barroisite series associated with chlorite, epidote, muscovite, albite, quartz and hematite.  相似文献   

Field measurement and modeling of near-bed sediment transport processes with fluid mud layer in Tokyo Bay     

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   

Recurrent novae     

K. Sekiguchi 《Astrophysics and Space Science》1995,230(1-2):75-82

A brief review of recurrent novae studies which have been undertaken in South Africa during the last ten years is given. These works have substantially altered our view of these objects as distinct sub-classes of cataclysmic variable stars. Observational results which led to new developments in our understanding of the recurrent novae are reviewed in some detail. Observations of V1017 Sgr, which had been suggested as a recurrent nova, are also mentioned.  相似文献   

Landslide risk evaluation and hazard zoning for rapid and long-travel landslides in urban development areas   总被引：8，自引：6，他引：2  

Kyoji?SassaEmail author  Gonghui?Wang  Hiroshi?Fukuoka  Fawu?Wang  Takahiro?Ochiai  Masanori?Sugiyama  Tatsuo?Sekiguchi 《Landslides》2004,1(3):221-235

Risk evaluation for earthquake-induced rapid and long-travel landslides in densely populated urban areas is currently the most important disaster mitigation task in landslide-threatened areas throughout the world. The research achievements of the IPL M-101 APERITIF project were applied to two urban areas in megacities of Japan. One site is in the upper slope of the Nikawa landslide site where previous movements were triggered by the 1995 Hyogoken-Nambu earthquake. During detailed investigation, the slope was found to be at risk from a rapid and long-travel landslide induced by sliding surface liquefaction by earthquakes similar in scale to the 1995 event. A new plan to prevent the occurrence of this phenomenon was proposed and the plan was implemented. Another area is the Tama residential area near Tokyo. A set of field and laboratory investigations including laser scanner, geological drilling and ring-shear tests showed that there was a risk of sliding surface liquefaction for both sites. A geotechnical computer simulation (Rapid/LS) using the quantitative data obtained in the study allowed urban landslide hazard zoning to be made at individual street level.  相似文献   

Estimation of the sequence and size of the Tozawagawa landslide,Niigata, Japan,using aerial photographs   总被引：1，自引：0，他引：1  

H?YamagishiEmail author  H?Marui  L?Ayalew  T?Sekiguchi  T?Horimatsu  M?Hatamoto 《Landslides》2004,1(4):299-303

On 5 January 2000, a landslide occurred along the right flank of the upper tributary of the Tozawagawa River in Niigata Prefecture, Japan. The landslide blocked the river and formed a temporary lake approximately 670 m long and 11 m deep. In this report, we estimated a time series of aerial photographs from 1947, 1976, 2000, and 2001 to describe the sequences of the landslide. There are some indications that the landslide is a reactivation of an old failure that occurred before 1947. In addition, we have attempted to calculate the scale and volume by aerial photogrammetry.  相似文献   

On the second and third modes of the moon's free libration     

N. Sekiguchi 《Earth, Moon, and Planets》1970,2(2):136-139

The probable semi-amplitudes of the second and third modes of the Moon's free librations are inferred from the observed semi-amplitude of its first mode, using the statistical relations between the exciting actions and the amplitudes of the free librations, derived in the author's previous paper (Sekiguchi, 1970). It is likely that the semi-amplitudes of these librations exceed some second of arc.  相似文献