On sexual dimorphism in Paleoparadoxia tabatai     

Yoshikazu  Hasegawa Yojiro  Taketani Hajime  Taru Osamu  Sakamoto Makoto  Manabe 《Island Arc》1994,3(4):513-521

Abstract Upon studying the well preserved skulls referred to Paleoparadoxia tabatai from Japan, the short and low skull of the Yanagawa specimen requires an explanation. Six cranial and dental characters lead us to suggest that the Yanagawa individual is a female while the Izumi, Ohnohara, and Itsukaichi skulls are male. The important characters in the Yanagawa skull are its shortness and shallow depth, less pronounced sagittal and nuchal crests, smaller zygoma, and the small dentition with especially poorly erupted canines, most of which are indicative of weak masticatory musculature.  相似文献   

Locally-induced nonlinear modes and multiple equilibria in planetary fluids     

T. Yamagata  K. Sakamoto  M. Arai 《Pure and Applied Geophysics》1990,133(4):733-748

It is demonstrated that nonlinear Rossby modes, such as modons and IG eddies, can be excited in planetary fluids by a sufficiently strong forcing of potential vorticity. When a weak forcing is balanced with a weak dissipation, two (linear and nonlinear) equilibrium states can be produced, depending on the initial condition. When the fluid is inviscid, a sufficiently strong steady forcing may generate a sequence of propagating nonlinear eddies. A weak forcing, by contrast, only generates linear Rossby waves. The criterion which divides the high amplitude nonlinear state and the low amplitude linear state may be interpreted in terms of a ratio of a time necessary to force the eddy to a time for a fluid particle to circulate about the nonlinear eddy once.  相似文献   

Swift and optical observations of GRB 050401     

Massimiliano De Pasquale  y P. Beardmore  S. D. Barthelmy  P. Boyd  D. N. Burrows  R. Fink  N. Gehrels  S. Kobayashi  K. O. Mason  R. McNought  J. A. Nousek  K. L. Page  D. M. Palmer  B. A. Peterson  P. A. Price  J. Rich  P. Roming  S. R. Rosen  T. Sakamoto  B. P. Schmidt  J. Tueller  A. A. Wells  S. Zane  B. Zhang  H. Ziaeepour 《Monthly notices of the Royal Astronomical Society》2006,365(3):1031-1038

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Influence of submarine fumaroles on the distribution of mercury in the sediment of Kagoshima Bay,Japan     

Takashi Tomiyasu  Tomomi Eguchi  Masahiko Yamamoto  Katsuro Anazawa  Hayao Sakamoto  Tetsuo Ando  Munetomo Nedachi  Katsumi Marumo 《Marine Chemistry》2007

To estimate the influence of mercury emitted from submarine fumaroles, the horizontal and vertical distribution of mercury in sediment of Kagoshima Bay was studied. The fumaroles are located in the northern bay head area, and the sediment samples had been taken from 52 points throughout the bay with a gravity core sampler. The core samples obtained were cut at a thickness of 1–2 cm and used for measurements. The total concentration of mercury in surface sediment in the northern and central areas of the bay was 51–679 μg kg^− 1 (average 199 μg kg^− 1, n = 22) and 23–100 μg kg^− 1 (average 55 μg kg^− 1, n = 30), respectively. The highest value was obtained in the vicinity of the fumaroles. The mercury concentration in sediment near the fumaroles varied with depth, which may reflect the variation in fumarolic activity. A successive extraction method was applied to the speciation of mercury in the sediment. The results showed that sediment taken in the vicinity of submarine fumaroles contained a higher percentage of mercury bound with organic matter.  相似文献   

Development of an operational coastal model of the Seto Inland Sea,Japan     

Kei Sakamoto  Goro Yamanaka  Hiroyuki Tsujino  Hideyuki Nakano  Shogo Urakawa  Norihisa Usui  Mikitoshi Hirabara  Koji Ogawa 《Ocean Dynamics》2016,66(1):77-97

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High resolution OSL dating back to MIS 5e in the central Sea of Okhotsk   总被引：1，自引：0，他引：1  

Saiko Sugisaki  Jan-Pieter Buylaert  Andrew Murray  Sumiko Tsukamoto  Yoshifumi Nogi  Hideki Miura  Saburo Sakai  Koichi Iijima  Tatsuhiko Sakamoto 《Quaternary Geochronology》2010,5(2-3):293-298

Marine sediments contain important archives of past ocean and climate changes, but at high latitudes the absence of carbonate has prevented the construction of accurate chronological models. We have begun a study to (1) determine the accuracy of luminescence ages in deep-sea marine sediments, e.g. by comparison with marine oxygen isotope stratigraphy where possible, (2) describe changes in sedimentation rate through time, and (3) test whether it is possible to date back to marine isotope stage 5e (MIS 5e). We show here that optical dating of fine grains of quartz from the central Sea of Okhotsk is able to provide an accurate and precise chronology for the reconstruction of the palaeoceanic and palaeoclimatic environment at our site. The upper 6.5 m of the 18.42 m long core MR0604-PC07A is believed, based on its magnetic susceptibility and the oxygen isotope (δ¹⁸O) records to contain the last ～150 ka. Forty OSL samples were taken from this upper part of the core. The single-aliquot regenerative-dose (SAR) procedure is used for equivalent dose (D_e) determination. The luminescence characteristics of fine-grained quartz (4–11 μm) extracted from the core are described. The OSL signal is dominated by the fast component and a dose recovery test shows that we can accurately measure a known dose given in the laboratory prior to any heat treatment. Dose rates were determined using high-resolution gamma spectrometry, and vary between 0.4 and 1.6 Gy/ka. The OSL ages from this section lie between ～140 ka and ～15 ka and are in very good agreement with the δ¹⁸O stratigraphy up to MIS 5e. A clear change in sedimentation rate is identified: between ～139 and 110 ka, the sedimentation rate was ～0.09 m/ka, but then from ～110 to 15 ka, the sedimentation rate decreases to a constant value of ～0.04 m/ka. Our data confirm that OSL dating using widely distributed fine-grain quartz has great potential for dating deep-sea sediments. Because luminescence methods use clastic materials, they do not depend on the presence of biogenic carbonate. As a result it is now likely that we can establish a chronology in regions of the ocean that were previously undatable.  相似文献   

Geochemical and Microbiological Analysis of Sambe Hot Springs,Shimane Prefecture,Japan     

Keiko Sasaki  Yoshitaka Uejima  Atsushi Sakamoto  Qianqian Yu  Junichiro Ishibashi  Naoko Okibe  Tsuyoshi Hirajima 《Resource Geology》2013,63(2):155-165

Microbiological contribution to the formation of the manganese deposits in Sambe hot springs, Shimane, was investigated in combination with water chemistry, characterization of sediments and microbial community structure. Analysis of bacterial and fungal community structure based on DNA extracted from a Mn‐oxidizing enrichment culture indicated close matches with Pseudomonas putida, Phoma sp. and Plectosphaerella cucumerina, all Mn‐oxidizing microorganisms. These sediments were poorly crystalline and formed at neutral pH values, which is characteristic of biogenic precipitates. The EPMA results demonstrated a positive correlation between Mn and Ba contents in well‐crystalline Mn oxide grains. Substantial Ba contents were observed inside Mn oxide grains. These findings indicated that Ba contents in sediments are influenced by not only aqueous Ba²⁺ concentrations but also crystallinity of biogenic birnessite. Barium would be incorporated in birnessite during biomineralization.  相似文献   

Western Boundary Current Separation Caused by a Deep Countercurrent     

Toshihiro Sakamoto 《地球物理与天体物理流体动力学》2013,107(3):179-199

It is shown that the deep western boundary current (DWBC) in the North Atlantic may contribute to premature separation of the Gulf Stream. A simple analytical study is made based on the linear barotropic vorticity equation in which a possible effect of the DWBC is introduced as anomalous stretching of the water column in a manner consistent with certain qualitative aspects of the observed features. This additional positive vorticity may be generated by a deep downwelling associated with horizontal shears of the DWBC. It is found that separation latitudes are farther to the south as the stretching is strengthened. Vertical motion required for a southward shift of order unity (e.g., 500 km) is estimated to be of the order of 0.05 mm s m 1 , in reasonable agreement with the observed values. It is suggested that since the DWBC is intimately linked with the thermohaline circulation, a meridional migration of the Gulf Stream separation might reflect long-term variations in the North Atlantic.  相似文献   

Photometric observations of 107P/Wilson-Harrington     

Seitaro Urakawa  Shin-ichiro Okumura  Tsuyoshi Sakamoto  Shinsuke Abe  Kohei Kitazato  Sunao Hasegawa  Nobuyuki Kawai  Shogo Nagayama  Michitoshi Yoshida 《Icarus》2011,215(1):17-26

We present lightcurve observations and multiband photometry for 107P/Wilson-Harrington using five small- and medium-sized telescopes. The lightcurve has shown a periodicity of 0.2979 day (7.15 h) and 0.0993 day (2.38 h), which has a commensurability of 3:1. The physical properties of the lightcurve indicate two models: (1) 107P/Wilson-Harrington is a tumbling object with a sidereal rotation period of 0.2979 day and a precession period of 0.0993 day. The shape has a long axis mode (LAM) of L₁:L₂:L₃ = 1.0:1.0:1.6. The direction of the total rotational angular momentum is around λ = 310°, β = −10°, or λ = 132°, β = −17°. The nutation angle is approximately constant at 65°. (2) 107P/Wilson-Harrington is not a tumbler. The sidereal rotation period is 0.2979 day. The shape is nearly spherical but slightly hexagonal with a short axis mode (SAM) of L₁:L₂:L₃ = 1.5:1.5:1.0. The pole orientation is around λ = 330°, β = −27°. In addition, the model includes the possibility of binary hosting. For both models, the sense of rotation is retrograde. Furthermore, multiband photometry indicates that the taxonomy class of 107P/Wilson-Harrington is C-type. No clear rotational color variations are confirmed on the surface.  相似文献   

Development of a new operational system for monitoring and forecasting coastal and open-ocean states around Japan     

Hirose  Nariaki  Usui  Norihisa  Sakamoto  Kei  Tsujino  Hiroyuki  Yamanaka  Goro  Nakano  Hideyuki  Urakawa  Shogo  Toyoda  Takahiro  Fujii  Yosuke  Kohno  Nadao 《Ocean Dynamics》2019,69(11):1333-1357

We developed a new system to monitor and forecast coastal and open-ocean states around Japan for operational use by the Japan Meteorological Agency. The system consists of an eddy-resolving analysis model based on four-dimensional variational assimilation and a high (2-km) resolution forecast model covering Japanese coastal areas that incorporates an initialization scheme with temporal and spatial filtering. Assimilation and forecast experiments were performed for 2008 to 2017, and the results were validated against various observation datasets. The assimilation results captured well the observed variability in sea surface temperature, coastal sea level, volume transport, and sea ice. Furthermore, the volume budget for the Japan Sea was significantly improved by the use of the 2-km resolution forecast model compared with the 10-km resolution analysis model. The forecast results indicate that this system has a predictive limit longer than 1 month in many areas, including in the Kuroshio current area south of Japan and the southern Japan Sea. In the forecast results of case studies, the 2017 Kuroshio large meander was well predicted, and warm water intrusions accompanying Kuroshio path variations south of Japan were also successfully reproduced. Sea ice forecasts for the Sea of Okhotsk largely captured the evolution of sea ice in late winter, but sea ice in early winter included relatively large errors. This system has high potential to meet operational requirements for monitoring and forecasting ocean phenomena at both meso- and coastal scales.

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