Precipitation of authigenic uranium in suboxic continental margin sediments from the Okinawa Trough   总被引：1，自引：0，他引：1  

Masatoshi Yamada  Zhong-Liang Wang  Yoshihisa Kato 《Estuarine, Coastal and Shelf Science》2006,66(3-4):570-579

Concentrations of U and Th isotopes in Okinawa Trough and East China Sea sediment cores were determined by isotope dilution inductively coupled plasma-mass spectrometry (ID-ICP-MS) to investigate the behavior of redox sensitive uranium in suboxic hemipelagic sediments and determine their significance in oceanic uranium balance. ²³⁸U concentrations and ²³⁸U/²³²Th activity ratios in the East China Sea sediments showed no remarkable variation with depth. However, ²³⁸U and ²³⁸U/²³²Th ratios in the Okinawa Trough sediments were low in the surface oxidizing layer but increased where the suboxic condition was encountered. The distribution profiles of ²³⁰Th and ²³²Th concentrations were relatively constant with depth in both the Okinawa Trough and East China Sea sediment cores. These results suggested that there has been post-depositional precipitation of authigenic uranium within the suboxic Okinawa Trough sediment column. The post-depositional precipitation rates of authigenic uranium were estimated to be 47 ± 5 to >62 ± 8 ng cm⁻² yr⁻¹; these rates were comparable to those previously reported for several anoxic sediments. A mechanism controlling precipitation of uranium may be the downward diffusion of uranium U(VI), reduction to U(IV) and finally precipitation onto the solid phase. The accumulation rate of uranium for the Okinawa Trough sediments was approximately eight times higher than the world average rate reported for suboxic sediments. This removal of uranium in the oceanic budget increases the importance of the suboxic sediment sink.  相似文献   

Large kinetic power in FRII radio jets     

Hirotaka Ito  Motoki Kino  Nozomu Kawakatu  Naoki Isobe  Shoichi Yamada 《Astrophysics and Space Science》2007,311(1-3):335-339

We investigate the total kinetic powers (L _j) and ages (t _age) of powerful jets of four FR II radio sources (Cygnus A, 3C 223, 3C 284, and 3C 219) by the detail comparison of the dynamical model of expanding cocoons with observed ones. It is found that these sources have quite large kinetic powers with the ratio of L _j to the Eddington luminosity (L _Edd) resides in 0.02<L _j/L _Edd<10. Reflecting the large kinetic powers, we also find that the total energy stored in the cocoon (E _c) exceed the energy derived from the minimum energy condition (E _min): 2<E _c/E _min<160. This implies that a large amount of kinetic power is carried by invisible components such as thermal leptons (electron and positron) and/or protons.  相似文献   

Reply to comment on ‘Yamada H,Nakamura F,Watanabe Y,Murakami M and Nogami T. 2005. Measuring hydraulic permeability in a streambed using the packer test. Hydrological Processes 19: 2507–2524’     

Hiroyuki Yamada  Futoshi Nakamura  Yasuharu Watanabe  Marie Murakami  Takeshi Nogami 《水文研究》2008,22(17):3545-3545

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The discovery of a massive supercluster at  z= 0.9  in the UKIDSS Deep eXtragalactic Survey     

A. M. Swinbank  A. C. Edge  Ian Smail  J. P. Stott  M. Bremer  Y. Sato  C. van Breukelen  M. Jarvis  I. Waddington  L. Clewley  J. Bergeron  G. Cotter  S. Dye  J. E. Geach  E. Gonzalez-Solares  P. Hirst  R. J. Ivison  S. Rawlings  C. Simpson  G. P. Smith  A. Verma  T. Yamada 《Monthly notices of the Royal Astronomical Society》2007,379(4):1343-1351

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Stratigraphic architecture of sedimentary basin induced by mantle diapiric upwelling and eustatic event   总被引：1，自引：0，他引：1  

Yoshiki Yamada  Masao Nakada   《Tectonophysics》2006,415(1-4):103-121

The stratigraphic architecture of sedimentary basin provides important constraints on the rheological structure of the upper mantle and the crust, eustatic events and tectonic movements. In this study, we examined the convective coupling between the uppermost mantle and ductile lower crust as a formation mechanism of sedimentary basins. In this mechanism, the lower crust is squeezed by the upper mantle flow associated with mantle diapiric upwelling, resulting in the surface subsidence and formation of sedimentary basin. We investigated the stratigraphic architecture by taking into account the horizontal migration of the upwelling in time and spatial domains. The sedimentary basin is characterized by both the thickness and formation period for its gross feature and the sequence stratigraphy. The decay of the upwelling causes the surface uplift, and some parts of sediments deposited during the surface subsidence are consequently eroded. The subsidence area moves as the activity of upwelling horizontally migrates, resulting in the formation of unconformity for the uplifted and eroded area over the previous upwelling. We also incorporated the effects of third order eustasy, with amplitude of 100 m and period of 1 Myr, into convective coupling model. An application of our model to Karatsu-Sasebo coalfield in the Tertiary of the northwest Kyushu, Japan, indicates that the stratigraphic architecture of sedimentary basin including two effects, i.e. convective coupling and eustasy, may provide important information about the viscosity structure of the lower crust and uppermost mantle and spatio-temporal growth and decay histories of the mantle diapiric upwelling.  相似文献   

AFM study on surface nanotopography of matrix olivines in Allende carbonaceous chondrite     

Jun Nozawa  Junya Yamada  Ken Nagashima  Hitoshi Miura 《Icarus》2009,204(2):681-654

By means of nanoscale surface observation, we have proposed a new approach for investigating fine crystals of cosmic materials to reveal their origin and growth conditions. Several different morphologies of polyhedral fine olivines with faceted faces have been found in Allende carbonaceous chondrite (4.5 byr in geochronological age). In the present work, molecular level topography of the faceted matrix olivine by Atomic Force Microscopy (AFM) has successfully been performed. The matrix olivine found to have preserved growth step pattern on its surface even though quite long time has passed since they formed in the early Solar System. The surface pattern suggests that the faceted matrix olivine could have been condensed from the gas phase, and possibly that these olivine crystals had continued to grow under a rapid cooling condition (0.1-1 K s⁻¹). The estimated cooling rate agrees well with predictions based on hypothetical rapid heating and cooling events such as shock wave heating.  相似文献   

Capability of the penetrator seismometer system for lunar seismic event observation   总被引：2，自引：0，他引：2  

R. Yamada  I. Yamada  S. Tanaka  N. Kobayashi  Y. Ishihara  K. Yomogida  A. Fujimura 《Planetary and Space Science》2009,57(7):751-763

We developed a seismometer system for a hard landing “penetrator” probe in the course of the former Japanese LUNAR-A project to deploy new seismic stations on the Moon. The penetrator seismometer system (PSS) consists of two short-period sensor components, a two-axis gimbal mechanism for orientation, and measurement electronics. To carry out seismic observations on the Moon using the penetrator, the seismometer system has to function properly in a lunar environment after a hard landing (impact acceleration of about 8000 G), and requires a signal-to-noise ratio to detect lunar seismic events. We evaluated whether the PSS could satisfactorily observe seismic events on the Moon by investigating the frequency response, noise level, and response to ground motion of our instrument in a simulated lunar environment after a simulated impact test. Our results indicate that the newly developed seismometer system can function properly after impact and is sensitive enough to detect seismic events on the Moon. Using this PSS, new seismic data from the Moon can be obtained during future lunar missions.  相似文献   

Lymanα Blobs: Discussions in Heidelberg     

Toru Yamada   《New Astronomy Reviews》2009,53(3):54

Lyα Blobs (LAB), large, extended Lyα emitters, are enigmatic objects that calls on much attention in the field of galaxy formation and evolution. So far, discovery of more than twenty giant (>60 kpc) LABs have been reported and new searches are on-going. Many of the groups who study LABs attended the workshop in Heidelberg, “Understanding Lyα Emitters”, 2008 October 6–10. We had useful discussions on the various important aspects of LABs including the search or detection methods, origins of the extended Lyα emission, and their physical properties.  相似文献   

Apparent downward CO2 flux observed with open-path eddy covariance over a non-vegetated surface     

K. Ono  A. Miyata  T. Yamada 《Theoretical and Applied Climatology》2008,92(3-4):195-208

Summary The open-path eddy covariance (EC) method often shows unlikely downward CO₂ fluxes in late winter and early spring over drained paddy fields with few active plants. To understand why, we carried out intensive measurements in a bare paddy field from 9 to 11 April 2003, simultaneously using open- and closed-path EC methods; aerodynamic and dynamic closed-chamber methods were also used. During this period, the open-path EC method showed downward daytime CO₂ fluxes ranging from 0 to −5.9 μmol m⁻² s⁻¹, even after application of the WPL correction (density correction) and ordinary quality control tests. Because the closed-path EC and aerodynamic methods showed upward CO₂ fluxes, the downward CO₂ fluxes observed with open-path EC appear not to represent true CO₂ transport. Diurnal variations in the downward daytime CO₂ fluxes appeared to be correlated with increases in solar radiation during the day, and also with increases in sensible heat flux in weak winds but not under strongly windy conditions. The daytime 10-Hz time series data of vertical wind and CO₂ mixing ratio demonstrated that updrafts were CO₂ depleted in the open-path system, whereas the same updrafts were CO₂ enriched in the closed-path system. Careful examination of the discrepancies between the open- and the closed-path EC measurements revealed that the amplitudes of the 10-Hz temperature signals from the sonic anemometer and the resultant sensible heat fluxes were too small to compensate for the discrepancies observed during the daytime. The open-path EC method with the conventional application of the WPL correction is not necessarily appropriate for measuring small magnitudes of CO₂ flux (≤5 μmol m⁻² s⁻¹) under such surface and atmospheric conditions that the magnitude of the WPL correction is as great as that of the uncorrected CO₂ flux itself. Author’s addresses: Keisuke Ono, 3-1-3 Kannondai, Tsukuba, Ibaraki 305-8604, Japan; Akira Miyata, Tomoyasu Yamada, National Institute for Agro-Environmental Sciences, Tsukuba, Japan  相似文献   

Study of the effect of water-soluble fractions of heavy-oil on coastal marine organisms using enclosed ecosystems,mesocosms   总被引：1，自引：0，他引：1  

Ohwada K  Nishimura M  Wada M  Nomura H  Shibata A  Okamoto K  Toyoda K  Yoshida A  Takada H  Yamada M 《Marine pollution bulletin》2003,47(1-6):78-84

Mesocosm facilities composed of 4 experimental and 2 reservoir tanks (1.5 m in diameter, 3.0 m in depth and 5 tons in capacity) made of FRP plastics, were constructed in the concrete fish rearing pond in the Fisheries Laboratory, The University of Tokyo. The water-soluble fraction of Rank A heavy residual oil was formed by mixing 500 g of the oil with 10 l of seawater, which was introduced to the 5000 l-capacity tanks. Experimental Run 4 was conducted from May 31 to June 7, 2000. Oil concentrations in the tanks were 4.5 microg/l called LOW, and 13.5 microg/l, called HIGH tank. Bacterial growth rates very quickly accelerated in the HIGH tank just after the loading of oil which corresponded with a high increase of bacterial cells in the same tank after 2 days. Later, bacterial numbers in HIGH tank rapidly decreased, corresponding with the rapid increase of heterotrophic nano-flagellates and virus numbers on the same day. Sediment traps were deployed at the bottom of the experimental tanks, and were periodically retrieved. These samples were observed both under light microscope and epi-fluorescent microscope with UV-excitation. It was observed that the main components of the vertical flux were amorphous suspended matter, mostly originating from dead phytoplankton and living diatoms. It was further observed from the pictures that vertical transport of oil emulsions were probably conducted after adsorption to amorphous suspended matter and living diatoms, and were settling in the sediment traps at the bottom of the tanks. This means that the main force which drives the soluble fraction of oil into bottom sediment would be vertical flux of such amorphous suspended particles and phytoplankton. Further incubation of the samples revealed that the oil emulsions were degraded by the activity of autochtonous bacteria in the sediment in aerobic condition.  相似文献