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Hideko Nomura 《Astrophysics and Space Science》2004,292(1-4):435-438
We have constructed self-consistent temperature and density profiles of irradiated active protoplanetary disks, using a two-dimensional radiative transfer calculation. By means of these profiles we have studied the stabilization of the convective instability by radiative heating and the magnetorotational instability (MRI) via ohmic dissipation, taking into account the effect of dust particle growth. Simple chemistry such as ionization by cosmic rays and recombination on dust grains are used to calculate the ionization degree of gas in the disks. Our results show that the dust growth stabilizes the convective instability due to the 2D effect of radiative transfer, while it enhances the MRI through the decrease in the recombination of ions on the dust grains. In addition, the influences of the dust settling toward the midplane of the disks on the instabilities are discussed. 相似文献
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Yoshida A Nomura H Toyoda K Nishino T Seo Y Yamada M Nishimura M Wada M Okamoto K Shibata A Takada H Kogure K Ohwada K 《Marine pollution bulletin》2006,52(1):89-95
Microbial responses to the addition of oil with or without a chemical dispersant were examined in mesocosm and microcosm experiments by using denaturing gradient gel electrophoresis of bacterial ribosomal DNA and direct cell counting. When a water-soluble fraction of oil was added to seawater, increases in cell density were observed in the first 24h, followed by a decrease in abundance and a change in bacterial species composition. After addition of an oil-dispersant mixture, increases in cell density and changes in community structure coincided, and the amount of bacteria remained high. These phenomena also occurred in response to addition of only dispersant. Our results suggest that the chemical dispersant may be used as a nutrient source by some bacterial groups and may directly or indirectly prevent the growth of other bacterial groups. 相似文献
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One of the Pre-Siwalik foreland basin sedimentary units, the Dumri Formation, is tectonically covered by the Lesser Himalayan Crystalline nappe and the Kuncha-Naudanda thrust sheet. It is narrowly distributed in the eastern margin of the Karnali klippe along the NNE–SSW trending Chakure Fault. The whole sequence of the fluvial Dumri Formation attaining 1500 m in thickness is weakly metamorphosed to muscovite phyllite and foliated phyllitic sandstone. The metamorphic grade decreases stratigraphically downward and underlying Nummulitic limestone of the middle Eocene Bhainskati Formation is converted into a slaty limestone. No metamorphic mica is detected from the late Cretaceous to Paleocene Amile Formation below the Bhainskati Formation. These facts indicate that the Tansen Group has undergone inverted metamorphism.A 40Ar/39Ar plateau age of 25.69±0.13 Ma was obtained from garnetiferous biotite gneiss in the lower part of the crystalline nappe. Another 40Ar/39Ar age spectrum from muscovite phyllite of the Dumri Formation suggests that metamorphism occurred at 16–17 Ma. The origin of the inverted metamorphism limited to the uppermost part of the Lesser Himalayan autochthon can be attributed to heat from the hot crystalline nappe and shearing along the sole thrust of the Kuncha-Naudanda thrust sheet. The depositional age of the Dumri Formation is estimated to be 26–17 Ma.Provenance of the Dumri Formation is considered to be from the Naudanda Quartzite, the Kuncha Formation and the Tibetan Tethys sediments, because the sandstone contains orthoquartzite pebbles, phyllitic lithic fragments and a sparry calcite cement. The sedimentary facies indicates deposition by meandering rivers on flood-plains in the distal part of the foreland basin. No proximal facies, such as alluvial fan and pebbly braided river deposits, could be detected from the formation, though it is near the Main Central Thrust (MCT). The northern continuation of the foreland basin sediments must be concealed beneath the Higher Himalayan Crystalline. Judging from the present distribution of the Dumri Formation from the south of the Main Boundary Thrust (MBT) to near the MCT and from the shortening of the Lesser Himalayan sediments by thrusts and folds, the width of the foreland basin where the Dumri Formation was deposited is estimated to have been more than 300 km. 相似文献
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Toshiro Saino Shaoling Shang Yoshihisa Mino Koji Suzuki Hideaki Nomura Sei-ichi Saitoh Hideo Miyake Toshiyuki Masuzawa Koh Harada 《Journal of Oceanography》1998,54(5):583-592
A sediment trap experiment was carried out in conjunction with an over flight of Ocean Color Temperature Scanner (OCTS) on
board Advanced Earth Observing Satellite (ADEOS) at 40°N, 143°E off Sanriku in April to May 1997. Short term variability of
particle fluxes was examined at depths of 450 m and 600 m from April 6 to May 1 with a sampling interval of two days, and
at 450 m with one day interval from 2nd to 10th May. Daily averaged mass flux at 450 m and 600 m was 815 mg m−2d−1 and 862 mg m−2d−1, respectively. A sharp increase in mass flux was observed during the period from April 26 to April 29 with the highest mass
flux of 8 g m−2d−1. About 85% of the total mass flux for the entire duration (26 days) was collected within these 4 days. Trapped material during
the peak flux period was mainly composed of diatoms dominated byThalassiosira spp. and resting spores ofChaetoceros spp. This suggested that the peak flux was the result of (a) diatom bloom(s) in the euphotic column. Current meter records
at 420 m showed that on April 26 and 27, the period when the peak flux was observed, the southwestward current had diminished
in strength and changed its direction northwestward. Low current speeds appeared to have enhanced trap efficiency to help
form the peak flux. A time series of OCTS Intensive-LAC (Local Area Coverage: Region B) images from mid-March to early May
was examined todetect phytoplankton bloom(s). In the March 26th Chl image, high concentration region was restricted to the
southwest off Cape Erimo, but spread around the warm core ring (WCR) 93A by April 10. East of the WCR93A, high Chl concentration
remained steady until May, but to the west of the WCR93A, Chl decreased rapidly before the 19th of April. From this observation
we suspect that the peak flux observed at the end of April originated from a bloom, which ceased on the 17th or 18th of April,
in the region north of 40°N and west of 143°E. Taking the current meter records into account, the source region for the trapped
material is most likely around southwest of the Cape Erimo. 相似文献
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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
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Hiroshi Tsuno Atsuyuki Ohta Hiroyuki Kagi Noboru Imai Hiroaki Tao Masaharu Nomura 《Geostandards and Geoanalytical Research》2006,30(1):55-62
The oxidation states of chromium in GSJ JSO-2 (artificially contaminated soil) and three other geochemical reference materials (GSJ JSO-1, JLS-1 and JMS-1) were observed using X-ray near edge structure (XANES). For comparison, other artificially contaminated soil materials (mimic-JSO-2) were prepared by adding Cr(VI) into JSO-1. Their oxidation states of chromium were determined using XANES. The chromium contents were 1118 μg g-1 for JSO-2, 1352 μg g-1 for mimic-JSO-2 and 69-113 μg g-1 for the other reference materials. Most chromium was present as hexavalent in mimic-JSO-2. No hexavalent species were detected in other samples. These results for chromium oxidation state in JSO-2 and mimic-JSO-2 obtained with XANES resembled those obtained from a chemical extraction method. The present JSO-2 has no trace of Cr(VI), although Cr(VI) was added as a major species during preparation. On the other hand, the content of Cr(VI) obtained in mimic-JSO-2 agreed with the original Cr(VI) content. A time-elapse study showed that Cr(VI) contents in mimic-JSO-2 decreased gradually to 70% of the original abundance during 240-day preservation in dry conditions. Moreover, the abundance of Cr(VI) decreased markedly to 15% after 240 days in the wet mimic-JSO-2 containing 20% m/m of water. These experiments suggested that soil humidity enhanced the reduction of Cr(VI) and that Cr(VI) was reduced even in dry conditions. Consequently, it is reasonable to infer that Cr(VI) doped into JSO-2 was completely reduced to Cr(III) during the preservation period of 5 years. The certification of the long-term stability of the chemical form in reference materials will be much more important in future. 相似文献
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Ritsuo Morishita 《Mathematical Geology》1998,30(4):409-434
The concept of an ideal rock texture, in which crystals are distributed randomly in space, is proposed for use in general analysis of rock textures. The spatial correlation function for the ideal rock texture was examined and the function, a specific kind of spatial correlation function, is related to crystal size distribution and to some extent to crystal boundaries. The function is unity at distance zero, and monotonically decreases with increasing distance for the ideal texture. This behavior of the function is observed for any size distribution. In an ideal texture, the function is directly related to crystal size distribution and crystal shape. It is important in stereology because the crystal size distribution in three dimensions may be deduced from analyzing a function that is obtained from analyzing two-dimensional section images. Crystal shape is also related to the function. If crystals are concave in shape, or have inclusions of other phases, the function may show a hump or plateau when plotted against distance. However, the crystal shape effect cannot produce values smaller than zero. If values become negative, the texture is no longer considered ideal. The ideal textures for two model size distributions—step and delta functions—are considered. The rate of decrease of values is more strongly dependent on size distribution than on system dimension. 相似文献
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Irizuki T Takimoto A Sako M Nomura R Kakuno K Wanishi A Kawano S 《Marine pollution bulletin》2011,62(10):2030-2041
This study focuses on the relationships of water and sediment quality with meiobenthos (Ostracoda) over the past 100 years, using a sediment core obtained from Suo-Nada in the Seto Inland Sea, Japan. We compared high-resolution ostracode results with geochemical and sedimentological data obtained from the study core as well as with rich environmental monitoring data that are available. R-mode cluster analysis revealed two bioassociations (BC, KA). Until the1960s, assemblages continued to show high diversity. They changed in approximately 1970, when excessive nutrients and organic matter began to be supplied, and most species decreased in number. All species of bioassociation BC were dominant again by the mid-1990s; however, those of bioassociation KA containing infaunal species did not increase and have been absent or rare since the 1970s because organic pollution of sediments has continued to date. This study provided robust baseline for ostracode-based long-term environmental monitoring in East Asia. 相似文献
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Daiki Nomura Nobue Kasamatsu Kazu TateyamaSakae Kudoh Mitsuo Fukuchi 《Continental Shelf Research》2011,31(13):1377-1383
The combined concentration of total dimethylsulfoniopropionate and dimethylsulfide (DMSP+DMS) were measured in Antarctic fast ice on the coast of Lützow-Holm Bay, eastern Antarctica. High bulk-ice DMSP+DMS and chlorophyll a concentrations were found at the bottom of the sea ice, and these concentrations were higher than those in the under-ice water. The bulk-ice DMSP+DMS and chlorophyll a concentrations were highly correlated (r2=0.68, P<0.001), suggesting that the high bulk-ice DMSP+DMS concentrations were caused mainly by the presence of algae assemblages in the ice. The calculated brine DMSP+DMS concentrations were as high as 1100 nM in the bottom ice layer, and the vertical profile patterns of brine DMSP+DMS concentrations were almost the same as for the bulk ice, mainly because of the small amount of variability in the vertical brine volume fraction. DMSP+DMS and chlorophyll a concentrations in the under-ice water increased, whereas the salinity of the under-ice water decreased, during the sampling period. These results reflect the supply of freshwater containing high levels of DMSP+DMS to the water just under the ice as the ice melted. These results suggest that sea-ice melting could be important to sulfur cycling in coastal ice-covered regions of the polar oceans. 相似文献