Early diagenesis of fatty acids in lacustrine sediments—II. A statistical approach to changes in fatty acid composition from recent sediments and some source materials     

Hiromi Matsuda  Tadashiro Koyama 《Geochimica et cosmochimica acta》1977,41(12):1825-1834

The percentage composition and total amounts of fatty acids from plankton, live and dead plants (waterweeds and higher plants) and a forest soil, considered as possible origins of autochthonous and allochthonous organic materials in lacustrine sediments, have been determined by gas-liquid chromatography. Statistical analyses were carried out by computing distance index of the fatty acid composition between these source materials and the uppermost sediment from Lake Suwa, and the composition diversity index (CDI) of fatty acids in the recent sediments from Lake Suwa.The distance index indicated that the fatty acid composition in the uppermost sediment is similar to those in diatoms, Zooplankton and forest soil, and the values for dead leaves were smaller than for live ones. It suggests that the autolysis and/or decomposition processes prior to deposition onto the top sediment makes the fatty acid composition of organic debris similar to the uppermost sediment. The CPI in recent sediments varied irregularly, whereas the CDI increased during early diagenesis to yield a value comparable to ancient sediments.  相似文献   

Dependence of the build-up of the colour–magnitude relation on cluster richness at z∼ 0.8     

Yusei Koyama  Tadayuki Kodama  Masayuki Tanaka  Kazuhiro Shimasaku  Sadanori Okamura 《Monthly notices of the Royal Astronomical Society》2007,382(4):1719-1728

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Future projections of Indian Summer Monsoon under multiple RCPs using a high resolution global climate model multiforcing ensemble simulations     

Varghese  Stella Jes  Surendran  Sajani  Rajendran  Kavirajan  Kitoh  Akio 《Climate Dynamics》2020,54(3):1315-1328

Climate Dynamics - Present-day simulations (1983–2003) of a global climate model of 60-km resolution with three deep convection schemes are analysed to find the best scheme for simulation of...  相似文献   

Spherical collapse in modified gravity with the Birkhoff theorem     

Björn Malte Schäfer  Kazuya Koyama 《Monthly notices of the Royal Astronomical Society》2008,385(1):411-422

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Dynamical response to supernova-induced gas removal in spiral galaxies with dark matter halo     

Hiroko Koyama  Masahiro Nagashima  Takayuki Kakehata  Yuzuru Yoshii 《Monthly notices of the Royal Astronomical Society》2008,389(1):237-249

We investigate the dynamical response, in terms of disc size and rotation velocity, to mass loss by supernovae in the evolution of spiral galaxies. A thin baryonic disc having the Kuzmin density profile embedded in a spherical dark matter halo having a density profile proposed by Navarro, Frenk & White is considered. For the purpose of comparison, we also consider the homogeneous and   r ⁻¹  profiles for dark matter in a truncated spherical halo. Assuming for simplicity that the dark matter distribution is not affected by mass-loss from discs and the change of baryonic disc matter distribution is homologous, we evaluate the effects of dynamical response in the resulting discs. We found that the dynamical response only for an adiabatic approximation of mass-loss can simultaneously account for the rotation velocity and disc size as observed particularly in dwarf spiral galaxies, thus reproducing the Tully–Fisher relation and the size versus magnitude relation over the full range of magnitude. Furthermore, we found that the mean specific angular momentum in discs after the mass-loss becomes larger than that before the mass-loss, suggesting that the mass-loss would most likely occur from the central disc region where the specific angular momentum is low.  相似文献   

Determination of Molybdenum, Antimony and Tungsten at sub μg g⁻¹ Levels in Geological Materials by ID-FI-ICP-MS     

Akio Makishima  Eizo Nakamura 《Geostandards and Geoanalytical Research》1999,23(2):137-148

We have developed a rapid and accurate method for the determination of Mo, Sb and W in geological samples using isotope dilution inductively coupled plasma-mass spectrometry with a flow injection system (ID-FI-ICP-MS). The chemical procedure requires HF digestion of the sample with a Mo-Sb-W mixed spike, subsequent evaporation and dissolution of Mo, Sb and W from Mg and Ca fluorides with HF. Recovery yields of Mo, Sb and W in the extraction were > 94% for samples of peridotite, basalt and andesite composition, with the exception of W in samples of peridotite composition for which recovery was 81%. No matrix effects were observed in the determination of the isotope ratios of Mo, Sb and W in solutions prepared from peridotite, basalt and andesite samples down to a dilution factor of 100. Detection limits of Mo, Sb and W in silicate materials were at the several ng g⁻¹ level. Analysis of the silicate reference materials PCC-1, DTS-1, BCR-1, BHVO-1, AGV-1 from the US Geological Survey and JP-1, JB-1, -2, -3, JA-1, -2, and -3 from the Geological Survey of Japan as well as the Smithsonian reference Allende powder yielded reliable Mo, Sb and W concentrations. The repeatability in the analysis of basalts and andesites was < 9%. This technique requires only 0.2 ml sample solution, and is therefore suitable for analyzing small and/or precious samples such as meteorites, mantle peridotites and their mineral separates.  相似文献   

Determination of Zirconium, Niobium, Hafnium and Tantalum at ng g-1 Levels in Geological Materials by Direct Nebulisation of Sample HF Solution into FI-ICP-MS     

Akio Makishima  Eizo Nakamura  Toshio Nakano 《Geostandards and Geoanalytical Research》1999,23(1):7-20

We have developed a rapid and accurate method to determine Zr, Nb, Hf and Ta (denoted as HFSE) in geological samples by inductively coupled plasma-mass spectrometry fitted with a flow injection system (FI-ICP-MS). The method involves sample decomposition by HF followed by HF dissolution of HFSE coprecipitated with insoluble M and Ca fluoride residues formed during the initial HF attack. This HF solution was directly nebulized into an ICP mass spectrometer. An external calibration curve method and an isotope dilution method (ID) were applied for the determination of Nb and Ta, and of Zr and Hf, respectively. Recovery yields of HFSE were > 96% for peridotite, basalt and andesite compositions, apart from Zr and Hf for peridotite (> 85%). No matrix effects for either signal intensities of HFSE or isotope ratios of Zr and Hf were observed in basalt, andesite and peridotite solutions down to a dilution factor of 100. Detection limits in silicate rocks were 40, 2, 1 and 0.1 ng g-1 for Zr, Nb, Hf and Ta, respectively. This technique required only 0.1 ml of sample solution, and thus is suitable for analysing small and/or precious samples such as meteorites, mantle peridotites and their mineral separates. We also present newly determined data for the Zr, Nb, Hf and Ta concentrations in USGS silicate reference materials DTS-1, PCC-1, BCR-1, BHVO-1 and AGV-1, GSJ reference materials JB-1, -2, -3, JA-1, -2 and -3, and the Smithsonian reference Allende powder.  相似文献   

Distributions of polycyclic aromatic hydrocarbons and alkylated polycyclic aromatic hydrocarbons in Osaka Bay,Japan     

Shizuho Miki  Seiichi Uno  Kazuki Ito  Jiro Koyama  Hiroyuki Tanaka 《Marine pollution bulletin》2014

Contaminations in sediments by polycyclic aromatic hydrocarbons (PAHs) and alkylated PAHs were investigated at 44 sites in Osaka Bay, Japan. Concentrations of total PAHs and alkylated PAHs were in the range 6.40–7800 ng/g dry weights and 13.7–1700 ng/g dry weights, respectively. The PAH concentrations tended to be higher along the shoreline in the vicinities of big ports, industrialized areas, and densely populated regions such as the cities of Osaka and Kobe. The major sources appeared to be pyrogenic or both pyrogenic and petrogenic at most of the sites. PAH concentrations were remarkably high at a site near Kobe, where the concentrations of dibenzo(a,h)anthracene and benzo(g,h,i)perylene exceeded the effects-range-medium concentration and eight PAHs were above the corresponding effects-range-low concentrations. Those PAHs may have been derived from the great fire associated with the large earthquake in 1995.  相似文献   

Simulated distribution and ecotoxicity-based assessment of chemically-dispersed oil in Tokyo Bay     

Jiro Koyama  Chie Imakado  Seiichi Uno  Takako Kuroda  Shouichi Hara  Takahiro Majima  Hideyuki Shirota  Nathaniel C. Añasco 《Marine pollution bulletin》2014

To assess risks of chemically-dispersed oil to marine organisms, oil concentrations in the water were simulated using a hypothetical spill accident in Tokyo Bay. Simulated oil concentrations were then compared with the short-term no-observed effect concentration (NOEC), 0.01 mg/L, obtained through toxicity tests using marine diatoms, amphipod and fish. Area of oil concentrations higher than the NOEC were compared with respect to use and non-use of dispersant. Results of the simulation show relatively faster dispersion near the mouth of the bay compared to its inner sections which is basically related to its stronger water currents. Interestingly, in the inner bay, a large area of chemically-dispersed oil has concentrations higher than the NOEC. It seems emulsifying oil by dispersant increases oil concentrations, which could lead to higher toxicity to aquatic organisms. When stronger winds occur, however, the difference in toxic areas between use and non-use of dispersant is quite small.  相似文献   

Global distributions of storm-time ionospheric currents as seen in geomagnetic field variations     

Atsuki Shinbori  Tomoaki Hori  Yoshimasa Tanaka  Yukinobu Koyama  Takashi Kikuchi  Tsutomu Nagatsuma 《极地研究(英文版)》2013,(4):296-314

To investigate temporal and spatial evolution of global geomagnetic field variations from high-latitude to the equator during geomagnetic storms, we analyzed ground geomagnetic field disturbances from high latitudes to the magnetic equator. The daytime ionospheric equivalent current during the storm main phase showed that twin-vortex ionospheric currents driven by the Region 1 field-aligned currents （R1 FACs） are intensified significantly and expand to the low-latitude region of-30~ magnetic latitude. Centers of the currents were located around 70~ and 65~ in the morning and afternoon, respectively. Corresponding to intensification of the R1 FACs, an enhancement of the eastward/westward equatorial electrojet occurred at the daytime/nighttime dip equator. This signature suggests that the enhanced convection electric field penetrates to both the daytime and nighttime equa- tor. During the recovery phase, the daytime equivalent current showed that two new pairs of twin vortices, which are different from two-cell ionospheric currents driven by the R1 FACs, appear in the polar cap and mid latitude. The former led to enhanced north- ward Bz （NBZ） FACs driven by lobe reconnection tailward of the cusps, owing to the northward interplanetary magnetic field （IMF）. The latter was generated by enhanced Region 2 field-aligned currents （R2 FACs）. Associated with these magnetic field variations in the mid-latitudes and polar cap, the equatorial magnetic field variation showed a strongly negative signature, produced by the westward equatorial electrojet current caused by the dusk-to-dawn electric field.  相似文献