Computer simulations of gas flow around close binary systems

A gas-dynamical model of gas streams around close binary systems is given. The velocity feld and the density distribution are determined for different parameter ranges. The results succeed in explaining the formation of a ring and a disk around the accreting component. The models furthermore reveal the existence of a tongue of matter extending from the inner Lagrangian point and a jet perpendicular to the system axis.     

On the formation of large-scale shock waves in barre galaxies

The behavior of the gaseous phase in a barred galaxy is followed by computer simulations of the gas flow in a fixed potential formed by a bar and a disk. The results support a hypothesis that the dark lanes observed on the leading side of the bar in many SB galaxies are coinciding with the shock waves. Furthermore the results reject an outflow explanation of the arms but suggest these to be formed mechanically by the bar. Ring-shaped features were not reproduced but double arms were occasionally detected.     

Two surveys for taking measures to cope with the coming earthquake to the Tokyo Metropolis

Although Tokyo City has frequently suffered from earthquake disasters, more than 70 years have passed since the last catastrophe of 1923. Because Tokyo has a greater probability now than ever of being hit by another major earthquake, the Tokyo Metropolitan Government has carried out two surveys for taking measures to cope with it; earthquake vulnerability assessment and earthquake damage prediction. The former assesses earthquake vulnerability regionally and is used for disaster-proof city planning. Damage due to the expected earthquake is quantitatively estimated in the latter. The results are used for making a regional disaster prevention plan in an emergency. Both physical and human geographers participate in these interdisciplinary surveys effectively.     

Degradation ofn-paraffin mixture by marine microorganisms in enriched seawater medium

The ability to degraden-paraffin mixture of two bacterial strains,Caulobacter sp. andFlavobacterium sp., isolated from sea water of Tokyo Bay was studied experimentally in the enriched seawater (ESW) medium. These bacteria degraded actively the mixture ofn-tridecane,n-tetradecane,n-pentadecane andn-hexadecane. The maximum rate of degradation was observed after a lag period of 2 to 8 day and these bacteria were found to degrade then-paraffin mixture at rates calculated to be in a range from 3.3×10^?12 to 3.4×10^?11 mg-oil cell^?1 h^?1 at 20°C. The maximum degradation rate,r _m mg-oil l^?1 h^?1, was correlated with the amount of the initial totaln-paraffin,S mg-oil l^?1, as expressed by the following equation: $$rm = (rm)\max \left( {\frac{S}{{S + Km}}} \right)$$ where (r _m )_max denotes the largest value ofr _m whenn-paraffin exists in large excess andK _m is a constant and represents the amount ofn-paraffin at which the degradation rate,r _m , reaches 1/2 of its largest value, (r _m )_max. The values of (r _m )_max andK _m were calculated to be as follows: In the case ofCaulobacter sp. (strain KM-1), (r _m )_max=6.0 mg-oil l^?1 h^?1 andK _m =191 mg-oillesw ^?1; in the case ofFlavobacterium sp., (r _m )_max=5.47 mg-oil l^?1 h^?1 andK _m =152 mg-oillesw ^?1.     

Fracture-zone conditions on a recently active fault: insights from mineralogical and geochemical analyses of the Hirabayashi NIED drill core on the Nojima fault, southwest Japan, which ruptured in the 1995 Kobe earthquake

An 1800-m-deep borehole into the Nojima fault zone was drilled at Nojima-Hirabayashi, Japan, after the 1995 Hyogo-ken Nanbu (Kobe) earthquake. Three possible fracture zones were detected at depths of about 1140, 1300, and 1800 m. To assess these fracture zones in this recently active fault, we analyzed the distributions of fault rocks, minerals, and chemical elements in these zones. The central fault plane in the shallowest fracture zone was identified by foliated blue-gray gouge at a depth of 1140 m. The degree of fracturing was evidently greater in the hanging wall than in the footwall. Minerals detected in this zone were quartz, orthoclase, plagioclase, and biotite, as in the parent rock (granodiorite), and also kaolinite, smectite, laumontite, stilbite, calcite, ankerite, and siderite, which are related to hydrothermal alteration. Biotite was absent in both the hanging wall and footwall across the central fault plane, but it was absent over a greater distance from the central fault plane in the hanging wall than in the footwall. Major element compositions across this zone suggested that hydrothermal alteration minerals such as kaolinite and smectite occurred across the central fault plane for a greater distance in the hanging wall than in the footwall. Similarly, H₂O+ and CO₂ had higher concentrations in the hanging wall than in the footwall. This asymmetrical distribution pattern is probably due to the greater degree of wall–rock fracturing and associated alteration in the hanging wall. We attributed the characteristics of this zone to fault activity and fluid–rock interactions. We analyzed the other fracture zones along this fault in the same way. In the fracture zone at about 1300 m depth, we detected the same kinds of hydrothermal alteration minerals as in the shallower zone, but they were in fewer samples. We detected relatively little H₂O+ and CO₂, and little evidence for movement of the major chemical elements, indicating little past fluid–rock interaction. In the fracture zone at about 1800 m depth, H₂O+ and CO₂ were very enriched throughout the interval, as in the fracture zone at about 1140 m depth. However, smectite was absent and chlorite was present, indicating the occurrence of chloritization, which requires a temperature of more than 200 °C. Only smectite can form under the present conditions in these fracture zones. The chloritization probably occurred in the past when the fracture zone was deeper than it is now. These observations suggest that among the three fracture zones, that at about 1140 m depth was the most activated at the time of the 1995 Hyogo-ken Nanbu (Kobe) earthquake.     

Ar and Sr isotopes of mantle-derived rocks from the Japanese Islands

⁴⁰Ar-³⁰Ar and Sr isotope analyses have been made for ultramatic nodules in basaltic rocks from Itinome-gata and the Oki-Dōgo Island, northeast and southwest of Japan respectively, in order to examine the state of the upper mantle under the Japanese Islands. ⁴⁰Ar-³⁰Ar analyses have revealed that ultramafic nodules from Oki-Dōgo Island were involved in events which caused Ar redistribution in these rocks and probably were related to their formation not older than several tens of millions of years ago. These nodules are relatively depleted in both Rb and Sr contents together with some other incompatible elements compared to similar nodules from the other regions in the world. This may be typical for ultramafic nodules from the Japanese Islands. Ultramafic nodules show mostly a little higher⁸⁷Sr/⁸⁶Sr ratios (0.704–0.706) than those of host basaltic rocks (0.703–0.705) indicating the accidental origin for these nodules. Present results also suggest both horizontal and vertical inhomogeneities of the uppermost part of the mantle with respect to Sr isotopes on a regional scale. Hence, the ultramafic nodules in volcanic rocks may not always directly represent the upper mantle materials from which the magma is produced at present. Such ultramafic nodules might be relatively old material from the uppermost part of the mantle under the Japanese Islands.     

Two-stage model of incorporation of seamount and oceanic blocks into sedimentary melange: Geochemical and biostratigraphic constraints in Jurassic Chichibu accretionary complex, Shikoku, Japan

Abstract The significance of timing and formation of mélange in accretionary prisms, particularly concerning basaltic and related rocks and pelagic sediments, is exemplified in the Sawadani area of the Jurassic Chichibu accretionary complex in Shikoku, southwest Japan. Major and trace element geochemistry of the basaltic and related rocks indicates that all are of a hot-spot origin which produced a seamount. Most of the rocks have a trend of differentiation from an alkalic parental magma. The time relationship between the blocks and matrices of the mélange deduced from radiolarian fossil evidence and macro- to microscopic characteristics of contacts between different lithologies indicates two stages of mixing of materials in the seafloor. The first mixing occurred on the flank of the seamount in the pelagic environments in the Late Permian, and the second occurred on the trench floor or in the accretionary prism after the Early Jurassic. These two stages show respectively the geological phenomena of a seamount within the Izanagi-Kula plate and its incorporation into the Asian continental margin.     

Microbial community structure analysis of euxinic sediments using phospholipid fatty acid biomarkers

Microbial community structure in sediments, as determined by the phospholipid ester-linked fatty acid (PLFA) analysis, collected from Kojima Lake during summer and winter was described with reference to the environmental quality of the lake. A characteristic feature of the study area was the persistence of anoxia in summer and winter in the deeper area, and the sediments were under the reduced condition with high levels of sulfide, chemical oxygen demand, and low values of oxidation-reduction potential. PLFA profiles of the sediment were dominated by the saturated, branched and monounsaturated fatty acids. Small amounts (less than 5% of the total PLFA) of polyunsaturated fatty acids (biomarker fatty acids of microeukaryotes) and long chain fatty acids were detected in sediments. Total PLFA concentrations in sediments were higher in summer than in winter. Microbial community structure in the lake sediments was predominated by the prokaryotes, as evidenced from the larger amounts of bacterial biomarker fatty acids in the range of C₁₀ to C₂₀. The presence of signature fatty acids of sulfate reducing bacteria in sediments was consistent with the high levels of sulfide in the sediment and anoxic condition in the study area. PLFA showed significant differences in PLFA profiles between shallow and deeper areas, indicating the differences in the lipid contributing communities. However, no such a significant difference was observed between summer and winter.