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排序方式： 共有105条查询结果，搜索用时 15 毫秒
71.
Ohtsuka Katsuhito Shimoda Chikara Yoshikawa Makoto Watanabe Jun-Ichi 《Earth, Moon, and Planets》1997,77(2):83-91
The detailed activity profile of the Sextandids - one of the day-time meteor showers - is poorly known and still unclear.
Using the forward-scatter radio technique we have successfully been able to obtain further detailed overall activity profile
of the Sextantids for seven consecutive years: 1991–1997. Analysis confirmed the Sextantid activity duration in solar longitude
(J2000) of at least 184–193° and the maximum solar longitude at 188.35 ± 0.10° with a full width at half maximum (FWHM) of
2.0 ± 0.2°. Performing the numerical integrations, we also substantiated a possibility of the association between Apollo-type
asteroid (3200) Phaethon and the Sextantids. Furthermore, we roughly estimated relative maximum flux rate of Sextantids :
Geminids as 1 : 3 amplitude ratio. Depending upon the flux rates and the time lags of the orbital evolution with Phaethon,
we conclude that the Sextantids are at a more progressive stage of orbital evolution than the Geminids if both meteor streams
are really associated with Phaethon.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
72.
Dynamical behaviour of an evaporating black hole is investigated for a Vaidya-type metric. The Raychaudhuri equation is examined with including terms up to the second order in the luminosity near the event horizon. Such a solution is found that the luminosity increases as the mass decreases during the evaporation. 相似文献
73.
We developed an iterative method for determining the three-dimensional temperature distribution in a spherical spinning body that is irradiated by a central star. The seasonal temperature change due to the orbital motion is ignored. It is assumed that material parameters such as the thermal conductivity and the thermometric conductivity are constant throughout the spherical body. A general solution for the temperature distribution inside a body is obtained using spherical harmonics and spherical Bessel functions. The surface boundary condition contains a term obtained using the Stefan–Boltzmann law and is nonlinear with respect to temperature because it is dependent on the fourth power of temperature. The coefficients of the general solution are fitted to satisfy the surface boundary condition by using the iterative method. We obtained solutions that satisfy the nonlinear boundary condition within 0.1% accuracy. We calculated the rate of change in the semimajor axis due to the diurnal Yarkovsky effect using the linear and nonlinear solutions. The maximum difference between the rates calculated using the two sets of solutions is 13%. Therefore current understanding of the diurnal Yarkovsky effect based on linear solutions is fairly good. 相似文献
74.
Abstract Six oil samples collected from the Sagara oil field, Shizuoka Prefecture, were geochemically analyzed. Unlike the Niigata oils, the Sagara oils: (i) are low-sulphur light oils dominated by gasoline and kerosene fractions; (ii) have low values of environment index in light hydrocarbon compositions; (iii) have high Pr/ n -C17 and low Ph/ n -C18 ratios and high oleanane/hopane ratios; (iv) have high relative abundance of C29 and low relative abundance of C28 regular steranes; and (v) have 'light' stable carbon isotope compositions. These characteristics show that the source rocks of the Sagara oils contain mainly marine organic matter, but with more input of terrigenous organic matter deposited under more oxic conditions compared to those of the Niigata oils. The light carbon isotope compositions and the low relative abundance of C28 regular steranes of the Sagara oils suggest that their source rock is not Miocene, but probably Paleogene in age. The Sagara oils probably migrated along faults from deeper parts of the basin. 相似文献
75.
Setouchi high-Mg andesites revisited: geochemical evidence for melting of subducting sediments 总被引：11，自引：0，他引：11
G Shimoda Y Tatsumi S Nohda K Ishizaka B.M Jahn 《Earth and Planetary Science Letters》1998,160(3-4):479-492
In order to evaluate the mechanism of production of unusual high-Mg andesite (HMA) magmas, Pb–Nd–Sr isotopic compositions were determined for HMAs and basalts from the Miocene Setouchi volcanic belt in the SW Japan arc. The isotopic compositions of Setouchi rocks form mixing lines between local oceanic sediments and Japan Sea backarc basin basalts, suggesting a significant contribution of the subducting sediment component to the HMA magma generation. Mixing calculations using compositions of an inferred original mantle and local oceanic sediments suggest that a sediment-derived melt, neither an H2O-rich fluid nor an amphibolite/eclogite-derived melt, could have been produced first and served as a plausible metasomatic agent for the HMA magma source. The unusual tectonic setting, including subduction of a newly-borne hence hot plate, may be responsible for melting of subducting sediments. 相似文献
76.
The time-sequence of polar magnetic substorms is discussed to clarify some controversies on the magnetospheric substorm model including the growth phase. The main purpose of the analyses is to examine magnetic variations in the polar cap and in low latitudes. The onset of the expansion phase is confirmed to be reasonably defined by a vector change of polar-cap magnetic disturbance, a sharp intensification of the auroral electrojet disturbance and the beginning of positive ΔH disturbance in midlatitudes near midnight. It is shown that the growth phase signatures so far proposed are consistent when the onset of the expansion phase is identified from the above mentioned features. 相似文献
77.
Akihiro Shiomoto Katsuyuki Sasaki Toru Shimoda Satsuki Matsumura 《Journal of Oceanography》1994,50(2):209-222
Primary productivity was measured byin situ method using13C in the offshore Oyashio region in the spring (May) and summer (September) of 1990. Most of the values were within the range of 0.1 to 4 gC 1–1 h–1 although a very large value, 7.96 gC l–1 h–1, was observed in summer. Most daily primary production fell within the range of 372 to 633 mgC m–2 d–1 although a very large value, 2,109 mgC m–2 d–1, was observed around the frontal area in summer. Chlorophylla (Chl.a) exceeded 1 g l–1 in many cases, and the maximum was 4.61 g l–1 in spring and 7.53 g l–1 in summer. Most primary productivity per unit Chl.a (photosynthetic assimilation ratio) was within the range of 0.1 to 3 gC gChl.a
–1 h–1 although higher values, 3–6 gC gChl.a
–1 h–1, were observed where small-size phytoplanktons (<2 m) were dominant. These results were compared with results obtained until now in the Oyashio region. The values beyond the range obtained so far in the offshore region were also observed in this study. Furthermore, it was pointed out that the size composition of phytoplankton community has significant influence on the results of Chl.a and photosynthetic assimilation ratio in the Oyashio region. 相似文献
78.
We grew a hydrogen-utilizing methanogen, Methanothermobacter thermoautotrophicus strain ΔH, in coculture and pure culture conditions to evaluate the hydrogen isotope fractionation associated with carbonate reduction under low (< several tens of μM; coculture) and high (>6 mM; pure culture) concentrations of H2 in the headspace. In the cocultures, which were grown at 55 °C with a thermophilic butyrate-oxidizing syntroph, the hydrogen isotopic relationship between methane and water was well represented by the following equation:
δDCH4=0.725(±0.003)·δDH2O-275(±3), 相似文献
79.
Robert C. Thunell William B. Curry Susumu Honjo 《Earth and Planetary Science Letters》1983,64(1):44-55
A mooring array with three automated sediment traps capable of collecting time series samples was deployed in the Panama Basin for one year beginning in December 1979. A series of six consecutive two-month long samples was collected at each of three depths (890, 2590 and 3560 m) in order to examine seasonal variation in the flux of planktonic foraminifera, and evaluate the contribution of foraminifera to the total carbonate flux.The flux of the larger planktonic foraminifera (250–500 μm and 500–1000 μm) is greatest during February–March when upwelling is most intense in the Panama Basin. In contrast, the maximum flux of the smaller foraminifera (125–250 μm) is associated with a phytoplankton bloom during the summer months (June through September). This size-dependent flux pattern appears to be a species specific effect. The flux of the larger foraminifera is dominated by non-spinose forms (i.e. Neogloboquadrina dutertrei and Globorotalia theyeri), while the flux of the smaller foraminifera consists predominantly of spinose species (i.e. Globigerinoides ruber, G. sacculifer and G. conglobatus). Although the magnitude of the flux varied throughout the year, the average weight of individual foraminiferal tests in different size fractions showed no seasonal variability.With the exception of the June–July period when there was a major coccolith bloom, planktonic foraminifera greater than 125 μm account for between 28 and 34% of the total carbonate flux at this location. During the coccolith bloom, planktonic foraminifera accounted for less than 2% of the total carbonate flux. Planktonic foraminifera in the 250–500 μm size range are the most significant contributors to the overall particulate flux, accounting for roughly 70–80% of the total foraminiferal fluxes measured at the three trap depths. 相似文献
80.
Yo-ichiro Otofuji Sadao Sasajima Susumu Nishimura Agus Dharma Fred Hehuwat 《Earth and Planetary Science Letters》1981,54(2):272-280
Paleomagnetic results from the northern arm of Sulawesi show that the arm has been subjected to a clockwise rotation of more than 90° and that its rotational motion began no later than the middle Miocene. The mean direction showing a normal polarity at the Eocene to the early Miocene isD = 98.0° andI = 6.9°. A declination value ofD = 50.1° obtained from Miocene rocks indicates a transition stage of the rotational motion. The datum from Plio-Pleistocene volcanics isD = ?4.6° andI = ?9.3°. This suggests that the rotational motion terminated before the initiation of volcanic activity during the Plio-Pleistocene. 相似文献