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21.
Tsutomu Nakazawa Akira Nishimura Yasufumi Iryu Tsutomu Yamada Hiroshi Shibasaki Satoshi Shiokawa 《Marine Geology》2008,247(1-2):35-45
Carbonate rock cores drilled on the Kikai Seamount, northern Philippine Sea are examined for better understanding of tectonic history of the northern Philippine Sea. The Kikai Seamount, the summit of which is at 1960 m water depth, is an isolated high on the northwestern part of the Amami Plateau formed by subduction-related arc volcanism, and is situated close to the axis of the Ryukyu Trench in front of the Ryukyu Arc, SW Japan. The seamount is capped with shallow-water carbonates such as coral rudstone. Detailed examinations of lithology, larger foraminiferal assemblages, and Sr isotope composition reveal that the core material comprises Miocene carbonates unconformably overlain by Early Pleistocene carbonates. It indicates rapid subsidence of the Kikai Seamount since the Early Pleistocene. The most probable cause of rapid subsidence is collision and subduction of the Amami Plateau laden with the Kikai Seamount. The rapid subsidence may have started when the western corner of the plateau reached the Ryukyu Trench and began subduction beneath the Ryukyu Arc. The onset of the subsidence is likely to be controlled by a motion change in the Philippine Sea Plate. The latest change in subduction direction from north to northwestward into northwestward to west has been believed to have occurred at 1-2 Ma during latest Pliocene to Early Pleistocene time. The change of direction resulted in the shift from oblique into right-angle subduction of the plate beneath the Ryukyu Arc and also the onset of the collision and subduction of the Amami Plateau. 相似文献
22.
Masami Izuho Yuichi Nakazawa Fumito Akai Tsutomu Soda Hirotaka Oda 《Geoarchaeology》2009,24(4):492-517
In order to better understand modern human behavioral variability in Hokkaido, Japan, we consider the geoarchaeology of the Kamihoronai‐Moi site in terms of its geochronology, stratigraphy, depositional environments, and post‐depositional disturbances. A Paleolithic component is stratigraphically situated between the Eniwa‐a (15,000–17,000 14C yr B.P.) and the Tarumae‐d (8000–9000 14C yr B.P.) tephras. Moreover, six AMS 14C ages on charcoal from a Pleistocene‐aged hearth feature are between 14,400 and 14,800 14C yr B.P. Quantitative examinations of patterns in artifact distributions show a low degree of vertical and horizontal displacement of chipped‐stone artifacts, suggesting that post‐depositional movement of the cultural material was insufficient to disrupt the original pattern of artifact distribution. © 2009 Wiley Periodicals, Inc. 相似文献
23.
Hiromoto Shibahashi 《Solar physics》1991,133(1):117-125
We devise two asymptotic inversion methods of inferring the density distribution in the outer part of the Sun from the p-mode frequency spectrum of the Sun. One of them is based on an integral equation of nonlinear inversion, while the other reduces the problem to a linear form which is derived from comparison of the observed eigenfrequencies of the true Sun and the theoretical eigenfrequencies of a solar model. 相似文献
24.
Of the formation processes in the solar system, the process of growth and sedimentation of dust grains in the primordial solar nebula is investigated for a region near the Earth's orbit. The growth equation for dust grains, which are sinking as well as being in thermal motion, is solved numerically in the wide mass range between 10?12 and 106 g. Any turbulent motions in the nebula are assumed to have already decayed when the sedimentation begins. The numerical simulation shows that the growth and sedimentation proceed faster than was found by Kusaka et al. (1970) but in accordance with the estimate of Safronov (1969) owing to a cooperative interaction of the growth and the sedimentation; that is, at about 3 × 103 years after the beginning of the growth and sedimentation a dust layer, composed of centimeter-sized grains, is formed at the equator of the solar nebula. Furthermore, the mass density of dust grains floating in the outer layers of the nebula is found to be of the order of 10?5 after 105 years compared with that before the sedimentation. From these results, it can be estimated that at about 5 × 103 years after the beginning of sedimentation the dust layer breaks up owing to the onset of gravitational instability. 相似文献
25.
A model of 3He enrichments, which was proposed recently, is extended to study enhancements of heavy ions in high-energy particles. With weak currents parallel to the ambient magnetic field, oblique ion-acoustic waves and H cyclotron waves can become unstable. The former can have much greater growth rates at frequencies 3
He than at 4
He near the marginal states of instabilities. The latter can be unstable at 3
He for a wide region of plasma parameters. Thus they could cause 3He enrichments through cyclotron resonances. At the same time, these waves can resonate with first or higher harmonics of cyclotron frequencies of many other ions. We investigate these resonant ions for several cases of plasma temperature. This model predicts enhancements of heavy elements and of neutron-rich isotopes at T 10 MK. It shows heavy ion enhancements also at T 4 MK. Clear differences between these two temperatures, however, can be seen in charge states of ions. At T 2 MK, light ions as well as heavy ions can have cyclotron resonances with these waves, which suggests that such low temperatures are excluded. 相似文献
26.
中国东部地区降水季内变化的季节锁相 总被引：9，自引：1，他引：9
用１９５４－１９８３年５－８月的逐日降水资料分析了中国东部地区降水的气候特征，并讨论了它同东亚季风季节内变化的联系。结果发现，江淮梅雨同华南夏季风降水都具有季节锁相特征，前者呈单峰分布，后者呈双峰分布。同时，降水量的季内变化均具有２０－２５天的周期振荡特征。江淮流域降水的峰值和华南地区的第一个峰值主要受副热带季风影响，同夏季风的季节性北进和加强有关，华南地区第二个降水峰值受南海热带季风影响，与同期 相似文献
27.
Harunobu Masuko Kohei Arai Naoto Ebuchi Masanori Konda Masahisa Kubota Kunio Kutsuwada Teruko Manabe Akira Mukaida Tetsuo Nakazawa Atsushi Nomura Akira Shibata Yoshihiko Tahara 《Journal of Oceanography》2000,56(5):495-505
In order to validate wind vectors derived from the NASA Scatterometer (NSCAT), two NSCAT wind products of different spatial resolutions are compared with observations by buoys and research vessels in the seas around Japan. In general, the NSCAT winds agree well with the wind data from the buoys and vessels. It is shown that the root-mean-square (rms) difference between NSCAT-derived wind speeds and the buoy observations is 1.7 ms–1, which satisfies the mission requirement of accuracy, 2 ms–1. However, the rms difference of wind directions is slightly larger than the mission requirement, 20°. This result does not agree with those of previous studies on validation of the NSCAT-derived wind vectors using buoy observations, and is considered to be due to differences in the buoy observation systems. It is also shown that there are no significant systematic trends of the NSCAT wind speed and direction depending on the wind speed and incidence angle. Comparison with ship winds shows that the NSCAT wind speeds are lower than those observed by the research vessels by about 0.7 ms–1 and this bias is twice as large for data observed by moving ships than by stationary ships. This result suggests that the ship winds may be influenced by errors caused by ship's motion, such as pitching and rolling. 相似文献
28.
The discovery of the solar global oscillations, and their identification to many radial and nonradial eigenmodes of the Sun, have opened a new important field of research called solar seismology, in which we may probe the internal structure of the Sun by using its oscillations. In recent years, pulsations and oscillation-related phenomena have also been discovered in many stars which were hitherto regarded as non-pulsating stars. They include white dwards (ZZ Ceti-stars), Ap-stars, early-type stars with slow and rapid rotation (53 Per and Oph-stars, respectively). Developments in high spectral and high time-resolution observations will be expected to reveal variability in many other stars as well, in near future.In this review, the general properties of stellar eigenmode oscillations are first discussed. Recent observational and theoretical developments in the solar seismology and on pulsations and oscillations of newly discovered variable stars will then be reviewed.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984. 相似文献
29.
Chushiro Hayashi Kiyoshi Nakazawa Hiroshi Mizuno 《Earth and Planetary Science Letters》1979,43(1):22-28
When the proto-Earth was growing by the accretion of planetesimals and its mass became greater than about 0.1 ME, where ME is the present Earth's mass, an appreciable amount of gas of the surrounding solar nebula was attracted towards the proto-Earth to form an optically thick, dense atmosphere. We have studied the structure of this primordial atmosphere under the assumptions that (1) it is spherically symmetric and in hydrostatic equilibrium, and (2) the net energy outflow (i.e., the luminosity) is constant throughout the atmosphere and is given by GMM/R with M = M/106yr or M/107yr where M and R are the mass and the radius of the proto-Earth, respectively.The results of calculations show that the temperature at the bottom of the atmosphere, namely, at the surface of the proto-Earth increases greatly with the mass of the proto-Earth and it is about 1500°K for M = 0.25 ME. This high temperature is due to the blanketing effect of the opaque atmosphere. Thus, as long as the primordial solar nebula was existing, the surface temperature of the proto-Earth was kept high enough to melt most of the materials and, hence, the melted iron sedimented towards the center to form the Earth's core. 相似文献
30.
Minoru Sekiya Kiyoshi Nakazawa Chushiro Hayashi 《Earth and Planetary Science Letters》1980,50(1):197-201
If the Earth was formed by accumulation of rocky bodies in the presence of the gases of the primordial solar nebula, the Earth at this formation stage was surrounded by a massive primordial atmosphere (of about 1 × 1026 g) composed mainly of H2 and He. We suppose that the H2 and He escaped from the Earth, owing to the effects of strong solar wind and EUV radiation, in stages after the solar nebula itself dissipated into the outer space.The primordial atmosphere also contained the rare gases Ne, Ar, Kr and Xe whose amounts were much greater than those contained in the present Earth's atmosphere. Thus, we have studied in this paper the dissipation of these rare gases due to the drag effect of outflowing hydrogen molecules. By means of the two-component gas kinetic theory and under the assumption of spherically symmetric flow, we have found that the outflow velocity of each rare gas relative to that of hydrogen is expressed in terms of only two parameters — the rate of hydrogen mass flow across the spherical surface under consideration and the temperature at this surface. According to this result, the rare gases were dissipated below the levels of their contents in the present atmosphere, when the mass loss rate of hydrogen was much greater than 1 × 1017 g/yr throughout the stages where the atmospheric mass decreased from 1 × 1026 g to 4 × 1019 g. 相似文献