Plasma motions in the flare of 1982 June 6 (X12)     

Tetsuya Watanabe 《Solar physics》1990,126(2):351-366

This paper analyzes soft X-ray spectra obtained from the Hinotori spacecraft for the investigation of plasma motions during the initial phase of the great flare, 1982 June 6. The wavelength calibration of the scanning spectrometers is determined from information on the spacecraft attitude and from the position of the Fexxv resonance line during the decay phase. Hard X-ray bursts, nonthermal line broadenings and blueshifted components in X-ray lines are temporally correlated with time differences of 0–30 s. The possible contribution of the blueshifted component to the line width decreases more rapidly than the nonthermal broadening, which suggests dominant plasma motions are taking place at higher and higher altitude in the corona, because of the increase of electron density in flaring loops. The evolution of the input kinetic energy content to the thermal plasma inferred from line broadenings in the impulsive phase resembles that of the thermal energy content in the source of the Fexxvi emission, which is different from that deduced for Fexxv source. This suggests that the origins of the nonthermal line broadening and Fexxvi source are closely coupled.  相似文献   

Chemical composition of primary cosmic rays with energies from 10 to 10 eV     

Y. Shirasaki  F. Kakimoto  S. Ogio  N. Gironda  M. Takeda  T. Kaneko  H. Yoshii  T. Baba  S. Sano  K. Nishi  N. Tajima  Y. Yamada  S. Shimoda  H. Nakatani  E. Gotoh  K. Murakami  Y. Toyoda  Y. Matsubara  Y. Mizumoto  W. Velasquez  A. Velarde  P. Miranda 《Astroparticle Physics》2001,15(4):118-381

The chemical composition of primary cosmic rays with energies from 10¹⁵ to 10^16.5 eV, so called “knee” region, is examined. We have observed the time structures of air Čerenkov light associated with air showers at Mt. Chacaltaya, Bolivia, since 1995. The distribution of a parameter that characterizes the observed time structures is compared with that calculated with a Monte Carlo technique for various chemical compositions. Then the energy dependence of the average logarithmic mass numbers ln A of the primary cosmic rays is determined. The present result at 10^15.3 eV is almost consistent with the result of JACEE (A12) and shows gradual increase in ln A as a function of the primary energy (A24 at 10¹⁶ eV). Form the comparison of the observational results with several theoretical models, we conclude that the supernova explosion of massive stars is a plausible candidate for the origin of cosmic rays around the “knee” region.  相似文献   

Phase transition in CaSiO₃ perovskite     

Tetsuya Komabayashi  Kei Hirose  Nagayoshi Sata  Yasuo Ohishi  Leonid S. Dubrovinsky 《Earth and Planetary Science Letters》2007,260(3-4):564-569

A phase transition in pure CaSiO₃ perovskite was investigated at 27 to 72 GPa and 300 to 819 K by in-situ X-ray diffraction experiments in an externally-heated diamond-anvil cell. The results show that CaSiO₃ perovskite takes a tetragonal form at 300 K and undergoes phase transition to a cubic structure above 490–580 K in a pressure range studied here. The transition boundary is strongly temperature-dependent with a slightly positive dT / dP slope of 1.1 (± 1.3) K/GPa. It is known that the transition temperature depends on Al₂O₃ content dissolved in CaSiO₃ perovskite [Kurashina et al., Phys. Earth Planet. Inter. 145 (2004) 67–74]. The phase transition in CaSiO₃(+ 3 wt.% Al₂O₃) perovskite therefore could occur in a cold subducted mid-oceanic ridge basalt (MORB) crust at about 1200 K in the upper- to mid-lower mantle. This phase transition is possibly ferroelastic-type and may cause large seismic anomalies in a wide depth range.  相似文献   

Tsunami Assessment for Risk Management at Nuclear Power Facilities in Japan     

Ken Yanagisawa  Fumihiko Imamura  Tsutomu Sakakiyama  Tadashi Annaka  Tomoyoshi Takeda  Nobuo Shuto 《Pure and Applied Geophysics》2007,164(2-3):565-576

The present study focuses on evaluation of the maximum and minimum water levels caused by tsunamis as risk factors for operation and management at nuclear power facilities along the coastal area of Japan. Tsunamis generated by submarine earthquakes are examined, basing literature reviews and databases of information on historical tsunami events and run-up heights. For simulation of water level along the coast, a numerical calculation system should be designed with computational regions covering a particular site. Also the calculation system should be verified by comparison of historical and calculated tsunami heights. At the beginning of the tsunami assessment, the standard faults, their locations, mechanisms and maximum magnitudes should be carefully estimated by considering historical earthquake-induced tsunamis and seismo-tectonics at each area. Secondly, the range of errors in the model parameters should be considered since earthquakes and tsunamis are natural phenomena that involve natural variability as well as errors in estimating parameters. For these reasons, uncertainty-induced errors should be taken into account in the process of tsunami assessment with parametric study of the tsunami source model. The element tsunamis calculated by the standard fault models with the errors would be given for the design. Then, the design tsunami can be selected among the element tsunamis with the most significant impact, maximum and minimum water levels, on the site, bearing in mind the possible errors in the numerical calculation system. Finally, the design tsunami is verified by comparison with the run-up heights of historical tsunamis, ensuring that the design tsunami is selected as the highest of all historical and possible future tsunamis at the site.  相似文献   

Tidal Winds on Titan Caused by Saturn     

Tetsuya TokanoFritz M. Neubauer 《Icarus》2002,158(2):499-515

The influence of Saturn's gravitational tide on the atmosphere of Titan is investigated by means of a three-dimensional general circulation model. Titan's orbital eccentricity of 0.0292 gives rise to time-dependent radial and librational tide whose potential circles eastward on Titan. Unlike atmospheric tides on terrestrial planets, Saturn's tide on Titan has a large impact on the dynamic meteorology down to the surface. The surface pressure oscillates by up to 1.5 hPa through the orbit. Near the surface the tidal wind dominates the atmospheric flow and exhibits strong temporal and spatial variation. The superposition of the annually present, thermally forced latitudinal pressure gradient and tidally caused pressure variation produces a unique wind pattern near the surface characterized by equatorward flow and high-latitude whirls. At higher levels the tidal wind manifests itself as eastward traveling planetary-scale wave of wavenumber 2 superposed on the background wind. In general tidal winds are more significant in the troposphere, where other forcing mechanisms are weak. Meridional tidal winds become as fast as 5 m s⁻¹ in the troposphere and change direction periodically through the orbit and along the parallel of latitude. Except in the lower troposphere, zonal winds always remain prograde because the tidal wind amplitude is usually smaller than the mean zonal wind. The tide also has a large impact on the mean zonal circulation in the stratosphere. A meridional drift of the descending Huygens Probe in the troposphere would be the easiest way to verify the tidal wind on Titan, but more complete observations of tropospheric wind and surface pressure by a future mission would be required to unveil the complete details of the tidal wind.  相似文献   

Abundance, Biomass, Production and Trophic Roles of Micro- and Net-Zooplankton in Ise Bay, Central Japan, in Winter     

Shin-Ichi Uye  Naoki Nagano  Tetsuya Shimazu 《Journal of Oceanography》2000,56(4):389-398

We investigated the geographical variations in abundance and biomass of the major taxonomic groups of micro- and net-zooplankton along a transect through Ise Bay, central Japan, and neighboring Pacific Ocean in February 1995. The results were used to estimate their secondary and tertiary production rates and assess their trophic roles in this eutrophic embayment in winter. Ise Bay nourished a much higher biomass of both micro- and net-zooplankton (mean: 3.79 and 13.9 mg C m^–3, respectively) than the offshore area (mean: 0.76 and 4.47 mg C m^–3, respectively). In the bay, tintinnid ciliates, naked ciliates and copepod nauplii accounted for, on average, 69, 18 and 13% of the microzooplankton biomass, respectively. Of net-zooplankton biomass, copepods (i.e. Acartia, Calanus, Centropages, Microsetella and Paracalanus) formed the majority (mean: 63%). Average secondary production rates of micro- and net-zooplankton in the bay were 1.19 and 1.87 mg C m^–3d^–1 (or 23.1 and 36.4 mg C m^–2d^–1), respectively, and average tertiary production rate of net-zooplankton was 0.75 mg C m^–3d^–1 (or 14.6 mg C m^–2d^–1). Available data approximated average phytoplankton primary production rate as 1000 mg C m^–2d^–1 during our study period. The transfer efficiency from primary production to zooplankton secondary production was 6.0%, and the efficiency from secondary production to tertiary production was 25%. The amount of food required to support the zooplankton secondary production corresponded to 18% of the phytoplankton primary production or only 1.7% of the phytoplankton biomass, demonstrating that the grazing impact of herbivorous zooplankton was minor in Ise Bay in winter.  相似文献   

Geochemical evolution of historical lavas from Askja Volcano, Iceland: Implications for mechanisms and timescales of magmatic differentiation     

Takeshi Kuritani  Tetsuya Yokoyama  Hiroshi Kitagawa  Eizo Nakamura 《Geochimica et cosmochimica acta》2011,75(2):570-587

The mechanisms and the timescales of magmatic evolution were investigated for historical lavas from the Askja central volcano in the Dyngjufjöll volcanic massif, Iceland, using major and trace element and Sr, Nd, and Pb isotopic data, as well as ²³⁸U-²³⁰Th-²²⁶Ra systematics. Lavas from the volcano show marked compositional variation from magnesian basalt through ferrobasalt to rhyolite. In the magnesian basalt-ferrobasalt suite (5-10 wt% MgO), consisting of lavas older than 1875 A.D., ⁸⁷Sr/⁸⁶Sr increases systematically with increasing SiO₂ content; this suite is suggested to have evolved in a magma chamber located at ∼600 MPa through assimilation and fractional crystallization. On the other hand, in the ferrobasalt-rhyolite suite (1-5 wt% MgO), including 1875 A.D. basalt and rhyolite and 20th century lavas, ⁸⁷Sr/⁸⁶Sr tends to decrease slightly with increasing SiO₂ content. It is suggested that a relatively large magma chamber occupied by ferrobasalt magma was present at ∼100 MPa beneath the Öskjuvatn caldera, and that icelandite and rhyolite magmas were produced by extraction of the less and more evolved interstitial melt, respectively, from the mushy boundary layer along the margin of the ferrobasalt magma chamber, followed by accumulation of the melt to form separate magma bodies. Ferrobasalt and icelandite lavas in the ferrobasalt-rhyolite suite have a significant radioactive disequilibrium in terms of (²²⁶Ra/²³⁰Th), and its systematic decrease with magmatic evolution is considered to reflect aging, along with assimilation and fractional crystallization processes. Using a mass-balance model in which simultaneous fractional crystallization, crustal assimilation, and radioactive decay are taken into account, the timescale for the generation of icelandite magma from ferrobasalt was constrained to be <∼3 kyr which is largely dependent on Ra crystal-melt partition coefficients we used.  相似文献   

Investigation of cutting methods for small samples of Hayabusa and future sample return missions     

Masayuki Uesugi  Ryo Noguchi  Tooru Matsumoto  Junya Matsuno  Takashi Nagano  Akira Tsuchiyama  Shigenori Harada  Kaori Yokoyama  Yoshiaki Yodo  Noboru Takeda  Toru Yada  Shogo Yakame  Yuzuru Karouji  Yukihiro Ishibashi  Masanao Abe  Tatsuaki Okada  Akio Fujimura  Mitsuru Ebihara  Fumio Kitajima  Keisuke Nagao  Tomoki Nakamura  Hiroshi Naraoka  Takaaki Noguchi  Ryuji Okazaki  Hisayoshi Yurimoto 《Meteoritics & planetary science》2014,49(7):1186-1201

We report the investigation of cutting methods for Hayabusa samples. The purpose of our study is to explore the possibility of applying multiple analyses to a single particle effectively. We investigated the cutting performance of a blade dicing saw, laser, focused ion beam (FIB), and physical breaking by microindenter. Cutting performance was examined by estimating the aspect ratio of the cut slit, i.e., depth over width of the slit. We also investigated the possible contamination and sample damage by cutting. The result of the investigation shows that we can cut the samples from <50 μm to 500 μm using those methods with aspect ratios from 10 to 20, although they would introduce some contamination or damage to the samples. Our investigations also provide an important basis for the analysis of samples obtained by future sample return missions.  相似文献   

Mineralogy of new Antarctic achondrites with affinity to Lodran and a model of their evolution in an asteroid     

Hiroshi Takeda  Hiroshi Mori  Takahiro Hiroi  Jun Saito 《Meteoritics & planetary science》1994,29(6):830-842

Abstract— We studied five new Antarctic achondrites, MacAlpine Hills (MAC) 88177, Yamato (Y)74357, Y75274, Y791491 and Elephant Moraine (EET)84302 by mineralogical techniques to gain a better understanding of the mineral assemblages of a group of meteorites with an affinity to Lodran (stony-iron meteorite) and their formation processes. This group is being called lodranites. These meteorites contain major coarse-grained orthopyroxene (Opx) and olivine as in Lodran and variable amounts of FeNi metal and troilite etc. MAC88177 has more augite and less FeNi than Lodran; Y74357 has more olivine and contains minor augite; Y791491 contains in addition plagioclase. EET84302 has an Acapulco-like chondritic mineral assembladge and is enriched in FeNi metal and plagioclase, but one part is enriched in Opx and chromite. The EET84302 and MAC88177 Opx crystals have dusty cores as in Acapulco. EET84302 and Y75274 are more Mg-rich than other members of the lodranite group, and Y74357 is intermediate. Since these meteorites all have coarse-grained textures, similar major mineral assemblages, variable amounts of augite, plagioclase, FeNi metal, chromite and olivine, we suggest that they are related and are linked to a parent body with modified chondritic compositions. The variability of the abundances of these minerals are in line with a proposed model of the surface mineral assemblages of the S asteroids. The mineral assemblages can best be explained by differing degrees of loss or movements of lower temperature partial melts and recrystallization, and reduction. A portion of EET84302 rich in metal and plagioclase may represent a type of component removed from the lodranite group meteorites. Y791058 and Caddo County, which were studied for comparison, are plagioclase-rich silicate inclusions in IAB iron meteorites and may have been derived by a similar process but in a different body.  相似文献   

Thermal evolution of flare plasma     

Tetsuya Watanabe  Katsuo Tanaka  Kyo Akita  Nariaki Nitta 《Solar physics》1983,86(1-2):107-113

The evolution of hot thermal plasma in solar flares is analyzed by a single-temperature model applied to continuum emission in the 5 keV < E ? 13 keV spectral range. The general trend that the thermal plasma observed in soft X-rays is heated by the non-thermal electrons that emit as the hard X-ray bursts is confirmed by the observation of an electron temperature increase at the time interval of hard X-ray spikes and a quantitative comparison between thermal energy content and hard X-ray energy input. Non-thermal electrons of 10 keV < E < 30 keV energy may play an important role in pre- and post-burst phases.  相似文献