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91.
Akira Tsuchiyama Masayuki Uesugi Kentaro Uesugi Tsukasa Nakano Ryo Noguchi Toru Matsumoto Junya Matsuno Takashi Nagano Yuta Imai Akira Shimada Akihisa Takeuchi Yoshio Suzuki Tomoki Nakamura Takaaki Noguchi Masanao Abe Toru Yada Akio Fujimura 《Meteoritics & planetary science》2014,49(2):172-187
In this study, the three‐dimensional (3‐D) microstructure of 48 Itokawa regolith particles was examined by synchrotron microtomography at SPring‐8 during the preliminary examination of Hayabusa samples. Moreover, the 3‐D microstructure of particles collected from two LL6 chondrites (Ensisheim and Kilabo meteorites) and an LL5 chondrite (Tuxtuac meteorite) was investigated by the same method for comparison. The modal abundances of minerals, especially olivine, bulk density, porosity, and grain size are similar in all samples, including voids and cracks. These results show that the Itokawa particles, which are surface materials from the S‐type asteroid Itokawa, are consistent with the LL chondrite materials in terms of not only elemental and isotopic composition of the minerals but also 3‐D microstructure. However, we could not determine whether the Itokawa particles are purely LL5, LL6, or a mixture of the two. No difference between the particles collected from Rooms A and B of the sample chamber, corresponding to the sampling sequence of the spacecraft's second and first touchdowns, respectively, was detected because of the statistically small amount of particles from Room B. 相似文献
92.
Masahiko Tanaka Tomoki Nakamura Takaaki Noguchi Aiko Nakato Hatsumi Ishida Toru Yada Kei Shirai Akio Fujimura Yukihiro Ishibashi Masanao Abe Tatsuaki Okada Munetaka Ueno Toshifumi Mukai 《Meteoritics & planetary science》2014,49(2):237-244
The crystallization temperatures of Itokawa surface particles recovered by the space probe Hayabusa were estimated by a plagioclase geothermometer using sodic plagioclase triclinicity. The Δ131‐index required for the thermometer, which is the difference in X‐ray diffraction peak positions between the 131 and 11 reflections of plagioclase, was obtained by a high‐resolution synchrotron Gandolfi camera developed for the third generation synchrotron radiation beamline, BL15XU at SPring‐8. Crystallization temperatures were successfully determined from the Δ131‐indices for four particles. The observed plagioclase crystallization temperatures were in a range from 655 to 660 °C. The temperatures indicate crystallization temperatures of plagioclases in the process of prograde metamorphism before the peak metamorphic stage. 相似文献
93.
We have carried out multi-station TV observations since 1994 in order to determine the orbit of the Arietid daytime meteor
stream. In 1999, one possible Arietid meteor was recorded by our simultaneous observations and its orbit was determined. In
2003, two Arietid meteors were observed from two stations of our observing site, those orbits were determined precisely, the
orbital elements were in good agreement with each other. This is the first time that determination of the precise orbit of
the Arietids has been made from optical observations. The orbit of these Arietid meteors, and comparison with the orbit obtained
from radar observations are discussed. 相似文献
94.
Raulin Jean Pierre Makhmutov Vladimir S. Kaufmann Pierre Pacini Alessandra Abe Lüthi Thomas Hudson Hugh S. Gary Dale E. 《Solar physics》2004,223(1-2):181-199
We present a report on the strong X5.3 solar flare which occurred on 25 August 2001, producing high-level γ-ray activity, nuclear lines and a dramatic long-duration white-light continuum. The bulk of millimeter radio fluxes reached a peak of ∼100 000 solar flux units at 89.4 GHz, and a few thousands of solar flux units were detected in the submillimeter range during the impulsive phase. In this paper we focus on and discuss (i) the implications inferred from high frequency radio observations during the impulsive phase; (ii) the dynamics of the low corona active region during the impulsive phase. In particular we found that 4–5 × 1036 accelerated (>20 keV) electrons s−1 radiating in a 1000–1100 G region, are needed to explain the millimeter to submillimeter-wave emissions. We present evidence that the magnetic field in the active region was very dynamic, and that strong non-thermal processes were triggered by the appearance of new, compact, low-lying (few thousand kilometers) loop systems, suggesting the acceleration site(s) were also located in the low solar atmosphere. 相似文献
95.
96.
Takahashi Keigo D. Makabe Ryosuke Takao Shintaro Kashiwase Haruhiko Moteki Masato 《Journal of Oceanography》2022,78(5):409-424
Journal of Oceanography - In the seasonal ice zone (SIZ), sea-ice algae have been hypothesized to influence phytoplankton species composition in seawater after melting from sea ice. However,... 相似文献
97.
Morphometrical analysis of two tropical mountain river basins of contrasting environmental settings, the southern Western Ghats, India 总被引:8,自引:4,他引:4
Jobin Thomas Sabu Joseph K. P. Thrivikramji George Abe N. Kannan 《Environmental Earth Sciences》2012,66(8):2353-2366
The morphometric analysis of river basins represents a simple procedure to describe hydrologic and geomorphic processes operating on a basin scale. A morphometric analysis was carried out to evaluate the drainage characteristics of two adjoining, mountain river basins of the southern Western Ghats, India, Muthirapuzha River Basin (MRB) in the western slopes and Pambar River Basin (PRB) in the eastern slopes. The basins, forming a part of the Proterozoic, high-grade, Southern Granulite Terrain of the Peninsular India, are carved out of a terrain dominantly made of granite- and hornblende-biotite gneisses. The Western Ghats, forming the basin divide, significantly influences the regional climate (i.e., humid climate in MRB, while semi-arid in PRB). The Survey of India topographic maps (1:50,000) and Shuttle Radar Topographic Mission digital elevation data were used as the base for delineation and analysis. Both river basins are of 6th order and comparable in basin geometry. The drainage patterns and linear alignment of the drainage networks suggest the influence of structural elements. The Rb of either basins failed to highlight the structural controls on drainage organization, which might be a result of the elongated basin shape. The irregular trends in Rb between various stream orders suggest the influence of geology and relief on drainage branching. The Dd values designate the basins as moderate- to well-drained with lower infiltration rates. The overall increasing trend of Rl between successive stream orders suggests a geomorphic maturity of either basins and confirmed by the characteristic I hyp values. The Re values imply an elongate shape for both MRB and PRB and subsequently lower vulnerability to flash floods and hence, easier flood management. The relatively higher Rr of PRB is an indicative of comparatively steeply sloping terrain and consequently higher intensity of erosion processes. Further, the derivatives of digital elevation data (slope, aspect, topographic wetness index, and stream power index), showing significant differences between MRB and PRB, are useful in soil conservation plans. The study highlighted the variation in morphometric parameters with respect to the dissimilarities in topography and climate. 相似文献
98.
Tatsu?KuwataniEmail author Kenji?Nagata Masato?Okada Mitsuhiro?Toriumi 《Contributions to Mineralogy and Petrology》2012,163(3):547-562
The chemical zoning profile in metamorphic minerals is often used to deduce the pressure–temperature (P–T) history of rock. However, it remains difficult to restore detailed paths from zoned minerals because thermobarometric evaluation
of metamorphic conditions involves several uncertainties, including measurement errors and geological noise. We propose a
new stochastic framework for estimating precise P–T paths from a chemical zoning structure using the Markov random field (MRF) model, which is a type of Bayesian stochastic
method that is often applied to image analysis. The continuity of pressure and temperature during mineral growth is incorporated
by Gaussian Markov chains as prior probabilities in order to apply the MRF model to the P–T path inversion. The most probable P–T path can be obtained by maximizing the posterior probability of the sequential set of P and T given the observed compositions of zoned minerals. Synthetic P–T inversion tests were conducted in order to investigate the effectiveness and validity of the proposed model from zoned Mg–Fe–Ca
garnet in the divariant KNCFMASH system. In the present study, the steepest descent method was implemented in order to maximize
the posterior probability using the Markov chain Monte Carlo algorithm. The proposed method successfully reproduced the detailed
shape of the synthetic P–T path by eliminating appropriately the statistical compositional noises without operator’s subjectivity and prior knowledge.
It was also used to simultaneously evaluate the uncertainty of pressure, temperature, and mineral compositions for all measurement
points. The MRF method may have potential to deal with several geological uncertainties, which cause cumbersome systematic
errors, by its Bayesian approach and flexible formalism, so that it comprises potentially powerful tools for various inverse
problems in petrology. 相似文献
99.
Takeshi Nishimura Masato Iguchi Ryohei Kawaguchi Surono Muhamad Hendrasto Umar Rosadi 《Bulletin of Volcanology》2012,74(4):903-911
We examine the basic characteristics of inflations at Semeru Volcano, Indonesia, to clarify the pressurization process prior
to two different styles of explosive eruptions: Vulcanian eruptions and gas bursts. Analysis of data obtained from tilt meters
installed close to the active crater allows clarification of the common features and the differences between the two styles
of eruptions. To improve the signal-to-noise ratio and to determine the mean characteristics of the inflations, we stack tilt
signals obtained from eruptions of different magnitudes and evaluate the maximum amplitude of the seismic signal associated
with these eruptions. Vulcanian eruptions, which explosively release large amounts of ash, are preceded by accelerating inflation
about 200–300 s before the eruption, which suggests volume expansion of the gas phase. In contrast, gas bursts, which rapidly
effuse water steam accompanied by explosive sounds, follow non-accelerating changes of inflation starting 20 s before each
emission. Tilt amplitudes increase with the magnitude of eruptions for both eruption styles. This suggests that the volume
and/or pressure of magma or gas stored in the conduit before eruptions controls the magnitude of volcanic eruptions. These
results further suggest that the magnitude of eruptions can be predicted from geodetic measurements of volcano inflation. 相似文献
100.
Excitation of Resonant Modes along the Japanese Coast by the 1993 and 1983 Tsunamis in the Japan Sea
Kuniaki Abe 《Pure and Applied Geophysics》2009,166(1-2):117-130
We observed seiches at 55 ports in Japan facing the Japan Sea and obtained dominant periods from their maximum spectral amplitudes. These periods were mostly determined ranging from 10 to 40 minutes. They were compared with dominant periods of the 1993 Hokkaido Nansei-oki tsunami and the 1983 Nihonkai Chubu-oki tsunami at the same ports. As a result, relations of dominant periods between seiches and tsunamis are classified into three types. The first one is fundamental mode excitation, the second is higher mode excitation and the third is no excitation. Plotting the maximum spectral amplitude normalized at an epicentral distance of 50 km versus the ratio of the tsunami dominant period to the seiche dominant period, we obtained resonance curves having maxima at one. This fact shows a contribution of resonance to the amplification. Thus it is recognized that the dominant period of seiching is an important factor in interpreting amplification and resonance of tsunami. 相似文献