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排序方式: 共有125条查询结果,搜索用时 15 毫秒
11.
Takahito OSAWA Hiroyuki KAGI Tomoki NAKAMURA Takaaki NOGUCHI 《Meteoritics & planetary science》2005,40(1):71-86
Abstract— Mid‐infrared absorption spectra for all types of carbonaceous chondrites were obtained in this study to establish a versatile method for spectroscopic classification of carbonaceous chondrites. Infrared spectra were measured using a conventional KBr pellet method and diamond press method. Spectra of hydrous carbonaceous chondrites exhibit intense O‐H stretching vibrations. CI chondrites are identifiable by a characteristic sharp absorption band appearing at 3685 cm?1, which is mainly attributable to serpentine. X‐ray diffraction analysis showed the presence of serpentine. However, Yamato (Y‐) 82162 (C1) does not have the band at 3685 cm?1 because of its thermal metamorphism. CM and CR chondrites have an intense absorption band at approximately 3600 cm?1. This absorption tends to appear in CM chondrites more strongly than CR chondrites because the intensity ratios of an OH stretching mode at 3520 cm?1 compared to 3400 cm?1 for CM chondrites are in the range of 0.95–1.04, which is systematically higher than those of CR chondrites (0.86–0.88). Therefore, the two types of chondrites are distinguishable by their respective infrared spectra. The spectrum feature of the Tagish Lake meteorite is attributable to neither CI nor CM chondrites. CO chondrites are characterized by weak and broad absorption at 3400 cm?1. CV chondrites have weak or negligible absorption of water. CK chondrites also have no water‐induced absorption. CH and CB chondrites have a sharp absorption at 3692 cm?1 indicating the presence of chrysotile, which is also supported by observations of X‐ray diffraction and TEM. The combination of spectroscopic classification and the diamond press method allows classification of carbonaceous chondrites of very valuable samples with small quantities. As one example, carbonaceous chondrite clasts in brecciated meteorites were classified using our technique. Infrared spectra for a fragment of carbonaceous clasts (<1 μg) separated from Willard (b) and Tsukuba were measured. The 3685 cm?1 band found in CI chondrites was clearly detected in the clasts, indicating that they are CI‐like clasts. 相似文献
12.
Masanori Iye Tatsuo Ueda Masafumi Noguchi Shinko Aoki 《Astrophysics and Space Science》1983,89(2):363-376
A new scheme has been devised to calculate discrete unstable global shearing spiral modes of gaseous disk models of galaxies. The scheme makes use of the Legendre expansion of eigen functions and the problem of stability analysis is reduced to an eigenvalue problem of an infinite matrix. The spiral patterns of these shearing wave solutions of linearized equations change their form in the course of time due to the differential rotation of the equilibrium disk. These shearing wave solutions are presumed to have intermediate characteristics between so-called density-waves and material arms. Comparison between these shearing modes and the non-shearing normal modes for a series of disk models is presented. 相似文献
13.
14.
Expanding on our previous N-body simulation of impacts between initially non-rotating rubble-pile objects [Takeda, T., Ohtsuki, K., 2007. Icarus 189, 256-273], we examine effects of initial rotation of targets on mass dispersal and change of spin rates. Numerical results show that the collisional energy needed to disrupt a rubble-pile object is not sensitive to initial rotation of the target, in most of the parameter range studied in our simulations. We find that initial rotation of targets is slowed down through disruptive impacts for a wide range of parameters. The spin-down is caused by escape of high-velocity ejecta and asymmetric re-accumulation of fragments. When these effects are significant, rotation is slowed down even when the angular momentum added by an impactor is in the same direction as the initial rotation of the target. Spin-down is most efficient when the impact occurs in the equatorial plane of the target, because in this case most of the ejected fragments originate from the equatorial region of the target and a significant amount of angular momentum can be easily removed. In the case of impacts from directions inclined relative to the target's equatorial plane, spin-down still occurs with reduced degree, unless impacts occur onto the pole region from the vertical direction. Our results suggest that such spin-down through disruptive impacts may have played an important role in spin evolution of asteroids through collisions in the gravity-dominated regime. 相似文献
15.
Takanori Shimizu Koji Tamai Ikuhiro Hosoda Shoji Noguchi Yuji Kominami Toshio Abe Kenzo Kitamura Ushio Kurokawa Delphis F. Levia Tayoko Kubota Naoki Kabeya Shin'ichi Iida Tatsuhiko Nobuhiro Shinji Sawano Sho Iwagami Akira Shimizu Yoshio Tsuboyama 《水文研究》2021,35(10):e14376
This data note introduces a database of long-term daily total precipitation and stream discharge data for seven forested watersheds in Japan that have been continuously monitored by the Forestry and Forest Products Research Institute. Three of the watersheds started data collection in the 1930s. Forest cover across the sites ranges from cool to warm temperate regions with the latitude spanning from 31 to 44° N and annual precipitation ranging from 1200 to 3000 mm yr−1. The effects of vegetation change via clearcutting, thinning and forest fire (among other stressors) on stream discharge can be analysed from the long-term observation sites. Moreover, this multi-site dataset allows for inter- and intra-site comparisons of annual water loss (difference of annual precipitation and stream discharge). These long-term datasets can provide comprehensive insights into the effects of climate change and other stressors on forested ecosystems, not only in Japan but across a spectrum of forest types, if combined with other long-term records from other forested watersheds across the world. 相似文献
16.
Vertical and cross-wind profiles of mean currents were measured systematically in vertical cross-sections of two wind-wave
tanks with aspect ratios of order one to study the secondary flow in the tanks. A pair of Langmuir cells turned out to be
driven by a close combination of the pressure gradient along the tank and the side-wall effects. That is, part of the adverse
pressure gradient produced a parabolic cross-wind profile with the smallest downwind current at the centerline and the largest
current along the two sidewalls. As a result, upwelling occurred in the center zone where the return flow was strongest, probably
because of the entrainment action of the wind-driven current. In order to compensate for this upwelling, downwelling occurred
along the two side-walls from the flow continuity. The resulting vertical circulation formed a pair of Langmuir circulations
across the span and served to maintain the parabolic profile formed by the pressure gradient. A positive feedback mechanism
is thus found between the primary and secondary circulations through upwelling of the return flow in the center zone. Vertical
shears of the span-averaged downwind current measured in two tanks were found to be systematically different from each other.
This difference seems to depend on the magnitude of the advective Reynolds stresses in the two tanks. 相似文献
17.
Hajime Fukushima Akiko Higurashi Yasushi Mitomi Teruyuki Nakajima Toshimitsu Noguchi Toshio Tanaka Mitsuhiro Toratani 《Journal of Oceanography》1998,54(5):417-430
This paper first describes the atmospheric correction algorithm for OCTS visible band data used at NASDA/EOC. Sharing a basic
structure with Gordon and Wang’s Sea WiFS algorithm, it uses 10 candidate aerosol models including the “Asian dust model”
introduced in consideration of the unique feature of aerosols over the east Asian waters. Based on the observations at 670
and 865 nm bands, the algorithm selects a pair of aerosol models that account best for the observed spectral reflectances,
and synthesizes the aerosol reflectance used for the atmospheric correction. Two different schemes for determining the value
of the parameter for the aerosol model selection are presented and their anticipated estimation error is analyzed in terms
of retrieved water reflectance at 443 nm. The results of our numerical simulation show that the standard deviation of the
estimation error of the “weighted average” scheme is mostly within the permissible level of ±0.002, reducing the error by
18% on average compared to the “simple average” scheme. The paper further discusses the expected error under the old CZCS-type
atmospheric correction, which assumes constant aerosol optical properties throughout the given image. Although our algorithm
has a better performance than the CZCS algorithm, further analysis shows that the error induced by the assumption taken in
the algorithm that the water-leaving radiance at 670 nm band is negligibly small may be large in high pigment concentration
waters, indicating the necessity for future improvements. 相似文献
18.
Keiji Misawa Mika Kohno Takayuki Tomiyama Takaaki Noguchi Tomoki Nakamura Keisuke Nagao Takashi Mikouchi Kunihiko Nishiizumi 《Earth and Planetary Science Letters》2010,289(1-2):287-297
Two silicate-rich dust layers were found in the Dome Fuji ice core in East Antarctica, at Marine Isotope Stages 12 and 13. Morphologies, textures, and chemical compositions of constituent particles reveal that they are high-temperature melting products and are of extraterrestrial origin. Because similar layers were found ~ 2000 km east of Dome Fuji, at EPICA (European Project for Ice Coring in Antarctica)-Dome C, particles must have rained down over a wide area 434 and 481 ka. The strewn fields occurred over an area of at least 3 × 106 km2. Chemical compositions of constituent phases and oxygen isotopic composition of olivines suggest that the upper dust layer was produced by a high-temperature interaction between silicate-rich melt and water vapor due to an impact explosion or an aerial burst of a chondritic meteoroid on the inland East Antarctic ice sheet. An estimated total mass of the impactor, on the basis of particle flux and distribution area, is at least 3 × 109 kg. A possible parent material of the lower dust layer is a fragment of friable primitive asteroid or comet. A hypervelocity impact of asteroidal/cometary material on the upper atmosphere and an explosion might have produced aggregates of sub-μm to μm-sized spherules. Total mass of the parent material of the lower layer must exceed 1 × 109 kg. The two extraterrestrial horizons, each a few millimeters in thickness, represent regional or global meteoritic events not identified previously in the Southern Hemisphere. 相似文献
19.
Experimental study on prevention of acid mine drainage by silica coating of pyrite waste rocks with amorphous silica solution 总被引:1,自引:1,他引:0
Masahiko Bessho Takaaki Wajima Takuro Ida Takashi Nishiyama 《Environmental Earth Sciences》2011,64(2):311-318
Acid mine drainage (AMD) is a widespread environmental problem associated with working and abandoned mining operations. It
results from the microbial oxidation of pyrite in the presence of water and air, affording an acidic solution that contains
toxic metal ions. Pyrite microencapsulation, utilizing silica coating, is a novel approach for controlling AMD that has been
shown to be very effective in controlling pyrite oxidation. The roles of the solution pH and silica concentration in the formation
mechanism for the AMD-preventing coating were investigated. A silica coating can be formed from silica solution at pH 7, at
which the amount of Fe eluted from pyrite into the solution is small. No coating was formed at other pH values, and the amounts
of eluted Fe were larger than at pH 7, especially at pH 11. The silica coating forms from 2,500 to 5,000 mg/L silica solutions,
but not from 0 or 1,000 mg/L silica solutions. The coating formation rate was slower in the 2,500 mg/L silica solution than
in the 5,000 mg/L silica solution. The formation of silica coating on pyrite surfaces depends on three main steps: formation
of Fe(OH)3 on the surface of pyrite, reaction between Fe(OH)3 and silicate in the solution on the pyrite surface, and growth of the silica layer on the first layer of silica. The best
pH condition to enable these steps was around 7, and the silica coating formation rate can be controlled by the concentration
of silica. 相似文献
20.
Satoshi Noguchi Naoyuki Shimoda Osamu Takano Nobutaka Oikawa Takao Inamori Tatsuo Saeki Tetsuya Fujii 《Marine and Petroleum Geology》2011,28(10):1817-1828
The reservoir architecture of methane hydrate (MH) bearing turbidite channels in the eastern Nankai Trough, offshore Japan is evaluated using a combination of 3-D seismic and well data. On the 3-D seismic section, the MH-bearing turbidite channels correspond to complex patterns of strong seismic reflectors, which show the 3-D internal architecture of the channel complex. A seismic-sequence stratigraphic analysis reveals that the channel complex can be roughly classified into three different stages of depositional sequence (upper, middle, and lower). Each depositional sequence results in a different depositional system that primarily controls the reservoir architecture of the turbidite channels. To construct a 3-D facies model, the stacking patterns of the turbidite channels are interpreted, and the reservoir heterogeneities of MH-bearing sediments are discussed. The identified channels at the upper sequence around the β1 well exhibit low-sinuosity channels consisting of various channel widths that range from tens to several hundreds of meters. Paleo-current flow directions of the turbidite channels are typically oriented along the north-northeast-to-south-southwest direction. High-amplitude patterns were identified above the channels along the north-to-south and north-northeast-to-south-southeast directions. These roughly coincide with the paleo-current flow of the turbidite channels. An interval velocity using high-density velocity analysis shows that velocity anomalies (>2000 m/s) are found on the northeastern side of the turbidite channels. The depositional stage of the northeastern side of the turbidite channels exhibits slightly older sediment stages than the depositional stages of the remaining channels. Hence, the velocity anomalies of the northeastern side of the channels are related to the different stages of sediment supply, and this may lead to the different reservoir architectures of the turbidite channels. 相似文献