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21.
Takaaki Noguchi Tomoki Nakamura Kyoko Okudaira Hajime Yano Seiji Sugita Mark J. Burchell 《Meteoritics & planetary science》2007,42(3):357-372
Abstract— Outside the Earth's atmosphere, silica aerogel is one of the best materials to capture finegrained extraterrestrial particles in impacts at hypervelocities. Because silica aerogel is a superior insulator, captured grains are inevitably influenced by frictional heat. Therefore, we performed laboratory simulations of hypervelocity capture by using light‐gas guns to impact into aerogels finegrained powders of serpentine, cronstedtite, and Murchison CM2 meteorite. The samples were shot at >6 km s?1 similar to the flyby speed at comet P/Wild‐2 in the Stardust mission. We investigated mineralogical changes of each captured particle by using synchrotron radiation X‐ray diffraction (SR‐XRD), transmission electron microscope (TEM), and field emission scanning electron microscope (FE‐SEM). SR‐XRD of each grain showed that the majority of the bulk grains keep their original mineralogy. In particular, SR‐XRD and TEM investigations clearly exemplified the presence of tochilinite whose decomposition temperature is about 300 °C in the interior of the captured Murchison powder. However, TEM study of these grains also revealed that all the samples experienced melting and vesiculation on the surface. The cronstedtite and the Murchison meteorite powder show remarkable fracturing, disaggregation, melting, and vesiculation. Steep thermal gradients, about 2500 °C/μm were estimated near the surface of the grains (<2 μm thick) by TEM observation. Our data suggests that the interior of >4 μm across residual grains containing abundant materials that inhibit temperature rise would have not experienced >300 °C at the center. 相似文献
22.
23.
Atsuyuki Ohta Noboru ImaiShigeru Terashima Yoshiko TachibanaKen Ikehara Hajime KatayamaAtsushi Noda 《Applied Geochemistry》2010
In all, 53 elements were analyzed in 1406 coastal sea sediment samples collected from an area off Hokkaido and the Tohoku region of Japan during a nationwide marine geochemical mapping project. The spatial distribution patterns of the elemental concentrations in coastal seas along with the existing geochemical maps in terrestrial areas were used to define natural geochemical background variation and mass transport processes. The terrestrial area is covered by mafic volcanic rocks and accretionary complexes associated with ophiolite, which has small amounts of felsic volcanic rocks and granite. The spatial distribution patterns of elements enriched in mafic lithologies such as Fe (Total Fe2O3) and Sc in marine environments are influenced by adjoining terrestrial materials. The spatial distribution patterns of Cr and Ni concentrations, which are highly abundant in ultramafic rocks on land, are used to evaluate the mass transport from land to the sea and the dispersive processes caused by oceanic currents. The scale of mass transport by oceanic currents occurs up to a distance of 100–200 km from the coast along the coastal areas. The regional differences of elements rich in felsic lithologies such as K (K2O), Nb and La in marine sediments are determined mainly by the relative proportion of minerals and lithic fragments enriching felsic materials to those associated with mafic materials. The spatial distribution of elemental concentration is not always continuous between the land areas and coastal sea areas. That difference is interpreted as resulting from (1) transportation of marine sediments by oceanic currents and storm waves, (2) contribution of volcanic materials such as tephra, (3) occurrence of shell fragments and foraminifera tests and (4) distribution of relict sediments of the last glacial age and early transgression age. Contamination with Cu, Zn, Cd, As, Mo, Sn, Sb, Hg, Pb and Bi was not observed in marine environments because the study area has little anthropogenic activity. Terrestrial materials are the dominant source for these metals. The Mo, Cd, Sn, Sb, Hg, Pb and Bi are abundant in silty and clayey sediments locally because of early diagenetic processes, authigenic precipitation and organic substances associated with these elements. The spatial distribution of As concentration shows exceptions: it is concentrated in some coarse and fine sands on the shelf. The enrichment is explained by adsorption of As, sourced from a coal field, to Fe hydroxide. 相似文献
24.
Atoll island vulnerability to flooding and inundation revealed by historical reconstruction: Fongafale Islet, Funafuti Atoll, Tuvalu 总被引:1,自引:1,他引:0
Hiroya Yamano Hajime Kayanne Toru Yamaguchi Yuji Kuwahara Hiromune Yokoki Hiroto Shimazaki Masashi Chikamori 《Global and Planetary Change》2007,57(3-4):407-416
The reef islands formed on coral atolls are generally small, low, and flat, with elevations of only a few meters. These islands are thus highly vulnerable to elevated sea levels caused by extreme events and global warming. Such vulnerability was recently evidenced at Fongafale Islet, the capital of Tuvalu, when it flooded during accelerated spring high tides possibly related to sea level rise caused by global warming. Many factors, not only environmental but also economic and social, determine the vulnerability of an island to sea level rise. In this study, we used data spanning 108 yrs to reconstruct changes in topography, land use/cover, population, and the distribution of buildings at Fongafale Islet. The results indicate that the vulnerability of Fongafale Islet relates to its original landform characteristics: the central part of the island was formerly dominated by swampland that flooded at high tides. Fongafale Islet experienced greater population in-migration and centralization beginning in the 1970s following the independence of Tuvalu and Kiribati. Migrants were also responding to declines in overseas mining operations and limited options for paid employment. As the population increased, construction took place in vulnerable swampland areas. Our results clearly demonstrate that examinations of global environmental issues should focus on characteristics specific to the region of interest. These characteristics should be specified using historical reconstruction to understand and address the vulnerability of an area to global environmental changes. 相似文献
25.
Shinsuke Abe Noboru Ebizuka Hideyuki Murayama Katsuhito Ohtsuka Satoru Sugimoto Masa-yuki Yamamoto Hajime Yano Jun-ichi Watanabe Jiří Borovička 《Earth, Moon, and Planets》2004,95(1-4):265-277
Spectra of persistent meteor trains were observed at wavelength between 300 and 930 nm. Two obtained train spectra during
the 1998 and 2001 Leonid meteor showers are reported here. During the 1998 Leonids, one train was detected by a photographic
camera with a spectrograph covering 370–640 nm region. On the other hand, during the 2001 Leonids, video observations were
carried out using image intensified cameras in ultraviolet (UV), visible and near infrared (near-IR) wavelengths. Temperatures
in persistent trains have been measured by atmospheric O2 A(0,1) band at the wavelength near 864.5 nm. From a video spectrum obtained just 7 s after parent fireball’s flare, a rotational
temperature of 250 K at altitude of 88.0±0.5 km was estimated. We can say that the cooling time scale of train strongly depends
on the initial mass of its fireball at least for Leonids. Based on cooling constant calculated from our results, we estimated
a temperature of ∼
∼130 K as a final exothermic temperature at early stage of persistent trains. 相似文献
26.
Daisaku Nogami † Taichi Kato Hajime Baba Rudolf Novák J. J. Lockley M. Somers 《Monthly notices of the Royal Astronomical Society》2001,322(1):79-84
We report on time-resolved photometry carried out during the 1995 short outburst and the 1997 long outburst in the eclipsing dwarf nova DV UMa. The revised orbital period is 0.0858526172 (67) d. We detected gigantic superhumps with an amplitude of ∼0.6 mag in the mid-phase of the 1997 outburst, revealing the SU UMa nature of DV UMa. The superhump period is 0.0887 (4) d. The superhumps became less clear during the late phase of the superoutburst, and we found two possible periods of 0.0885 (15) and 0.0764 (15). During both outbursts, the eclipse was wide and shallow near the maximum, and then became narrower and deeper, which is qualitatively well explained by the current disc instability theory. 相似文献
27.
This study investigates stem waves, propagating along a vertical wall, due to obliquely incident random waves through laboratory experiments and numerical simulations. Attention is paid to the difference or similarity between the stem waves due to periodic waves and random waves, the nonlinear and linear characteristics, and the effect of wave breaking on the evolution of stem waves. The following were found from this study: as the incident angle of waves become large or the nonlinearity of the incident waves become small, the significant stem wave height, normalized by the incident significant wave height, becomes large. This tendency is the same as that generated by the Stokes waves or cnoidal waves. However, regardless of the nonlinearity of incident waves, the width of stem waves is almost the same. This is a different point between the stem waves due to periodic and random waves. The wave breaking suppresses the growth of the stem waves. 相似文献
28.
Kotaro Kohno Koichiro Nakanishi Tomoka Tosaki Kazuyuki Muraoka Rie Miura Hajime Ezawa Ryohei Kawabe 《Astrophysics and Space Science》2008,313(1-3):279-285
Dense molecular medium plays essential roles in galaxies. As demonstrated by the tight and linear correlation between HCN(1–0)
and FIR luminosities among star-forming galaxies, from very nearby to high-z ones, the observation of a dense molecular component
is indispensable to understand the star formation laws in galaxies. In order to obtain a general picture of the global distributions
of dense molecular medium in normal star-forming galaxies, we have conducted an extragalactic CO(3–2) imaging survey of nearby
spiral galaxies using the Atacama Submillimeter Telescope Experiment (ASTE). From the survey (ADIoS; ASTE Dense gas Imaging
of Star-forming galaxies), CO(3–2) images of M 83 and NGC 986 are presented. Emphasis is placed on the correlation between
the CO(3–2)/CO(1–0) ratio and the star formation efficiency in galaxies. In the central regions of some active galaxies, on
the other hand, we often find enhanced or overluminous HCN(1–0) emission. The HCN(1–0)/CO(1–0) and HCN(1–0)/HCO+(1–0) intensities are often enhanced up to ∼0.2–0.3 and ∼2–3, respectively. Such elevated ratios have never been observed
in the nuclear starburst regions. One possible explanation for these high HCN(1–0)/CO(1–0) and HCN(1–0)/HCO+(1–0) ratios is X-ray induced chemistry in X-ray dominated regions (XDRs), i.e., the overabundance of the HCN molecule in
the X-ray irradiated dense molecular tori. If this view is true, the known tight correlation between HCN(1–0) and the star-formation
rate breaks in the vicinity of active nuclei. Although the interpretation of these ratios is still an open question, these
ratios have a great potential for a new diagnostic tool for the energy sources of dusty galaxies in the ALMA era because these
molecular lines are free from dust extinction. 相似文献
29.
Masanobu Shimada Hiromi Oaku Yasushi Mitomi Hiroshi Murakami Akira Mukaida Yasuhisa Nakamura Joji Ishizaka Hiroshi Kawamura Tasuku Tanaka Motoaki Kishino Hajime Fukushima 《Journal of Oceanography》1998,54(5):401-416
We present calibration and validation results of the OCTS’s ocean color version-3 product, which mainly consists of the chlorophyll-a concentration (Chl-a) and the normalized water-leaving radiance (nLw). First, OCTS was calibrated for the inter-detector sensitivity difference, offset, and absolute sensitivity using external
calibration source. It was also vicariously calibrated using in-situ measurements for water (Chl-a andnLw) and atmosphere (optical thickness), which were acquired synchronously with OCTS under cloud-free conditions. Second, the
product was validated using selected 17 in-situ Chl-a and 11 in-situnLw measurements. We confirmed that Chl-a was estimated with an accuracy of 68% for Chl-a less than 2 mg/m3, andnLw from 94% (band 2) to 128% (band 4). Geometric accuracy was improved to 1.3 km. Stripes were significantly reduced by modifying
the detector normalization factor as a function of input radiance. 相似文献
30.
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