Time filter

Source Type

Yoshida H.,Nagoya University | Metcalfe R.,Quintessa Ltd. | Nishimoto S.,Nagoya City Science Museum | Yamamoto H.,University of Fukui | Katsuta N.,Gifu University
Applied Geochemistry | Year: 2011

Weathering rinds formed in Mesozoic sandstone and basalt cobbles buried in terrace deposits for up to 300ka have been investigated. The aim was to determine the formation process and elemental mass balances during rind development. The ages of terraces distributed in the western part of Fukui prefecture, central Japan have been determined as 50ka, 120ka and 300ka based on a tephro-stratigraphic method. Detailed investigations across the weathering rinds, consisting of microscopic observations, porosity measurements, and mineralogical and geochemical analyses using X-ray diffractometry (XRD), X-ray fluorescence (XRF), secondary X-ray analytical microscopy (SXAM), scanning electron microanalyser (SEM) and electron probe microanalysis (EPMA) have been carried out. The results revealed that the Fe concentrations in the weathering rind of a basalt cobble slightly decreased from the cobble's surface (rim) towards the unweathered core. In contrast, in a sandstone cobble formed under the same environmental conditions over the same period of time there is an Fe-rich layer at some distance below the cobble's surface. Elemental mass balances across the rinds were determined by using open system mass balance (τi,j) calculations and show that the Fe was precipitated as Fe-oxyhydroxides in the basalt cobbles, although Fe was slightly removed from the rims. In sandstone cobbles, on the other hand, Fe migrated along a Fe concentration gradient by diffusion and precipitated as Fe-oxyhydroxide minerals to form the weathering rinds. Presumably, precipitation was due to the relatively higher pH conditions caused by mineral dissolution within the pores, principally involving calcite, but probably also silicates including feldspar. The detailed characterization of the weathering rinds revealed the influence of lithology on the accumulation and dissolution of Fe-oxyhydroxides, causing weathering rinds with different characteristics to develop in different kinds of buried cobbles under the same conditions. Relatively large climatic changes in the study area did not cause discernable variations in the mean formation rates of the studied rinds, which were in the order of 10-8 m/a for both basalt and sandstone cobbles. These rates are 1-2 orders of magnitude slower than those reported for tropical areas elsewhere, most probably due to the lower rainfall in the studied area. © 2011 Elsevier Ltd.

Nishimoto S.,Nagoya City Science Museum | Yoshida H.,Nagoya University
Lithos | Year: 2010

This paper investigates the mineralogical effects of hydrothermal alteration at depth in fractures in granite. A fracture accompanied by an alteration halo and filled with clay was found at a depth of 200 m in a drill core through Toki granite, Gifu, central Japan. Microscopic observation, XRD, XRF, EPMA and SXAM investigations revealed that the microcrystalline clays consist of illite, quartz and pyrite and that the halo round the fracture can be subdivided into a phyllic zone adjacent to the fracture, surrounded by a propylitic zone in which Fe-phyllosilicates are present, and a distinctive outer alteration front characterized by plagioclase breakdown. The processes that result in these changes took place in three successive stages: 1) partial dissolution of plagioclase with partial chloritization of biotite; 2) biotite dissolution and precipitation of Fe-phyllosilicate in the dissolution pores; 3) dissolution of K-feldspar and Fe-phyllosilicate, and illite precipitation associated with development of microcracks. These hydrothermal alterations of the granite proceed mainly by a dissolution-precipitation process resulting from the infiltration of hydrothermal fluid along microcracks. Such infiltration causes locally high mobility of Al and increases the ratio of fluid to rock in the alteration halo. These results contribute to an understanding of how granitic rock becomes altered in orogenic fields such as the Japanese island arc. © 2009 Elsevier B.V. All rights reserved.

Kawabata K.S.,Hiroshima University | Akitaya H.,Hiroshima University | Yamanaka M.,Konan University | Yamanaka M.,Kyoto University | And 47 more authors.
Astrophysical Journal Letters | Year: 2014

We present optical and near-infrared multi-band linear polarimetry of the highly reddened Type Ia supernova (SN) 2014J that appeared in M82. SN 2014J exhibits large polarization at shorter wavelengths, e.g., 4.8% in the B band, which decreases rapidly at longer wavelengths, while the position angle of the polarization remains at approximately 40° over the observed wavelength range. These polarimetric properties suggest that the observed polarization is likely predominantly caused by the interstellar dust within M82. Further analysis shows that the polarization peaks at a wavelengths much shorter than those obtained for the Galactic dust. The wavelength dependence of the polarization can be better described by an inverse power law rather than by the Serkowski law for Galactic interstellar polarization. These points suggest that the nature of the dust in M82 may be different from that in our Galaxy, with polarizing dust grains having a mean radius of <0.1 μm. © 2014. The American Astronomical Society. All rights reserved.

Tian K.,Nagoya University | Endo M.,Chukyo University | Urata M.,Nagoya University | Mouri K.,Nagoya City Science Museum | Yasuda T.,Nagoya University
International Journal of Interactive Mobile Technologies | Year: 2014

It is possible to improve learners' understanding of the concept of lunar phases by using Observation based Learning (OBL). In this research, Smartphone Augmented Reality (AR) technology was used to develop a multiviewpoint AR-based mobile learning (M-VARML) system for moon observation that can be used in the real world environment. An experiment was conducted to evaluate the usefulness of our system. Participants were given five moon observation tasks, which they had to perform manually and using the M-VARML system. After each task, they were given follow-up questionnaires on the usefulness of the functions in the system. Finally, they were asked about the operational usability and the effect our system had in motivating them to pursue lunar observation. The results show that the M-VARML system is effective in improving the observation and learning of students and in enhancing their motivation to pursue lunar learning.

Takeda Y.,Japan National Astronomical Observatory | Honda S.,University of Hyogo | Ohnishi T.,Nagoya City Science Museum | Ohkubo M.,Kyoto University | And 2 more authors.
Publications of the Astronomical Society of Japan | Year: 2013

In an attempt to carry out a systematic study on the behavior of the photospheric abundances of Li, C, and O (along with Fe) for Hyades main-sequence stars in the Teff range of ̃ 5000-7000 K, we conducted an extensive spectrum-synthesis analysis applied to four spectral regions (comprising lines of Fe-group elements, Li I 6708 line, C I 7111-7119 lines, and O I 6156-8 lines), based on the high-dispersion spectra of 68 selected F-G type stars belonging to this cluster. The abundances of C and O turned out to be fairly uniform in a marginally supersolar level, such as like the case of Fe: h[C=H]i = +0.15 (σ = 0.08), h[O=H]i = +0.22 (σ = 0.14), and h[Fe=H]i = +0.11 (σ = 0.08), suggesting that the primordial abundances are almost retained for these elements. Strictly, however, they show a slightly increasing trend with a decrease in Teff (typically on the order of ̃10-4 dexK-1); while this might be due to an improper choice of atmospheric parameters, we found it difficult to give a quantitatively reasonable explanation. Regarding Li, we confirmed the well-known Teff-dependent trend in the Li abundance reported so far (a conspicuous Li-trough at 6300K̃Teff̃6700K and a progressive decrease toward a lower Teff at Teff̃6000 K), which means that the surface Li of Hyades stars is essentially controlled only by Teff ; other parameters, such as the rotational velocity, are almost irrelevant. © 2013. Astronomical Society of Japan.

Discover hidden collaborations