Twin formation in hematite during dehydration of goethite     

Genki Saito  Yuji Kunisada  Takahiro Nomura  Norihito Sakaguchi  Tomohiro Akiyama 《Physics and Chemistry of Minerals》2016,43(10):749-757

Twin formation in hematite during dehydration was investigated using X-ray diffraction, electron diffraction, and high-resolution transmission electron microscopy (TEM). When synthetic goethite was heated at different temperatures between 100 and 800 °C, a phase transformation occurred at temperatures above 250 °C. The electron diffraction patterns showed that the single-crystalline goethite with a growth direction of [001]_G was transformed into hematite with a growth direction of [100]_H. Two non-equivalent structures emerged in hematite after dehydration, with twin boundaries at the interface between the two variants. As the temperature was increased, crystal growth occurred. At 800 °C, the majority of the twin boundaries disappeared; however, some hematite particles remained in the twinned variant. The electron diffraction patterns and high-resolution TEM observations indicated that the twin boundaries consisted of crystallographically equivalent prismatic (100) (010), and (1\(\bar{1}\)0) planes. According to the total energy calculations based on spin-polarized density functional theory, the twin boundary of prismatic (100) screw had small interfacial energy (0.24 J/m²). Owing to this low interfacial energy, the prismatic (100) screw interface remained after higher-temperature treatment at 800 °C.  相似文献   

Effects of mass sedimentation events after the 2011 off the Pacific coast of Tohoku Earthquake on benthic prokaryotes and meiofauna inhabiting the upper bathyal sediments     

Hidetaka Nomaki  Tomohiro Mochizuki  Tomo Kitahashi  Takuro Nunoura  Kazuno Arai  Takashi Toyofuku  Gengo Tanaka  Shuichi Shigeno  Eiji Tasumi  Katsunori Fujikura  Shuichi Watanabe 《Journal of Oceanography》2016,72(1):113-128

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Multi‐scale Decomposition of Co‐seismic Deformation from High Resolution DEMs: a Case Study of the 2004 Mid‐Niigata Earthquake   总被引：1，自引：0，他引：1  

ZHAO Yu  KONAGAI Kazuo  FUJITA Tomohiro 《《地质学报》英文版》2012,86(4):1013-1021

Decomposing co-seismic deformation is an immediate need for researchers who are interested in earthquake inversion analysis and geo-hazard mapping. However, conventional InSAR or digital elevation models (DEMs) imagery analyses only provide the displacement in the Line-of-Sight (LOS) direction or elevation changes. The 2004 Mid-Niigata earthquake in Japan provides lessons on how to decompose co-seismic deformation from two sets of DEMs. If three adjacent points undergo a rigid-body-translation movement, their co-seismic deformation can be decomposed by solving simultaneous equations. Although this method has been successfully used to discuss tectonic deformations, the algorithm needed improvement and a more rigorous algorithm, including a new definition of nominal plane, DEMs comparability improvement and matrix condition check is provided. Even with these procedures, the obtained decomposed displacement often showed remarkable scatter prompting the use of the moving average method, which was used to determine both tectonic and localized displacement characteristics. A cut-off window and a pair of band-pass windows were selected according to the regional geology and construction activities to ease the tectonic and localized displacement calculations, respectively. The displacement field of the tectonic scale shows two major clusters of large lateral components, and coincidently major visible landslides were found mostly within them. The localized displacement helps to reveal hidden landslides in the target area. As far as the Kizawa hamlet is concerned, the obtained vectors show down-slope movements, which are consistent with the observed traces of dislocations that were found in the Kizawa tunnel and irrigation wells. The method proposed has great potential to be applied to understanding post-earthquake rehabilitation in other areas.  相似文献   

ISRM Suggested Method for Monitoring Rock Displacements Using the Global Positioning System (GPS)     

Norikazu Shimizu  Shinichiro Nakashima  Tomohiro Masunari 《Rock Mechanics and Rock Engineering》2014,47(1):313-328

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Generation of tidal bedding in a circular flume experiment: formation process and preservation potential of mud drapes     

Tomoyuki Sato  Keisuke Taniguchi  Tomohiro Takagawa  Fujio Masuda 《Geo-Marine Letters》2011,31(2):101-108

Flume experiments aimed to produce flaser bedding were conducted using fine sand and clay in a circular flume. The formation process of mud drapes during the slack-water stage was revealed in detail. When the tidal current declines, a uniform mobile mud layer initially settles from suspension and drapes the entire rippled sand bed (type A mud). When the remaining flow velocity is very low, a more fluid mud begins to settle out (type B mud) that preferentially fills the ripple troughs, the ripples and mud together forming a flat surface. At slack tide, the two-phase mud drape is temporarily stationary. After the onset of the reversed flow phase, most of the type B mud is resuspended, while the type A mud is eroded from the crests, leaving behind a remnant mud drape (flaser) in the troughs that is subsequently buried by migrating ripples. Type B mud generally contains variable amounts of sand derived from eroded ripple crests, but does not show any visible internal sedimentary structures. Type A mud represents the ‘mud drapes’ commonly described in the literature, the temporary existence of type B mud having gone unnoticed because of its low preservation potential. When present, it can be recognized by its sand content and the occurrence of flame structures in ripple troughs. Tidal deposits reflecting the existence and depositional characteristics of both type A and type B mud are found in, for example, the macrotidal Oligocene Ashiya Group, Japan.  相似文献   

Geochemistry of 4 Vesta based on HED meteorites: Prospective study for interpretation of gamma ray and neutron spectra for the Dawn mission     

Tomohiro USUI  Harry Y. McSween 《Meteoritics & planetary science》2007,42(2):255-269

Abstract— Asteroid 4 Vesta, believed to be the parent body of the howardite, eucrite, and diogenite (HED) meteorites, will be investigated by the Dawn orbiting spacecraft. Dawn carries a gamma ray and neutron detector (GRaND) that will measure and map some major‐ and trace‐element abundances. Drawing on HED geochemistry, we propose a mixing model that uses element ratios appropriate for the interpretation of GRaND data. Because the spatial resolution of GRaND is relatively coarse, the analyzed chemical compositions on the surface of Vesta will likely reflect mixing of three endmember components: diogenite, cumulate eucrite, and basaltic eucrite. Reliability of the mixing model is statistically investigated based on published whole‐rock data for HED meteorites. We demonstrate that the mixing model can accurately estimate the abundances of all the GRaND‐analyzed major elements, as well as of minor elements (Na, Cr, and Mn) not analyzed by this instrument. We also show how a similar mixing model can determine the modal abundance of olivine, and we compare estimated and normative olivine data for olivine‐bearing diogenites. By linking the compositions of well‐analyzed HED meteorites with elemental mapping data from GRaND, this study may help constrain the geological context for HED meteorites and provide new insight into the magmatic evolution of Vesta.  相似文献   

Estimation of sub-annual inter-catchment groundwater flow using short-term water balance method     

Tomohiro Egusa  Tomoki Oda  Takanori Sato  Tomo'omi Kumagai 《水文研究》2021,35(9):e14368

Predicting inter-catchment groundwater flow (IGF) is essential because IGF greatly affects stream water discharge and water chemistry. However, methods for estimating sub-annual IGF and clarifying its mechanisms using minimal data are limited. Thus, we quantified the sub-annual IGF and elucidated its driving factors using the short-term water balance method (STWB) for three forest headwater catchments in Japan (named here catchment A, B and As). Our previous study using the chloride mass balance indicated that annual IGF of catchment A (49.0 ha) can be negligible. Therefore, we calculated the daily evapotranspiration (ET) rate using the Priestley–Taylor expression and the 5-year water balance in catchment A (2010–2014). The sub-annual IGF of the three catchments was then calculated by subtracting the ET rate from the difference between rainfall and stream discharge during the sub-annual water balance periods selected using the STWB. The IGF rates of catchment B (7.0 ha), which is adjacent to catchment A, were positive in most cases, indicating that more groundwater flowed out of the catchment than into it, and exhibited positive linear relationships with rainfall and stream discharge. This suggested that as the catchments became wetter, more groundwater flowed out of catchment B. Conversely, the IGF rates of catchment As (5.3 ha), included in catchment A, were negative in most cases, indicating that more groundwater flowed into the catchment than out from it, and exhibited negative linear relationships with rainfall and stream discharge. Given the topography of the catchments studied, infiltration into the bedrock was the probable reason for the IGF outflow from catchment B. We hypothesized that in catchment As, the discrepancy between the actual hydrological boundary and the surface topographic boundary could have caused an IGF inflow. This study provides a useful tool for determining an IGF model structure to be incorporated into rainfall-runoff models.  相似文献   

Wave dissipation by vegetation with layer schematization in SWAN   总被引：1，自引：0，他引：1  

Tomohiro Suzuki  Marcel ZijlemaBastiaan Burger  Martijn C. MeijerSiddharth Narayan 《Coastal Engineering》2012,59(1):64-71

The energy of waves propagating through vegetation is dissipated due to the work done by the waves on the vegetation. Dalrymple et al. (1984) estimated wave dissipation by integrating the force on a cylinder over its vertical extent. This was extended by Mendez and Losada (2004) to include varying depths and the effects of wave damping due to vegetation and wave breaking for narrow-banded random waves. This paper describes the wave dissipation over a vegetation field by the implementation of the Mendez and Losada formulation in a full spectrum model SWAN, with an extension to include a vertical layer schematization for the vegetation. The present model is validated with the original equation and results from Mendez and Losada (2004). The sensitivity of the model to the shape of the frequency spectrum, directional spreading and layer schematization are investigated. The model is then applied to field measurements by using a vegetation factor. This model has the ability to calculate two-dimensional wave dissipation over a vegetation field including some important aspects such as breaking and diffraction as used in SWAN model.  相似文献   

Grain growth in the forsterite-diopside system     

Tomohiro Ohuchi  Michihiko Nakamura 《Physics of the Earth and Planetary Interiors》2007,160(1):1-21

Grain growth experiments in dunite, clinopyroxenite, and wehrlites with various forsterite/diopside ratios were performed to investigate the effect of modal composition on grain growth kinetics in the Earth's uppermost mantle. The experiments were conducted using a piston-cylinder apparatus at 1200 °C and 1.2 GPa for 2-763 h under dry conditions. Normal grain growth (NGG) occurred in dunite, clinopyroxenite, and relatively forsterite-poor wehrlites (≤70 vol.% of forsterite). Grain growth rates of forsterite and diopside in relatively forsterite-poor wehrlites were much slower than those in dunite and clinopyroxenite. In the forsterite-rich wehrlites (≥80 vol.% of forsterite), NGG of diopside and abnormal grain growth (AGG) of forsterite occurred. The growth rate of diopside was significantly slower than that in clinopyroxenite, while the growth rate of forsterite by AGG was found to be similar to that by NGG in dunite. The presence of ≤20 vol.% diopside had the effect of inhibiting the forsterite grain growth during the initial stage, resulting in AGG of forsterite, thus overtaking the growth rate in dunite. Our experimental results suggest that there would be a significant difference in grain growth rate and consequently in effective viscosity between olivine-rich peridotites (depleted mantle) and relatively olivine-poor peridotites (fertile mantle) in the case of grain size-sensitive creep. Variation of mean grain sizes in the upper mantle would result not only from differences in temperature and phase assemblage, but also from the variation of modal compositions.  相似文献   

Kizawa tunnel cracked on 23 October 2004 Mid-Niigata earthquake: An example of earthquake-induced damage to tunnels in active-folding zones     

Kazuo Konagai  Shigeki Takatsu  Tetsuo Kanai  Tomohiro Fujita  Takaaki Ikeda  Jörgen Johansson 《Soil Dynamics and Earthquake Engineering》2009

Earthquakes in active-folding zones often trigger long-lasting landform changes. Since an underground structure closely follows the motion of its surrounding soils and rocks even after it was damaged in an intense earthquake, experts in charge of reconstruction have to wait until they are convinced that the soils and rocks have been stabilized. Kizawa tunnel was seriously cracked during the 23 October 2004 Mid-Niigata Earthquake. The upper half of the tunnel's cross-section near the north mouth shifted about 0.5 m sideways. Since a ring-shaped cross-section of a tunnel sustains the surrounding soil pressure, this crack pattern seemed to be serious. The authors collaborated with the Nagaoka Regional Development Bureau, Niigata Prefectural Government, in investigating the causes of the damage and in conducting long-term observation of the soils and rocks. This paper summarizes some findings for rational rehabilitations through the investigations.  相似文献