The layered structure of lunar maria: Identification of the HF-radar reflector in Mare Serenitatis using multiband optical images     

Shoko Oshigami  Shinya Okuno  Yasushi Yamaguchi  Makiko Ohtake  Junichi Haruyama  Takao Kobayashi  Atsushi Kumamoto  Takayuki Ono 《Icarus》2012,218(1):506-512

Comparison of the Lunar Radar Sounder (LRS) data to the Multiband Imager (MI) data is performed to identify the subsurface reflectors in Mare Serenitatis. The LRS is FM-CW radar (4–6 MHz) and the 2 MHz bandwidth leads to the range resolution of 75 m in a vacuum, whereas the sampling interval in the flight direction is about 75 m when an altitude of the spacecraft with polar orbit is nominal (100 km). Horizontally continuous reflectors were clearly detected by LRS in limited areas that consist of about 9% of the whole maria. The typical depth of the reflectors is estimated to be a few hundred meters. Layered structures of mare basalts are also discernible on some crater walls in the MI data of the visible bands (VIS). The VIS range has nine wavelengths of 415, 750, 900, 950, and 1000 nm, and their spatial resolution is 20 m/pixel at a nominal altitude. The stratigraphies around Bessel and Bessel-H craters in Mare Serenitatis are examined in this paper. It was revealed that the subsurface reflectors lie on the boundaries between basalt units with different chemical compositions. In addition, model calculations using the simplified radar equation indicate that the subsurface reflectors are not compositional interfaces but layer boundaries with a high-porosity contrast. These results suggest that the detected reflectors in Mare Serenitatis are regolith accumulated during so long hiatus of mare volcanisms enough for chemical composition of magma to change, not instantaneously. Therefore combination of the LRS and MI data has a potential to reveal characteristics of a series of magmatism forming each lithostratigraphic unit in Mare Serenitatis and other maria.  相似文献   

Retraction Note to: Real-time slope water table forecasting by multi-tank model combined with dual ensemble Kalman filter     

Jun Xiong  Tomofumi Koyama  Satoshi Nisiyama  Yuzo Ohnishi  Kenji Takahashi 《Landslides》2012,9(2):303-303

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Characterising and modelling the excavation damaged zone in crystalline rock in the context of radioactive waste disposal   总被引：3，自引：0，他引：3  

John A. Hudson  A. Bäckström  J. Rutqvist  L. Jing  T. Backers  M. Chijimatsu  R. Christiansson  X.-T. Feng  A. Kobayashi  T. Koyama  H.-S. Lee  I. Neretnieks  P.-Z. Pan  M. Rinne  B.-T. Shen 《Environmental Geology》2009,57(6):1275-1297

This paper describes current knowledge about the nature of and potential for thermo–hydro–mechanical–chemical modelling of the excavation damaged zone (EDZ) around the excavations for an underground radioactive waste repository. In the first part of the paper, the disturbances associated with excavation are explained, together with reviews of Workshops that have been held on the subject. In the second part of the paper, the results of a DECOVALEX [DEmonstration of COupled models and their VALidation against EXperiment: research funded by an international consortium of radioactive waste regulators and implementers (http://www.decovalex.com)] research programme on modelling the EDZ are presented. Four research teams used four different models to simulate the complete stress–strain curve for Avro granite from the Swedish Äspö Hard Rock Laboratory. Subsequent research extended the work to computer simulation of the evolution of the repository using a ‘wall-block model’ and a ‘near-field model’. This included assessing the evolution of stress, failure and permeability and time-dependent effects during repository evolution. As discussed, all the computer models are well suited to sensitivity studies for evaluating the influence of their respective supporting parameters on the complete stress–strain curve for rock and for modelling the EDZ.  相似文献   

Clockwise phase propagation of semi-diurnal tides in the Gulf of Thailand   总被引：2，自引：0，他引：2  

Tetsuo Yanagi  Toshiyuki Takao 《Journal of Oceanography》1998,54(2):143-150

The phase of semi-diurnal tides (M₂ and S₂) propagates clockwise in the central part of the Gulf of Thailand, although that of the diurnal tides (K₁, O₁ and P₁) is counterclock-wise. The mechanism of clockwise phase propagation of semi-diurnal tides at the Gulf of Thailand in the northern hemisphere is examined using a simple numerical model. The natural oscillation period of the whole Gulf of Thailand is near the semi-diurnal period and the direction of its phase propagation is clockwise, mainly due to the propagation direction of the large amplitude part of the incoming semi-diurnal tidal wave from the South China Sea. A simplified basin model with bottom slope and Coriolis force well reproduces the co-tidal and co-range charts of M₂ tide in the Gulf of Thailand.  相似文献   

Storm surge simulation using wind-wave-surge coupling model     

Kyeong Ok Kim  Takao Yamashita 《Journal of Oceanography》2008,64(4):621-630

Simulation of a storm surge caused by Typhoon 9918 in the Yatsushiro Sea, Kyushu, Japan was hindcasted by the synchronous coupled wind-wave-surge model composed of a Meso-scale meteorological model (MM5) for the wind and sea surface pressure, a spectral third-generation wind-wave model (Wavewatch III) for waves, and the coastal ocean model (Princeton Ocean Model). Inclusion of the whitecap wave breaking stresses (whitecap dissipation stress) in the coastal ocean model made it possible to reproduce the extreme surge height in the extremely shallow bay.  相似文献   

1-Gbps VLBI, The First Detection of Fringes     

J. Nakajima  Y. Koyama  M. Sekido  N. Kurihara  T. Kondo  M. Kimura  N. Kawaguchi 《Experimental Astronomy》2001,11(1):57-69

We report on the detection of VLBI fringes from quasars by a new VLBI system operating at 1 Gbps (1024 Mbits-per-second). Newly developed 1024 Msps (mega sample-per-second) AD samplers and 1024 Mbps recorders were used for the observations. A correlator with external buffers was used for the 1024 Mbps correlation processing of the tapes data.Our new VLBI system enabled 1024 Mbps VLBI, and this allowed the sampling of a 512 MHz bandwidth from a radio telescope receiver. This is the highest sampling speed ever used for VLBI, and the widest bandwidth used for VLBI observation. Initial sensitivity as evaluated by SNR comparison with earlier VLBI systems produced results to matched the expanded bandwidth. In our first observations, simultaneous optical fibre linked real-time VLBI observations were made to check the validity of data and precisely detemine the clock offsets among the radio telescopes.  相似文献   

Global instability of thin stellar discs     

Takao Fujiwara  Shunsuke Hozumi 《Astrophysics and Space Science》1986,119(1):199-200

We have determined the dominant global modes of stellar discs by integrating the linearized collisionless Boltzmann equation. The models examined are the Kuzmin discs with two types of the distribution function. It is found that the growth rate correlates well with the central value ofQ.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.  相似文献   

Examination of the resonance theory on Pcs by means of an analysis of magnetic fluctuations in the magnetosheath and the magnetosphere     

Takao Saito  Kazue Takahashi  Tohru Sakurai 《Planetary and Space Science》1979,27(6):809-816

Magnetic fluctuations observed in the magnetosheath and the outer magnetosphere with Ogo-5 during 6 months from November 1968, are analyzed to examine the resonance theory that monochromatic waves excited outside the magnetosphere are transmitted in the compressional mode into the magnetosphere, being transmitted further along the closed field lines in the torsional mode and are finally observed as long-period pcs on the Earth's surface. Ten observed results on the wave characteristics of the fluctuations including variance, spectrum, relation to the plasma stream, integrated power, longitudinal dependence are obtained and summarized. The fluctuations in the magnetosheath are found to be dominantly Alfvénic. Several pieces of evidence to support the resonance theory are found.  相似文献   

Environmental factors regulating stream nitrate concentrations at baseflow condition in a large region encompassing a climatic gradient     

Soyoka Makino  Naoko Tokuchi  Yukio Komai  Takao Kunimatsu 《水文研究》2021,35(5):e14200

Though high rates of nitrate (NO₃⁻) leaching from forests are undesirable, the factors significantly regulating stream NO₃⁻ concentration is not clarified yet. In Japan, not only near metropolitan areas but also the Japan Sea-side area with heavy snowfall is well known for receiving more than 10 kg-N ha⁻¹ year⁻¹ of nitrogen (N) deposition. However, NO₃⁻ concentration in stream water is relatively low in the Japan Sea-side area compared with its concentration in other areas. We examined important environmental factors regulating stream NO₃⁻ concentrations at baseflow condition in a large region of Japan, the Kinki region (KIN) including a part of Japan Sea-side (JSK) using Random Forest regression. The amounts of N deposition and precipitation were common regulating factors for stream NO₃⁻ concentration at baseflow condition. Random forest showed the significant correlation between the factors related to ecosystem N retention and stream NO₃⁻ concentration at baseflow condition, and it suggests that large N deposited during the growing season was incorporated into the ecosystem in the entire KIN. Heavy rain and snow flush N and wash out N accumulated in the surface soil, causing small N accumulation in forests. Also, large precipitation dilute NO₃⁻ concentration in baseflows. These things lowered stream NO₃⁻ concentration at baseflow condition. Especially in JSK, most of N deposed with the heavy snow flushed out during the snowmelt period. We provided the first statistical confirmation using Random Forest regression that N accumulation and cycling in forest ecosystems were related to NO₃⁻ leaching from forests into streams.  相似文献   

The motion of a test particle in the Kaluza-Klein-type of gravitational theory with variable rest mass     

Takao Fukui 《Astrophysics and Space Science》1988,141(2):407-413

The geodesic equation in a viable 5D space-time-mass theory of gravity is calculated for the purpose of presenting quantities accessible to experiments and observations. Determining the values of the constants in the theory is left for future tests concerning the principle of equivalence. But qualitatively we can show that the five-velocity is a function of not only of time but also mass. And in general case a possible change of mass depends onm as well ast.  相似文献