Gas flow in a two component galactic disk     

M. Noguchi  I. Shlosman 《Astrophysics and Space Science》1994,216(1-2):347-351

Numerical simulations of two-component (stars + gas) self-gravitating galactic disks show that the interstellar gas can significantly affect the dynamical evolution of the disk even if its mass fraction (relative to the total galaxy mass) is as low as several percent. Aided by efficient energy dissipation, the gas becomes gravitationally unstable onlocal scale and forms massive clumps. Gravitational scattering of stars by these clumps leads to suppression of bar instability usually seen in heavy stellar disks. In this case, gas inflow towards the galactic center is driven by dynamical friction which gas clumps suffer instead of bar forcing.  相似文献   

Nonlinear astrophysical dynamo: Three-mode interaction     

Satoshi Hinata 《Astrophysics and Space Science》1982,87(1-2):403-406

The effect of mode-coupling on the temporal variation of the linearly unstable magnetic mode is investigated for weakly unstable dynamos. It is shown that the nonlinear coupling of the unstable mode to itself is the dominant effect which stabilizes the mode at a certain amplitude rather than the coupling to other damped modes.  相似文献   

Size distribution of detrital mineral grains suspended in surface waters of the Yellow Sea and East China sea     

Satoshi Yamamoto 《Journal of Oceanography》1979,35(2):91-99

Anisotropic detrital mineral grains were segregated microscopically from the suspended matter in surface waters of the Yellow Sea and East China Sea. Microscopic grain-size measurements of the anisotropic minerals were carried out for more than 80 slide specimens which are distributed homogeneously in the Yellow Sea and East China Sea. The distribution maps of mean grain size and sorting coefficients indicate that the mean size becomes coarser as one goes offshore, and the sorting coefficients are larger in the southern portion and smaller in the northern portion of this region. The clay-sized minerals in the suspended sediments carried out by the deltaic rivers of the continent were deposited in the nearshore area while coarser silt-sized minerals were suspended in offshore waters. The larger sorting coefficients (standard deviations) in the southern portion may imply that the silt-sized grains of offshore waters contain coarser sand-sized grains. The sand-sized grains may be supplied from offshore Taiwan and the Bashi Channel and transported by the main flow of the Kuroshio current.  相似文献   

A low cost meteor observation system using radio forward scattering and the interferometry technique     

Waleed Madkour  Masa-yuki Yamamoto  Yoshihiro Kakinami  Satoshi Mizumoto 《Experimental Astronomy》2016,41(1-2):243-257

We present a low cost meteor observation system based on the radio forward scattering and interferometry technique at Kochi University of Technology (KUT). The system can be a suitable model for low budget educational institutes that target practical learning of astronomical objects and upper atmospheric characteristics. The system methodology for the automatic counting of meteor echoes, filtering noise and detecting meteor echo directions is described. Detection of the meteor echo directions, which is the basic element for determining the meteor trajectories and the orbital parameters of parent comets, is based on a software system developed for analysis of phase differences detected by interferometry. Randomly selected observation samples measured by the radio interferometer are compared to simultaneous optical observations by video cameras to verify the system accuracy. Preliminary error analysis revealed that the system accuracy is directly related to the duration of observed meteor echoes. Eighty percent of meteor echo samples with durations longer than 3 s showed agreement in azimuth and elevation angles measurements to within a 10° error range, while meteor echo samples with shorter durations showed lower agreement levels probably due to the low system sampling resolution of 0.1 s. The reasonable agreement level of meteor echoes with duration longer than 3 s demonstrated the applicability of the system methodology. Accurate observation of shorter duration meteor echoes could possibly be achieved by improving the system resolution.  相似文献   

Three-Dimensional Particle Acceleration in Electromagnetic Cylinder and Torus     

Koichi Noguchi  Edison Liang 《Astrophysics and Space Science》2007,307(1-3):305-308

Particle acceleration via Poynting vector with toroidal magnetic field is studied in 3D PIC simulation of electron-positron plasma. We choose two different initial magnetic field configurations to compare how the particle acceleration is affected by the expansion of electromagnetic wave. In the cylindrical case, the electromagnetic field strength decays as (ct)⁻², and particles are accelerated in the radial direction as well as the axial direction. Rayleigh-Taylor instability is also observed at the center of the cylinder. In the torus case, the field strength decays as (ct)⁻³, making the acceleration less efficient. Particles accelerated in the axial direction by E × B force creates strong charge separation.  相似文献   

A new typhoon bogussing scheme to obtain the possible maximum typhoon and its application for assessment of impacts of the possible maximum storm surges in Ise and Tokyo Bays in Japan     

Shinya Shimokawa  Tomokazu Murakami  Satoshi Iizuka  Jun Yoshino  Takashi Yasuda 《Natural Hazards》2014,74(3):2037-2052

We developed the new typhoon bogussing scheme to obtain the possible maximum typhoon approaching any region under any climatic conditions by using a potential vorticity inversion method. Numerical simulations with the new typhoon bogussing scheme are conducted for assessment of storm surges by possible maximum typhoons under the present-day and global warming climatic conditions in Ise and Tokyo Bays in Japan. The results suggest that the storm tide higher than the maximum storm tide in recorded history can occur in Ise and Tokyo Bays even for the present-day climate and the storm tide higher than the design sea level can cause severe damage to Nagoya and Tokyo megacities, in particular, airport facilities in Ise Bay for the global warming climate. These results suggest that the new typhoon bogussing scheme we developed is useful for assessment of impacts of storm surge by the possible maximum typhoons.  相似文献   

Cassini VIMS observations of latitudinal and hemispheric variations in Saturn’s infrared auroral intensity     

Sarah V. Badman  Chihiro Tao  Adrian Grocott  Satoshi Kasahara  Henrik Melin  Robert H. Brown  Kevin H. Baines  Masaki Fujimoto  Tom Stallard 《Icarus》2011,216(2):367-375

The intensity of Saturn’s infrared aurora is investigated using Cassini VIMS images acquired during October 2006–February 2009. Polar and main oval auroral regions were defined in both hemispheres, which extend between 0–10° and 10–25° co-latitude, respectively. Average intensities were computed for these regions and compared. While the northern and southern main oval regions covered a similar range of intensities, the southern main oval was on average more intense by a factor of ∼1.3. The emission from the southern polar region was usually less intense than the main oval emissions, while this was only the case for approximately half of the northern hemisphere images. The northern hemisphere polar region displayed intensities more than twice as high as those in the south and the difference between the two hemispheres was most pronounced on the dayside. In general, more intense polar emissions were accompanied by more intense main oval emissions. Possible explanations for the hemispheric and latitudinal differences are discussed in terms of particle energies and fluxes, ionospheric conductivity, temperature and magnetic field strength.  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

  相似文献   

Petrogenesis of the Kaikomagatake granitoid pluton in the Izu Collision Zone, central Japan: implications for transformation of juvenile oceanic arc into mature continental crust   总被引：1，自引：0，他引：1  

Satoshi Saito  Makoto Arima  Takashi Nakajima  Kenichiro Tani  Takashi Miyazaki  Ryoko Senda  Qing Chang  Toshiro Takahashi  Yuka Hirahara  Jun-Ichi Kimura 《Contributions to Mineralogy and Petrology》2012,163(4):611-629

The Miocene Kaikomagatake pluton is one of the Neogene granitoid plutons exposed in the Izu Collision Zone, which is where the juvenile Izu-Bonin oceanic arc is colliding against the mature Honshu arc. The pluton intrudes into the Cretaceous to Paleogene Shimanto accretionary complex of the Honshu arc along the Itoigawa-Shizuoka Tectonic Line, which is the collisional boundary between the two arcs. The pluton consists of hornblende–biotite granodiorite and biotite monzogranite, and has SiO₂ contents of 68–75 wt%. It has high-K series compositions, and its incompatible element abundances are comparable to the average upper continental crust. Major and trace element compositions of the pluton show well-defined chemical trends. The trends can be interpreted with a crystal fractionation model involving the removal of plagioclase, biotite, hornblende, quartz, apatite, and zircon from a potential parent magma with a composition of ~68 wt% SiO₂. The Sr isotopic compositions, together with the partial melting modeling results, suggest that the parent magma is derived by ~53% melting of a hybrid lower crustal source comprising ~30% Shimanto metasedimentary rocks of the Honshu arc and ~70% K-enriched basaltic rocks of the Izu-Bonin rear-arc region. Together with previous studies on the Izu Collision Zone granitoid plutons, the results of this study suggest that the chemical diversity within the parental magmas of the granitoid plutons reflects the chemical variation of basaltic sources (i.e., across-arc chemical variation in the Izu-Bonin arc), as well as a variable contribution of the metasedimentary component in the lower crustal source regions. In addition, the petrogenetic models of the Izu Collision Zone granitoid plutons collectively suggest that the contribution of the metasedimentary component is required to produce granitoid magma with compositions comparable to the average upper continental crust. The Izu Collision Zone plutons provide an exceptional example of the transformation of a juvenile oceanic arc into mature continental crust.  相似文献   

High-temperature compression experiments of CaSiO3 perovskite to lowermost mantle conditions and its thermal equation of state     

Masanao Noguchi  Tetsuya Komabayashi  Kei Hirose  Yasuo Ohishi 《Physics and Chemistry of Minerals》2013,40(1):81-91

In order to examine pressure–volume–temperature (P–V–T) relations for CaSiO₃ perovskite (Ca-perovskite), high-temperature compression experiments with in situ X-ray diffraction were performed in a laser-heated diamond anvil cell (DAC) to 127 GPa and 2,300 K. We also employed an external heating system in the DAC in order to obtain P–V data at a moderate temperature of 700 K up to 113 GPa, which is the reference temperature for constructing an equation of state. The P–V data at 700 K were fitted to the second-order Birch–Murnaghan equation of state, yielding K _700,1bar = 207 ± 4 GPa and V _700,1bar = 46.5 ± 0.1 Å³. Thermal pressure terms were evaluated in the framework of the Mie–Grüneisen–Debye model, yielding γ _700,1bar = 2.7 ± 0.3, q _700,1bar = 1.2 ± 0.8, and θ _700,1bar = 1,300 ± 500 K. A thermodynamic thermal pressure model was also employed, yielding α_700,1bar = 5.7 ± 0.5 × 10^?5/K and (?K/?T) _V  = ?0.010 ± 0.004 GPa/K. Computed densities along a lower mantle geotherm demonstrate that Ca-perovskite is denser than the surrounding lower mantle, suggesting that Ca-perovskite-rich rocks do not rise up through the lower mantle. One of such rocks might be a residue of partial melting of subducted mid-oceanic ridge basalt (MORB) at the base of the mantle. Since the partial melt is FeO-rich and therefore denser than the mantle, all the components of subducted MORB may not return to shallow levels.  相似文献