Magnetodynamic Formation of Jets in Accretion Process of Magnetized Mass onto the Central Gravitator — Cases of Forming Stars and Active Galactic Nuclei     

Y. Uchida  M. Nakamura  S. Hirose  S. Uemura 《Astrophysics and Space Science》1998,264(1-4):195-212

A magnetodynamic model to deal with the acceleration and collimation of jets as a part of the global process of gravitational contraction of the magnetized gas to the central gravitator is discussed. We first review its application to the star forming jet case with several observational supporting evidence. Then, a justification will be given for the extension of this to the AGN jet case, despite of the difference in orders of magnitudes in the scales as well as in the physical parameters. The results of actual application of this magnetodynamic mechanism to the AGN case will be presented together with the discussions for the origin of the radio lobes and hotspots, and we show that this mechanism can explain the enhancement of accretion and the formation of the jet + lobe system consistently with the genetic consideration of the system. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Na-Ca-Cl-SO₄-type submarine formation waters at the seikan undersea tunnel,Japan. chemical and isotopic documentation and its interpretation     

Masakatsu Mizukami  Hitoshi Sakai  Osamu Matsubaya 《Geochimica et cosmochimica acta》1977,41(9):1201-1212

  相似文献   

Developing a hybrid multi‐model for peak flood forecasting     

Yupa Chidthong  Hitoshi Tanaka  Seree Supharatid 《水文研究》2009,23(12):1725-1738

The present study aims to develop a hybrid multi‐model using the soft computing approach. The model is a combination of a fuzzy logic, artificial neural network (ANN) and genetic algorithm (GA). While neural networks are low‐level computational structures that perform well dealing with raw data, fuzzy logic deal with reasoning on a higher level by using linguistic information acquired from domain experts. However, fuzzy systems lack the ability to learn and cannot adjust themselves to a new environment. Moreover, experts occasionally make mistakes and thus some rules used in a system may be false. A network type structure of the present hybrid model is a multi‐layer feed‐forward network, the main part is a fuzzy system based on the first‐order Sugeno fuzzy model with a fuzzification and a defuzzification processes. The consequent parameters are determined by least square method. The back‐propagation is applied to adjust weights of network. Then, the antecedent parameters of the membership function are updated accordingly by the gradient descent method. The GA was applied to select the fuzzy rule. The hybrid multi‐model was used to forecast the flood level at Chiang Mai (under the big flood 2005) and the Koriyama flood (2003) in Japan. The forecasting results are evaluated using standard global goodness of fit statistic, efficient index (EI), the root mean square error (RMSE) and the peak flood error. Moreover, the results are compared to the results of a neuro‐genetic model (NGO) and ANFIS model using the same input and output variables. It was found that the hybrid multi‐model can be used successfully with an efficiency index (EI) more than 0·95 (for Chiang Mai flood up to 12 h ahead forecasting) and more than 0·90 (for Koriyama flood up to 8 h ahead forecasting). In general, all of three models can predict the water level with satisfactory results. However, the hybrid model gave the best flood peak estimation among the three models. Therefore, the use of fuzzy rule base, which is selected by GA in the hybrid multi‐model helps to improve the accuracy of flood peak. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Tsunami Bores in Kitakami River     

Elena Tolkova  Hitoshi Tanaka 《Pure and Applied Geophysics》2016,173(12):4039-4054

  相似文献   

Validation of a new generation system for bottom boundary layer beneath solitary wave     

Hitoshi Tanaka  Bambang Winarta 《Coastal Engineering》2012,59(1):46-56

Understanding of sea bottom boundary layer characteristics, especially bottom shear stress acting on the sea bed, is an important step needed in sediment transport modeling for practical application purposes. In the present study, a new generation system for bottom boundary layer under solitary wave is proposed. Applicability of this system is examined by comparing measured and numerical solution velocities. Moreover, transitional behavior from laminar to turbulence was investigated. It is concluded that the critical Reynolds number in the experiments shows good agreement with DNS result of Vittori and Blondeaux (2008) and laboratory data of Sumer et al. (2010), indicating validity of the generation system. Since the present generation system enables continuous measurement to obtain ensemble averaged quantities, it can be effectively utilized for future experimental studies on solitary wave boundary layers, including sediment transport experiments with movable bed.  相似文献   

Green’s function approach for calibrating tides in a circulation model for the East Asian marginal seas     

Jae-Hong Moon  Naoki Hirose  Akihiko Morimoto 《Journal of Oceanography》2012,68(2):345-354

A simple effective method of inverse estimation provided by model Green’s functions is examined to calibrate tides in a regional circulation model for the East Asian marginal seas. The Green’s function optimization derived by perturbing the model parameters significantly improves the estimate relative to observation as compared with baseline integration. Among the optimized model parameters, the largest effects on cost function reduction come first from the harmonic constant of M₂ along the open boundaries with the optimized values of 89.7 ± 0.8% for amplitude, and second from the bottom friction with the optimized value of (3.06 ± 0.08) × 10⁻³.  相似文献   

Estimation of inner-core rotation rate by using the Earth’s free oscillation     

Kanako Tomiyama  Hitoshi Oda 《Acta Geophysica》2008,56(4):939-956

We estimate a rate of inner-core differential rotation from time variations of splitting functions of seven core modes of the Earth’s free oscillations excited by eight large earthquakes in a period of 1994–2003. The splitting functions and moment tensor elements are simultaneously determined for each core mode by a spectral fitting technique. The estimated moment tensor well agrees with Harvard CMT solution. The splitting functions are corrected for the effect of mantle heterogeneity using a 3D mantle velocity model. Inner-core rotation angle about the Earth’s spin axis is determined for each core mode as a function of event year by comparison of the corrected and reference splitting functions. Mean rotation rate of six core modes is estimated at 0.03±0.18° per year westward, and this value is insignificantly different from zero. Therefore, the inner core is not rotating at a significant rate relatively to the crust and mantle.  相似文献   

Electrical conductivities of pyrolitic mantle and MORB materials up to the lowermost mantle conditions     

Kenji Ohta  Kei Hirose  Masahiro Ichiki  Katsuya Shimizu  Nagayoshi Sata  Yasuo Ohishi 《Earth and Planetary Science Letters》2010,289(3-4):497-502

The electrical conductivities of natural pyrolitic mantle and MORB materials were measured at high pressure and temperature covering the entire lower mantle conditions up to 133 GPa and 2650 K. In contrast to the previous laboratory-based models, our data demonstrate that the conductivity of pyrolite does not increase monotonically but varies dramatically with depth in the lower mantle; it drops due to high-spin to low-spin transition of iron in both perovskite and ferropericlase in the mid-lower mantle and increases sharply across the perovskite to post-perovskite phase transition at the D″ layer. We also found that the MORB exhibits much higher conductivity than pyrolite. The depth–conductivity profile measured for pyrolite does not match the geomagnetic field data below about 1500-km depth, possibly suggesting the existence of large quantities of subducted MORB crust in the deep lower mantle. The observations of geomagnetic jerks suggest that the electrical conductivity may be laterally heterogeneous in the lowermost mantle with high anomaly underneath Africa and the Pacific, the same regions as large low shear-wave velocity provinces. Such conductivity and shear-wave speed anomalies are also possibly caused by the deep subduction and accumulation of dense MORB crust above the core–mantle boundary.  相似文献   

Topography of the Seismic Velocity Discontinuities beneath the Chugoku and Shikoku Districts,Southwest Japan     

Hitoshi?OdaEmail author  Michiro?Okamoto  Motoko?Ishise 《Pure and Applied Geophysics》2005,162(12):2389-2407

The first P-arrival-time data from 513 local earthquakes were analyzed to study lateral variation of the depth to the Conrad and Moho discontinuities beneath the Chugoku and Shikoku districts, southwest Japan, as well as to determine earthquake hypocenters and P-wave station corrections. The depth to the discontinuity was estimated by minimizing the travel-time residuals of more than 8700 first P arrivals observed at 55 seismic stations. The Conrad and Moho discontinuities are located within depth ranges of 15–25 km and 30–40 km, respectively. The Moho is deeper under the mountain area than under the Seto Inland Sea area, and especially deep under the Pacific Coast of the Shikoku district and the mountain area in the Chugoku district. The depth variation of the Moho is quite similar to the Bouguer gravity anomaly distribution and the lateral variations of the P-wave velocity. The deep Moho under the southern Shikoku is located at the portion in which the continental Moho under the island arc meets the oceanic Moho that is the boundary interface between the oceanic crust and the Philippine Sea (PHS) plate dipping toward the back arc. Although there are high mountains in the northern and middle Shikoku, the Moho is not so deep because subduction of the PHS plate prevents the Moho from getting deep, while the Moho is deep due to isostatic balance under the mountain area in the Chugoku district. In addition, we indicated the possibility that the upper boundary of the oceanic crust just above the high-velocity PHS plate is in contact with the deep Moho under the western Chugoku. The contact of the Moho with the oceanic crust can explain the markedly negative gravity anomaly observed in the western Chugoku and the later phase that appears just after the first P arrival from local earthquakes.  相似文献   

Transformation functions of soil color and climate     

Yang  Shengli  Fang  Xiaomin  Li  Jijun  An  Zhisheng  Chen  Shiyue  Hitoshi  Fukusawa 《中国科学:地球科学(英文版)》2001,44(1):218-226

Measurements on modern soil color suggest well functional relationships between the soil formation process and the present climatic factors. The redness and yellowness of soil are chiefly caused by the contents of hematite and fullonite, and their correlations to climate are the best in humid regions in tropic and warm temperate regions. The lightness of soil mainly correlates to the organic accumulation, humification and carbonatization processes, and its correlation to climate can only be found in the humid-arid extratropical belt. The humidity and surface roughness of soil have so strong influence on soil color that there are great errors on the measurement of colorness in the field. The study on soil colors of typical loess sections shows that soil color can record the characteristics of Asia monsoon and the global climatic fluctuations well at millennial and ten-thousand-year scales. It can also indicate the pedogenesis and the climatic characteristics which magnetic susceptibility could not be reflected in humidity areas. Therefore, soil color can be used as a new climatic proxy which is easy and quick to measure, and will make an active influence on the study of global changes, geomorphology and Quaternary.

  相似文献