The global biogeochemical sulphur cycle,SCOPE 19: M. V. Ivanov and J. R. Freney (eds.), 1983. John Wiley and Sons, 470 pp., £42.50     

H. Sakai 《Geochimica et cosmochimica acta》1984,48(9):1874

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Oxygen isotope variations in magmatic differentiation processes of the volcanic rocks in Japan     

Y. Matsuhisa  O. Matsubaya  H. Sakai 《Contributions to Mineralogy and Petrology》1973,39(4):277-288

The ¹⁸O/¹⁶O ratios were analyzed for 35 volcanic rocks from the Izu-Hakone region, Oki-Dogo Island, Asama Volcano and Kiso-Ontake Volcano in the Japanese Islands. The ¹⁸O-enrichment in magma during crystallization differentiation is recognized in every rock series. The magnitude of solid-liquid isotope fractionation in the magma of tholeiite series is similar to that of alkali rock series, while the apparent isotope fractionation of calc-alkali rock series is larger than that of the above two series. The ¹⁸O value of the tholeiite magma in the Izu- Hakone region is +5.7 relative to SMOW, which suggests its origin from the fresh upper mantle material. The primary magma of the calc-alkali rock series in Asama Volcano is assumed to have the ¹⁸O value similar to or slightly higher than that of the Izu-Hakone primary magma. The alkali rock series of Oki-Dogo Island in the continental side of the island arc is by 1 heavier than the Izu-Hakone rock suite. This may imply that Oki-Dogo rock series might have exchanged their oxygen with ¹⁸O-rich crustal materials, or they might have originated from somewhat ¹⁸O-rich upper mantle material.  相似文献   

3-D MHD SIMULATION OF X-TYPE COALESCENCE OF TWO CURRENT-LOOPS     

Sakai  Jun-ichi  de Jager  Cornelis 《Solar physics》1997,173(2):347-358

We present simulation results of X-type coalescence of two current-loops, by using a 3-D resistive MHD code. The results are compared with the limb flare observed by Yohkoh on 2 August, 1993 at 08:30 UT, which is a good example of partial X-type coalescence. It is shown that the maximum temperature enhancement near the cross-point of the two loops, obtained from the simulation, agrees well with the observations when the plasma is 0.08.  相似文献   

Acceleration through X-type coalescence in a small energetic flare     

Jun-Ichi Sakai  Cornelis de Jager 《Solar physics》1989,123(2):389-392

We studied the acceleration conditions in the small but fairly energetic flare of May 21, 1984 at 1326 UT. The most pronounced aspect of this flare was a series of 13 microwave/X-ray spikes, each lasting for about 0.1 s. A previous study has shown that each of these was due to a series of successive sudden formations of small plasma knots of high-energy particles. Each of these knots lost its energy in about 50 ms. In the present study we show that these knots can originate by the process of X-type (3-D) flux tube coalescence. The predicted rise time (30 to 50 ms) and energy are in good agreement with the observationally derived parameters.  相似文献   

Plasma jet and shock formation during current loop coalescence in solar flares     

Jun-Ichi Sakai 《Solar physics》1989,120(1):117-124

We report on the results of plasma jet and shock formation during the current loop coalescence in solar flares. It is shown by a theoretical model based on the ideal MHD equation that the spiral, two-sided plasma jet can be explosively driven by the plasma rotational motion induced during the two current loop coalescence process. The maximum velocity of the jet can exceed the Alfvén velocity, depending on the plasma (= c _s ² v _A ² ) ratio. The acceleration time getting to the maximum jet velocity is quite short and le than 1 s. The rebound following the plasma collapse driven by magnetic pinch effect can strongly induce super-Alfvénic flow. We present the condition of the shock formation. We briefly discuss the high-energy particle acceleration during the plasma collapse as well as by the shocks.  相似文献   

Mechanism of two rapid and long-runout landslides in the 16 April 2016 Kumamoto earthquake using a ring-shear apparatus and computer simulation (LS-RAPID)   总被引：3，自引：3，他引：0  

Khang Dang  Kyoji Sassa  Hiroshi Fukuoka  Naoki Sakai  Yuji Sato  Kaoru Takara  Lam Huu Quang  Doan Huy Loi  Pham Van Tien  Nguyen Duc Ha 《Landslides》2016,13(6):1525-1534

Around hundred landslides were triggered by the Kumamoto earthquakes in April 2016, causing fatalities and serious damage to properties in Minamiaso village, Kumamoto Prefecture, Japan. The landslides included many rapid and long-runout landslides which were responsible for much of the damage. To understand the mechanism of these earthquake-triggered landslides, we carried out field investigations with an unmanned aerial vehicle to obtain DSM and took samples from two major landslides (Takanodai landslide and Aso-ohashi landslide) to measure parameters of the initiation and the motion of landslides. A series of ring-shear tests and computer simulations were conducted using a measured Kumamoto earthquake acceleration record from KNet station KMM005, 10 km west of Aso-ohashi landslide. The research results supported our assumed mechanism of sliding-surface liquefaction for the rapid and long-runout motion of these landslides.  相似文献   

Prompt high-energy particle acceleration during two-current-loop collisions     

Jie Zhao  Bidzina Chargeishvili  Jun-Ichi Sakai 《Solar physics》1993,146(2):331-341

We present a model of prompt high-energy particle acceleration during two-current-loop collisions. By investigating test proton and test electron motions in the electromagnetic field derived from the MHD equations, we found that high-energy particle acceleration occurs only in the case ofY-type, loop-loop collisions. The results depend strongly on the plasma and initial position of the test particle. When the plasma increases, the particle acceleration rate decreases. The particles near the edge of the collision region can be accelerated to higher energy than the ones inside it. It has been shown that both protons and electrons can be accelerated to 10 GeV within 0.001 s and 5 MeV within 10^–6 s, respectively. In the case ofY-type loop-loop collisions, one may expect that high-energy gamma-ray and neutrons will be generated from interaction between high-energy particles and the low atmospheric plasma.  相似文献   

Mechanism for enhanced diffusivity in the deep-sea perpetual salt fountain     

Xinrong Zhang  Shigenao Maruyama  Koutaro Tsubaki  Seigo Sakai  Masud Behnia 《Journal of Oceanography》2006,62(2):133-142

The mechanism of enhanced diffusivity occurring in the deep-sea perpetual salt fountain has been investigated experimentally and numerically. Some factors which possibly contribute to the enhanced diffusivity were found to be the pipe oscillation with ocean waves and its baffled wall surface. Field experiments in the ocean (Onagawa Bay of Miyagi, Japan) and numerical simulations were performed to study and confirm the dynamics of the flow and heat transport with enhanced diffusivity occurring in upwelling deep-sea water. The agreement between the field experimental data and the numerical solutions of an oscillating-wall boundary condition imposed on the baffled pipe is encouraging, and it indicates the baffled pipe surface subject to the oscillatory motion leads to the enhanced diffusivity. The buoyancy force and then upwelling velocity can be greatly increased by the enhanced diffusivity. The dominant mechanism is the occurrence of complicated vortices and vortex shedding leading to efficient mixing and enhanced diffusion.  相似文献   

Phytoplankton community reorganization driven by eutrophication and warming in Lake Biwa   总被引：1，自引：0，他引：1  

Chih Hao Hsieh  Kanako Ishikawa  Yoichiro Sakai  Toshiyuki Ishikawa  Satoshi Ichise  Yoshimasa Yamamoto  Ting Chun Kuo  Ho Dong Park  Norio Yamamura  Michio Kumagai 《Aquatic Sciences - Research Across Boundaries》2010,72(4):467-483

We compiled and analyzed long-term data, including chemical, physical and phytoplankton community data, for the Lake Biwa ecosystem from 1962 to 2003. Analyses on environmental data indicate that Lake Biwa had experienced intensified eutrophication (according to total phosphorus concentration) in the late 1960s and returned to a less eutrophic status around 1985, and then exhibited rapid warming and thus increased water column stability since 1990. Total phytoplankton cell volume largely followed the trend of total phosphorus concentration, albeit short-term fluctuations existed. However, phytoplankton community shifted dramatically in response to those changes of environmental states. These shifts were cause by changes in trophic status driven by phosphorus loadings and physical properties in the water column driven by warming. Moreover, most phytoplankton species did not show a strong linear correlation with environmental variables, suggesting nonlinear transitions among different states.  相似文献   

Shock wave phenomena in collisions between a current loop and a plasmoid     

Zhang  Hui-Min  Sokolov  Igor  Sakai  Jun-Ichi 《Solar physics》1999,188(1):125-140

We present the results of 3-D MHD simulations of collisions between an equilibrium current and a plasmoid. Three typical equilibrium configurations were analyzed. Our simulation results show that when a plasmoid approaches a current loop, an active region is created in front of the plasmoid bounded on the front side by a bow shock wave and on the back side by a reverse shock wave. The collision process modifies the current system and a strong electric field is also induced in the active region. An additional magnetic field generated by the induced current upsets the initial equilibrium condition. As a result, the whole loop is compressed and heated. We found that when the plasmoid approaches the loop, before reaching it the induced electric field amounts to its maximum value. The current loop is curved under the collision. The core of the plasmoid can not drive into the loop, it is sprung back by a magnetic counterpressure. This collision process between a plasmoid and a current loop may be responsible for the triggering of a solar flare observed by Yohkoh.  相似文献