http://dx.doi.org/10.1016/j.gsf.2016.04.002   总被引：1，自引：1，他引：0  

Takanori Sasaki  Toshikazu Ebisuzaki 《地学前缘(英文版)》2017,8(2):215-222

Population synthesis studies into planet formation have suggested that distributions consistent with observations can only be reproduced if the actual Type Ⅰ migration timescale is at least an order of magnitude longer than that deduced from linear theories.Although past studies considered the effect of the Type I migration of protoplanetary embryos,in most cases they used a conventional formula based on static torques in isothermal disks,and employed a reduction factor to account for uncertainty in the mechanism details.However,in addition to static torques,a migrating planet experiences dynamic torques that are proportional to the migration rate.These dynamic torques can impact on planet migration and predicted planetary populations.In this study,we derived a new torque formula for Type Ⅰ migration by taking into account dynamic corrections.This formula was used to perform population synthesis simulations with and without the effect of dynamic torques.In many cases,inward migration was slowed significantly by the dynamic effects.For the static torque case,gas giant formation was effectively suppressed by Type I migration;however,when dynamic effects were considered,a substantial fraction of cores survived and grew into gas giants.  相似文献   

Subsidence of the Miyako‐Sone submarine carbonate platform,east of Miyako‐jima Island,northwestern Pacific Ocean     

Kohsaku Arai  Hideaki Machiyama  Shun Chiyonobu  Hiroki Matsuda  Keiichi Sasaki  Marc Humblet  Yasufumi Iryu 《Island Arc》2014,23(1):1-15

Bathymetric mapping and observations of the seafloor using a remotely operated vehicle (ROV, Hyper‐Dolphin 3K) were carried out on the slopes of the Miyako‐Sone submarine platform, east of Miyako‐jima in the Ryukyu Islands, northwestern Pacific Ocean. The bathymetric map indicates that terraces are present at water depths of approximately 140 m, 330 m, 400 m, and 680 m on the northwestern slope of the platform. A number of NW–SE trending lineaments, probably faults, extend perpendicular to the axis of the Ryukyu Island Arc. Two ROV surveys were conducted at water depths ranging from 519 m (on the slope) to 121 m (shallowest part of the platform). The surveys revealed that well‐indurated carbonate rocks are exposed at terrace margins and on upper slopes, and that the lower slopes are covered with modern sediments consisting of unconsolidated, coarse‐sand‐sized bioclastic carbonates. Calcareous nannofossils from the well‐indurated carbonate rocks indicate a Middle–Late Pleistocene age, which suggests that the rocks correlate with the Quaternary reef and fore‐reef deposits of the Ryukyu Group (Ryukyu Limestone) on the Ryukyu Islands. No siliciclastic deposits corresponding to the upper Miocene–lower Pleistocene Shimajiri Group (as exposed on Okinawa‐jima and Miyako‐jima islands) were recovered during the surveys. Coeval well‐indurated carbonate rocks, all of which formed in a similar sedimentary environment, have been downthrown towards the west due to displacements on the western sides of normal faults. Subsidence of the Miyako‐Sone submarine platform was the result of large vertical displacements on such normal faults. The timing of initial subsidence cannot be tightly constrained, but the presence of the youngest limestone at progressively lower levels towards the west suggests the subsidence continued until after 0.265 Ma.  相似文献   

Quasi-stationary striations in basin-scale oceanic circulation: vorticity balance from observations and eddy-resolving model     

Oleg V. Melnichenko  Nikolai A. Maximenko  Niklas Schneider  Hideharu Sasaki 《Ocean Dynamics》2010,60(3):653-666

Recently, prominent jet-like features of the ocean circulation, called striations, with a meridional scale of O(300–500 ;km) and extending for thousands of kilometers in length, have been detected in satellite and in situ observations and in high-resolution numerical models. In this paper, we study quasi-stationary striations, which are best seen in the multi-year time-averaged velocity fields. Using 1993–2002 mean dynamic ocean topography, satellite altimeter observations, and output of the Ocean General Circulation Model for the Earth Simulator, the dynamics of the quasi-stationary striations in the eastern parts of the subtropical North and South Pacific are examined by assessing individual terms in the time-averaged equations of relative and potential vorticity. While non-linear effects are found to be essential in the dynamics of the striations, rejecting some linear hypotheses forwarded in the earlier studies, the relevance of the Rhines mechanism is not confirmed. Eddy flux does not act as a relative vorticity source for the striations. Using the potential vorticity (PV) diagnostics, we show that the time-mean PV is not conserved along the time-mean streamlines, and on the scale of the striations these changes in PV are largely induced by the eddy flux of layer thickness. The fact that eddy fluxes contribute to the striations’ time-mean PV budget suggests that the striations are not a kinematical artifact of time-averaging of westward-propagating eddies.  相似文献   

Predicting the displacement of triple pendulum™ bearings in a full‐scale shaking experiment using a three‐dimensional element     

Nhan D. Dao  Keri L. Ryan  Eiji Sato  Tomohiro Sasaki 《地震工程与结构动力学》2013,42(11):1677-1695

The accuracy of a series spring model to predict the peak displacement and displacement history of Triple Pendulum? (TP) bearings in a strongly shaken, full‐scale building is evaluated in this paper. The series spring model was implemented as a self‐contained three‐dimensional TP bearing element in OpenSees and is now available for general use. The TP bearing element contains the option for constant friction or a generalized friction model that accounts for the effect of instantaneous velocity and compression load on the friction coefficient. Comparison between numerical simulation and experimental data of a five‐story steel moment frame building shows that the peak displacement of isolation system can generally be predicted with confidence using a constant friction coefficient model. The friction coefficient model accounting for the effect of axial load and velocity leads to minor improvement over the constant friction coefficient models in some cases. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Distribution of local Cs anomalies on the seafloor near the Fukushima Dai-ichi Nuclear Power Plant     

Blair Thornton  Seiki Ohnishi  Tamaki Ura  Naoteru Odano  Shun Sasaki  Tsuneo Fujita  Tomowo Watanabe  Kaoru Nakata  Tsuneo Ono  Daisuke Ambe 《Marine pollution bulletin》2013

An estimated 3.5 ± 0.7 × 10¹⁵ Bq of ¹³⁷Cs is thought to have been discharged into the ocean following the melt down at Fukushima Dai-ichi Nuclear Power Plant (F1NPP). While efforts have been made to monitor seafloor radiation levels, the sampling techniques used cannot capture the continuous distribution of radionuclides. In this work, we apply in situ measurement techniques using a towed gamma ray spectrometer to map the continuous distribution of ¹³⁷Cs on the seafloor within 20 km of the F1NPP. The results reveal the existence of local ¹³⁷Cs anomalies, with levels of ¹³⁷Cs an order of magnitude higher than the surrounding seafloors. The sizes of the anomalies mapped in this work range from a few meters to a few hundreds of meters in length, and it is demonstrated that the distribution of these anomalies is strongly influenced by meter scale features of the terrain.  相似文献   

Performance of dry-separation processes in the recovery of cenospheres from fly ash and their implementation in a recovery unit     

H.T.B.M. Petrus  Tsuyoshi Hirajima  Yuji Oosako  Moriyasu Nonaka  Keiko Sasaki  Takashi Ando 《International Journal of Mineral Processing》2011,98(1-2):15-23

Cenospheres recovery is one of the coal fly ash beneficiations, providing economic as well as environmental benefits. Current techniques, such as lagoon or other wet-separation processes, consume large amounts of water and add to water pollution due to leaching of toxic materials from fly ash. The other possible disadvantage is the need for a wide operational area, which is unsuitable for densely populated countries. As wet-separation processes have some disadvantages, an improved and/or sustainable alternative recovery technique is required. An air classifier is one of the alternative techniques. In this study, two types of air classifiers, namely a closed-type pneumatic separator and a micron separator, have been investigated. In terms of separation efficiency, it was found that the micron separator has the potential to be applied in cenospheres recovery from coal fly ash, giving a Newton's efficiency of 0.44, as compared to a value of about 0.26 for the closed-type pneumatic separator. The cenospheres recoveries of both pieces of equipment at their optimum Newton's efficiencies were similar at over 60 wt.%. The separation performance was further assessed from the particle distributions of the overflow and underflow products obtained from both pieces of equipment, as well as from SEM images. It was found that the lower Newton's efficiency of the closed-type pneumatic separator was due to the re-concentration of fine particles in the underflow product at air-flow rates higher than 2.2 m/s (the underflow product yield was about 55 wt.%).In order to further confirm the applicability of this technique, the micron separator, which had provided higher separation efficiency and cenospheres recovery, was deployed in a cenospheres recovery unit prior to the use of a wet-separation process (float and sink tank). About 80% of the cenospheres was recovered, with an 87.8% reduction in the total mass of fly ash to be separated in the float and sink tank. Consequently, much less water was needed for the process of cenospheres recovery. Moreover, it was also confirmed that the micron separator could yield higher quality fly ashes, that is, fly ash types I and II, from lower feed quality of fly ash type IV, which is the lowest category in commercial classification of fly ash according to JIS A6201.  相似文献   

Comparison of vegetation changes along grazing gradients with different numbers of livestock     

A. Hoshino  Y. Yoshihara  T. Sasaki  T. Okayasu  U. Jamsran  T. Okuro  K. Takeuchi 《Journal of Arid Environments》2009,73(6-7):687-690

The objective of this study was to clarify whether the changes in percent cover of plant functional types (i.e., life forms and growth forms) along a grazing gradient reflect the livestock number, which would reinforce the reliability of using a grazing gradient design and improve the management of rangeland. We selected two livestock camps that for many years have had different numbers of livestock, with approximately six times more sheep-equivalents at site 1 than at site 2. Vegetation was sampled in 10 quadrats on five transects along the grazing gradient at each site. In each quadrat, we recorded percent cover of each plant species. Our findings suggested that vegetation changes along the grazing gradient under different livestock numbers were characterized by changes in the cover of life forms: perennial species were replaced by annual species near the camps (10–50 m). However, we did not find growth form change that reflected the difference in the number of livestock.  相似文献   

Electron beam emission from the EXOS-B (JIKIKEN) satellite as a powerful diagnostic tool in the magnetosphere     

Nobuki Kawashima  Kazunori Akai  Yukio Murasato  Susumu Sasaki 《Astrophysics and Space Science》1984,106(1):117-123

In an electron beam emission experiment on board the EXOS-B (JIKIKEN) satellite (200 V, 1 mA-maximum), several types of waves are strongly excited by the beam such as plasma frequency, upper hybrid frequency, electron cyclotron frequency, their harmonics and nonlinear coupling of these waves. Measurements of these waves give information on local plasma density and magnetic field strength and it is revealed that the electron beam emission from the spacecraft is a powerful diagnostic tool in the magnetosphere. A long term observation in this electron beam experiment has provided us with the average plasma density profile in the magnetosphere. It is also useful for the detection of the plasmapause. Plasma density measurements down to the order of 10 cm^–3 are possible. The instrument itself is very simple and compact, so that it will be a powerful plasma diagnostic tool in future magnetospheric and planetary explorations.  相似文献   

Periodic response of a rigid block resting on a footing subjected to harmonic excitation     

Kunihito Matsui  Masashi Iura  Toshimi Sasaki  Iku Kosaka 《地震工程与结构动力学》1991,20(7):683-697

This study presents the dynamic behaviour of a rigid block which rests on a footing supported by a spring and a dashpot on a rigid base. The response of the rigid body is examined carefully when the base is excited by a harmonic force. It is found that a periodic motion appears in three different modes: stick-stick, stick-slip and slip-slip. The conditions that initiate the stick-stick and slip-slip modes are derived in explicit forms and the maximum sliding displacement is also obtained analytically. Useful dimensionless parameters are proposed for the presentation of the dynamic behaviour. The accuracy of results is confirmed by the response history computed by the Nigam-Jennings method.  相似文献   

The Cretaceous Ofuku Pluton and Its Relation to Mineralization in the Western Akiyoshi Plateau,Yamaguchi Prefecture,Japan          下载免费PDF全文

Yuka Sasaki  Teruyoshi Imaoka  Mariko Nagashima  Kazuo Nakashima  Takafumi Sonehara  Koshi Yagi  Tetsumaru Itaya 《Resource Geology》2016,66(2):85-113

The relationship between the magmatism of the Cretaceous Ofuku pluton and mineralization in and around the Akiyoshi Plateau, Yamaguchi Prefecture, Japan was investigated using a combination of field observation, petrographic and geochemical analyses, K–Ar geochronology, and fluid inclusion data. The Ofuku pluton has a surface area of 1.5 × 1.0 km, and was intruded into the Paleozoic accretionary complexes of the Akiyoshi Limestone, Ota Group and Tsunemori Formation in the western part of the Akiyoshi Plateau. The pluton belongs to the ilmenite‐series and is zoned, consisting mainly of early tonalite and granodiorite that share a gradational contact, and later granite and aplite that intruded the tonalite and granodiorite. Harker diagrams show that the Ofuku pluton has intermediate to silicic compositions ranging from 60.4 to 77.9 wt.% SiO₂, but a compositional gap exists between 70.5 to 73.4 wt.% SiO₂ (anhydrous basis). Modal and chemical variations indicate that the assumed parental magma is tonalitic. Quantitative models of fractional crystallization based on mass balance calculations and the Rayleigh fractionation model using major and trace element data for all crystalline phases indicate that magmatic fractionation was controlled mainly by crystal fractionation of plagioclase, hornblende, clinopyroxene and orthopyroxene at the early stage, and quartz, plagioclase, biotite, hornblende, apatite, ilmenite and zircon at the later stage. The residual melt extracted from the granodiorite mush was subsequently intruded into the northern and western parts of the Ofuku pluton as melt lens to form the granite and aplite. The age of the pluton was estimated at 99–97 Ma and 101–98 Ma based on K–Ar dating of hornblende and biotite, respectively. Both ages are consistent within analytical error, indicating that the Ofuku pluton and the associated Yamato mine belong to the Tungsten Province of the San‐yo Belt, which is genetically related to the ilmenite‐series granitoids of the Kanmon to Shunan stages. The aplite contains Cl‐rich apatite and REE‐rich monazite‐(Ce), allanite‐(Ce), xenotime and bastnäsite‐(Ce), indicating that the residual melt was rich in halogens and REEs. The tonalite–granodiorite of the Ofuku pluton contains many three‐phase fluid inclusions, along with daughter minerals such as NaCl and KCl, and vapor/liquid (V/L) volume ratios range from 0.2 to 0.9, suggesting that the fluid was boiling. In contrast, the granite and aplite contain low salinity two‐phase inclusions with low V/L ratios. The granodiorite occupies a large part of the pluton, and the inclusions with various V/L ratios with chloride daughter minerals suggest the boiling fluids might be related to the mineralization. This fluid could have carried base metals such as Cu and Zn, forming Cu ore deposits in and around the Ofuku pluton. The occurrence and composition of fluid inclusions in the igneous rocks from the Akiyoshi Plateau are directly linked to Cu mineralization in the area, demonstrating that fluid inclusions are useful indicators of mineralization.  相似文献