Dust ring formation due to sublimation of dust grains drifting radially inward by the Poynting-Robertson drag: An analytical model     

Hiroshi Kobayashi  Sei-ichiro Watanabe  Tetsuo Yamamoto 《Icarus》2009,201(1):395-405

Dust particles exposed to the stellar radiation and wind drift radially inward by the Poynting-Robertson (P-R) drag and pile up at the zone where they begin to sublime substantially. The reason they pile up or form a ring is that their inward drifts due to the P-R drag are suppressed by stellar radiation pressure when the ratio of radiation pressure to stellar gravity on them increases during their sublimation phases. We present analytic solutions to the orbital and mass evolution of such subliming dust particles, and find their drift velocities at the pileup zone are almost independent of their initial semimajor axes and masses. We derive analytically an enhancement factor of the number density of the particles at the outer edge of the sublimation zone from the solutions. We show that the formula of the enhancement factor reproduces well numerical simulations in the previous studies. The enhancement factor for spherical dust particles of silicate and carbon extends from 3 to more than 20 at stellar luminosities L_?=0.8-500L_⊙, where L_⊙ is solar luminosity. Although the enhancement factor for fluffy dust particles is smaller than that for spherical particles, sublimating particles inevitably form a dust ring as long as their masses decrease faster than their surface areas during sublimation. The formulation is applicable to dust ring formation for arbitrary shape and material of dust in dust-debris disks as well as in the Solar System.  相似文献   

Evidence for energy injection and a fine-tuned central engine at optical wavelengths in GRB 070419A     

A. Melandri  C. Guidorzi  S. Kobayashi  D. Bersier  C. G. Mundell  P. Milne  A. Pozanenko  W. Li  A. V. Filippenko  Y. Urata  M. Ibrahimov  I. A. Steele  A. Gomboc  R. J. Smith  N. R. Tanvir  E. Rol  K. Huang 《Monthly notices of the Royal Astronomical Society》2009,395(4):1941-1949

We present a comprehensive multiwavelength temporal and spectral analysis of the 'fast rise exponential decay' GRB 070419A. The early-time emission in the γ-ray and X-ray bands can be explained by a central engine active for at least 250 s, while at late times the X-ray light curve displays a simple power-law decay. In contrast, the observed behaviour in the optical band is complex (from 10² up to 10⁶ s). We investigate the light-curve behaviour in the context of the standard forward/reverse shock model; associating the peak in the optical light curve at ∼450 s with the fireball deceleration time results in a Lorenz factor  Γ≈ 350  at this time. In contrast, the shallow optical decay between 450 and 1500 s remains problematic, requiring a reverse shock component whose typical frequency is above the optical band at the optical peak time for it to be explained within the standard model. This predicts an increasing flux density for the forward shock component until   t ∼ 4 × 10⁶ s  , inconsistent with the observed decay of the optical emission from   t ∼ 10⁴ s  . A highly magnetized fireball is also ruled out due to unrealistic microphysic parameters and predicted light-curve behaviour that is not observed. We conclude that a long-lived central engine with a finely tuned energy injection rate and a sudden cessation of the injection is required to create the observed light curves, consistent with the same conditions that are invoked to explain the plateau phase of canonical X-ray light curves of γ-ray bursts.  相似文献   

Dietary analysis of harbour seals (Phoca vitulina) from faecal samples and overlap with fisheries in Erimo,Japan          下载免费PDF全文

Tabitha C. Y. Hui  Yuka Morita  Yumi Kobayashi  Yoko Mitani  Kazushi Miyashita 《Marine Ecology》2017,38(3)

The number of harbour seals in Japan has been rebounding since protection began in the mid‐1980s. With the increase in seal numbers, increased conflict with fisheries has occurred through depredation and the belief that seals compete with fisheries for prey. However, competition can only be determined if the prey species and quantities seals consume over time are known. We studied the diet of harbour seals in Erimo, site of the largest population of harbour seals in Japan, from 2011 to 2012 and assessed the degree of prey overlap with local fisheries. We used both hard parts and DNA techniques to identify prey items in seal scats, and compared these results to local fisheries data. A total of 46 prey occurrences was detected by both methods, of which 17 matched between techniques at least to the family level. Hard parts methods identified five incidences of prey undetected by DNA methods in five scats (one incidence per scat). DNA methods identified 24 additional prey occurrences in 13 scats, for which no hard part evidence for that prey had been found. This more than doubled the total number of prey occurrences across the 15 scats compared. Overall, the most frequently occurring harbour seal prey were walleye pollock (Theragra chalcogramma), sculpins and snailfishes. In contrast, the top three groups targeted by fisheries were codfishes, salmon and invertebrates. Many species common in the harbour seal's diet such as snailfishes and blennies were not targeted by fisheries. Fishes such as greenlings, sculpins, rockfishes and Japanese anchovy (Engraulis japonicus) were common in the diet of harbour seals, but made up a very small proportion of fisheries catches in Erimo. The importance of other prey species varied between seasons. Sculpins, greenlings and forage fishes were the top three prey groups for harbour seals in spring by percent modified frequency of occurrence, whereas the most important target groups by percentage mass caught by fisheries were codfishes, cephalopods and other invertebrates. Sculpins and rockfishes remained as important prey items for harbour seals in summer and autumn, in addition to codfishes, snailfishes and blennies. In contrast, the main groups caught by fisheries in summer were other fishes, particularly Japanese amberjack (Seriola quinqueradiata) and various species of sharks and eels, and invertebrates. By autumn, Erimo fisheries had focussed on catching salmon. Salmon were taken by harbour seals as well during this period, but at a relatively lower frequency compared to other prey groups. The results of our study show that although harbour seals consumed several of the prey species targeted by fisheries, the relative importance of these species to seals and fisheries and the seasons in which they were targeted were different.  相似文献   

A multiple-code simulation study of the long-term EDZ evolution of geological nuclear waste repositories     

Jonny Rutqvist  Ann Bäckström  Masakazu Chijimatsu  Xia-Ting Feng  Peng-Zhi Pan  John Hudson  Lanru Jing  Akira Kobayashi  Tomofumi Koyama  Hee-Suk Lee  Xiao-Hua Huang  Mikael Rinne  Baotang Shen 《Environmental Geology》2009,57(6):1313-1324

This simulation study shows how widely different model approaches can be adapted to model the evolution of the excavation disturbed zone (EDZ) around a heated nuclear waste emplacement drift in fractured rock. The study includes modeling of coupled thermal-hydrological-mechanical (THM) processes, with simplified consideration of chemical coupling in terms of time-dependent strength degradation or subcritical crack growth. The different model approaches applied in this study include boundary element, finite element, finite difference, particle mechanics, and elasto-plastic cellular automata methods. The simulation results indicate that thermally induced differential stresses near the top of the emplacement drift may cause progressive failure and permeability changes during the first 100 years (i.e., after emplacement and drift closure). Moreover, the results indicate that time-dependent mechanical changes may play only a small role during the first 100 years of increasing temperature and thermal stress, whereas such time-dependency is insignificant after peak temperature, because of decreasing thermal stress.  相似文献   

Infrared camera picnic and first results     

Y. Kobayashi  G. Fang  T. Minezaki  K. Waseda  K. Nakamura  S. Sato 《Experimental Astronomy》1994,3(1-4):135-136

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Distribution of fault rocks in the fracture zone of the Nojima Fault at a depth of 1140 m: Observations from the Hirabayashi NIED drill core     

Kenta Kobayashi  Satoshi Hirano  Takashi Arai  Ryuji Ikeda  Kentaro Omura  Hiroyuki Sano  Takashi Sawaguchi  Hidemi Tanaka  Tomoaki Tomita  Naoto Tomida  Tatsuo Matsuda  Akiko Yamazaki 《Island Arc》2001,10(3-4):411-421

Abstract Characteristics of deformation and alteration of the 1140 m deep fracture zone of the Nojima Fault are described based on mesoscopic (to the naked eye) and microscopic (by both optical and scanning electron microscopes) observations of the Hirabayashi National Research Institute for Earth Science and Disaster Prevention (NIED) drill core. Three types of fault rocks; that is, fault breccia, fault gouge and cataclasite, appear in the central part of the fault zone and two types of weakly deformed and/or altered rocks; that is, weakly deformed and altered granodiorite and altered granodiorite, are located in the outside of the central part of the fault zone (damaged zone). Cataclasite appears occasionally in the damaged zone. Six distinct, thin foliated fault gouge zones, which dip to the south-east, appear clearly in the very central part of the fracture zone. Slickenlines plunging to the north-east are observed on the surface of the newest gouge. Based on the observations of XZ thin sections, these slickenlines and the newest gouge have the same kinematics as the 1995 Hyogo-ken Nanbu earthquake (Kobe earthquake), which was dextral-reverse slip. Scanning electron microscopy observations of the freeze-dried fault gouge show that a large amount of void space is maintained locally, which might play an important role as a path for fluid migration and the existence of either heterogeneity of pore fluid pressure or strain localization.  相似文献   

Examination of mineral assemblage and chemical composition in the fracture zone of the Nojima Fault at a depth of 1140 m: Analyses of the Hirabayashi NIED drill cores     

Tatsuo Matsuda  Takashi Arai  Ryuji Ikeda  Kentaro Omura  Kenta Kobayashi  Hiroyuki Sano  Takashi Sawaguchi  Hidemi Tanaka  Tomoaki Tomita  Naoto Tomida  Satoshi Hirano  Akiko Ymazaki 《Island Arc》2001,10(3-4):422-429

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Thermal diffusivity of stishovite     

Masahiro Osako  Yoji Kobayashi 《Physics of the Earth and Planetary Interiors》1979,18(2):P1-P4

The thermal diffusivity of synthetic polycrystalline stishovite was determined by the Ångstrom method in the temperature range 300–550 K at 1 atm. The calculated thermal conductivity of stishovite at 300 K is 0.086 W cm^?1 K^?1 which is comparable to that for TiO₂-rutile but much lower than for GeO₂ and SnO₂. The observed thermal conductivities of rutile-structure oxides increase systematically with increasing density, in contrast with the expected behavior for isostructural compounds.  相似文献   

Equivalent linear method considering frequency dependent characteristics of stiffness and damping   总被引：4，自引：0，他引：4  

Nozomu Yoshida  Satoshi Kobayashi  Iwao Suetomi  Kinya Miura 《Soil Dynamics and Earthquake Engineering》2002,22(3)

Equivalent linear dynamic response analysis of ground is based on complex moduli and Fourier series expansion; therefore, it is not an equivalent method but an approximate method. Two deficiencies in the conventional equivalent linear method represented by SHAKE are described first. The maximum shear strength is overestimated, resulting in overestimation of the peak acceleration under a strong ground motion, and the amplification is underestimated at high frequency. The latter sometimes results in underestimation of the peak acceleration under weak ground shaking, and gives an incident wave with unrealistic large accelerations or a divergence of analysis in deconvolution analysis under strong ground motion. Both deficiencies are shown to come from the same cause, i.e. computing the effective strain as a constant fraction of the maximum strain. Since this is a key concept of the equivalent linear analysis, one cannot overcome both deficiencies at the same time in the conventional method. An apparent frequency dependence in stiffness and damping is shown to appear in the dynamic response, although soil itself does not show frequency dependent characteristics. Following this observation, the effective strain is expressed in terms of frequency from the similarity concept of the strain–frequency relationship between time domain and frequency domain. This enables the reduction of both deficiencies at the same time, resulting in a marked improvement in the equivalent linear analysis. The accuracy of the proposed method is examined by the simulations of three vertical array records during large earthquakes. The proposed method always gives much better prediction than conventional equivalent linear methods for both convolution and deconvolution analyses, and it is confirmed to be applicable at more than 1% shear strain.  相似文献   

Numerical studies on the influence of the variations of the Kuroshio Path on the transport of fish eggs and larvae   总被引：2，自引：0，他引：2  

Takashige Sugimoto Dr.  Masato Kobayashi Dr. 《GeoJournal》1988,16(1):113-117

Main spawning and nursery grounds of the Pacific Sardine are formed in the coastal boundary regions of the Kuroshio S of Kyushu and S of Honshu, respectively. Numerical experiments on the transport and dispersion of particles in and neighbouring areas of the Kuroshio were done to investigate the transport process of the fish eggs and larvae from the spawning ground to the downstream nursery ground. Surface currents measured with GEK in the past were averaged for both paths with and without large meanders of the Kuroshio in the S of Honshu and used as the data basis. Particles were released in the Kuroshio SE of Kyushu. The results show that the transport rate of them into the S coastal waters of Honshu during large meandered path is larger than the rate during the straight path period. However, recruitment rates of the Pacific Sardine in the S coastal waters of Honshu decreases during the large meander periods of the Kuroshio path. This inverse correlation is considered to be caused by the poorer food environment strongly influenced by the intrusion of the Kuroshio water.  相似文献