Weathering mechanisms and their effects on landsliding in pelitic schist     

Shintaro Yamasaki  Masahiro Chigira 《地球表面变化过程与地形》2011,36(4):481-494

Physical, chemical, and mineralogical analyses of undisturbed drill cores of pelitic schist from a landslide area in Japan clarified the mechanisms of chemical weathering of pelitic schist. Oxidizing surface water percolates downward and reaches an oxidation front, where chlorite is altered to Al‐vermiculite, graphite and pyrite are oxidized and depleted, and goethite precipitates. Oxidation of pyrite also occurs just below the oxidation front, probably by ferric iron. Pyrite oxidation yields sulphuric acid, which penetrates further downward, interacting with and weakening the rocks. In addition to this chemical weakening, stress release and shearing along schistosities form an incipient shear zone, which propagates to a sliding zone that forms the rupture surface of a landslide. Once a sliding zone has developed, it inhibits downward groundwater flow across it because of its low permeability, slowing the downward propagation of the weathering zone until this filtration barrier is broken by landslide movement. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Latitudinal and local variations of the life history characteristics of the thalassinidean decapod, Upogebia yokoyai: A hypothesis based on trophic conditions     

Miho Yamasaki  Takahiro Nanri  Shino Taguchi  Yoshitake Takada  Masayuki Saigusa 《Estuarine, Coastal and Shelf Science》2010

Mean total length of the eldest cohort (MTLe) of the thalassinidean decapod, Upogebia yokoyai sampled at 16 sites showed a latitudinal variation from south-west islands of the Ryukyu Archipelago (24° N) to the Seto-Inland Sea of Japan (34° N). Local variations were however also found from sites in the same latitudes. The level of the organic content in each habitat showed a positive correlation with MTLe. We hypothesized that MTLe is strongly affected by the trophic condition, resulting in the local variations. To test this hypothesis, two estuaries with different organic content were compared; Kodono River (Kochi Prefecture, 33° N) which was relatively oligotrophic and Sakata River (Hiroshima Prefecture, 34° N) which was highly eutrophicated. The Kodono River population showed slow growth after settlement, and growth stopped in May to June. This population survived for only one or two years, resulting in small MTLe. On the other hand, the Sakata River population showed fast growth from August to December. This population survived for three years, resulting in large MTLe. Maturation was estimated to occur two years after settlement in both populations. Low salinities may partially affect MTLe. Habitats in the Seto-Inland Sea (33.5–34.8° N) were eutrophicated, but many habitats in the subtropical islands (24–31° N) were relatively oligotrophic. Latitudinal variation of MTLe was reflected by the geographical difference in trophic condition. A negative relationship between population density and growth was found, which was explained in terms of reduced survival of recruits in the eutrophicated habitats.  相似文献   

Lagrangian meshfree particles method (SPH) for large deformation and failure flows of geomaterial using elastic–plastic soil constitutive model     

Ha H. Bui  Ryoichi Fukagawa  Kazunari Sako  Shintaro Ohno 《国际地质力学数值与分析法杂志》2008,32(12):1537-1570

Simulation of large deformation and post‐failure of geomaterial in the framework of smoothed particle hydrodynamics (SPH) are presented in this study. The Drucker–Prager model with associated and non‐associated plastic flow rules is implemented into the SPH code to describe elastic–plastic soil behavior. In contrast to previous work on SPH for solids, where the hydrostatic pressure is often estimated from density by an equation of state, this study proposes to calculate the hydrostatic pressure of soil directly from constitutive models. Results obtained in this paper show that the original SPH method, which has been successfully applied to a vast range of problems, is unable to directly solve elastic–plastic flows of soil because of the so‐called SPH tensile instability. This numerical instability may result in unrealistic fracture and particles clustering in SPH simulation. For non‐cohesive soil, the instability is not serious and can be completely removed by using a tension cracking treatment from soil constitutive model and thereby give realistic soil behavior. However, the serious tensile instability that is found in SPH application for cohesive soil requires a special treatment to overcome this problem. In this paper, an artificial stress method is applied to remove the SPH numerical instability in cohesive soil. A number of numerical tests are carried out to check the capability of SPH in the current application. Numerical results are then compared with experimental and finite element method solutions. The good agreement obtained from these comparisons suggests that SPH can be extended to general geotechnical problems. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

A photometric study of the Algol system Y Hydri     

Duerbeck  H. W.  Yamasaki  A. 《Astrophysics and Space Science》1986,119(2):345-352

297UBV observations of the Algol type eclipsing binary Y Hyi are presented and analyzed by a synthetic light curve technique. The system is semi-detached and shows complete eclipses.Based on observations collected at the European Southern Observatory, La Silla, Chile.  相似文献   

Outflow Propagation in Collapsars: Collimated Jets and Expanding Outflows     

Akira Mizuta  Tatsuya Yamasaki  Shigehiro Nagataki  Shin Mineshige 《Astrophysics and Space Science》2007,307(1-3):23-27

We investigate the outflow propagation in the collapsar in the context of gamma-ray bursts (GRBs) with 2D relativistic hydrodynamic simulations. We vary the specific internal energy and bulk Lorentz factor of the injected outflow from non-relativistic regime to relativistic one, fixing the power of the outflow to be 10⁵¹erg s⁻¹. We observed the collimated outflow, when the Lorentz factor of the injected outflow is roughly greater than 2. To the contrary, when the velocity of the injected outflow is slower, the expanding outflow is observed. The transition from collimated jet to expanding outflow continuously occurs by decreasing the injected velocity. Different features of the dynamics of the outflows would cause the difference between the GRBs and similar phenomena, such as, X-ray flashes.  相似文献   

Mechanism for the rapid motion of the Qianjiangping landslide during reactivation by the first impoundment of the Three Gorges Dam reservoir, China   总被引：10，自引：6，他引：4  

Fawu Wang  Yeming Zhang  Zhitao Huo  Xuanming Peng  Shimei Wang  Shintaro Yamasaki 《Landslides》2008,5(4):379-386

The first impoundment of the Three Gorges Dam reservoir in China started from a water surface elevation of 95 m on June 1, 2003 and reached 135 m on June 15, 2003. Shortly after the water level reached 135 m, many slopes began to deform and some landslides occurred. The Qianjiangping landslide is the largest one; it occurred on the early morning of July 14, 2003 and caused great loss of lives and property. Field investigation revealed that, although failure occurred after the reservoir reached 135 m, the stability of the slope was already reduced by preexisting sheared bedding planes. To study the mechanism of the rapid motion of this reactivated landslide, two soil samples were taken from a yellow clay layer and a black silt layer in the sliding zone, respectively, and a series of ring shear tests were conducted on the samples. One series of ring shear tests simulates the creep deformation behavior, while the other series simulates different shear rates. Conclusions drawn from analysis of the ring shear tests indicate that the mechanism of the rapid motion of the reactivated landslide was caused by the rate effect of the black silt layer during the motion phase after the creep failure. The yellow clay layer did not play any important role in the rapid motion in the 2003 event.  相似文献   

The main sequence stars and the photon-neutrino coupling theory of weak interactions     

Minoru Nishida  Atsuma Yamasaki 《Astrophysics and Space Science》1974,28(1):225-231

The tetrad field equations of general relativity discussed in previous articles are applied to Robertson-Walker cosmological models. A generalized Friedmann equation is derived and some of its consequences are discussed.  相似文献   

Floral changes in calcareous nannofossils and their paleoceanographic significance in the equatorial Pacific Ocean during the last 500 000 years     

Shun  Chiyonobu  Tokiyuki  Sato  Reika  Narikiyo  Makoto  Yamasaki 《Island Arc》2006,15(4):476-482

Abstract   The late Quaternary calcareous nannofossil assemblages from Ocean Drilling Program Holes 807A and 846B, located in the western and eastern equatorial Pacific Ocean, respectively, were analyzed to clarify changes in surface-water conditions during the last 500 000 years. The uppermost Quaternary sediments in both holes contain abundant nannofossils, and their assemblages are characterized by high species diversity. The absolute abundances of coccoliths (specimens/g) and relative numbers of small reticulofenestrids decreased drastically in both holes between 0.3 and 0.2 Ma, whereas the relative abundance of warm-water species and Florisphaera profunda increased suddenly at this time. These data indicate that upwelling around the western and eastern equatorial Pacific regions weakened after 0.2 Ma, which was caused by a decrease in trade-wind strength.  相似文献   

Gonadal histology and serum vitellogenin levels of bigeye tuna Thunnus obesus from the Northern Pacific Ocean--absence of endocrine disruption bio-indicators     

Hashimoto S  Kurihara R  Strüssmann CA  Yamasaki T  Soyano K  Hara A  Shiraishi H  Morita M 《Marine pollution bulletin》2003,46(4):459-465

Endocrine disrupting chemicals such as organochlorines have been detected in a large number of marine fish. Histological observation of the gonads, measurement of serum vitellogenin (VTG) level and of liver polychlorinated biphenyl (PCB) content were performed to evaluate the reproductive health and the contamination with endocrine disruptors in bigeye tuna Thunnus obesus, collected in the northern Pacific Ocean in 1999 and 2000. Abnormalities commonly found in species affected by endocrine disruptors such as the presence of oocytes in the testis or elevated serum VTG levels were not found in any of males examined. Both males and females had only small amounts of liver PCB content. The results suggest that currently there is little if any risk of organochlorine contamination or endocrine disruption of gonadal function in bigeye tuna from the northern Pacific Ocean. However, further studies are necessary to evaluate the health status of the open sea fishery resources.  相似文献   

Interactive behavior of soil–pile-superstructure system in transient state to liquefaction by means of large shake table tests     

Shintaro Yao  Koichi Kobayashi  Nozomu Yoshida  Hiroshi Matsuo 《Soil Dynamics and Earthquake Engineering》2004,24(5):572-409

Shaking table tests were conducted by means of a large-scale laminar box with 4 m in length, 2 m in width and 2 m in height in order to investigate behavior of a soil-pile-superstructure system in liquefiable ground. A model two-storey structure, supported by a pile group, was set in a saturated sand deposit, and subjected to a sinusoidal base motion with increasing amplitude. Discussions are focused on the transient behavior until soil liquefaction occurs. Main interests are characteristics of springs used in a sway-rocking model and a multi-freedom lumped mass (MFLM) model that are frequently used in soil–pile interaction analysis. The spring constant in the sway-rocking model is represented by restoring force characteristics at the pile head, and that in the MFLM system is represented by an interaction spring connecting the pile to the free field. The transient state prior to soil liquefaction is shown to be important in the design of a pile because dynamic earth pressure shows peak response in this state. The reduction of the stiffness due to excess porewater generation and strain dependent nonlinear behavior is evaluated.  相似文献