Petrographic study of the Miocene Mizunami Group,Central Japan: Detection of unrecognized volcanic activity in the Setouchi Province     

Eiji Sasao 《Island Arc》2013,22(2):170-184

A petrographic study of sandstones from the Miocene Mizunami Group in Central Japan has been performed on core samples from a single borehole, in order to evaluate the provenance of the sedimentary rock. Evaluation of the provenance is based on bulk mineral, heavy mineral and plagioclase contents and on whole rock chemical compositions. The sandstones studied are divisible into three types; the first type is characterized by the occurrence of biotite and plagioclase ranging from albite to oligoclase, the second type is characterized by the dominance of amphibole and labradorite with pyroxene (clinopyroxene > orthopyroxene), and the third type is characterized by the dominance of pyroxene (orthopyroxene > clinopyroxene) and andesine with lesser labradorite, bytownite and anorthite. The first type is interpreted to be derived from the basement granite, whereas the others were derived mostly from volcanic ash, judging from their mineral compositions. The volcanic activity that supplied the volcanic ash to the Mizunami Basin occurred in two phases, distinguishable by variations in their mineralogical and geochemical compositions, an indication of change in character of the volcanic activity. This petrographic study of the sandstones in the Mizunami Group suggests that unrecognized volcanic activity occurred around the Mizunami Basin, even though potential provenance of the volcanic ash has not yet been identified.  相似文献   

Western Arctic primary productivity regulated by shelf-break warm eddies     

Eiji Watanabe  Michio J. Kishi  Akio Ishida  Maki Noguchi Aita 《Journal of Oceanography》2012,68(5):703-718

The response of phytoplankton to the Beaufort shelf-break eddies in the western Arctic Ocean is examined using the eddy-resolving coupled sea ice–ocean model including a lower-trophic marine ecosystem formulation. The regional model driven by the reanalysis 2003 atmospheric forcing from March to November captures the major spatial and temporal features of phytoplankton bloom following summertime sea ice retreat in the shallow Chukchi shelf and Barrow Canyon. The shelf-break warm eddies spawned north of the Barrow Canyon initially transport the Chukchi shelf water with high primary productivity toward the Canada Basin interior. In the eddy-developing period, the anti-cyclonic rotational flow along the outer edge of each eddy moving offshore occasionally traps the shelf water. The primary production inside the warm eddies is maintained by internal dynamics in the eddy-maturity period. In particular, the surface central area of an anti-cyclonic eddy acquires adequate light, nutrient, and warm environment for photosynthetic activity partly attributed to turbulent mixing with underlying nutrient-rich water. The simulated biogeochemical properties with the dominance of small-size phytoplankton inside the warm eddies are consistent with the observational findings in the western Arctic Ocean. It is also suggested that the light limitation before autumn sea ice freezing shuts down the primary production in the shelf-break eddies in spite of nutrient recovery. These results indicate that the time lag between the phytoplankton bloom in the shelf region following the summertime sea ice retreat and the eddy generation along the Beaufort shelf break is an important index to determine biological regimes in the Canada Basin.  相似文献   

Sound velocity measurements in dhcp-FeH up to 70 GPa with inelastic X-ray scattering: Implications for the composition of the Earth's core     

Yuki Shibazaki  Eiji Ohtani  Hiroshi Fukui  Takeshi Sakai  Seiji Kamada  Daisuke Ishikawa  Satoshi Tsutsui  Alfred Q.R. Baron  Naoya Nishitani  Naohisa Hirao  Kenichi Takemura 《Earth and Planetary Science Letters》2012

We have determined the density evolution of the sound velocity of dhcp-FeH_x (x ≈ 1) up to 70 GPa at room temperature, by inelastic X-ray scattering and by X-ray diffraction. We find that the variation of V_P with density is different for the ferromagnetic and nonmagnetic dhcp-FeH_x, and that only nonmagnetic dhcp-FeH_x follows Birch's law. Combining our results with Birch's law for iron and assuming an ideal two-component mixing model, we obtain an upper bound of the hydrogen content in the Earth's inner core, 0.23(6) wt.% H, corresponding to FeH_0.13(3). The iron alloy with 0.23(6) wt.% H can satisfy the density, and compressional and shear sound velocities of the PREM inner core, assuming that there are no other light elements in the inner core.  相似文献   

LQR control with frequency‐dependent scheduled gain for a semi‐active floor isolation system          下载免费PDF全文

Yundong Shi  Tracy C. Becker  Sachi Furukawa  Eiji Sato  Masayoshi Nakashima 《地震工程与结构动力学》2014,43(9):1265-1284

Floor isolation is an alternative to base isolation for protecting a specific group of equipment installed on a single floor or room in a fixed‐base structure. The acceleration of the isolated floor should be mitigated to protect the equipment, and the displacement needs to be suppressed, especially under long‐period motions, to save more space for the floor to place equipment. To design floor isolation systems that reduce acceleration and displacement for both short‐period and long‐period motions, semi‐active control with a newly proposed method using the linear quadratic regulator (LQR) control with frequency‐dependent scheduled gain (LQRSG) is adopted. The LQRSG method is developed to account for the frequency characteristics of the input motion. It updates the control gain calculated by the LQR control based on the relationship between the control gain and dominant frequency of the input motion. The dominant frequency is detected in real time using a window method. To verify the effectiveness of the LQRSG method, a series of shake table tests is performed for a semi‐active floor isolation system with rolling pendulum isolators and a magnetic‐rheological damper. The test results show that the LQRSG method is significantly more effective than the LQR control over a range of short‐period and long‐period motions. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Sedimentation rate and heavy metal pollution in sediments in Harima Nada (Harima Sound), Seto Inland Sea     

Akira Hoshika  Takayuki Shiozawa  Eiji Matsumoto 《Journal of Oceanography》1983,39(2):82-87

Sedimentation rates were determined with the²¹⁰Pb technique in six sediment cores from Harima Nada (Harima Sound), Seto Inland Sea. The rate of deposition varies from 0.11 g cm^–2y^–1 in the northern part to 0.33 g cm^–2 y^–1 in the southern part of the basin. A marked increase in copper and zinc content was observed above a depth in the core corresponding to about 1900 A.D. as a result of increasing human activities. Anthropogenic input of copper and zinc decreased slightly after 1970. Natural background levels of copper and zinc in the sediment in this sound are 11–16 ppm and 100–120 ppm, respectively. The total amounts of anthropogenic copper and zinc in the sediments were estimated to be 110–180g cm^–2 and 610–1,280g cm^–2, respectively. These values constitute 40–50% of the total sedimentary input of copper and zinc in the sediments since about 1900 A.D.  相似文献   

Sedimentation rates in Funka Bay,HokkaidÔ     

Eiji Matsumoto  Shigeko Togashi 《Journal of Oceanography》1980,35(6):261-267

Undisturbed sediment cores were collected by a modified gravity corer from Funka Bay. The sedimentation rate is determined by both²¹⁰Pb and pumice chronological methods. The sedimentation rates by²¹⁰Pb method are concordant with those by pumice methods. The derived rate varies from 0.06 to 0.22 g cm^–2 y^–1, and an average is 0.09 g cm^–2 y^–1.  相似文献   

Thermoelastic properties of chromium oxide Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> (eskolaite) at high pressures and temperatures     

Anna M. Dymshits  Peter I. Dorogokupets  Igor S. Sharygin  Konstantin D. Litasov  Anton Shatskiy  Sergey V. Rashchenko  Eiji Ohtani  Akio Suzuki  Yuji Higo 《Physics and Chemistry of Minerals》2016,43(6):447-458

A new synchrotron X-ray diffraction study of chromium oxide Cr₂O₃ (eskolaite) with the corundum-type structure has been carried out in a Kawai-type multi-anvil apparatus to pressure of 15 GPa and temperatures of 1873 K. Fitting the Birch–Murnaghan equation of state (EoS) with the present data up to 15 GPa yielded: bulk modulus (K _0,T0), 206 ± 4 GPa; its pressure derivative K′_0,T , 4.4 ± 0.8; (?K _0,T /?T) = ?0.037 ± 0.006 GPa K^?1; a = 2.98 ± 0.14 × 10^?5 K^?1 and b = 0.47 ± 0.28 × 10^?8 K^?2, where α _0,T  = a + bT is the volumetric thermal expansion coefficient. The thermal expansion of Cr₂O₃ was additionally measured at the high-temperature powder diffraction experiment at ambient pressure and α _0,T0 was determined to be 2.95 × 10^?5 K^?1. The results indicate that coefficient of the thermal expansion calculated from the EoS appeared to be high-precision because it is consistent with the data obtained at 1 atm. However, our results contradict α ₀ value suggested by Rigby et al. (Brit Ceram Trans J 45:137–148, 1946) widely used in many physical and geological databases. Fitting the Mie–Grüneisen–Debye EoS with the present ambient and high-pressure data yielded the following parameters: K _0,T0 = 205 ± 3 GPa, K′_0,T  = 4.0, Grüneisen parameter (γ ₀) = 1.42 ± 0.80, q = 1.82 ± 0.56. The thermoelastic parameters indicate that Cr₂O₃ undergoes near isotropic compression at room and high temperatures up to 15 GPa. Cr₂O₃ is shown to be stable in this pressure range and adopts the corundum-type structure. Using obtained thermoelastic parameters, we calculated the reaction boundary of knorringite formation from enstatite and eskolaite. The Clapeyron slope (with \({\text{d}}P/{\text{d}}T = - 0.014\) GPa/K) was found to be consistent with experimental data.  相似文献   

Effects of mass sedimentation events after the 2011 off the Pacific coast of Tohoku Earthquake on benthic prokaryotes and meiofauna inhabiting the upper bathyal sediments     

Hidetaka Nomaki  Tomohiro Mochizuki  Tomo Kitahashi  Takuro Nunoura  Kazuno Arai  Takashi Toyofuku  Gengo Tanaka  Shuichi Shigeno  Eiji Tasumi  Katsunori Fujikura  Shuichi Watanabe 《Journal of Oceanography》2016,72(1):113-128

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Decreasing precipitation extremes at higher temperatures in tropical regions     

Eduardo Eiji Maeda  Nobuyuki Utsumi  Taikan Oki 《Natural Hazards》2012,64(1):935-941

It has been often accepted that rising troposphere temperatures will lead to higher precipitation intensities. This argument is based on the Clausius?CClapeyron (C?CC) relation, which indicates an increase in atmospheric moisture storage capacity of approximately 7?% K^?1. However, recent studies carried out in mid-latitude regions indicate that changes in precipitation intensity as a function of temperature do not necessarily follow the C?CC relation. This study aimed to evaluate the correlation between precipitation extremes and temperature in tropical regions, using measured data obtained at low latitude ranges over Brazil. The results indicate that, at daily timescale, the C?CC relation alone is unlikely to explain the relation between precipitation extremes and temperatures in tropical regions. Additional aspects, such as moisture availability and the duration of precipitation events, should be further analyzed to allow a comprehensive understanding of the relationship between temperature and precipitation intensity. Moreover, we show that in tropical regions, higher temperatures may reduce the magnitude of extreme precipitation events at daily timescales, independent of the season of the year.  相似文献   

The high-pressure phase relation of the MgSO₄-H₂O system and its implication for the internal structure of Ganymede     

Ryo Nakamura  Eiji Ohtani 《Icarus》2011,211(1):648-654

We have determined the phase relation of the MgSO₄-H₂O binary system using an externally heated diamond anvil cell in the compositional range of 0-30 wt.% MgSO₄, and under temperature and pressure conditions from 298 to 500 K and up to 4.5 GPa. Using our experimental results, we were able to estimate the composition of the ice mantle of the large icy satellites of Jupiter, such as Ganymede.In our experiments, we identified the following phases in the MgSO₄-H₂O system up to 4 GPa at 298 K: Ices VI and VII, magnesium heptahydrate, MgSO₄·7H₂O, and a liquid phase. The present phase relations suggest that there may be a deep internal ocean down to a depth about 800 km in the interior of Ganymede.  相似文献