The Wide Band Spectrometer on the SOLAR-A     

M. Yoshimori  K. Okudaira  Y. Hirasima  T. Igarashi  M. Akasaka  Y. Takai  K. Morimoto  T. Watanabe  K. Ohki  J. Nishimura  T. Yamagami  Y. Ogawara  I. Kondo 《Solar physics》1991,136(1):69-88

The SOLAR-A spacecraft has spectroscopic capabilities in a wide energy band from soft X-rays to gamma-rays. The Wide Band Spectrometer (WBS), consisting of three kinds of spectrometers, soft X-ray spectrometer (SXS), hard X-ray spectrometer (HXS) and gamma-ray spectrometer (GRS), is installed on SOLAR-A to investigate plasma heating, high-energy particle acceleration, and interaction processes. SXS has two proportional counters and each counter provides 128-channel pulse height data in the 2–30 keV range every 2 s and 2-channel pulse count data every 0.25 s. HXS has a NaI scintillation detector and provides 32-channel pulse height data in the 20–400 keV range every 1 s and 2-channel pulse count data every 0.125 s. GRS has two identical BGO scintillation detectors and each detector provides 128-channel pulse height data in the 0.2–10 MeV range every 4 s and 4-channel pulse count data (0.2–0.7, 0.7–4, 4–7, and 7–10 MeV) every 0.25–0.5 s. In addition, each of the BGO scintillation detectors provides 16-channel pulse height data in the 8–100 MeV range every 4 s and 2-channel pulse count data (8–30 and 30–100 MeV) every 0.5 s. The SXS observations enable one to study the thermal evolution of flare plasma by obtaining time series of electron temperatures and emission measures of hot plasma; the HXS observations enable one to study the electron acceleration and heating mechanisms by obtaining time series of the electron spectrum; and the GRS observations enable one to study the high-energy electron and ion acceleration and interaction processes by obtaining time series of electron and ion spectra.After the launch the name of SOLAR-A has been changed to YOHKOH.  相似文献   

Upper Cretaceous depositional environments and bivalve assemblages of far-east Asia: the Himenoura Group, Kyushu, Japan     

Toshifumi Komatsu  Maiko Ono  Hajime Naruse  Taro Kumagae 《Cretaceous Research》2008,29(3):489-508

The depositional environments and bivalve assemblages are determined for the Upper Cretaceous Hinoshima Formation of the Himenoura Group, Kamishima, Amakusa Islands, Kyushu, Japan. The Hinoshima Formation is characterized by a thick transgressive succession that varies from incised-valley-fill deposits to submarine slope deposits with high aggradation rates of depositional systems. The incised valley is filled with fluvial, bayhead delta, brackish-water estuary, and marine embayment deposits, and is overlain by thick slope deposits.Shallow marine bivalves are grouped into five fossil assemblages according to species composition: Glycymeris amakusensis (foreset beds of a bayhead delta), Nippononectes tamurai (foreset beds of a bayhead delta), Ezonuculana mactraeformis–Nucula formosa (central bay), Glycymeris amakusensis–Apiotrigonia minor (slope), and Inoceramus higoensis–Parvamussium yubarensis (slope). These bivalve assemblages all represent autochthonous and parautochthonous conditions except for a Glycymeris amakusensis–Apiotrigonia minor assemblage found in debris flow and slump deposits. The life habitats of these bivalves and the compositions of the assemblages are discussed in terms of the ecological history of fossil bivalves of the mid- to Late Cretaceous.  相似文献   

The Krakatau islands: The geotectonic setting     

Susumu Nishimura Dr.  H. Harjono Dr.  S. Suparka 《GeoJournal》1992,28(2):87-98

The Sunda Strait is located in a transitional zone between two different modes of subduction, the Java frontal and Sumatra oblique subductions. Western Java and Sumatra are, however, geologically continuous.The Krakatau complex lies at the intersection of two graben zones and a north-south active, shallow seismic belt, which coincides with a fracture zone along this seismic belt with fissure extrusion of alkali basaltic rocks commencing at Sukadana and continuing southward as far as the Panaitan island through Rajabasa, Sebuku and Krakatau.Paleomagnetic studies suggest that the island of Sumatra has been rotating clockwise relative to Java from at least 2.0 Ma to the present at a rate of 5–10h/Ma, and therefore the opening of the Sunda Strait might have started before 2 Ma (Nishimura et al. 1986).From geomorphological and seismological studies, it is estimated that the western part of Sumatra has been moving northward along the Semangko fault and the southern part of Sunda Strait has been pulled apart.Assuming that the perpendicular component (58 mm/yr; Fitch 1972) of the oblique subduction has not changed, we can estimate that the subduction started at 7–10 Ma. Huchon and LePichon (1984) also estimated that the subduction started at 13 Ma.Recent crustal earthquakes in the Sunda Strait area are clustered into three groups: (1) beneath the Krakatau complex where they are typically of tectonic origin, (2) inside a graben in the western part of the strait, and (3) in a more diffuse zone south of Sumatra. The individual and composite focal mechanisms of the events inside the strait show an extensional regime. A stress tensor, deduced from the individual focal mechanisms of the Krakatau group shows that the tensional axis has a N 130°E orientation (Harjono et al. 1988).These studies confirm that the Sunda Strait is under a tensional tectonic regime as a result of clockwise rotation along the continental margin and northward movement of the Sumatra sliver plate along the Semangko fault zone.  相似文献   

Snow ripples and their contribution to the mass transport in drifting snow     

Kenji Kosugi  Kouichi Nishimura  Norikazu Maeno 《Boundary-Layer Meteorology》1992,59(1-2):59-66

Morphological characteristics of snow ripples formed by drifting snow were investigated as functions of wind velocity in a cold wind tunnel at -15 °C. Wave-length, wave height and migration rate of snow ripples increased from 5 to 20 cm, 3 to 5 mm and 1 to 8 cm/min, respectively, with increasing wind velocity from 5 to 7 m/s. Measured size distributions of snow particles in snow ripples showed sorting of large particles in ridges, suggesting that the snow ripple migration is caused by creeping of large particles. The snow drift rate caused by creep, that is, by the ripple migration, was estimated to amount, at least, to 6% of the total snow drift rate.  相似文献   

Alvin-SeaBeam studies of the Sumisu Rift, Izu-Bonin arc     

B. Taylor  G. Brown  P. Fryer  J.B. Gill  A.G. Hochstaedter  H. Hotta  C.H. Langmuir  M. Leinen  A. Nishimura  T. Urabe 《Earth and Planetary Science Letters》1990,100(1-3)

Bimodal volcanism, normal faulting, rapid sedimentation, and hydrothermal circulation characterize the rifting of the Izu-Bonin arc at 31°N. Analysis of the zigzag pattern, in plan view, of the normal faults that bound Sumisu Rift indicates that the extension direction (080° ± 10°) is orthogonal to the regional trend of the volcanic front. Normal faults divide the rift into an inner rift on the arc side, which is the locus for maximum subsidence and sedimentation, and an outer rift further west. Transfer zones that link opposing master faults and/or rift flank uplifts further subdivide the rift into three segments along strike. Volcanism is concentrated along the ENE-trending transfer zone which separates the northern and central rift segments. The differential motion across the zone is accommodated by interdigitating north-trending normal faults rather than by ENE-trending oblique-slip faults. Volcanism in the outer rift has built 50–700 m high edifices without summit craters whereas in the inner rift it has formed two multi-vent en echelon ridges (the largest is 600 m high and 16 km long). The volcanism is dominantly basaltic, with compositions reflecting mantle sources little influenced by arc components. An elongate rhyolite dome and low-temperature hydrothermal deposits occur at the en echelon step in the larger ridge, which is located at the intersection of the transfer zone with the inner rift. The chimneys, veins, and crusts are composed of silica, barite and iron oxide, and are of similar composition to the ferruginous chert that mantles the Kuroko deposits. A 1.2-km transect of seven alvin heat flow measurements at 30°48.5′N showed that the inner-rift-bounding faults may serve as water recharge zones, but that they are not necessarily areas of focussed hydrothermal outflow, which instead occurs through the thick basin sediments. The rift basin and arc margin sediments are probably dominated by permeable rhyolitic pumice and ash erupted from submarine arc calderas such as Sumisu and South Sumisu volcanoes.  相似文献   

Planform evolution of deltas with graded alluvial topsets: Insights from three‐dimensional tank experiments,geometric considerations and field applications          下载免费PDF全文

Tetsuji Muto  Ryuji Furubayashi  Arti Tomer  Tomoyuki Sato  Wonsuck Kim  Hajime Naruse  Gary Parker 《Sedimentology》2016,63(7):2158-2189

The profile of a river that conveys sediment without net deposition and net erosion is referred to as ‘graded’ with respect to vertical aggradation of the river segment. Three experimental series, designed in terms of the autostratigraphic view of alluvial grade, were conducted to clarify the diagnostic spatial behaviour of graded alluvial–deltaic rivers: an ‘R series’, which utilized a moving boundary setting with a stationary base level; an ‘F series’ in a fixed boundary setting with a stationary base level to produce ‘forced grade’; and an ‘M series’ in a moving boundary setting with constant base‐level fall to produce ‘autogenic grade.’ The results of the three experimental series, combined with geometrical modelling of the effects of basin water depth and other experimental data, suggest the following: (i) in a graded alluvial–deltaic system, lateral shifting and avulsing of active distributary channels are suppressed regardless of whether the downstream boundary of the deltaic system is fixed; (ii) in a delta with a downstream‐fixed boundary, the graded streams are stabilized within a valley that is incised in the axial part of the delta plain, whereby the alluvial plain outside the valley is abandoned and terraced; (iii) in moving boundary settings, the graded river simply extends basinward as a linearly elongated channel and lobe system without cutting a valley; and (iv) a modern forced‐graded alluvial river is most likely to be found in a valley incised into a fan delta in front of very deep water, and the stratigraphic signal of fossil autogenic‐graded rivers will be found in deltaic successions that accumulated in the outer to marginal areas of deltaic continental shelves during sea‐level falls. This renewed autostratigraphic view of alluvial grade suggests a thorough reconsideration of the conventional understanding that an alluvial river feeding a progradational delta is graded with a stationary base level.  相似文献   

Near-infrared observations of the dust coma of Comet Kohoutek (1973f) with a tilting-filter Fabry-Perot photometer     

C. Barbieri  C.B. Cosmovici  K.W. Michel  T. Nishimura  A.E. Roche 《Icarus》1974,23(4):568-576

By means of narrow-band Fabry-Perot filters, which exclude the interference from molecular line fluorescence, the brightness of Comet Kohoutek (1973f) has been measured at 8560 and 8748 Å. Data reduction on the basis of averaged Mie-scattering cross sections indicates that the dust production rate was different before and after perihelion at the same heliocentric distances. This asymmetry suggests that vaporization and dust entrainment were governed by fractionation of a multicomponent mixture of parent molecules in a comparatively porous cometary nucleus.  相似文献   

Gravity and S-wave modelling across the Jan Mayen Ridge,North Atlantic; implications for crustal lithology   总被引：1，自引：0，他引：1  

Rolf Mjelde  Inger Eckhoff  Ståle Solbakken  Shuichi Kodaira  Hideki Shimamura  Karl Gunnarsson  Ayako Nakanishi  Hajime Shiobara 《Marine Geophysical Researches》2007,28(1):27-41

The horizontal components from fourteen Ocean Bottom Seismometers deployed along four profiles focused along the western margin of the Jan Mayen microcontinent, North Atlantic, have been modelled with regard to S-waves, based on P-wave models obtained earlier. The seismic models have furthermore been constrained by 2D gravity modelling. High V _p/V _s-ratios (2.3–7.9) within the Cenozoic sedimentary section are attributed to significant porosities, whereas V _p/V _s-ratios in the order of 1.9–2.2 for the Mesozoic and Paleozoic sedimentary rocks indicate shale-dominated lithology throughout the area. The eastern side of the Jan Mayen Ridge is interpreted as a passive, volcanic margin, based on relatively high crustal V _p/V _s-ratios (1.9), whereas lower V _p/V _s-ratios (1.75–1.8) suggest the presence of intermediate composition crust and non-volcanic margin on the western side of the ridge. In the westernmost part of the Jan Mayen Basin, slightly increased upper mantle V _p/V _s-ratios may indicate some degree of serpentization of upper mantle peridotites.  相似文献   

Improvements in navigation using SeaBeam crossing errors     

Clyde E. Nishimura  Donald W. Forsyth 《Marine Geophysical Researches》1988,9(4):333-352

Adjustments to satellite constrained navigation are required to match SeaBeam bathymetric data at track crossings due to errors in dead reckoning and inaccuracies in satellite fixes. By shifting one of the SeaBeam swaths involved in a track crossing relative to the other and calculating the sum of the squares of the differences in bathymetry within the area of overlapping coverage, we map a two-dimensional error surface whose minimum corresponds to the best estimate of the correction to navigation required at the crossing point. Estimates of the covariance of this correction are derived from the error surface. We employ the curve fitting technique of Tarantola and Valette (1982) to invert for a smooth correction function to a starting model of the position of the ship as a function of time. This technique incorporates formal errors assigned to dead reckoning, satellite fixes, and the shifts required to match bathymetric swaths at crossing points in a simultaneous inversion for the correction function for all tracks within the study area.In a test of the method in a study area on the southern Mid-Atlantic Ridge, a data set involving two cruises, 30 days of SeaBeam data, and 753 track crossings, we found that crossing SeaBeam swaths can potentially resolve the relative position of the ship on the two tracks to within 30 to 70 m. The inversion procedure yielded a much better constrained navigation function and much improved match of bathymetry. The final model of the navigation fit crossing shifts about as well as satellite data (with respect to their assigned data errors) with the RMS value of the crossing shifts decreasing from 1200 m in the original satellite-constrained navigation to 200 m in the final solution. However, the potential resolution of position using SeaBeam swaths was not fully achieved in the solution because there are systematic bathymetric artifacts in SeaBeam data, multiple local minima in the error surfaces in highly lineated topography, inadequate dead reckoning data, occasional bad satellite fixes, and limitations on the short period corrections allowed in the model.  相似文献   

Algal Growth Potential and the limiting nutrient in Mikawa Bay     

Masao Kondo  Tsutomu Sakai  Hajime Yamamoto  Yukio Arakawa 《Journal of Oceanography》1984,40(5):391-396

The Algal Growth Potential (AGP) of water samples collected off Gamagori in Mikawa Bay was measured from May 1978 through February 1979, and the limiting nutrient was determined using regression analysis and enrichment bioassays. The surface and bottom water samples had AGP that produced increments of chemical oxygen demand (COD) of 2.1 mg l^–1 and 3.1 mg l^–1, respectively, on average. These values ofCOD correspond to 46% and 97% of the average COD values of the raw water samples at the surface and bottom, respectively. Seasonal changes of AGP showed a close correlation with those of dissolved inorganic nitrogen (DIN) concentration. Enrichment bioassays showed that DIN was the most deficient nutrient. The DIN:phosphate-phosphorus (PO₄ ^3–-P) ratios and DIN: dissolved phosphorus (DP) ratios in the water samples were below the cellular N:P ratios of the natural algal populations. These results suggest that AGP was mainly limited by DIN concentration.  相似文献