Iron Kα linewidths in magnetic cataclysmic variables     

Coel Hellier  Koji Mukai  & J. P. Osborne 《Monthly notices of the Royal Astronomical Society》1998,297(2):526-530

Following a recent report that AO Psc has broad iron Kα emission lines we have looked at the ASCA spectra of 15 magnetic cataclysmic variables. We find that half of the systems have Kα lines broadened by ∼ 200 eV, while the remainder have narrow lines. We argue that the Doppler effect is insufficient to explain the finding and propose that the lines originate in accretion columns on the verge of optical thickness, where Compton scattering of resonantly trapped line photons broadens the profile. We suggest that the broadening is a valuable diagnostic of conditions in the accretion column.  相似文献   

Crack-wave dispersion at a fluid-filled fracture withlow-velocity layers     

Koji Nagano 《Geophysical Journal International》1998,134(3):903-910

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Grain-size dependence of two-dimensional micromagnetic structures for pseudo-single-domain magnetite (0.2–2.5  μm)     

Koji Fukuma  & David J. Dunlop 《Geophysical Journal International》1998,134(3):843-848

Micromagnetic modelling with a Monte Carlo method was performed to obtain 2-D micromagnetic structures of pseudo-single-domain (PSD) magnetite (0.2–2.5  μm). Cubic model grains were subdivided into a 2-D array with a maximum of 100×100 cells. In order to find an appropriate cell size, the variation of the self-consistency parameter ( S ) with cell size was examined. We regard solutions with S >0.95, which corresponds to cell sizes ≤0.03  μm, as representing realistic micromagnetic structures. For saturation remanence states, we found vortex structures for small PSD grains (≤0.25  μm) and closure domain structures for larger PSD grains (0.6–2.5  μm). Between 0.25 and 0.6  μm, structures remained chaotic even after a very large number of Monte Carlo steps. In grains with a closure domain structure, domain walls were usually subdivided into several segments with opposite polarities of magnetization rotation.  相似文献   

Soil Condition and Seismic Characteristics in Shiga Prefecture,Japan     

Fujiwara  Teizo  Fukumoto  Kazumasa  Matsunami  Koji  Morii  Takeshi 《Natural Hazards》2003,29(3):523-542

The seismic observation network in Shiga prefecture iscomposed of four systems.All the observation data obtained were used to estimatethe dynamic characteristicsof the surface soils around the lake and the seismichazard for Hikone City. Since1995, 21 records have been obtained at the USP site ofwhich those for the 1999Shigaken-Hokubu Earthquake and 1999 Wakayarnaken-HokubuEarthquake wereused in this study. Transfer functions of the surfacesoil in each ward of ShigaPrefecture based on the Mt. Kojin site (KJY), whichhas relatively hard soil, werecalculated from the records of the two earthquakes.Assuming a scenario earthquakeat the Hyakusaiji fault close to Hikone City, maximumground motions were obtainedfor 15 city blocks in order to establish a damageestimation for that city. The numberof collapsed wooden houses and the damage ratiowere calculated based on the distributionof construction of wooden houses by year. Blockswith a larger ratio of old, wooden housesin Hikone showed a close correlation with blockswith a large ratio of aged persons inthem, indicative that weak persons, such as theelderly, may find themselves in a severesituation during a natural disaster.  相似文献   

Parameters of the fluid core resonance inferred from superconducting gravimeter data     

Tadahiro Sato  Yoshiaki Tamura  Koji Matsumoto  Yuichi Imanishi  Herbert McQueen 《Journal of Geodynamics》2004,38(3-5):375

We have estimated the parameters of fluid core resonance (FCR) due to the nearly diurnal free wobble of the Earth's core based on the superconducting gravimeter (SG) data obtained at the following four observation sites; Esashi and Matsushiro in Japan, Canberra in Australia and Membach in Belgium. By fitting the tidal admittances normalized with the O1 wave at each site to a model of the damped harmonic oscillator, we obtained values of 429.66 ± 1.43 sidereal days, 9350–10,835, −4.828E−4 ± 3.4E−6, −3.0E−5 ± 4.5E−6 for the eigenperiod, the Q-value and the real and imaginary parts of the resonance strength, respectively. Our values obtained from only using the gravity data are very consistent with those inferred from the VLBI nutation data. Our study strongly indicates that the systematic difference between two estimations from the gravity and the nutation in particular for the Q-value, which has been shown in previous works, is mainly caused by the inaccurate correction for the ocean tide effects. The error in the ocean tide correction is discussed based on the comparison among four global ocean tide models; Schwiderski model (1980), NAO.99b (Matsumoto et al., 2000), CSR4.0 (Eanes and Bettadpur, 1994) and GOT99.2b (Ray, 1999).  相似文献   

The 1989 submarine eruption off eastern Izu Peninsula,Japan: ejecta and eruption mechanisms     

Takahiro Yamamoto  Tatsunori Soya  Shigeru Suto  Kozo Uto  Akira Takada  Keiichi Sakaguchi  Koji Ono 《Bulletin of Volcanology》1991,53(4):301-308

The submarine eruption of a new small knoll, which was named Teishi knoll, off eastern Izu Peninsula behind the Izu-Mariana arc occurred in the evening of 13 July 1989. This is the first historic eruption of the Higashi-Izu monogenetic volcano group. The eruption of 13 July followed an earthquake swarm near Ito city starting on 30 June. There were subsequent volcanic tremors on 11 and 12 July, and the formation of the Teishi knoll on the 100 m deep insular shelf 4 km northeast of Ito city. There were five submarine explosions, which were characterized by intermittent domelike bulges of water and black tephra-jets, which occurred within 10 min on 13 July. Ejecta of the eruption was small in volume and composed of highly crystalline basalt scoria, highly vesiculated pumice, and lithic material. Petrographical features suggest that the pumice was produced by vesiculation of reheated wet felsic tuff of an older formation. The Teishi knoll, before the eruption, was a circular dome, 450 m across and 25 m high, with steep sides and a flat summit. Considerations of submarine topographic change indicate the knoll was raised by sill-like intrusion of 10⁶ m³ of magma beneath a 30 m thick sediment blanket. This shallow intrusion is assumed to have started on 11 July when volcanic tremors were observed for the first time, but there was no indications of violent interaction between wet host sediments and intruding magma. The submarine eruption of 13 July appears to have been Friggered by a major lowering of the magma-column. The basalt scoria, having crystal-contents of more than 60%, is assumed to be derived from the cooled plastic margin of the shallow intrusive body. However, glassy scoria, which would indicate the interaction between hot fluidal magma and external water, was not observed. A scenario for the 1989 submarine eruption is as follows. When rapid subsidence of the hot interior of the intrusive magma occurred, reduced pressure caused the implosion of cooled plastic magma, adjacent pressurized, hot host material, and wet sediment. The mixing of these materials triggered the vigorous vapor explosions.  相似文献   

Laboratory measurements of spatial fluctuation and attenuation of elastic waves by scattering due to random heterogeneities     

Koji Matsunami 《Pure and Applied Geophysics》1990,132(1-2):197-220

To study the effects of strong scattering on elastic waves, spatial fluctuation and scattering attenuation ofP waves were examined by laboratory experiments for 2-D models of random media approximately characterized by a triangular correlation function in the range of 2<ka<33, wherek is the wave number anda is the correlation distance of the heterogeneities, i.e., the heterogeneity size. The results obtained are as follows: (1) Forka>10, both the intensity and the correlation distance of the amplitude fluctuation are approximate for any phase of theP-wave train. The correlation distance nearly agrees with the heterogeneity size. These fluctuation properties are quite consistent with the theoretical prediction by the forward-scattering approximation. (2) For 3<ka<6, the fluctuation intensity becomes stronger in later phases of theP-wave train. This shows that scattering is approximately isotropic, and therefore, the scattered energy increases with time within theP-wave train. The correlation distance of the amplitude fluctuation disagrees with the heterogeneity size, and it shows a frequency-dependent property decreasing from 7a to 4a with the increase ofka from 3 to 6. These properties for 3<ka<6 have not yet been predicted theoretically. (3) Forka<3, though the fluctuation is considerably smaller compared with that ofka>10 and 3<ka<6, the fluctuation property is considered similar to that of 3<ka<6. (4) The observed scattering attenuation,Q ^–1, increases withka forka<3, has a peak aroundka=35, and then decreases withka. (5) When _min = 15° and = 0.075, the theoreticalQ ^–1 curve, predicted by the approximate theory of Wu, roughly matches the observedQ ^–1 values, where _min is the minimum scattering angle measured from the propagation direction of theP waves and is the rms of fractional velocity fluctuation. This suggests that the energy scattered in the range of >15° is lost from theP waves, while the energy scattered in the range of <15° is retained; and that the approximate theory overestimates by about three times the value of the model media used owing to the neglect of multiple scattering. (6) When the size of velocity heterogeneities responsible for forward scattering at 3<ka<6 is estimated from the _min value of 15° on the basis of Wu's theory, it nearly agrees with the correlation distance for the initial phase of theP-wave train.  相似文献   

Wind-dependent formation of phytoplankton spring bloom in Otsuchi Bay,a ria in Sanriku,Japan     

Ken Furuya  Koji Takahashi  Hitoshi Iizumi 《Journal of Oceanography》1993,49(4):459-475

Spring blooms of phytoplankton composed of centric diatoms developed in late February, March, and April in Otsuchi Bay on Sanriku ria coast, Japan. During this period, associated with prolonged seasonal west wind (>1 day), intense exchange of waters occurred between inside and outside the bay: outflow of nearsurface brackish water over inflow of oceanic water at depth. This circulation interrupted formation of the blooms, and transported phytoplankton populations seaward. By such water movements, a significant amount of nutrients in the bay was carried out, otherwise replenished into the bay, depending on water masses located outside the bay. Owing to irregular features of wind events, a bloom lasted from several days to a week. From February to April, supply of nutrients seemed to be replete except for the latter half of the bloom period, and estimates of the critical depth exceeded the depth of the bottom consistently. Thus, net growth of phytoplankton was expected throughout the observation period, and potentially blooms could be formed. However, the blooms were only formed under calm weather. We hypothesize that the exchange of waters dilutes populations in the bay, and that formation of the bloom, that is, accumulation of biomass depends on a balance between the growth of phytoplankton and the dilution of bay water.  相似文献   

Distribution and sources of organic matter in surficial sediments on the shelf and slope off Tokachi, western North Pacific, inferred from C and N stable isotopes and C / N ratios     

Toshihiro Usui  Seiya Nagao  Masanobu Yamamoto  Koji Suzuki  Isao Kudo  Shigeru Montani  Atsushi Noda  Masao Minagawa 《Marine Chemistry》2006,98(2-4):241-259

Organic carbon (C) and total nitrogen (N) contents and corresponding isotope ratios were determined in surficial sediment (0–3 cm) at 94 stations ranging from 21 to 1995 m water depth off Tokachi, Hokkaido, Japan, to elucidate the distribution and source of sedimentary organic matter. Suspended particulate organic matter (POM) in the seawater and suspended POM and sediment in the Tokachi River were also examined. δ¹³C, δ¹⁵N and C / N ratios of the samples in the Tokachi River suggest that the spring snowmelt is an important process for the transport of terrestrial organic matter to the coastal waters. δ¹³C values of suspended POM in the surface seawater were higher in May and November than in August, while δ¹⁵N values of the POM were higher in May and August than in November. These changes are attributed to seasonal changes in phytoplankton growth rate and nitrate availability. δ¹³C and δ¹⁵N values in the sediments off Tokachi were lowest near the Tokachi River mouth, and increased offshore to constant values that persisted from 134 to 1995 m water depth. The spatial variation in C / N ratios in the sediment mirrored those of δ¹³C and δ¹⁵N. Comparison of δ¹³C, δ¹⁵N and C / N ratios in the sediments off Tokachi with those in the Tokachi River and seawater indicates that about half of the organic matter in the sediment was of terrestrial origin near the Tokachi River mouth, and the sedimentary organic matter from 134 to 1995 m water depth was of marine origin. The organic C content in the sediment was high near the Tokachi River mouth, and also around 1000 m water depth. The C content was significantly correlated with silt plus clay content, with different regression lines for those stations shallower and deeper than 134 m, owing to several stations of higher C content with the elevated C / N ratio on the inner shelf. These results suggest that transport and deposition of organic-rich fine sediment particles by hydrodynamic processes were major factors controlling C content off Tokachi. In addition, the supply of a fraction of terrestrial organic matter with high C / N probably also affected C content on the inner shelf.  相似文献   

Errors in sampling procedure for the determination of dissolved oxygen by Winkler method     

Yoshio Horibe  Yukio Kodama  Koji Shigehara 《Journal of Oceanography》1972,28(5):203-206

Sources of systematic error in the sampling procedure by Winkler method were examined. In the laboratory experiment, the dissolution of atmospheric oxygen into oxygenfree sea water during sampling amounts to 0.022 ml/l, and the effect of dissolved oxygen in sea water remaining in oxygen bottle is 0.019 ml/l. The effect of reagents added amounts to 0.017 ml/l. In the sampling procedures aboard, the effect of dissolution became bigger, and the table is presented for the correction to the reported value of dissolved oxygen measured by the “Manual of Oceanographic Observation”. The corrected value of dissolved oxygen in the routine analysis may not be correct within 0.02 ml/l.  相似文献