The Hinode/XRT Full-Sun Image Corrections and the Improved Synoptic Composite Image Archive     

Aki Takeda  Keiji Yoshimura  Steven H. Saar 《Solar physics》2016,291(1):317-333

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Evaluation of the Residual Mass Fractionation in High-Precision Cr Isotopic Analysis with TIMS     

Tetsuya Yokoyama  Yusuke Ohkuma  Keiji Nishikawa  Koki Sumiya  Ikshu Gautam 《Geostandards and Geoanalytical Research》2023,47(2):415-435

The Cr isotope ratios of terrestrial and extra-terrestrial materials are emerging as one of the most important tracers in geosciences. Previous studies on Cr isotopic measurements using TIMS have found that there is residual Cr isotopic fractionation between the mass-fractionation-corrected ⁵³Cr/⁵²Cr and ⁵⁴Cr/⁵²Cr ratios, which may cause an offset of obtained ratios from the reference values. The residual fractionation was thought to be caused by the evaporation of Cr-oxide species during thermal ionisation, but the mechanism by which this residual fractionation could be reduced remained unclear. Here we revisit the issue of residual fractionation and propose that this problem can be alleviated by utilising W filaments instead of conventionally used Re filaments for Cr ionisation. Using W filaments, the formation of CrO⁺ was suppressed during heating as the filament temperature was ~ 100 °C lower than when Re filaments were used. In repeated measurement of a carbonaceous chondrite, the intermediate precisions of ⁵³Cr/⁵²Cr and ⁵⁴Cr/⁵²Cr ratios in the W filament runs were two to three times better than those of the Re filament runs. Therefore, the new finding of this study will be of key importance for future studies of Cr isotopes for terrestrial and extra-terrestrial materials.  相似文献   

Deep water observations of extreme waves with moored and free GPS buoys   总被引：1，自引：1，他引：0  

Takuji Waseda  Masato Sinchi  Keiji Kiyomatsu  Tomoya Nishida  Shunsuke Takahashi  Sho Asaumi  Yoshimi Kawai  Hitoshi Tamura  Yasumasa Miyazawa 《Ocean Dynamics》2014,64(9):1269-1280

Point-positioning GPS-based wave measurements were conducted by deep ocean (over 5,000 m) surface buoys moored in the North West Pacific Ocean in 2009, 2012, and 2013. The observed surface elevation bears statistical characteristics of Gaussian, spectrally narrow ocean waves. The tail of the averaged spectrum follows the frequency to the power of ?4 slope, and the significant wave height and period satisfies the Toba’s 3/2 law. The observations compare well with a numerical wave hindcast. Two large freak waves exceeding 13 m in height were observed in October 2009 and three extreme waves around 20 m in height were observed in October 2012 and in January 2013. These extreme events are associated with passages of a typhoon and a mid-latitude cyclone. Horizontal movement of the buoy revealed that the orbital motion of the waves at the peak of the wave group mostly exceed the weakly nonlinear estimate. For some cases, the orbital velocity exceeded the group velocity, which might indicate a breaking event but is not conclusive yet.  相似文献   

Two extraterrestrial dust horizons found in the Dome Fuji ice core,East Antarctica     

Keiji Misawa  Mika Kohno  Takayuki Tomiyama  Takaaki Noguchi  Tomoki Nakamura  Keisuke Nagao  Takashi Mikouchi  Kunihiko Nishiizumi 《Earth and Planetary Science Letters》2010,289(1-2):287-297

Two silicate-rich dust layers were found in the Dome Fuji ice core in East Antarctica, at Marine Isotope Stages 12 and 13. Morphologies, textures, and chemical compositions of constituent particles reveal that they are high-temperature melting products and are of extraterrestrial origin. Because similar layers were found ～ 2000 km east of Dome Fuji, at EPICA (European Project for Ice Coring in Antarctica)-Dome C, particles must have rained down over a wide area 434 and 481 ka. The strewn fields occurred over an area of at least 3 × 10⁶ km². Chemical compositions of constituent phases and oxygen isotopic composition of olivines suggest that the upper dust layer was produced by a high-temperature interaction between silicate-rich melt and water vapor due to an impact explosion or an aerial burst of a chondritic meteoroid on the inland East Antarctic ice sheet. An estimated total mass of the impactor, on the basis of particle flux and distribution area, is at least 3 × 10⁹ kg. A possible parent material of the lower dust layer is a fragment of friable primitive asteroid or comet. A hypervelocity impact of asteroidal/cometary material on the upper atmosphere and an explosion might have produced aggregates of sub-μm to μm-sized spherules. Total mass of the parent material of the lower layer must exceed 1 × 10⁹ kg. The two extraterrestrial horizons, each a few millimeters in thickness, represent regional or global meteoritic events not identified previously in the Southern Hemisphere.  相似文献   

The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: Overview and Performance     

J. Todd Hoeksema  Yang Liu  Keiji Hayashi  Xudong Sun  Jesper Schou  Sebastien Couvidat  Aimee Norton  Monica Bobra  Rebecca Centeno  K. D. Leka  Graham Barnes  Michael Turmon 《Solar physics》2014,289(9):3483-3530

The Helioseismic and Magnetic Imager (HMI) began near-continuous full-disk solar measurements on 1 May 2010 from the Solar Dynamics Observatory (SDO). An automated processing pipeline keeps pace with observations to produce observable quantities, including the photospheric vector magnetic field, from sequences of filtergrams. The basic vector-field frame list cadence is 135 seconds, but to reduce noise the filtergrams are combined to derive data products every 720 seconds. The primary 720 s observables were released in mid-2010, including Stokes polarization parameters measured at six wavelengths, as well as intensity, Doppler velocity, and the line-of-sight magnetic field. More advanced products, including the full vector magnetic field, are now available. Automatically identified HMI Active Region Patches (HARPs) track the location and shape of magnetic regions throughout their lifetime. The vector field is computed using the Very Fast Inversion of the Stokes Vector (VFISV) code optimized for the HMI pipeline; the remaining 180^° azimuth ambiguity is resolved with the Minimum Energy (ME0) code. The Milne–Eddington inversion is performed on all full-disk HMI observations. The disambiguation, until recently run only on HARP regions, is now implemented for the full disk. Vector and scalar quantities in the patches are used to derive active region indices potentially useful for forecasting; the data maps and indices are collected in the SHARP data series, hmi.sharp_720s. Definitive SHARP processing is completed only after the region rotates off the visible disk; quick-look products are produced in near real time. Patches are provided in both CCD and heliographic coordinates. HMI provides continuous coverage of the vector field, but has modest spatial, spectral, and temporal resolution. Coupled with limitations of the analysis and interpretation techniques, effects of the orbital velocity, and instrument performance, the resulting measurements have a certain dynamic range and sensitivity and are subject to systematic errors and uncertainties that are characterized in this report.  相似文献   

Interlayer proton transfer in brucite under pressure by polarized IR spectroscopy to 5.3 GPa     

Keiji Shinoda  Nobuyuki Aikawa 《Physics and Chemistry of Minerals》1998,25(3):197-202

In order to investigate the behaviour of proton in brucite under pressure, polarized IR absorption spectra and polarized absorbance distributions of (001) and (110) oriented single crystal of brucite under high pressure were measured by Fourier transform polarized infrared microspectroscopy with diamond anvil cell. A pressure-induced absorption peak at 3645 cm⁻¹ observed under pressures over 2.9 GPa was confirmed to be due to a secondarily formed OH dipole. Polarized absorbance distribution measured under pressure of (110) suggests that the secondary OH dipole is oriented 136.0° to c-axis under 5.3 GPa. Isotropic absorbance distribution of (001) suggests that the secondary OH dipole is disorderly trifurcated. Abrupt onset of the secondary peak and its reverse pleochroism suggest that the process of secondary OH dipole formation is due to proton transfer between layers in brucite. The calculated orientation of the secondary OH dipole consistent with the O-H···O′ angle revealed by neutron diffraction supports the existence of proton transfer along H···O′. The secondary OH dipole implies a new site of proton in brucite under pressure. Received: 6 March 1997 / Revised, accepted: 9 June 1997  相似文献   

Three-Dimensional Subsurface Structure Model of Kansai International Airport by Integration of Borehole Data and Seismic Profiles     

Naoto Inoue  Naoko Kitada  Keiji Takemura  Koji Fukuda  Tsuyoshi Emura 《Geotechnical and Geological Engineering》2013,31(3):881-890

The three-dimensional subsurface structure model around Kansai International Airport (KIX) has been developed based on the geologically and geotechnically investigated results of a large amount of borehole data for estimation of subsidence. The model consists of the alternation of marine clay and coarse deposits. The many seismic surveys and borehole drillings were carried out around the KIX before the constructing the airport. The stratigraphy of the model was renewed by the KIX18-1, which was about 1,300 m long drilling core and was drilled near the 2nd runway of the KIX from 2006 to 2007. In this study, the subsurface geological model was revised by integration of renewed borehole data and seismic profiles to incorporate complex warping structure and heterogenic lateral variation.  相似文献   

Mass dispersal and angular momentum transfer during collisions between rubble-pile asteroids. II. Effects of initial rotation and spin-down through disruptive collisions     

Takaaki Takeda  Keiji Ohtsuki 《Icarus》2009,202(2):514-524

Expanding on our previous N-body simulation of impacts between initially non-rotating rubble-pile objects [Takeda, T., Ohtsuki, K., 2007. Icarus 189, 256-273], we examine effects of initial rotation of targets on mass dispersal and change of spin rates. Numerical results show that the collisional energy needed to disrupt a rubble-pile object is not sensitive to initial rotation of the target, in most of the parameter range studied in our simulations. We find that initial rotation of targets is slowed down through disruptive impacts for a wide range of parameters. The spin-down is caused by escape of high-velocity ejecta and asymmetric re-accumulation of fragments. When these effects are significant, rotation is slowed down even when the angular momentum added by an impactor is in the same direction as the initial rotation of the target. Spin-down is most efficient when the impact occurs in the equatorial plane of the target, because in this case most of the ejected fragments originate from the equatorial region of the target and a significant amount of angular momentum can be easily removed. In the case of impacts from directions inclined relative to the target's equatorial plane, spin-down still occurs with reduced degree, unless impacts occur onto the pole region from the vertical direction. Our results suggest that such spin-down through disruptive impacts may have played an important role in spin evolution of asteroids through collisions in the gravity-dominated regime.  相似文献   

Spin rates of fast-rotating asteroids and fragments in impact disruption     

Toshihiko Kadono  Masahiko Arakawa  Takashi Ito  Keiji Ohtsuki 《Icarus》2009,200(2):694-697

We present a new experimental result of fragment spin-rate in impact disruption, using a thin glass plate. A cylindrical projectile impacts on a side (edge) of the plate. Dispersed fragments are observed using a high-speed camera and the spin rates of fragments are measured. We find that the measured fragment spin-rate decreases with increasing size. Assuming that the rotational energy of fragments is supplied from the residual stress, the spin rate ω decreases with increasing fragment size r as ω∼r−1, which explains the above experimental results. This size-dependence is similar to that of the observed spin rates of small fast-rotating asteroids. Our results suggest that spin rates of fragments of small asteroids immediately after disruption may have a similar size-dependence, and can provide constraints on the subsequent spin-state evolution of small asteroids due to thermal torques.  相似文献   

Non-uniform across-shelf variations in thickness, grain size, and frequency of turbidites in a transgressive outer-shelf, the Middle Pleistocene Kakinokidai Formation, Boso Peninsula, Japan     

Keiji Horikawa  Makoto Ito 《Sedimentary Geology》2009,220(1-2):105-115

Across-shelf variations in thickness, grain size, and frequency of sandstone beds in a transgressive outer-shelf succession were investigated from the Middle Pleistocene (ca. 0.7 Ma) Kakinokidai Formation on the Boso Peninsula, Japan. The transgressive deposits are generally muddy and contain slumps and slump scars. The intercalated sandstone beds are interpreted to have been formed from turbidity currents as a response to erosion and resuspension of sandridge-complex deposits in the southwestern upslope area during storm events. Mapping of volcanic ash beds and a transgressive surface in the base of the formation permits detailed bed-by-bed correlation of the outer-shelf sandstone beds. Although, overall, thickness, grain size, and frequency of sandstone beds decrease in the downslope direction, some sandstone beds locally thin out and coarsen in association with slump scars in the surrounding muddy deposits. These sandstone beds subsequently thicken and fine, and finally thin out in the farther downslope area. In addition to the local thinning of sandstone beds, the frequency of sandstone beds first decreases and then increases in the farther offshore direction. From this evidence, we concluded that these non-uniform patterns of across-outer-shelf variations in thickness, grain size, and frequency of sandstone beds were caused by the local increases in flow speeds and subsequent expansion and reduced speeds of turbidity currents, along with a local increase in the seafloor gradient that was induced by the development of slump scars in the transgressive outer-shelf floor. These physiographic features in the outer shelf are interpreted not to have permitted monotonous downslope thinning and fining of sandstone beds, compared with the bed-shape models of depletive turbidity currents and with the proximality trend of shelf sandstones from modern and ancient highstand-stage shelf systems.  相似文献