Trace-element characteristics of east–west mantle geochemical hemispheres     

Hikaru Iwamori  Hitomi Nakamura  Masaki Yoshida  Takashi Nakagawa  Kenta Ueki  Atsushi Nakao  Tatsuji Nishizawa  Satoru Haraguchi 《Comptes Rendus Geoscience》2019,351(2-3):209-220

Recent statistical analyses on the isotopic compositions of oceanic, arc, and continental basalts have revealed that the Earth's mantle is broadly divided into eastern and western hemispheres. The present study aimed to characterize the isotopically defined east–west geochemical hemispheres using trace-element concentrations. Basalt data with Rb, Sr, Nd, Sm, Pb, Th, and U in addition to the isotopic ratios ⁸⁷Sr/⁸⁶Sr, ¹⁴³Nd/¹⁴⁴Nd, ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb were selected mostly from the GEOROC and PetDB databases. A total of 4787 samples were used to investigate the global geochemical variations. The results show that the wide trace-element variations are broadly explained by the melting of melt-metasomatized and fluid-metasomatized mantle sources. The larger amount of the fluid component derived from subducted plates in the eastern hemisphere than that in the western hemisphere is inferred from the basalts. These characteristics support the hypothesis that focused subduction towards the supercontinent created the mantle geochemical hemispheres.  相似文献   

Eruptive history of Sundoro volcano,Central Java,Indonesia since 34 ka     

Oktory Prambada  Yoji Arakawa  Kei Ikehata  Ryuta Furukawa  Akira Takada  Haryo Edi Wibowo  Mitsuhiro Nakagawa  M. Nugraha Kartadinata 《Bulletin of Volcanology》2016,78(11):81

  相似文献   

Response to short communication on ‘Relaxation method for pounding action between adjacent buildings at expansion joint’          下载免费PDF全文

Hideo Takabatake  Masaaki Yasui  Yoshihisa Nakagawa  Akiko Kishida 《地震工程与结构动力学》2015,44(1):163-165

  相似文献   

RXTE observation of NGC 6240: a search for the obscured active nucleus     

Yasushi Ikebe  Karen Leighly  Yasuo Tanaka  Takao Nakagawa  Yuichi Terashima  Stefanie Komossa 《Monthly notices of the Royal Astronomical Society》2000,316(2):433-441

We present new data taken at 850 μm with SCUBA at the James Clerk Maxwell Telescope for a sample of 19 luminous infrared galaxies. Fourteen galaxies were detected. We have used these data, together with fluxes at 25, 60 and 100 μm from IRAS , to model the dust emission. We find that the emission from most galaxies can be described by an optically thin, single temperature dust model with an exponent of the dust extinction coefficient ( k _λ ∝ λ ^{− β} ) of β ≃1.4–2. A lower β ≃1 is required to model the dust emission from two of the galaxies, Arp 220 and NGC 4418. We discuss various possibilities for this difference and conclude that the most likely is a high dust opacity. In addition, we compare the molecular gas mass derived from the dust emission, M _850 μm, with the molecular gas mass derived from the CO emission, M _CO, and find that M _CO is on average a factor 2–3 higher than M _850 μm.  相似文献   

Effects of Recharge Wells and Flow Barriers on Seawater Intrusion   总被引：2，自引：0，他引：2  

Roger Luyun Jr.  Kazuro Momii  Kei Nakagawa 《Ground water》2011,49(2):239-249

The installation of recharge wells and subsurface flow barriers are among several strategies proposed to control seawater intrusion on coastal groundwater systems. In this study, we performed laboratory‐scale experiments and numerical simulations to determine the effects of the location and application of recharge wells, and of the location and penetration depth of flow barriers, on controlling seawater intrusion in unconfined coastal aquifers. We also compared the experimental results with existing analytical solutions. Our results showed that more effective saltwater repulsion is achieved when the recharge water is injected at the toe of the saltwater wedge. Point injection yields about the same repulsion compared with line injection from a screened well for the same recharge rate. Results for flow barriers showed that more effective saltwater repulsion is achieved with deeper barrier penetration and with barriers located closer to the coast. When the flow barrier is installed inland from the original toe position however, saltwater intrusion increases with deeper barrier penetration. Saltwater repulsion due to flow barrier installation was found to be linearly related to horizontal barrier location and a polynomial function of the barrier penetration depth.  相似文献   

Joint inversion of refraction and gravity data for the three-dimensional topography of a sediment–basement interface     

Afnimar  Kazuki Koketsu  Koichi Nakagawa 《Geophysical Journal International》2002,151(1):243-254

  相似文献   

Far-infrared detection limits – II. Probing confusion including source confusion     

Woong-Seob Jeong  Chris P. Pearson †  Hyung Mok Lee  Soojong Pak  Takao Nakagawa 《Monthly notices of the Royal Astronomical Society》2006,369(1):281-294

We present a comprehensive analysis for the determination of the confusion levels for the current and the next generation of far-infrared surveys assuming three different cosmological evolutionary scenarios. We include an extensive model for diffuse emission from infrared cirrus in order to derive absolute sensitivity levels taking into account the source confusion noise due to point sources, the sky confusion noise due to the diffuse emission, and instrumental noise. We use our derived sensitivities to suggest best survey strategies for the current and the future far-infrared space missions Spitzer , AKARI ( ASTRO-F ), Herschel and SPICA . We discuss whether the theoretical estimates are realistic and the competing necessities of reliability and completeness. We find the best estimator for the representation of the source confusion and produce predictions for the source confusion using far-infrared source count models. From these confusion limits considering both source and sky confusions, we obtain the optimal, confusion limited redshift distribution for each mission. Finally, we predict the cosmic far-infrared background (CFIRB), which includes information about the number and distribution of the contributing sources.  相似文献   

Far-infrared detection limits – I. Sky confusion due to Galactic cirrus     

Woong-Seob Jeong  Hyung Mok Lee  Soojong Pak  Takao Nakagawa  Suk Minn Kwon  Chris P. Pearson  Glenn J. White 《Monthly notices of the Royal Astronomical Society》2005,357(2):535-547

Fluctuations in the brightness of the background radiation can lead to confusion with real point sources. This type of confusion with background emission is relevant when making infrared (IR) observations with relatively large beam sizes, since the amount of fluctuation tends to increase with the angular scale. To quantitively assess the effect of the background emission on the detection of point sources for current and future far-IR observations by space-borne missions such as Spitzer , ASTRO-F , Herschel and Space Infrared Telescope for Cosmology and Astrophysics ( SPICA ), we have extended the Galactic emission map to a higher level of angular resolution than that of the currently available data. Using this high-resolution map, we estimate the sky confusion noise owing to the emission from interstellar dust clouds or cirrus, based on fluctuation analysis and detailed photometry over realistically simulated images. We find that the confusion noise derived by simple fluctuation analysis agrees well with the results from realistic simulations. Although sky confusion noise becomes dominant in long wavelength bands  (>100 μm)  with 60–90 cm aperture missions, it is expected to be two orders of magnitude lower for the next generation of space missions (with larger aperture sizes) such as Herschel and SPICA .  相似文献   

Solar source of the interplanetary planar magnetic structures     

Tomoko Nakagawa 《Solar physics》1993,147(1):169-197

Planar magnetic structure (PMS) is an interplanetary magnetic structure in which magnetic field vectors are all parallel to a plane but highly variable in both magnitude and direction in that plane. This magnetic structure corresponds to re-entrant loops of magnetic field lines in the photosphere that emanate into interplanetary space. To find information on the generation site, occurrence properties of PMSs are investigated by using the interplanetary magnetic field data obtained by Sakigake and ISEE-3 spacecraft. No significant correlation is found between PMS occurrence and the solar wind velocity gradient which would suggest interplanetary formation of PMSs. No significant correlation is found between the PMS events and flares or filaments, either. Instead, a half of the PMSs were projected to the vicinity of the sector boundary in the source surface magnetic field, although there are exceptions when PMS appeared in the center of a sector. The PMS planes were not parallel to the current sheet at the sector boundary. Sometimes PMSs were observed recurrently at the same heliospheric longitude in successive rotations of the Sun, suggesting persistence of the source of PMS on the Sun. The orientation of the PMS planes were not conserved in the recurrent PMSs.  相似文献   

Hazard assessment of the formation and failure of the Sunkoshi landslide dam in Nepal     

Badri Bhakta Shrestha  Hajime Nakagawa 《Natural Hazards》2016,82(3):2029-2049

  相似文献