Laboratory Enrichment of Radioactive Assemblages and Estimation of Thorium and Uranium Radioactivity in Fractions Separated from Placer Sands in Southeast Bangladesh     

Takayuki Sasaki  Mohammad Rajib  Masafumi Akiyoshi  Taishi Kobayashi  Ikuji Takagi  Toshiyuki Fujii  Md. Mashrur Zaman 《Natural Resources Research》2015,24(2):209-220

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小型激光天文动力学空间计划概念   总被引：1，自引：0，他引：1  

倪维斗  朱进  武向平  褚桂柏  杨彬  高健  关敏  汤健仁  周翊  张中豪  黄天衣  曲钦岳  易照华  李广宇  陶金河  吴岸明  罗俊  叶贤基  周泽兵  熊耀恒  毕少兰  须重明  吴雪君  唐孟希  包芸  李芳昱  黄珹  杨福民  叶叔华  张书练  张元仲  聂玉昕  陈光  Joergen Christensen-Dalsgaard  Hansjoerg Dittus  Yasunori Fujii  Claus Laemmerzahl  Jean Francois Mangin  Achim Peters  Albrecht Ruediger  Etienne Samain  Stephan Schiller 《天文研究与技术》2002,(3):123-136

小型激光天文动力学空间计划是 :使用在太阳轨道上无拖曳航天器和地面站以激光干涉和脉冲测距的方法 ,精确地探讨天文动力学 ,检测相对论与时空基本定律 ,改进探测引力波的灵敏度以及更准确地测定太阳、行星和小行星的参数。 1 969年开始的月球激光 (反射 )测距 ,对地球物理、参考坐标的选定、相对论的检验均有重要的贡献。 3 0年来 ,激光技术的长足进步 ,使现在正是适合于开始进行研究空间有源 (主动 )测距和光波空间通讯的时候。激光天文动力学的兴起是必然的趋势 ,其精确度将比现在提高 3到 6个数量级 ,将是天文动力学革命性的发展。小型激光天文动力学空间计划可以起到带头作用。它的关键技术有三 ,即 :弱光锁相、极精确无拖曳航天和高衰减日冕仪。弱光锁相已有长足的进步。对高衰减日冕仪的研究 ,也有了初步的方案。LISA空间计划将于 2 0 0 6年 8月发射SMART -2 ,研究测试极精确无拖曳航天。小型激光天文动力学空间计划的关键技术已日趋成熟。在第一届国际激光天文动力学研讨会 ( 2 0 0 1 ,9.1 3 -2 3 )中介绍了各相关学科背景及前沿研究 ,讨论了激光天文动力学空间计划科学目标及相关技术 ,并召开了两次小型激光天文动力学空间计划预研究筹备会 ,建立了和欧洲的合作关系。会后着手进行此项对基础  相似文献   

X-ray emission associated with gamma-ray bursts     

J. Nishimura  M. Fujii  T. Yamagami 《Astrophysics and Space Science》1983,93(1):87-96

The energy spectra of gamma-ray bursts differ from those of black-body radiation and are similar to the thermal bremsstrahlung spectra of optically thin plasma. This could be realized if the source is located in the outer atmosphere of a neutron star. In this case, almost one half of the emitted photons hit the surface of the star. The surface of the star is heated to a temperature of the order 10⁷ K, and a dominant flux of X-rays with a black-body spectrum would be expected. The X-rays produced by this mechanism are detectable in the energy range from a few keV to 10 keV. This model is discussed in relation to the recent observations in the X-ray region at the time of gamma-ray bursts, and modifications of this model are also presented. The observation in this energy range will bring us valuable information on the nature of gamma-ray burst sources.  相似文献   

A multiphysics and multiscale software environment for modeling astrophysical systems     

Simon Portegies Zwart  Steve McMillan  Stefan Harfst  Derek Groen  Michiko Fujii  Breanndán Ó Nualláin  Evert Glebbeek  Douglas Heggie  James Lombardi  Piet Hut  Vangelis Angelou  Sambaran Banerjee  Houria Belkus  Tassos Fragos  John Fregeau  Evghenii Gaburov  Rob Izzard  Mario Jurić  Stephen Justham  Andrea Sottoriva  Marcel Zemp 《New Astronomy》2009,14(4):369-378

We present MUSE, a software framework for combining existing computational tools for different astrophysical domains into a single multiphysics, multiscale application. MUSE facilitates the coupling of existing codes written in different languages by providing inter-language tools and by specifying an interface between each module and the framework that represents a balance between generality and computational efficiency. This approach allows scientists to use combinations of codes to solve highly coupled problems without the need to write new codes for other domains or significantly alter their existing codes. MUSE currently incorporates the domains of stellar dynamics, stellar evolution and stellar hydrodynamics for studying generalized stellar systems. We have now reached a “Noah’s Ark” milestone, with (at least) two available numerical solvers for each domain. MUSE can treat multiscale and multiphysics systems in which the time- and size-scales are well separated, like simulating the evolution of planetary systems, small stellar associations, dense stellar clusters, galaxies and galactic nuclei. In this paper we describe three examples calculated using MUSE: the merger of two galaxies, the merger of two evolving stars, and a hybrid N-body simulation. In addition, we demonstrate an implementation of MUSE on a distributed computer which may also include special-purpose hardware, such as GRAPEs or GPUs, to accelerate computations. The current MUSE code base is publicly available as open source at http://muse.li.  相似文献   

Dense gas in normal and active galaxies     

Kotaro Kohno  Koichiro Nakanishi  Tomoka Tosaki  Kazuyuki Muraoka  Rie Miura  Hajime Ezawa  Ryohei Kawabe 《Astrophysics and Space Science》2008,313(1-3):279-285

Dense molecular medium plays essential roles in galaxies. As demonstrated by the tight and linear correlation between HCN(1–0) and FIR luminosities among star-forming galaxies, from very nearby to high-z ones, the observation of a dense molecular component is indispensable to understand the star formation laws in galaxies. In order to obtain a general picture of the global distributions of dense molecular medium in normal star-forming galaxies, we have conducted an extragalactic CO(3–2) imaging survey of nearby spiral galaxies using the Atacama Submillimeter Telescope Experiment (ASTE). From the survey (ADIoS; ASTE Dense gas Imaging of Star-forming galaxies), CO(3–2) images of M 83 and NGC 986 are presented. Emphasis is placed on the correlation between the CO(3–2)/CO(1–0) ratio and the star formation efficiency in galaxies. In the central regions of some active galaxies, on the other hand, we often find enhanced or overluminous HCN(1–0) emission. The HCN(1–0)/CO(1–0) and HCN(1–0)/HCO⁺(1–0) intensities are often enhanced up to ∼0.2–0.3 and ∼2–3, respectively. Such elevated ratios have never been observed in the nuclear starburst regions. One possible explanation for these high HCN(1–0)/CO(1–0) and HCN(1–0)/HCO⁺(1–0) ratios is X-ray induced chemistry in X-ray dominated regions (XDRs), i.e., the overabundance of the HCN molecule in the X-ray irradiated dense molecular tori. If this view is true, the known tight correlation between HCN(1–0) and the star-formation rate breaks in the vicinity of active nuclei. Although the interpretation of these ratios is still an open question, these ratios have a great potential for a new diagnostic tool for the energy sources of dusty galaxies in the ALMA era because these molecular lines are free from dust extinction.  相似文献   

Mapping the change of coral reefs using remote sensing and in situ measurements: a case study in Pangkajene and Kepulauan Regency,Spermonde Archipelago,Indonesia     

La Ode Muhammad Yasir Haya  Masahiko Fujii 《Journal of Oceanography》2017,73(5):623-645

As elsewhere in Indonesia, local inhabitants in the Pangkajene and Kepulauan (PANGKEP) Regency, Spermonde Archipelago area and along the south-west coast of Sulawesi traditionally regard the coral reefs as their livelihood source. Since human activities as well as natural disturbances pose major threats to the coral reefs, these livelihoods may also be at risk. Currently, no comprehensive information on the status and condition of coral reefs in this area is available for this resource management. We determined the changes of coral reef habitat over a period of 20 years from 1994 to 2014 using a satellite Landsat multi-temporal image substantiated with in situ measurement data collected in 2014. The spectral value of coral reefs was extracted from multi-temporal Landsat imagery data, while the diffuse attenuation coefficient of water was obtained by using statistical analysis between the ratio of live coral cover and the spectral value of the visible bands. By using the unsupervised classification integrated with the data ground truth, it is stated that there has been a decline in live coral cover over a period of 20 years from 7716 ha in 1994 to 4236 ha in 2014, with a degradation rate of 174 ha/year. Based on the results, the ratio of the coral cover in the coral reef transects varied from the average of 24% for live corals to 96% for coral rubbles, implying the degraded status of coral reefs in the study area.  相似文献   

Fractured Rock Permeability as a Function of Temperature and Confining Pressure     

A. K. M. Badrul Alam  Yoshiaki Fujii  Daisuke Fukuda  Jun-ichi Kodama  Katsuhiko Kaneko 《Pure and Applied Geophysics》2015,172(10):2871-2889

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Lunar photometric properties at wavelengths 0.5-1.6 μm acquired by SELENE Spectral Profiler and their dependency on local albedo and latitudinal zones     

Yasuhiro Yokota  Tsuneo Matsunaga  Junichi Haruyama  Satoru Yamamoto  Tomokatsu Morota  Kazuto Saiki  Kohei Kitazato  Akira Iwasaki  Naru Hirata  Rie Honda  Hitoshi Mizutani 《Icarus》2011,215(2):639-660

The lunar photometric function, which describes the dependency of the observed radiance on the observation geometry, is used for photometric correction of lunar visible/near-infrared data. A precise photometric correction parameter set is crucial for many applications including mineral identification and reflectance map mosaics. We present, for the first time, spectrally continuous photometric correction parameters for both sides of the Moon for wavelengths in the range 0.5-1.6 μm and solar phase angles between 5° and 85°, derived from Kaguya (SELENE) Spectral Profiler (SP) data. Since the measured radiance also depends on the surface albedo, we developed a statistical method for selecting areas with relatively uniform albedos from a nearly 7000-orbit SP data set. Using the selected data set, we obtained empirical photometric correction parameter sets for three albedo groups (high, medium, and low). We did this because the photometric function depends on the albedo, especially at phase angles below about 20° for which the shadow hiding opposition effect is appreciable. We determined the parameters in 160 bands and discovered a small variation in the opposition effect due to the albedo variation of mafic mineral absorption. The consistency of the photometric correction was checked by comparing observations made at different times of the same area on the lunar surface. Variations in the spectra obtained were lower than 2%, except for the large phase angle data in mare. Lastly, we developed a correction method for low solar elevation data, which is required for high latitude regions. By investigating low solar elevation data, we introduced an additional correction method. We used the new photometric correction to generate a 1° mesh global lunar reflectance map cube in a wavelength range of 0.5-1.6 μm. Surprisingly, these maps reveal that high latitude (?75°) regions in both the north and south have much lower spectral continuum slopes (color ratio r_1547.7nm/r_752.8nm ? 1.8) than the low and medium latitude regions, which implies lower degrees of space weathering.  相似文献   

Evolution of Mount Fuji,Japan: Inference from drilling into the subaerial oldest volcano,pre‐Komitake     

Mitsuhiro Yoshimoto  Toshitsugu Fujii  Takayuki Kaneko  Atsushi Yasuda  Setsuya Nakada  Akikazu Matsumoto 《Island Arc》2010,19(3):470-488

A buried, old volcanic body (pre‐Komitake Volcano) was discovered during drilling into the northeastern flank of Mount Fuji. The pre‐Komitake Volcano is characterized by hornblende‐bearing andesite and dacite, in contrast to the porphyritic basaltic rocks of Komitake Volcano and to the olivine‐bearing basaltic rocks of Fuji Volcano. K‐Ar age determinations and geological analysis of drilling cores suggest that the pre‐Komitake Volcano began with effusion of basaltic lava flows around 260 ka and ended with explosive eruptions of basaltic andesite and dacite magma around 160 ka. After deposition of a thin soil layer on the pre‐Komitake volcanic rocks, successive effusions of lava flows occurred at Komitake Volcano until 100 ka. Explosive eruptions of Fuji Volcano followed shortly after the activity of Komitake. The long‐term eruption rate of about 3 km³/ka or more for Fuji Volcano is much higher than that estimated for pre‐Komitake and Komitake. The chemical variation within Fuji Volcano, represented by an increase in incompatible elements at nearly constant SiO₂, differs from that within pre‐Komitake and other volcanoes in the northern Izu‐Bonin arc, where incompatible elements increase with increasing SiO₂. These changes in the volcanism in Mount Fuji may have occurred due to a change in regional tectonics around 150 ka, although this remains unproven.  相似文献   

The role of the hyporheic zone for a benthic fish in an intermittent river: a refuge, not a graveyard     

R. Kawanishi  M. Inoue  R. Dohi  A. Fujii  Y. Miyake 《Aquatic Sciences - Research Across Boundaries》2013,75(3):425-431

In lotic systems, the hyporheic zone has been suggested as a potential refuge for aquatic organisms during disturbances (hyporheic refuge hypothesis). However, the supporting evidence is unclear, especially regarding the survival of hyporheic refugees and their contribution to the recovery of post-disturbance populations. Moreover, few studies have focused on the importance of the hyporheic refuge for aquatic vertebrates such as fish. In this study, we present evidence that the hyporheic zone acts as a refuge for a small benthic fish (Cobitis shikokuensis) following surface drying in an intermittent river. We examined its survival during and recolonization after dry periods by direct hyporheic sampling and mark-and-recapture surveys. When the streambed dried, hyporheic sampling was conducted 58 times across 33 locations in the intermittent reach and 31 individuals of C. shikokuensis were captured from extracted hyporheic water. Mark-and-recapture surveys revealed that recolonizers after re-wetting included C. shikokuensis individuals that had survived dry periods in the hyporheic refuge. The condition factor of C. shikokuensis significantly declined after dry periods, suggesting that most recolonizers suffered from physiological stress, probably within the hyporheic refuge. These results clearly support the long-debated, hyporheic refuge hypothesis, and provide a striking example of the critical role of the hyporheic zone in population maintenance of lotic organisms.  相似文献