The effects of radiative transfer on the reionization of an inhomogeneous universe     

Taishi Nakamoto  Masayuki Umemura  Hajime Susa 《Monthly notices of the Royal Astronomical Society》2001,321(4):593-604

Assuming simple dynamics for the growth of density fluctuations, we implement six-dimensional (6D) radiative transfer calculations to elucidate the effects of photon propagation during the reionization of an inhomogeneous universe. The ionizing sources are postulated to be AGN-like in this paper. The present simulations reveal that radiative transfer effects are still prominent considerably after the percolation epoch, in which patchy ionized regions connect with each other. In other words, owing to the collective opacity, the Universe does not become perfectly transparent against ionizing radiation even though strongly self-shielded regions disappear. It turns out that the inhomogeneity of the medium enhances the opacity effects and delays the end of reionization. Owing to such radiative transfer effects, the reionization in an inhomogeneous universe proceeds fairly slowly, in contrast to the prompt reionization in a homogeneous universe, and as a result the surface of reionization is not so sharply edged, but highly uneven. As a signature of the uneven surface of reionization, the cosmic IR background (CIB) radiation, which is produced by Ly photons resulting from radiative recombination, could exhibit strong anisotropies, reflecting the amplitude of density fluctuations at the reionization era. The predicted CIB intensity lies on a level of possible detection by forthcoming IR space telescope facilities.  相似文献   

Cosmological radiative transfer codes comparison project – I. The static density field tests     

Ilian T. Iliev  Benedetta Ciardi  Marcelo A. Alvarez  Antonella Maselli  rea Ferrara  Nickolay Y. Gnedin  Garrelt Mellema  Taishi Nakamoto  Michael L. Norman  Alexei O. Razoumov  Erik-Jan Rijkhorst  Jelle Ritzerveld  Paul R. Shapiro  Hajime Susa  Masayuki Umemura  Daniel J. Whalen 《Monthly notices of the Royal Astronomical Society》2006,371(3):1057-1086

Radiative transfer (RT) simulations are now at the forefront of numerical astrophysics. They are becoming crucial for an increasing number of astrophysical and cosmological problems; at the same time their computational cost has come within reach of currently available computational power. Further progress is retarded by the considerable number of different algorithms (including various flavours of ray tracing and moment schemes) developed, which makes the selection of the most suitable technique for a given problem a non-trivial task. Assessing the validity ranges, accuracy and performances of these schemes is the main aim of this paper, for which we have compared 11 independent RT codes on five test problems: (0) basic physics; (1) isothermal H  ii region expansion; (2) H  ii region expansion with evolving temperature; (3) I-front trapping and shadowing by a dense clump and (4) multiple sources in a cosmological density field. The outputs of these tests have been compared and differences analysed. The agreement between the various codes is satisfactory although not perfect. The main source of discrepancy appears to reside in the multifrequency treatment approach, resulting in different thicknesses of the ionized-neutral transition regions and the temperature structure. The present results and tests represent the most complete benchmark available for the development of new codes and improvement of existing ones. To further this aim all test inputs and outputs are made publicly available in digital form.  相似文献   

Phase-lagged warming and the disruption of climatic rhythms during the Matuyama–Brunhes magnetic polarity transition     

Ikuko Kitaba  Masayuki Hyodo  Shigehiro Katoh  Mariko Matsushita 《Gondwana Research》2012,21(2-3):595-600

The influence of the geomagnetic field on climate, a long hotly disputed issue, was examined for the Matuyama–Brunhes (MB) magnetic polarity transition using palynological and paleomagnetic data sets from a high accumulation rate (ca. 50 cm/kyr) sediment core from Osaka Bay. During the period from marine oxygen isotope stages (MIS) 20 to 18, climate change is well correlated with global ice volume variation in the precession cycle, with the exception of the early half of MIS 19. The postglacial warming after substage 20.2 was interrupted by cooling that began just before the sea-level highstand correlated with substage 19.3 and persisted until about a mid-point between 19.3 and 19.2, followed by a rapid warming. The thermal maximum clearly postdates the highest sea-level highstand by 6–7 kyr, and the connection between orbital forcing and climate was disrupted. The cooling event coincided with the center of the paleointensity low during the MB transition. This unusual climate cooling across a sea-level peak is very likely related to the field intensity decrease. The data from Osaka Bay may suggest an instance where the geomagnetic field has influenced climate in the past.  相似文献   

Strength Anisotropy of Compacted Decomposed Granite Soils     

Tae-Gew Ham  Yukio Nakata  Rolando Orense  Masayuki Hyodo 《Geotechnical and Geological Engineering》2012,30(1):119-127

In order to investigate the strength and deformation anisotropy of compacted decomposed granite soils, a series of drained triaxial compression tests was performed on unsaturated and saturated decomposed granite soils. The specimens were subjected to compression tests such that the angle δ of the direction of the major principal stress, σ ₁, during triaxial compression relative to the compaction plane (bedding plane) varies, with δ = 0°, 45° and 90°. Test results indicated that the compressive strain of the specimens subjected to isotropic consolidation was influenced strongly by the angle δ. In addition, the effect of the angle δ on the triaxial compressive strength and deformation was more evident in unsaturated specimens than in saturated specimens. Based on the test results, a procedure which can be used to estimate the shear strength of unsaturated soils taking into account various angles δ was proposed.  相似文献   

Reliability of Relative Paleointensity Recorded in Chinese Loess–Paleosol Sediments     

YANG Tianshui  LI Haiyan  WU Huaichun  YANG Zhenyu  ZHANG Shihong  HYODO Masayuki 《《地质学报》英文版》2012,86(5):1276-1288

A detailed paleomagnetic and rock-magnetic investigation spanning loess L7 to paleosol S8 has been carried out at the Baoji and Xifeng sections. Results of anisotropy of magnetic susceptibility confirm that the studied loess–paleosol sediments retain primary sedimentary fabrics. Stepwise thermal demagnetization shows that two well-defined magnetization components can be isolated from both loess and paleosol specimens. A low-temperature component, isolated between 100°C and 200°C, is consistent with the present geomagnetic field direction, and a high-temperature component, isolated between 200–300°C and 620–680°C, includes clearly normal and reversed polarities. Isothermal remanent magnetization and thermomagnetic analyses indicate that characteristic remanent magnetization is mainly carried by magnetite and hematite. The Day plot, together with the stratigraphic variations of rock-magnetic parameters, shows that the uniformity of magnetic mineralogy and grain size fulfills the criteria for relative paleointensity (RPI) studies. RPI records have been constructed using natural remanent magnetization (NRM) intensity after thermal demagnetization at 300°C normalized by low-frequency magnetic susceptibility (NRM300/χ). The results show that the RPI record from the Baoji section, where pedogenesis is quite weak, is compatible with the stacked PISO-1500 paleointensity record, suggesting that it might reflect the paleointensity variation of the geomagnetic field. The RPI record from the Xifeng section, where pedogenesis is rather strong, indicates a clear dissimilarity with the stacked PISO-1500 paleointensity record, implying that it does not reflect the paleointensity variation of the geomagnetic field. Our new results show that the NRM300/χ from the strongly pedogenetic paleosols does not completely eliminate the pedogenetic (climatic) influence, so it might be unsuitable for a reliable paleointensity study.  相似文献   

Structural changes of synthetic opal by heat treatment   总被引：1，自引：0，他引：1  

Akane Arasuna  Masayuki Okuno  Hiroki Okudera  Tomoyuki Mizukami  Shoji Arai  Shin’ichi Katayama  Mikio Koyano  Nobuaki Ito 《Physics and Chemistry of Minerals》2013,40(9):747-755

The structural changes of synthetic opal by heat treatment up to 1,400 °C were investigated using scanning electron microscopy, X-ray diffraction, and Fourier transform infrared and Raman spectroscopies. The results indicate that the dehydration and condensation of silanol in opal are very important factors in the structural evolution of heat-treated synthetic opal. Synthetic opal releases water molecules and silanols by heat treatment up to 400 °C, where the dehydration of silanol may lead to the condensation of a new Si–O–Si network comprising a four-membered ring structure of SiO₄ tetrahedra, even at 400 °C. Above 600 °C, water molecules are lost and the opal surface and internal silanol molecules are completely dehydrated by heat effect, and the medium-temperature range structure of opal may begin to thermally reconstruct to six-membered rings of SiO₄ tetrahedra. Above 1,000 °C, the opal structure almost approaches that of silica glass with an average structure of six-membered rings. Above 1,200 °C, the opal changes to low-cristobalite; however, minor evidence of low-tridymite stacking was evident after heat treatment at 1,400 °C.  相似文献   

Evaluation of the structural damage of high‐rise reinforced concrete buildings using ambient vibrations recorded before and after damage          下载免费PDF全文

Hirotoshi Uebayashi  Masayuki Nagano  Takenori Hida  Takehiko Tanuma  Mitoshi Yasui  Shigeki Sakai 《地震工程与结构动力学》2016,45(2):213-228

Evaluation of the degrees of structural damage suffered by high‐rise residential buildings after being subjected to strong ground motions is extremely important to the development of life continuity planning for building residents. However, these evaluations cannot be based on strong‐motion records alone, because earthquake observation equipment is not installed in most such buildings in Japan. In this study, we propose simple equations for estimating the stiffness degradation rate and the peak inter‐story drift ratio (PIDR) by using ambient vibration records instead of strong‐motion records when high‐rise RC buildings are subjected to a severe earthquake. More specifically, we propose one equation that relates the square root of the stiffness degradation rate, which is the ratio of natural frequencies at the maximum response to the preliminary tremor response (elastic state), in strong‐motion records with the ratio of natural frequencies identified from ambient vibrations before and after damage was suffered. We also propose an equation that relates the PIDR with the stiffness degradation rate on the basis of the stiffness‐degrading bilinear restoring force characteristic derived from the strong‐motion records of 13 high‐rise buildings for the 1995 Hyogoken‐Nanbu Earthquake (Mw 6.9) and the 2011 Tohoku‐Oki Earthquake (Mw 9.0). Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Impact of land uses on heavy metal distribution in the Selenga River system in Mongolia   总被引：1，自引：0，他引：1  

Orgilbold Myangan  Masayuki Kawahigashi  Bolormaa Oyuntsetseg  Nobuhide Fujitake 《Environmental Earth Sciences》2017,76(9):346

The Selenga River contributes to 50% of the total inflow to Lake Baikal. Large tracts of the Selenga River Basin have been developed for industry, urbanization, mining, and agriculture, resulting in the release of suspended solids (SS) that affect downstream water quality and primary productivity. This study addressed SS as the main factor controlling pollutant transport and the primary indicator of land degradation in the Selenga River system. Tributaries with larger areas dedicated to agricultural use had higher SS concentrations, reaching 862 mg L^?1, especially during the high runoff and intensive cultivation season. Although the large SS flux was detected in the main river, the small tributaries were distinguished by high SS concentrations. The high SS concentration corresponded to widespread development in the watershed. Watersheds with high potential of SS release are sensitive to intensive land uses. SS in the river system had a constant elemental composition consisting mainly of Fe and Al oxides, indicating that surface soils were major constituents of the tributary SS. Three minor heavy metals (Zn, Cu, and Cr) appeared in high concentrations downstream of urban and mining areas (two- to sixfold increases), indicating that these contaminants are carried by SS. At two tributary junctions, the concentration of contaminants on the SS decreased due to a large influx of SS with low heavy metal contents. Changes in electric conductivity and pH at downstream of tributary junctions enhanced the sedimentation of SS and the removal of contaminants from the water phase after aggregation of the SS. Land use changes in the tributary watersheds are major controlling factors for the fate of contaminants in the river system.  相似文献   

Aluminum in the East China Sea and Okinawa Trough, marginal sea areas of the Western North Pacific     

Masayuki Minakawa  Yasunori Watanabe 《Journal of Oceanography》1998,54(6):629-640

The distribution of aluminum (Al) in seawater has been investigated in the continental slope and the Okinawa Trough areas of the East China Sea, which is one of the marginal seas in the western North Pacific Ocean. Aluminum concentration in waters over the slope and the Trough ranged from 5.6 to 25 nmol/kg in the surface layer (0–100 m), and had a minima of 1.1 nmol/kg between 400 and 500 m depth and ranged from 1.3 to 9.7 nmol/kg in the deep or bottom waters. Aluminum values were higher than in the surface waters of the central North Pacific, while minimum values were similar to levels in the intermediate or deep waters of the central North Pacific, except for the bottom water over the slope. This suggests that the high Al concentration in the surface reflects the large atmospheric input of Asian dust around the western side of the North Pacific region. On the continental slope, Al concentrations in the upper 500 m depth decreased slopeward. This horizontal gradient of Al can be explained from the combination of dilution by upwelling of Al-poor water originated from the North Pacific Intermediate Water (NPIW) which intrudes into the mid-depth of the Okinawa Trough and the scavenging of Al by biogenic particles in the continental slope zone.  相似文献   

Clean and safe supply of fish and shellfish to clear the HACCP regulation by use of clean and cold deep ocean water in Rausu, Hokkaido, Japan     

Masayuki Mac Takahashi Kazunori Yamashita 《中国海洋大学学报(英文版)》2005,4(3):219-223

For the supply of fish and shellfish to consumers in fresh condition, clean handling after catch from the sea is essential. According to HACCP （Hazard Analysis and Critical Control Points）, it is important to meet such requirement by keeping fish and shellfish under a certain low temperature and clean conditions after catching. The deep ocean water （DOW） characterized by low temperature and cleanliness has been chosen for fish and shellfish handlings, particularly for salmon, cod, and sea urchin in Town ＇Rausu＇ in Hokkaido, Japan. DOW below 2.9℃ of an amount of nearly 5 000 m^3 is planned to be pumped up every day from a depth of about 350 m, and temporarily stored in a large simulated tank on land. DOW is then supplied to fish boats through hydrants distributed throughout the harbor and used for keeping salmon in clean and cold conditions. Ice made from DOW is also used for lowering temperature if necessary. DOW and ice made from DOW are also used during the transportation of fish and shellfish. The entire system is scheduled to be completed by the summer of 2005.  相似文献