Near- and mid-infrared imaging polarimetry of NGC 1068     

S. L. Lumsden  T. J. T. Moore  C. Smith  T. Fujiyoshi  J. Bland-Hawthorn  M. J. Ward 《Monthly notices of the Royal Astronomical Society》1999,303(2):209-220

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Crustal structure of central Japan and its petrological implications     

Oguz Ozel  Takaya Iwasaki  Takeo Moriya  Shin'ichi Sakai  Takuya Maeda  Chengshi Piao  Toshikatsu Yoshii  Shinya Tsukada  Akihito Ito  Masayuki Suzuki  Akira Yamazaki  & Hiroki Miyamachi 《Geophysical Journal International》1999,138(1):257-274

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Organic matters and acid‐sulfate alteration in Itomuka mercury mine,Hokkaido, Japan: Implications for the transportation and deposition mechanisms of Hg     

Takuya Echigo  Mitsuyoshi Kimata  Masahiro Shimizu 《Resource Geology》2020,70(2):204-213

In order to examine the transportation and deposition mechanisms of Hg, we investigated the ore and hydrothermal alteration minerals and solid organic matters from Itomuka mercury mine located in the eastern part of central Hokkaido. In addition to the ore minerals, native mercury and cinnabar, quartz, marcasite, alunite, kaolinite, and minor amounts of pyrite and smectite were identified in the Hg ore by powder X‐ray diffraction (XRD) analysis. This mineral assemblage of acid sulfate alteration was likely developed under the conditions of low temperature (≤100°C) and low pH (≤2) in the steam‐heated environment. The H₂SO₄ was produced above the water table by the oxidation of H₂S separated from deep, near‐neutral fluids by boiling. The dominance of native mercury over cinnabar in Hg ore indicates that the greater part of mineralized Hg was transported as Hg⁰ in aqueous solution and vapor with low sulfur fugacity. The solid organic matters found in the Hg ore were analyzed with SEM‐EDS, micro‐XRD, and micro‐Fourier transform infrared (FTIR) spectroscopy, and these results suggest that the organic matters contributed to keeping the low fO₂ of the Hg‐bearing fluid and transportation of Hg as Hg⁰ in S‐poor condition. Because the solubility of Hg in acidic fluid is low, neutral to alkaline fluid seems to have leached Hg from the basement sedimentary rocks of Hidaka Group which also supplied the organic matters to the fluid. The oxidation and cooling of Hg‐bearing solution and vapor triggered the deposition of liquid Hg as a primary phase.  相似文献   

Coupling behavior of shear deformation and end rotation of elastomeric seismic isolation bearings          下载免费PDF全文

Ken Ishii  Masaru Kikuchi  Takuya Nishimura  Cameron J. Black 《地震工程与结构动力学》2017,46(4):677-694

This paper presents a mechanical model for predicting the behavior of elastomeric seismic isolation bearings subject to combined end rotations and shear deformation. The mechanical model consists of a series of axial springs at the top, mid‐height and bottom of the bearing to vertically reproduce asymmetric bending moment distribution in the bearings. The model can take into account end rotations of the bearing, and the overall rotational stiffness includes the effect of the variation of vertical load on the bearing and the imposed shear deformation. Static bending tests under various combinations of vertical load and shear deformation were performed to identify the mechanical characteristics of bearings. The test results indicate that bearing rotational stiffness increases with increasing vertical load but decreases with increasing shear deformation. Simulation analyses were conducted to validate the new mechanical model. The results of analyses using the new model show very good agreement with experimental observations. A series of seismic response analyses were performed to demonstrate the dynamic behavior of top‐of‐column isolated structures, a configuration where the end rotations of isolation bearings are typically expected to be larger. The results suggest that the end rotations of elastomeric bearings used in practical top‐of‐column isolated structures do not reduce the stability limit of isolation system. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Numerical experiment for strontium-90 and cesium-137 in the Japan Sea     

Hideyuki Kawamura  Toshimichi Ito  Takuya Kobayashi  Shigeyoshi Otosaka  Naoki Hirose  Orihiko Togawa 《Journal of Oceanography》2010,66(5):649-662

A numerical experiment is carried out to reproduce distribution of concentration of ⁹⁰Sr and ¹³⁷Cs, estimate their total amount and verify their source in the Japan Sea. Model results are in good agreement with observational findings in the Japan Sea expeditions between 1997 and 2002 by the Japan Atomic Energy Agency. Vertical profiles of the concentration of ⁹⁰Sr and ¹³⁷Cs show exponential decreases with depth from the sea surface to the sea bottom. From the model and observational results, it is suggested that the concentration of ⁹⁰Sr and ¹³⁷Cs in the surface layer is approximately in the range of 1.0–1.5 Bq/m³ and 2.0–2.5 Bq/m3, respectively. On the other hand, it is found that the concentration in the intermediate and deep layer is higher than that observed in the northwestern Pacific Ocean, suggesting active winter convection in the Japan Sea. The total amount of ⁹⁰Sr and ¹³⁷Cs in the seawater is evaluated to be 1.34 × 10¹⁵ Bq and 2.02 × 10¹⁵ Bq, respectively, in the numerical experiment, which demonstrates an estimation by observational data obtained in the Japan Sea expeditions. The total amount of ⁹⁰Sr and ¹³⁷Cs changed during the second half of 20th century corresponding to deposition at the sea surface with the maximums of 4.86 × 10¹⁵ Bq for ⁹⁰Sr and 7.33 × 10¹⁵ Bq for ¹³⁷Cs, respectively, in the mid-1960s. The numerical experiment suggests that the main source of ⁹⁰Sr and ¹³⁷Cs has been global fallout, although there have been some potential sources in the Japan Sea.  相似文献   

High organic carbon deposition in the northern margin of the Aleutian Basin (Bering Sea) before the last deglaciation   总被引：1，自引：0，他引：1  

Boo-Keun Khim  Sunghan Kim  Masao Uchida  Takuya Itaki 《Ocean Science Journal》2010,45(4):203-211

High-resolution geochemical, isotope and elemental data from core PC23A in the northern margin of the Aleutian Basin (Bering Sea) were used to reconstruct distinct paleoceanographic features of the last deglaciation (pre-Boreal[PB], Bølling-Allerød[BA], Younger Dryas[YD]). The PB and BA intervals are characterized by increased siliceous (diatom) and calcareous (coccolithophores and foraminifers) productivity represented by high biogenic opal and CaCO₃ contents, respectively. The enhanced productivity can plausibly be attributed to an elevated sea-surface nutrient supply from increased melt-water input and enhanced Alaskan Stream injection under warm, restricted sea-ice conditions. High C_org/N ratios and low δ¹³C values of sediment organic matter during the PB and BA intervals reflect the contribution of terrestrial organic matters. The PB and BA intervals were also identified by laminated sediment layers of core PC23A, characterized by high Mo/Al and Cd/Al ratios, indicating that the bottom water condition remained anoxic. High δ¹⁵N values during the same period were attributed mainly to the increased nutrient utilization and subsequent denitrification of seawater nitrate. Part of high δ¹⁵N values may also be due to incorporation of inorganic nitrogen in the clay minerals. It is worthy of note that high total organic carbon (TOC) deposition occurred approximately 3,000 years before onset of the last deglaciation. Simultaneous high C_org/N ratios and low δ¹³C values clearly suggest that the high TOC content should be related to terrestrial organic carbon input. Low δ¹⁵N values during the high TOC interval also confirm the contribution of terrigenous organic matter. Although abundant calcareous phytoplankton production under cold, nutrient-poor conditions represented by Baex data was reported for high TOC deposition preceding the last deglaciation in an earlier study of the Okhotsk Sea, the main reason for the enhanced TOC deposition in the Bering Sea is an increased terrigenous input from the submerged continental shelves (Beringia) with a sea-level rise; this is further supported by Al enrichment of bulk sediments during the high TOC deposition.  相似文献   

Seismic resistance capacity of beam–column connections in high‐rise buildings: E‐Defense shaking table test     

Yu‐Lin Chung  Takuya Nagae  Tomohiro Matsumiya  Masayoshi Nakashima 《地震工程与结构动力学》2011,40(6):605-622

A series of E‐Defense shaking table tests are conducted on a large‐scale test specimen that represents a high‐rise steel building. Two types of connections featuring the connection details commonly used in 1970s, in the early days of high‐rise construction in Japan, are adopted: the field‐welded connection consisting of welded unreinforced flanges and a bolted web type, and the shop‐welded connection in which the flanges and web are all‐welded to the column flange in the shop. To examine the seismic capacity of a total of 24 beam‐to‐column connections of the specimen, particularly when it is subjected to long‐period ground motion characterized not so much by large amplitude as by very many cycles of repeated loading, the test specimen is shaken repeatedly until the connections fractured. The test results indicate that a few of the field‐welded connections fractured from the bottom flange weld boundary in a relatively small cumulative rotation primarily due to the difficulties in ensuring the welding and inspection performance in the actual field welding. The shop‐welded connections are able to sustain many cycles of plastic rotation, with an averaged cumulative plastic rotation of 0.86 rad. Two shop‐welded connections exhibit ductile fractures but only after experiencing many cycles. The presence of RC floor slabs promotes the strain concentration at the toe of the weld access hole in the bottom flange by at least twice compared with the case without the slab, which had resulted in a decrease in the cumulative plastic rotation by about 50%. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Long-term high-frequency measurements of dibromomethane in the atmosphere at algae-rich and algae-poor coastal sites     

Yoko?YokouchiEmail author  Takuya?Saito  Hitoshi?Mukai 《Journal of Atmospheric Chemistry》2018,75(2):171-180

Dibromomethane (CH₂Br₂), a natural stratospheric ozone depleting substance, is mostly emitted from the ocean, but the relative importance of coastal (or macroalgae) and open ocean emissions is unknown. We made long-term high-frequency measurements of CH₂Br₂ concentrations at two remote coastal sites in Japan, on the subtropical Hateruma Island (poor in macroalgae) and at Cape Ochiishi (rich in macroalgae). CH₂Br₂ concentrations at Hateruma showed prominent seasonal variation, being lower in summer (around 0.94 ppt) than in winter (around 1.23 ppt). In contrast, CH₂Br₂ concentrations at Ochiishi were highly variable, often exceeding 2 ppt in the summer but with minimum baseline concentrations close to those from Hateruma; in the winter the concentrations were almost constant at about 1.3 ppt. Analysis of the data suggested that (1) emissions from macroalgae were not likely to extend offshore, but instead were localized near the shore, (2) strong macroalgal emissions of CH₂Br₂ were almost limited to the summer, but it was not reflected in the seasonality of the baseline concentrations of CH₂Br₂ in the atmosphere, and therefore (3) macroalgal or coastal emissions of CH₂Br₂ in the temperate zone might have a rather limited contribution to the global CH₂Br₂ sources. These findings are especially important for the understanding of the tropospheric and stratospheric bromine budget.  相似文献   

Sea surface temperature record off central Japan since the Last Glacial Maximum using planktonic foraminiferal Mg/Ca thermometry     

Takuya Sagawa  Kazuhiro Toyoda  Tadamichi Oba 《第四纪科学杂志》2006,21(1):63-73

We conducted paired measurements of the Mg/Ca ratio and δ¹⁸O of planktonic foraminifera, Globigerina bulloides, from a sediment core (MD01‐2420) off central Japan in the northwest Pacific, to reconstruct current movements since the Last Glacial Maximum (LGM). These methods make it possible to determine the magnitude and timing of the sea surface temperature (SST) changes and to reconstruct the variations of the past seawater δ¹⁸O (δ¹⁸Ow) off central Japan. The amplitude of Mg/Ca‐based SST changes between the Holocene and the LGM was about 10°C. The strong resemblance of the SSTs estimated from both methods, Mg/Ca‐based and δ¹⁸O‐based, suggests that the SST changes were caused primarily by latitudinal displacement of the Kuroshio–Oyashio currents and no distinct change in the carbonate dissolution of the core. The southward migration of the water mass was 5–6° in latitude at the LGM. The values for regional δ¹⁸Ow changes, which were obtained by subtracting the ice volume contribution from the calculated δ¹⁸Ow, describe the millennial‐scale water mass migration over the last 30 kyr. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Radio and infrared recombination studies of the southern massive star forming region G333.6−0.2     

Takuya Fujiyoshi  Craig H. Smith  James L. Caswell  Toby J. T. Moore  Stuart L. Lumsden  David K. Aitken  Patrick F. Roche 《Monthly notices of the Royal Astronomical Society》2006,368(4):1843-1855

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