A numerical experiment on the variations of western boundary currents: Part II. Response to a moving typhoon     

Masahiro Endoh 《Journal of Oceanography》1973,29(1):28-43

Response of the barotropic western boundary current to typhoon passage is investigated by the use of the numerical models described in Part I. Steady states obtained in Part I are chosen as the initial conditions for undisturbed currents. In these models it is assumed that an axially symmetric typhoon (radius = 100 km, maximum wind speed = 27.4 m/sec) moves parallel to the western boundary.For the model with a flat bottom the boundary flow diminishes its strength and broadens its width after the passage of the typhoon offshore. For the model with a continental slope the effect of the typhoon is significantly different depending on the distance of the path of the typhoon from the western boundary. Specifically the north wind on the continental slope causes the formation of cyclonic vortex, which progresses southwards along the slope in the northern hemisphere. Linear theory of continental shelf waves indicates that the phase speed of the propagation of the vortex is 2.4 m/sec. Anomalies of the water level along the coast are also calculated from geostrophic relationships.  相似文献   

Graphitization of carbonaceous matter during metamorphism with references to carbonate and pelitic rocks of contact and regional metamorphisms,Japan   总被引：4，自引：0，他引：4  

Hideki Wada  Toshihiro Tomita  Kazuhiro Matsuura  Keisuke Tuchi  Masahiro Ito  Toshiro Morikiyo 《Contributions to Mineralogy and Petrology》1994,118(3):217-228

This study is an attempt to correlate the graphitization process of carbonaceous matter during metamorphism with metamorphic grade. Graphitization can be parameterized using crystal structure and chemical and isotopic compositions. The extent of graphitization could be characterized mainly by temperature, duration of metamorphism and rock composition. We compared the graphitization trends for two metamorphic terrains, a contact aureole of the Kasuga area and a regional metamorphic terrain of high-temperature/low pressure type of the Ryoke metamorphic terrain in Northern Kiso area, Central Japan, and for two different lithologies (carbonate and pelite), using X-ray diffractogram, DTA-TG analysis, and chemical and stable isotope analyses. During contact metamorphism, graphitization and carbon isotopic exchange reactions proceeded simultaneously in pelitic and carbonate rocks. The decreases in basal spacing d(002) of the carbonaceous matter in carbonate rocks is greatly accelerated at temperatures higher than about 400° C. Furthermore, carbon isotopic ratios of graphite in carbonate rocks also change to ¹³C-enriched values implying exchange with carbonates. The beginning of this enrichment of ¹³C in the carbonaceous matter coincides with an abrupt increase of the graphitization processes. Carbon isotopic shifting up to 5 in pelites could be observed as metamorphic temperature increased probably by about 400° C. Carbonaceous matter in pelitic rocks is sometimes a mixture of poorly crystallized organic matter and well-crystallized graphite detritus. DTA-TG analysis is an effective tool for the distinction of detrital graphitic material. Two sources for the original carbon isotopic composition of carbonaceous matter in pelites in the Kasuga contact aureole can be distinguished, about-28 and-24 regardless of the presence of detrital graphite, and were mainly controlled by depositional environment of the sediments. Graphitization in limestones and pelitic rocks in regional metamorphism proceeds further than in a contact aureole. In the low-temperature range, the differences in extent of graphitization between the two metamorphic regions is large. However, at temperatures higher than 600° C, the extent of graphitization in both regions is indistinguishable. The degree of graphitization is different in limestones and pelitic rocks from the Ryoke metamorphic terrain. We demonstrate that the graphitization involves a progressive re-construction process of the crystal structure. The sequence of the first appearance of crystal inter planar spacing correlates with the metamorphic grade and indicates the crystal growth of three-dimensional structured graphite.  相似文献   

Robustness,uncertainties, and emergent constraints in the radiative responses of stratocumulus cloud regimes to future warming   总被引：1，自引：0，他引：1  

Yoko Tsushima  Mark A. Ringer  Tsuyoshi Koshiro  Hideaki Kawai  Romain Roehrig  Jason Cole  Masahiro Watanabe  Tokuta Yokohata  Alejandro Bodas-Salcedo  Keith D. Williams  Mark J. Webb 《Climate Dynamics》2016,46(9-10):3025-3039

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Nutrient dynamics in core sediments of an artificial basal medium prepared with steelmaking slag and dredged materials     

Ayumi Tsukasaki  Nobuo Tsurushima  Tetsuya Nakazato  Yu Huang  Terumi Tanimoto  Masahiro Suzumura  Wataru Nishijima 《Journal of Oceanography》2016,72(6):867-881

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Binary formation with different metallicities: dependence on initial conditions     

Masahiro N. Machida  Kazuyuki Omukai  Tomoaki Matsumoto  Shu-ichiro Inutsuka 《Monthly notices of the Royal Astronomical Society》2009,399(3):1255-1263

The fragmentation process in collapsing clouds with various metallicities is studied using three-dimensional nested-grid hydrodynamics. Initial clouds are specified by three parameters: cloud metallicity, initial rotation energy and initial cloud shape. For different combinations of these parameters, we calculate 480 models in total and study cloud evolution, fragmentation conditions, orbital separation and binary frequency. For the cloud to fragment during collapse, the initial angular momentum must be higher than a threshold value, which decreases with decreasing metallicity. Although the exact fragmentation conditions depend also on the initial cloud shape, this dependence is only modest. Our results indicate a higher binary frequency in lower metallicity gas. In particular, with the same median rotation parameter as in the solar neighbourhood, a majority of stars are born as members of binary/multiple systems for  <10⁻⁴ Z_⊙  . With initial mass  <0.1 M_⊙  , if fragments are ejected in embryo from the host clouds by multibody interaction, they evolve to substellar-mass objects. This provides a formation channel for low-mass stars in zero- or low-metallicity environments.  相似文献   

Ore Mineralogy and Mineral Chemistry of the Ashanti Gold Deposit at Obuasi, Ghana     

Shiloh OSAE  Katsuo KASE  Masahiro YAMAMOTO 《Resource Geology》1999,49(1):1-11

Abstract: The gold deposit at Ashanti occurs in the Proterozoic Birimian formation of Ghana. Two main ore types mined from the deposit are gold-bearing quartz veins, and gold-sulfide disseminations in metasediments and metavolcanics. The main sulfide minerals in the gold-sulfide disseminated ores are arsenopyrite, pyrite and pyrrhotite, and to a very minor extent, sphalerite and tetrahedrite. Carbonate alteration and sericitization are prominent in the metavolcanics and the metasediments, respectively. In the quartz veins, pyrite and arsenopyrite commonly occur in small amounts, but gold mostly occurs in contact with tetrahedrite, chalcopyrite, galena, aurostibite, and sphalerite. Pyrrhotite is absent in the quartz veins.
Microprobe studies indicate that As content of homogeneous arsenopyrite grains ranges from 27. 0 to 31. 7 atm%, and gives mineralization temperatures from 170 to 430°C, although mostly from 300 to 400°C. Chlorite geothermometry using temperature dependence of substitution of Al for Si in the tetrahedral site gives formation temeratures of 330 to 400°C, comparable to the arsenopyrite temperatures. Applying sphalerite–pyrite–pyrrhotite geobarometry to sphalerite with FeS contents from 13. 6 to 12. 5 mol%, the pressure was estimated to be in a range from 5. 9 to 7. 0 kb at the stage of elevated temperatures.
Mineralogical observations, especially absence of pyrrhotite in the quartz veins, together with microprobe data for gold and associated minerals suggest that the fluids having ascended through fissures in the Ashanti deposit were reduced by the reaction with carbonaceous materials in the metasediments during the declining stage of the regional metamorphism.  相似文献   

Subhorizontal boundary between ultrahigh-pressure and low-pressure metamorphic units in the Sulu–Tjube area of the Kokchetav Massif, Kazakhstan     

Masahiro Ishikawa  Yoshiyuki Kaneko  Ryo Anma and  Hiroshi Yamamoto 《Island Arc》2000,9(3):317-327

Abstract The Kokchetav Massif of Kazakhstan includes high to ultrahigh-pressure (HP–UHP) metamorphic rocks (some of which were recrystallized at depths in excess of 150 km), juxtaposed against much lower pressure metamorphic components. We investigated the relationship between the HP–UHP metamorphic unit and the low pressure (LP) unit (Daulet Suite) in the Sulu–Tjube area, where the metamorphic rocks have previously been interpreted as constituting a megamelange with subvertical structural attitudes. Analyses of fold structures suggest that the HP–UHP metamorphic unit overlies the LP unit across a west-dipping subhorizontal boundary. In addition, kinematic indicators display top-to-the-north senses of shear along the tectonic contact between the two units, indicating that the HP–UHP unit has been extruded northward onto the LP unit. Following the juxtaposition of the two units, upright folds developed in both units, and these are associated with the previously reported steeply dipping metamorphic foliations. These data have important implications for the mode of exhumation of the UHP rocks from upper mantle to shallow crustal depths.  相似文献   

Fractional Determination of Gold in Twenty Six Geological Reference Materials by Sequential Extraction with Graphite Furnace Atomic Absorption Spectrometry     

Shigeru Terashima  Masahiro Taniguchi 《Geostandards and Geoanalytical Research》2000,24(1):7-17

A method is described to estimate the chemical form of gold (Au) in a variety of geological reference samples, combining a sequential extraction scheme with graphite furnace atomic absorption spectrometry, after extraction of Au as iodide or chloride with methyl isobutyl ketone. The fractions dissolved by sequential extraction are empirically defined as the exchangeable, amorphous, metallic, aqua regia-soluble and residual fractions. The amounts of Au in the amorphous fraction have been derived mainly from oxide or amorphous phases, and the chemical forms of Au are considered to be mostly amorphous and partly metallic. The metallic fraction of Au is likely to exist as submicroscopic grains of native metal which are relatively free from the rock-forming minerals, whereas the aqua regia-soluble or residual fraction of Au may be bound more intimately perhaps as inclusions or solid solutions of either native metal or electrum in most cases. Satisfactory agreement was observed between the sum of the Au values from exchangeable to residual fractions and the reported total Au values, except for a few samples which contained a large amount of reducing materials. Analytical results of Au for twenty six geological reference materials are tabulated, and geochemical and mineralogical features are discussed.  相似文献   

Residual structural capacity evaluation of steel moment‐resisting frames with dynamic‐strain‐based model updating method          下载免费PDF全文

Akiko Suzuki  Masahiro Kurata  Xiaohua Li  Shota Shimmoto 《地震工程与结构动力学》2017,46(11):1791-1810

This paper presents a method for evaluating the residual structural capacity of earthquake‐affected steel structures. The method first quantifies the damage severity of a beam by computing the dynamic‐strain‐based damage index. Next, the model used to analyze the structure is updated based on the damage index, to reflect the observed damage conditions. The residual structural capacity is then estimated in terms of changes in stiffness and strength, which can be applied by structural engineers, via a nonlinear static analysis of the updated model. The main contributions of this paper are in performance evaluation of the dynamic‐strain‐based damage index for seismically induced damage using a newly developed substructure testing environment, consideration of various damage patterns in composite beams, and extension of a local damage evaluation technique to a residual capacity estimation procedure by incorporating the model‐updating technique. In laboratory testing, the specimens were damaged quasi‐statically, and vibration tests were conducted as the damage proceeded. First, a bare steel beam–column connection was tested, and then a similar one with a floor slab was used for a more realistic case. The estimated residual structural capacities for these specimens were compared with the static test results. The results verified that the proposed method can provide fine estimates of the stiffness and strength deteriorations within 10% for the specimen without the floor slab and within 30% for that with the floor slab. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

He+ ion implantation and electron irradiation effects on cathodoluminescence of plagioclase     

Masahiro Kayama  Hirotsugu Nishido  Shin Toyoda  Kosei Komuro  Adrian A. Finch  Martin R. Lee  Kiyotaka Ninagawa 《Physics and Chemistry of Minerals》2013,40(7):531-545

Cathodoluminescence (CL) spectra of unirradiated, He⁺ ion-implanted and electron-irradiated plagioclase minerals contain the following emission bands: (1) below 300 nm due to Pb²⁺, (2) at ~320 and ~350 nm to Ce³⁺, (3) at 380–420 nm to Eu²⁺, Ti⁴⁺ and/or Al–O^?–Al/Ti defects, (4) at 560–580 nm to Mn²⁺ and (5) at 720–760 nm to Fe³⁺. During the implantation of He⁺ ion, much of their energy may be dissipated by partial destruction and strain of the feldspar framework, resulting in quenching of CL. Deconvolution of CL spectra acquired from albite and oligoclase reveals an emission component at 1.86 eV (666 nm) assigned to a radiation-induced defect center associated with Na⁺ atoms. As its intensity increases with radiation dose, this emission component has potential for geodosimetry and geochronometry. Electron irradiation causes Na⁺ migration in plagioclase, and then a considerable reduction in intensity of emissions assigned to impurity centers, which is responsible for an alteration in the energy state or a decrease in luminescence efficiency following the change of activation energy. Emission intensity at 1.86 eV positively correlates with electron irradiation time for unimplanted and He⁺ ion-implanted albite and oligoclase, but negatively for the implanted albite above 1.07 × 10^?4 C/cm². It implies that radiation halo produced by α-particles should not be measured using CL spectroscopy to estimate β radiation dose on albite in the high radiation level.  相似文献