Single-crystal X-ray diffraction study of cation distribution in MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript>–MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript> spinel solid solution     

A.?NakatsukaEmail author  H.?Ueno  N.?Nakayama  T.?Mizota  H.?Maekawa 《Physics and Chemistry of Minerals》2004,31(5):278-287

Synthesis experiments in the system MgAl₂O₄–MgFe₂O₄ [MgAl_2–xFe_xO₄ (0 x 2)] were carried out using a PbF₂ flux. The crystalline products synthesized in the compositional range of 0.6 <x 1.2 consisted of two spinel phases, whereas those synthesized in the compositional ranges of 0.0 x 0.6 and 1.2 < x 2.0 crystallized as single spinel phases. Structure refinements of the spinel single crystals, which grew in the ranges of 0.0 x 0.6 and 1.2 < x 2.0, show that the degree of randomness of cation distribution between A and B sites increases as x approaches the two-phase region. This means that the degree of the size mismatch among Mg²⁺, Fe³⁺ and Al³⁺occupying each equivalent mixing site increases as x approaches the two-phase region. Consequently, if the coexistence of two spinels observed in the intermediate compositions reveals the existence of a miscibility gap at low temperatures, this increase in the degree of the size mismatch among the three cations is suggested as a factor of energetic destabilization to form the miscibility gap.  相似文献   

Specific accumulation of persistent organochlorines in bluefin tuna collected from Japanese coastal waters     

Ueno D  Iwata H  Tanabe S  Ikeda K  Koyama J  Yamada H 《Marine pollution bulletin》2002,45(1-12):254-261

Concentrations of persistent organochlorines (OCs) such as PCBs, DDTs, chlordanes (CHLs), HCHs and HCB were determined in the liver of bluefin tuna (Thunnus thynnus) collected from Japanese coastal waters in order to elucidate accumulation profiles and to evaluate the suitability of this species as a biomonitor for pollution in the open sea ecosystem. Concentrations of PCBs, DDTs and CHLs in bluefin tuna increased significantly with body length (30–190 cm). HCHs and HCB residues were comparable among all the sampling regions, and the levels of these chemicals did not show correlation with body length. These results suggest significance of dietary uptake of PCBs, DDTs and CHLs compared to the intake via the gill. On the other hand, equilibrium partitioning with ambient water is a major determinant of the levels of HCHs and HCB in tuna. Body-length normalized values (BLNV) of PCBs, DDTs and CHLs concentrations in bluefin tuna were calculated using the linear regression equation obtained from the plot of concentrations and body length. BLNV of these chemicals on a lipid wt basis, which was adjusted for 100 cm body length, were indicative of the present state water pollution by PCBs, DDTs and CHLs. These results suggest that bluefin tuna is a suitable bioindicator for monitoring OCs contamination in the open sea ecosystem.  相似文献   

Carbon isotope chemostratigraphy of a Precambrian/Cambrian boundary section in the Three Gorge area, South China: Prominent global-scale isotope excursions just before the Cambrian Explosion     

Tomoko Ishikawa  Yuichiro Ueno  Tsuyoshi Komiya  Yusuke Sawaki  Jian Han  Degan Shu  Yong Li  Shigenori Maruyama  Naohiro Yoshida   《Gondwana Research》2008,14(1-2):193

Carbon isotope chemostratigraphy has been used for worldwide correlation of Precambrian/Cambrian (Pc/C) boundary sections, and has elucidated significant change of the carbon cycle during the rapid diversification of skeletal metazoa (i.e. the Cambrian Explosion). Nevertheless, the standard δ¹³C curve of the Early Cambrian has been poorly established mainly due to the lack of a continuous stratigraphic record. Here we report high-resolution δ¹³C chemostratigraphy of a drill core sample across the Pc/C boundary in the Three Gorge area, South China. This section extends from an uppermost Ediacaran dolostone (Dengying Fm.), through a lowermost Early Cambrian muddy limestone (Yanjiahe Fm.) to a middle Early Cambrian calcareous black shale (Shuijingtuo Fm.). As a result, we have identified two positive and two negative isotope excursions within this interval. Near the Pc/C boundary, the δ¹³C_carb increases moderately from 0 to + 2‰ (positive excursion 1: P1), and then drops dramatically down to − 7‰ (negative excursion 1: N1). Subsequently, the δ¹³C_carb increases continuously up to about + 5‰ at the upper part of the Nemakit–Daldynian stage. After this positive excursion, δ¹³C_carb sharply decreases down to about − 9‰ (N2) just below the basal Tommotian unconformity. These continuous patterns of the δ¹³C shift are irrespective of lithotype, suggesting a primary origin of the record. Moreover, the obtained δ¹³C profile, except for the sharp excursion N2, is comparable to records of other sections within and outside of the Yangtze Platform. Hence, we conclude that the general feature of our δ¹³C profile best represents the global change in seawater chemistry. The minimum δ¹³C of the N1 (− 7‰) is slightly lower than carbon input from the mantle, thus implying an enhanced flux of ¹³C-depleted carbon just across the Pc/C boundary. Hence, the ocean at that time probably became anoxic, which may have affected the survival of sessile or benthic Ediacaran biota. The subsequent δ¹³C rise up to + 5‰ (P2) indicates an increase of primary productivity or an enhanced rate of organic carbon burial, which should have resulted in lowering pCO₂ and following global cooling. This scenario accounts for the cause of the global-scale sea-level fall at the base of the Tommotian stage. The subsequent, very short-term, and exceptionally low δ¹³C (− 9‰) in N2 could have been associated with the release of methane from gas hydrates due to the sea-level fall. The inferred dramatic environmental changes (i.e., ocean anoxia, increasing productivity, global cooling and subsequent sea-level fall with methane release) appear to coincide with or occur just before the Cambrian Explosion. This may indicate synchronism between the environmental changes and rapid diversification of skeletal metazoa.  相似文献   

The X-ray spectrum and variability of the Seyfert 2 galaxy NGC 7172     

M. Guainazzi  G. Matt  L. A. Antonelli  F. Fiore  L. Piro  & S. Ueno 《Monthly notices of the Royal Astronomical Society》1998,298(3):824-830

We present evidence of flux variability, on both short (hours) and long (months) time-scales, of the Seyfert 2 galaxy NGC 7172. These results are based on the ASCA observation of NGC 7172 performed in 1996 May. The source was detected at a rather low flux level, about 3 times fainter than its usual state (including 1 yr before, when it was also observed by ASCA ).   The source also varied by about 30 per cent during the observation, confirming the presence of a type 1 nucleus in its centre. However, its spectrum appears to be flatter than the typical Seyfert 1 spectrum (in agreement with findings on other Seyfert 2s), posing problems for the unification model unless complex absorption is invoked.  相似文献   

A direct numerical approach to the Chandrasekhar'sH-functions for arbitrary characteristic functions     

Kiyoshi Kawabata  Takehiko Satoh  Sueo Ueno 《Astrophysics and Space Science》1991,182(2):249-260

The purpose of this paper is to present a numerical technique to directly compute the Chandrasekhar'sH ()-function for anisotropic scattering in terms of the roots of the characteristic equations as well as the quadrature points of a certain degreen employed to approximate the definite integral involved in the basic equation. The principal feature of the algorithm proposed here is a compact computer code to enumerate _n C _m combinations ofn distinct integers {1,...,n} takenm at a time. With these quantities available, the coefficients of the polynomial equation of the characteristics equation can be readily computed for any given characteristic function, so that a standard technique such as the Laguerre method can be applied to find all the roots.It is shown that the results obtained for some representativeH()-functions using the present technique with relatively low-order formula (e.g.,n=7) are sufficiently accurate for all practical purposes.  相似文献   

A comparative analysis of large-scale flood disasters     

Nakasu  Tadashi  Kurahara  Munetaka 《Natural Hazards》2021,106(3):1839-1865

Natural Hazards - The purpose of this study is to analyze and compare the human suffering exacerbation processes in the coastal metropolitan areas of Nagoya, New Orleans and Metro Manila caused by...  相似文献   

Subsurface hydrographic structures and the temporal variations of Aleutian eddies     

Rui Saito  Ichiro Yasuda  Kosei Komatsu  Hiromu Ishiyama  Hiromichi Ueno  Hiroji Onishi  Takeshi Setou  Manabu Shimizu 《Ocean Dynamics》2016,66(5):605-621

  相似文献   

GAME-TIBET青藏高原云和降水综合观测概况及初步结果   总被引：13，自引：7，他引：6  

刘黎平  楚荣忠  宋新民  周筠君  冯锦明  陈成品  张彤  S.Shimizu  K.Ueno  T.Koike  H.Fujii  H.Yamada  Y.Aoi  T.Ueno  J.Horikomi  M.Kajikawa  R Shirooka  J.Teshima 《高原气象》1999,18(3):441-450

对中日合作青藏高原能量水分循环试验项目中云和降水的多普勒雷达观测使用的气象观测仪器和获取的资料等情况进行了总结,并给出了那曲地区水的日变化,不同 雨量计测量降水的对比分析,风速对测量降水影响,多普勒雷达资料的个例分析及云的数值模拟的等初步结果。  相似文献   

2006 Fragmentation of Comet 73P/Schwassmann-Wachmann 3B observed with Subaru/Suprime-Cam     

Masateru Ishiguro  Fumihiko Usui  Munetaka Ueno 《Icarus》2009,203(2):560-960

The fragmentation of the split Comet 73P/Schwassmann-Wachmann 3 B was observed with the prime-focus camera Suprime-Cam attached to the Subaru 8.2-m telescope. The fragmentation revealed dozens of miniature comets [Fuse, T., Yamamoto, N., Kinoshita, D., Furusawa, H., Watanabe, J., 2007. Publ. Astron. Soc. Jpn. 59 (2), 381-386]. We analyzed the Subaru/Suprime-Cam images, detecting no fewer than 154 mini-comets, mostly extending to the southwest. Three were close to the projected orbit of fragment B. We applied synchrone-syndyne analysis, modified for rocket effect analysis, to the mini-fragment spatial distribution. We found that most of these mini-comets were ejected from fragment B by an outburst occurring around 1 April 2006, and three fragments on the leading side of nucleus B could have been released sunward on the previous return. Several fragments might have been released by successive outbursts around 24 April and 2 May 2006. The ratio of the rocket force to solar gravity was 7-23 times larger than that exerted on fragment B. No significant color variation was found. The mean color index, V-R = 0.50 ± 0.07, was slightly redder than that of the Sun and similar to that of the largest fragment, C, which suggests that these mini-fragments were detected mainly through sunlight reflected by dust particles and materials on the nuclei. We examined the surface brightness profiles of all detected fragments and estimated the sizes of 154 fragments. We found that the radius of these mini-fragments was in the 5- to 108-m range (equivalent size of Tunguska impactor). The power-law index of the differential size distribution was q = −3.34 ± 0.05. Based on this size distribution, we found that about 1-10% of the mass of fragment B was lost in the April 2006 outbursts. Modeling the cometary fragment dynamics [Desvoivres, E., Klinger, J., Levasseur-Regourd, A.C., Lecacheux, J., Jorda, L., Enzian, A., Colas, F., Frappa, E., Laques, P., 1999. Mon. Not. Roy. Astron. Soc. 303 (4), 826-834; Desvoivres, E., Klinger, J., Levasseur-Regourd, A.C., Jones, G.H., 2000. Icarus 144, 172-181] revealed that it is likely that mini-fragments smaller than ∼10-20 m could be depleted in water ice and become inactive, implying that decameter-sized comet fragments could survive against melting and remain as near-Earth objects. We attempted to detect the dust trail, which was clearly found in infrared wavelengths by Spitzer. No brightness enhancement brighter than 30.0 mag arcsec⁻² (3σ) was detected in the orbit of fragment B.  相似文献   

The Influence Of Urban Canopy Configuration On Urban Albedo   总被引：6，自引：0，他引：6  

Akira Kondo  Megumi Ueno  Akikazu Kaga  Katsuhito Yamaguchi 《Boundary-Layer Meteorology》2001,100(2):225-242

We propose a calculation method for shortwave radiation flux and longwave radiation flux within the urban canopy and investigate the influence of urban canopy configuration on net radiation flux. In the assumed urban configuration, buildings of equal size are arranged in a regular lattice within the urban canopy. The net shortwave radiation flux and longwave radiation flux within the urban canopy were calculated by the photon tracking method based on the Monte Carlo method. The albedo value obtained by this method shows close agreement with experimental data, and the average sky view factor shows almost perfect agreement with the theoretical value. Moreover, we calculated the urban albedo for the urban canopy configuration including roads and building height distribution.%Moreover, we calculated net radiation within the urban canopy in %consideration of roads and building height distribution.We found that the sky view factor of the ground surface is high when building coverage is low, building height is low, open space by roads exists, and building height is non-uniform. Moreover, we found that the albedo value is high when building height is small, open space by roads is wide, and building height is uniform. The albedo value was found to vary in a complicated manner with change in building coverage.  相似文献