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91.
Megan Damon Masanori C. Kameyama Michael Knox David H. Porter Dave Yuen Erik O. D. Sevre 《Visual Geosciences》2008,13(1):49-57
The current availability of thousands of processors at many high performance computing centers has made it feasible to carry
out, in near real time, interactive visualization of 3D mantle convection temperature fields, using grid configurations having
10–100 million unknowns. We will describe the technical details involved in carrying out this endeavor, using the facilities
available at the Laboratory of Computational Science and Engineering (LCSE) at the University of Minnesota. These technical
details involve the modification of a parallel mantle convection program, ACuTEMan; the usage of client–server socket based
programs to transfer upwards of a terabyte of time series scientific model data using a local network; a rendering system
containing multiple nodes; a high resolution PowerWall display, and the interactive visualization software, DSCVR. We have
found that working in an interactive visualizastion mode allows for fast and efficient analysis of mantle convection results.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
92.
Hidekazu Yoshida Koshi Yamamoto Yuki Murakami Nagayoshi Katsuta Toru Hayashi Takeshi Naganuma 《Environmental Geology》2008,55(6):1363-1374
Takashikozo is a phenomenon of Quaternary sediments in Japan. They are cylindrical Fe-oxyhydroxide nodules that form as plaques round
plant roots, where Fe is preferentially concentrated to develop a solid wall. Structural features suggest that after the roots
have decayed, the central space where the roots were situated acts as a flow path for oxidized water. Analysis of microbial
16S rDNA extracted from the nodules identified iron-oxidizing bacteria encrusted round the roots where they are the likely
initiators of nodule formation. Direct microscopic observation revealed an accumulation of Fe-oxyhydroxides that fill the
pore spaces and is also likely to be linked with the encrusting microbial colonies. Geological history and nanofossil evidence
suggest that these Fe-nodules may have been buried at a depth of up to several tens of meters for at least 105 years in reducing Quaternary sediments. Thus Fe-oxyhydroxide nodules that have formed in a geological environment at the
interfaces between water and rock by microbial mediation can persist under reducing conditions. If this is the case, the phenomenon
is significant as an analogue of post-closure conditions in radioactive waste repositories, since it could influence nuclide
migration. 相似文献
93.
Dr. S. Okamura Dr. G. Y. Wu Dr. C. H. Zhao Dr. H. Kagami Dr. T. Yoshida Dr. Y. Kawano 《Mineralogy and Petrology》1997,60(1-2):81-98
Summary Southwestern Yunnan, comprising the Yangtze and Shan-Thai microcontinents and the Simao block, has successively undergone subduction of an oceanic plate, followed by a collision of the microcontinents and intracontinental rifting associated with basaltic volcanism during Late Paleozoic to Mesozoic.The Triassic Nanjian basalts, erupted on the Yangtze microcontinent, have more enriched isotopic ratios and higher LREE/HFSE and LREE/HREE ratios. This suggests the existence of an enriched subcontinental lithosphere under the Yangtze microcontinent which stabilized over long periods of the earth's history (> 2Ga).The Middle Jurassic Simao basalts have more depleted geochemical features and also have element enrichments characteristic of a subduction zone environment, although the basalts were erupted in an intracontinental graben. It may be inferred that the lithospheric mantle of the Simao block was modified by subduction processes during Latest Carboniferous to Late Triassic prior to the onset of the Middle Jurassic continental rifting. The lack of correlation between depletion of HFSE, Y and HREE, and relative enriched Nd isotopic ratios suggests that the source depletion of the Simao basalts is not an old feature and has been contemporaneous with the subduction-related enrichment through mantle metasomatism shortly before the basalts were produced.The Middle Jurassic Baoshan basalts which erupted during the continental rifting on the Shan-Thai microcontinent have an Sr-Nd isotopic composition similar to the bulk earth and higher concentrations of incompatible trace elements. These features suggest that the subcontinental lithosphere under the Shan-Thai microcontinent underwent mantle metasomatism just prior to eruption of the Baoshan basalt.
With 8 Figures
Visiting Fellow, Geology Department, Australian National University, Australia 相似文献
Geochemie mesozoischer interkontinentaler Basalte aus Jünnan, Südchina: Hinweise auf die geochemische Entwicklung der subkontinentalen Lithosphäre
Zusammenfassung Südwestjünnan umfaßt den Jangtse und den Shan-Thai Mikrokontinent und den Simao Block. Das Gebiet wurde von aufeinander folgenden Subduktionsphasen einer ozeanischen Platte betroffen, auf die Kollision der Mikrokontinente und interkontinentales Rifting folgte. Dieses war mit basaltischem Vulkanismus während des späten Paläozoikums bis ins Mesozoikum assoziiert.Die triassischen Nanjian-Basalte, die auf dem Jangtse Mikrokontinent eruptierten, haben mehr angereicherte Isotopenverhältnisse und höhere LREE/HFSE und LREE/HREE Verhältnisse. Dieses weist auf eine angereicherte subkontinentale Lithosphäre unter dem Jangtse Mikrokontinent hin, die sich während langer Perioden der Erdgeschichte stabilisierte (>2Ga).Die mittel jurassischen Simao-Basalte haben eine mehr verarmte geochemische Signatur aber auch Elementanreicherungen, die für ein Subduktionszonen-Milieu charakteristisch sind, obwohl die Basalte in einem interkontinentalen Graben ausgetreten sind. Man kann daraus schließen, daß der lithosphärische Mantel des Simao-Blockes durch Subduktionsprozesse während des jüngsten Karbons bis in die späte Trias vor dem Beginn des mittel-jurassischen kontinentalen Riftings modifiziert worden war. Das Fehlen einer Korrelation zwischen der Anreicherung von HFSE, Y und HREE und relativ angereicherter Nd-Isotopenverhältnisse weist darauf hin, daß die Verarmung der Quelle der Simaobasalte nicht weit zurückreicht. Sie dürfte viel eher gleichaltrig mit der subduktions-bedingten Anreicherung durch Mantel-Metasomatose kurz vor der Entstehung der Basalte sein.Die mittel-jurassischen Baoshan-Basalte, die während des kontinentalen Riftings auf den Shan-Thai Mikrokontintent eruptierten, haben eine Sr-Nd-Isotopensignatur, die ähnlich der Gesamterde ist, jedoch höhere Konzentrationen inkompatibler Spurenelemente zeigt. All dies legt nahe, daß die subkontinentale Lithosphäre unter dem Shan-Thai-Mikrokontinent kurz vor der Eruption der Baoshan-Basalte von Mantel-Metasomatose betroffen worden ist.
With 8 Figures
Visiting Fellow, Geology Department, Australian National University, Australia 相似文献
94.
Hisatoshi Sato Miyuki Tahata Yusuke Sawaki Shigenori Maruyama Naohiro Yoshida Degan Shu Jian Han Yong Li Tsuyoshi Komiya 《地学前缘(英文版)》2016,7(4):663-671
Cap Carbonates overlie the Marinoan Snowball Earth-related glacial diamictite,and possibly record the drastic surface environmental change and biological evolution after the Snowball Earth.We conducted on-land drilling from the Liantuo Formation,through the Nantuo,to the lower Doushantuo Formation in the Three Gorges area of South China to collect fresh,continuous samples in the Three Gorges area.We obtained high-resolution chemostratigraphies of δ~(13)C and δ~(18)O values of carbonates from the topmost part of the Nantuo Formation to the Cap Carbonate,in order to decode the detailed surface environmental change in the shallow marine setting.The δ~(13)C chemostratigraphy possesses some unique characteristics:(1) stable δ~(13)C values as a whole,but ubiquitous low δ~(13)C anomalies through the Cap Carbonate,(2) increase of the δ~(13)C values from-3 to +5‰ across the C2/C3 boundary,(3) no δ~(13)C anomaly between the C1 and C2 boundary,and(4) presence of an anomalous high δ~(13)C value(+2.3‰)and a faint positive correlation between δ~(13)C and δ~(18)O values in the C1 unit.Evidence of quite low δ~(13)C anomalies(with a nadir of-41‰),ubiquitous negative δ~(13)C anomalies through the Cap Carbonate,and a high δ~(13)C anomaly accompanied with a faint positive correlation between δ~(13)C and δ~(18)O values in the C1 unit supports decomposition and formation of methane hydrate during Cap Carbonate formation.The drastic increase of δ~(13)C values from the upper C2 to C3 units indicates enhancement of primary productivity and organic carbon burial,possibly due to high continental fluxes after the Snowball Earth event,evidenced by high Sr isotope values.The increase is restricted to the proximal side of the inner shelf in South China,and the timing of the increase of δ~(13)C values of carbonates is earlier at Three Gorges area than any other area,suggesting that the enhancement of primary productivity started in the proximal environment because of higher continental influxes.The increase in oxygen contents of seawater due to the enhanced primary productivity possibly resulted in the emergence of multicellular animals soon after Cap Carbonate deposition. 相似文献
95.
The quasi-biweekly oscillation(QBWO) is the second most dominant intraseasonal mode over the western North Pacific(WNP) during boreal summer. In this study, the modulation of WNP tropical cyclogenesis(TCG) by the QBWO and its association with large-scale patterns are investigated. A strong modulation of WNP TCG events by the QBWO is found.More TCG events occur during the QBWO's convectively active phase. Based on the genesis potential index(GPI), we further evaluate the role of environmental factors in affecting WNP TCG. The positive GPI anomalies associated with the QBWO correspond well with TCG counts and locations. A large positive GPI anomaly is spatially correlated with WNP TCG events during a life cycle of the QBWO. The low-level relative vorticity and mid-level relative humidity appear to be two dominant contributors to the QBWO-composited GPI anomalies during the QBWO's active phase, followed by the nonlinear and potential intensity terms. These positive contributions to the GPI anomalies are partly offset by the negative contribution from the vertical wind shear. During the QBWO's inactive phase, the mid-level relative humidity appears to be the largest contributor, while weak contributions are also made by the nonlinear and low-level relative vorticity terms.Meanwhile, these positive contributions are partly cancelled out by the negative contribution from the potential intensity.The contributions of these environmental factors to the GPI anomalies associated with the QBWO are similar in all five flow patterns—the monsoon shear line, monsoon confluence region, monsoon gyre, easterly wave, and Rossby wave energy dispersion associated with a preexisting TC. Further analyses show that the QBWO strongly modulates the synoptic-scale wave trains(SSWs) over the WNP, with larger amplitude SSWs during the QBWO's active phase. This implies a possible enhanced(weakened) relationship between TCG and SSWs during the active(inactive) phase. This study improves our understanding of the modulation of WNP TCG by the QBWO and thus helps with efforts to improve the intraseasonal prediction of WNP TCG. 相似文献
96.
Sekiko Yoshida 《Planetary and Space Science》1965,13(12):1165-1170
It is shown that VLF emissions are greatly affected by the polar cap absorption caused by the bombardment of solar protons. Characteristics of the PCA effect on VLF emissions are examined and they are in agreement with those obtained by other studies, such as the polar blackout and the cosmic radio absorption. Therefore, the earlier conclusion that the occurrence frequency of VLF emissions decreases in high latitudes during magnetic storms is likely to be due to the PCA effect.
Taking this PCA effect into account, it is established that an enhancement of occurrence of VLF emissions occurs at geomagnetic latitudes lower than 67° during the magnetic storm. This suggests that enhanced VLF emissions during geomagnetic storms are generated in the co-rotating region of the magnetosphere or in the outer radiation belt, but not in the tail region. 相似文献
97.
Studies of mixing were done at the northern flank of Georges Bank in the summer and autumn of 1988. Two time-series of the evolution and intensity of microstructure were examined over a tidal period in the context of tidal forcing and the evolution of the density and velocity field at the site. From the CTD, ADCP and microstructure observations (EPSONDE) on Georges Bank, several interesting features of the mixing processes were found. High dissipation and diffusivity regions appear near the bottom of the Bank. Turbulence near the bottom is highest in intensity and reaches farthest from the bottom at peak tidal flow and diminishes in intensity and vertical extent as the flow decreases. The thickness of the bottom turbulent layer has its maximum value when the flow is strongest and the stratification is weakest. Characterization of the dissipation rate and turbulent diffusivities in respect to buoyancy frequency N, current shear S, Richardson Number Ri and ε/νN2 was done. Dissipation and χT showed little dependence on shear or N2 but decreased at larger Ri. χt was found to be higher in regions of higher N2 and increased as ε/νN2 increased. KT, K and Kν, were all highest near the bottom in excess of 10−2m2s−1 and decreased towards the surface. There was little suggestion of a dependence of mixing efficiency on S2, Ri or ε/νN2, but some indication that Γ decreases with decreasing N2. 相似文献
98.
On wave-free floating-body forms in heaving oscillation 总被引:1,自引:0,他引:1
Some wave-free heaving forms are obtained in a manner similar to Bessho's earlier work by using a source and vertical dipole combination to generate bulbous-shaped two and three-dimensional bodies which have zero radiation damping. Then the combinations of higher singularities, such as triple-pole and quadra-pole, are considered. Using the thin-ship approximation, where the boundary condition is satisfied on the centreline, a simple procedure for generating any arbitrary shape that has the same property is established. The existence of wave-free frequencies of such bodies are verified numerically, in two dimensions by a standard singularity-distribution method based on the actual body-contour and in three-dimensions by using vortex-ring distribution for an axisymmetric body. Experiments are carried out for the models obtained theoretically and the results support the theoretical predictions fairly well. Finally, some suggestions are made to apply such a wave-free body to a moored buoy to suppress its heaving oscillation. 相似文献
99.
The two-dimensional problem of wave transformation by, and motions of, moored floating objects is solved numerically as a boundary value problem by direct use of Green's identity formula for a potential function. The cross-sectional shape of the floating object, the bottom configuration and the mooring arrangements may be all arbitrary. For a given incident wave, the three modes of body motion, the wave system and mooring forces are all solved at the same time. A laboratory experiment is conducted to verify the theory. Generally good agreements between the theory and experiments are obtained as long as the viscous damping due to flow separation is small. A numerical experiment indicates that a conventional sluck mooring is to worsen the wave attenuation by a floating breakwater and that a properly arranged elastic mooring can considerably improve the wave attenuation by a floating breakwater. 相似文献
100.
Masanori Konda Norihisa Imasato Katsuya Nishi Takashi Toda 《Journal of Oceanography》1994,50(1):17-30
The sea surface emissivity in the infrared region is determined on the basis of data analyses. Net radiation, surface irradiance and other oceanographical and meteorological variables are measured throughout most of the year at the oceanographical observatory tower in Tanabe Bay, Japan. We have found that 0.984±0.004 is a reliable emissivity value from the night time data. Surface emission radiates not from the subsurface water but from the sea surface. The thermal skin layer on the sea surface, however, is disturbed and disappears under high wind speed over 5 m/s through the analyses of the radiation observation using the emissivity value of 0.984. Under low wind speed, the sea surface can be cooler or warmer than the subsurface due to overlying thermal conditions and the skin layer can be neutral as the transient process between them. By using an emissivity value of 0.984, the temperature difference between the sea surface temperature and the temperature determined from surface irradiance that has been reported in the satellite data analyses is found to be reduced by half. 相似文献