排序方式: 共有48条查询结果,搜索用时 15 毫秒
11.
E. Kallio T.L. Zhang R. Jarvinen P. Janhunen J.-A. Sauvaud J.-J. Thocaven H. Andersson K. Brinkfeldt M. Holmström M. Yamauchi W. Baumjohann A.J. Coates D.O. Kataria K.C. Hsieh M. Grande T. Säles P. Riihelä N. Krupp J.G. Luhmann S. Orsini A. Mura M. Maggi P. Brandt K. Szego R.A. Frahm J.R. Sharber P. Bochsler 《Planetary and Space Science》2008,56(6):796-801
Plasma and magnetic field measurements made onboard the Venus Express on June 1, 2006, are analyzed and compared with predictions of a global model. It is shown that in the orbit studied, the plasma and magnetic field observations obtained near the North Pole under solar minimum conditions were qualitatively and, in many cases also, quantitatively in agreement with the general picture obtained using a global numerical quasi-neutral hybrid model of the solar wind interaction (HYB-Venus). In instances where the orbit of Venus Express crossed a boundary referred to as the magnetic pileup boundary (MPB), field line tracing supports the suggestion that the MPB separates the region that is magnetically connected to the fluctuating magnetosheath field from a region that is magnetically connected to the induced magnetotail lobes. 相似文献
12.
The Domingos Petrolini Swamp, located on the Southern Coastal Plain of Rio Grande do Sul, near the town of Rio Grande, constitutes an ample holocene lagoonal deposit. Events related to the holocene transgression and their diverse phases of glacial-eustatic ocillations were found through palynological analysis. Bases on these palynological data, four distinct phases to the paleoenvironmental evolution of the ecosystem were identified. It has also shown a transgressive restricted marine sequence on the base , which suggests the existence of a coastal brackish lagoon or a marisme type of environment. Later, there was a gradation for continentality conditions along with a scarce pollinical record. The third phase is characterized by the presence of marine components and halophyte vegetation, showing another transgressive event in that place. Lastly, the end of direct marine influence over the swamp was recorded and also the vegetation development as it appears these days. 相似文献
13.
A. Galli P. Wurz S. Barabash Y. Futaana H. Gunell R. Lundin K. Brinkfeldt N. Krupp W. Baumjohann T.L. Zhang A.J. Coates D.O. Kataria K.C. Hsieh J.A. Sauvaud C. Mazelle M. Grande T. Sales P. Riihela J. Kozyra S. McKenna-Lawlor R. Cerulli-Irelli A. Milillo E. Roelof C.T. Russell D. Winningham J. Scherrer 《Planetary and Space Science》2008,56(6):807-811
The ASPERA-4 instrument on board the Venus Express spacecraft offers for the first time the possibility to directly measure the emission of energetic neutral atoms (ENAs) in the vicinity of Venus. When the spacecraft is inside the Venus shadow a distinct signal of hydrogen ENAs usually is detected. It is observed as a narrow tailward stream, coming from the dayside exosphere around the Sun direction. The intensity of the signal reaches several , which is consistent with present theories of the plasma and neutral particle distributions around Venus. 相似文献
14.
The equations governing the propagation of linear gravity waves in ice-covered waters of finite depth is delineated for the linear elastic deformation of the ice plates that are modeled as elastically supported. The possible limiting condition for the validity of the assumptions involved in the formulation of the problem is discussed. A solution procedure for the solution of the wave dispersion equation under ice is discussed and a set of coefficients synthesized using the properties of infinite series and Padé approximants. Direct application of these coefficients for the calculation of wave characteristics in ice-covered sea will eliminate the need for iterative procedure, and hence will reduce the computational time. The derived coefficients were used for the computation of the wave characteristics of laboratory simulated waves and compared with the values obtained through iteration and the error was found to be less than 2%. 相似文献
15.
U. Altenberger G. Prosser A. Grande C. Günter A. Langone 《Contributions to Mineralogy and Petrology》2013,166(4):975-994
Pseudotachylyte veins frequently associated with mylonites and ultramylonites occur within migmatitic paragneisses, metamonzodiorites, as well as felsic and mafic granulites at the base of the section of the Hercynian lower crust exposed in Calabria (Southern Italy). The crustal section is tectonically superposed on lower grade units. Ultramylonites and pseudotachylytes are particularly well developed in migmatitic paragneisses, whereas sparse fault-related pseudotachylytes and thin mylonite/ultramylonite bands occur in granulite-facies rocks. The presence of sillimanite and clinopyroxene in ultramylonites and mylonites indicates that relatively high-temperature conditions preceded the formation of pseudotachylytes. We have analysed pseudotachylytes from different rock types to ascertain their deep crustal origin and to better understand the relationships between brittle and ductile processes during deformation of the deeper crust. Different protoliths were selected to test how lithology controls pseudotachylyte composition and textures. In migmatites and felsic granulites, euhedral or cauliflower-shaped garnets directly crystallized from pseudotachylyte melts of near andesitic composition. This indicates that pseudotachylytes originated at deep crustal conditions (>0.75 GPa). In mafic protoliths, quenched needle-to-feather-shaped high-alumina orthopyroxene occurs in contact with newly crystallized plagioclase. The pyroxene crystallizes in garnet-free and garnet-bearing veins. The simultaneous growth of orthopyroxene and plagioclase as well as almandine, suggests lower crustal origin, with pressures in excess of 0.85 GPa. The existence of melts of different composition in the same vein indicates the stepwise, non-equilibrium conditions of frictional melting. Melt formed and intruded into pre-existing anisotropies. In mafic granulites, brittle faulting is localized in a previously formed thin high-temperature mylonite bands. migmatitic gneisses are deformed into ultramylonite domains characterized by s-c fabric. Small grain size and fluids lowered the effective stress on the c planes favouring a seismic event and the consequent melt generation. Microstructures and ductile deformation of pseudotachylytes suggest continuous ductile flow punctuated by episodes of high-strain rate, leading to seismic events and melting. 相似文献
16.
J. Aroba J. A. Grande J. M. Andújar M. L. de la Torre J. C. Riquelme 《Environmental Geology》2007,53(1):135-145
In this article, a set of clustering algorithms based on Fuzzy Logic and Data Mining are applied, allowing to obtain data
in the form of linguistic rules and charts about the behaviour of the Tinto and Odiel river estuary (SW Spain) affected by
Acid Mine Drainage (AMD). In order to provide researchers with no skills on data mining techniques an easy and intuitive interpretation,
we have developed a computer tool based on fuzzy logic that allows immediate qualitative analysis of the data contained in
a data from the estuary water chemical analyses, and serves as a contrast to functioning models previously proposed with classical
statistics. 相似文献
17.
Lunar X-ray fluorescence observations by the Chandrayaan-1 X-ray Spectrometer (C1XS): Results from the nearside southern highlands 总被引:1,自引:0,他引:1
S. Narendranath P.S. Athiray B.J. Kellett C.J. Howe M. Grande I.A. Crawford S. Lalita S.Z. Weider L.R. Nittler D. Rothery N. Bhandari M.A. Wieczorek the CXS team 《Icarus》2011,214(1):53-66
The Chandrayaan-1 X-ray Spectrometer (C1XS) flown on-board the first Indian lunar mission Chandrayaan-1, measured X-ray fluorescence spectra during several episodes of solar flares during its operational period of ∼9 months. The accompanying X-ray Solar Monitor (XSM) provided simultaneous spectra of solar X-rays incident on the Moon which are essential to derive elemental chemistry. In this paper, we present the surface abundances of Mg, Al, Si, Ca and Fe, derived from C1XS data for a highland region on the southern nearside of the Moon. Analysis techniques are described in detail including absolute X-ray line flux derivation and conversion into elemental abundance. The results are consistent with a composition rich in plagioclase with a slight mafic mineral enhancement and a Ca/Al ratio that is significantly lower than measured in lunar returned samples. We suggest various possible scenarios to explain the deviations. 相似文献
18.
S.Z. Weider B.J. Kellett B.M. Swinyard I.A. Crawford K.H. Joy M. Grande C.J. Howe J. Huovelin S. Narendranath L. Alha M. Anand P.S. Athiray N. Bhandari J.A. Carter A.C. Cook L.C. d'Uston V.A. Fernandes O. Gasnault M. Wieczorek 《Planetary and Space Science》2012,60(1):217-228
We present X-ray fluorescence observations of the lunar surface, made by the Chandrayaan-1 X-ray Spectrometer during two solar flare events early in the mission (12th December 2008 and 10th January 2009). Modelling of the X-ray spectra with an abundance algorithm allows quantitative estimates of the MgO/SiO2 and Al2O3/SiO2 ratios to be made for the two regions, which are in mainly basaltic areas of the lunar nearside. One of these ground tracks includes the Apollo 14 landing site on the Fra Mauro Formation. Within the 1σ errors provided, the results are inside the range of basaltic samples from the Apollo and Luna collections. The Apollo 14 soil composition is in agreement with the results from the January flare at the 1σ uncertainty level. Discrepancies are observed between our results and compositions derived for the same areas by the Lunar Prospector gamma-ray spectrometer; some possible reasons for this are discussed. 相似文献
19.
J. A. Grande T. Valente M. L. de la Torre M. Santisteban J. C. Cerón E. Pérez-Ostalé 《Environmental Earth Sciences》2014,71(6):2729-2738
The present work aims to propose a methodology for quantifying the sources of acid mine drainage (AMD) and to characterize the magnitude of the affected areas in the Iberian Pyrite Belt (SW Spain). Such an approach allows the creation of a support tool for managing land and natural resources valorization, which may be easily applied in similar mining regions. The motivation and usefulness of this work can be realized by focusing on two main emerging strategic issues: (1) water resources management, with the example of Alcolea dam that will receive water from affected areas in the Iberian Pyrite Belt; and (2) mineral resources valorization, especially, regarding copper exploration due to increasing market prices. The used methodology included the following general steps: it started with an inventory of the mines in the Iberian Pyrite Belt, followed by field cartography campaigns and finally the quantification of affected areas and contaminant discharges. The results of the present work serve to confirm and quantify the magnitude of the AMD pollution in the Pyrite Belt. A total affected area of about 4,847 ha was estimated. Taking into account this figure and combining it with the annual average precipitation (650 L/m2) results in an estimation of 31,503,680 m3/year of discharging water affected by the presence of sulphides. In this scenario, a total annual contribution of 260,056 tonnes/year was obtained for sulphates, which means more than 712 tonnes a day. In the case of arsenic, a toxic element, the total annual contribution is more than 20 tonnes, or close to 55 kg/day. Regarding copper, this economically interesting metal translates into total contributions of 10,364 tonnes/year in the generating medium. This gave more than 28 tonnes/day, which today sits at 8,200 dollars/tonne. This result suggests that solutions aimed at recovering this resource should be searched. It may represent a financial return at the same time that it would mean overcome environmental liabilities. 相似文献
20.
The instability of the sand–silt mixtures with different amount of fines contents were studied in this paper. It showed that the slope of the instability lines increases with the increasing relative densities, and it approaches the slope of the failure line (steady state line) at a high relative density. The relationship between the peak stress ratio and the intergranular void ratio can be described by a common curve for all the mixtures with fines contents less than the transitional fines content. There may also exist a unique curve for the relationship between the peak stress ratio and interfine void ratio for the mixtures with fines contents higher than the transitional fines content. If the yield strength ratio is used instead of the peak stress ratio, the relationships can be characterized in the same way. 相似文献