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排序方式: 共有764条查询结果,搜索用时 15 毫秒
731.
Itziar Aretxaga David H. Hughes Kristen Coppin Angela M. J. Mortier Jeff Wagg James S. Dunlop Edward L. Chapin Stephen A. Eales Enrique Gaztañaga Mark Halpern Rob J. Ivison Eelco van Kampen Douglas Scott Stephen Serjeant Ian Smail Thomas Babbedge rew J. Benson Scott Chapman David L. Clements Loretta Dunne Simon Dye Duncan Farrah Matt J. Jarvis Robert G. Mann Alexandra Pope Robert Priddey Steve Rawlings Marc Seigar Laura Silva Chris Simpson Mattia Vaccari 《Monthly notices of the Royal Astronomical Society》2007,379(4):1571-1588
732.
L. A. L. Da Silva 《Astrophysics and Space Science》1993,202(2):215-236
The present status of the Minkowski-Zwicky supernova classification is reviewed. Some very recent theoretical and observational results are mentioned, and their direct impact in our knowledge of the physics of supernovae and their classification are discussed. We also examine the possibility of imagine an alternative based taxonomy for supernovae, derived mainly from what we know about the physical processes involved in those stars, trying to correlate these physical types to the observational evidences available, in order to see if such a scheme would be useful, in practical terms. 相似文献
733.
U---Pb SHRIMP and Sm---Nd age constraints on the timing and sources of the Pan-African Cape Granite Suite, South Africa 总被引:1,自引:0,他引:1
L.C. Da Silva P.G. Gresse R. Scheepers N.J. McNaughton L.A. Hartmann I. Fletcher 《Journal of African Earth Sciences》2000,30(4):164
Geochemical and isotopic U---Pb SHRIMP and Sm---Nd studies in three granitic plutons from the Pan-African Neoproterozoic/Cambrian Saldania Mobile Belt, southwestern South Africa supports differences in the sources and timing of emplacement of the main plutons related to the Cape Granite Suite as established by previous researchers. The Phase I, early syn-tectonic Darling Batholith Granitoid reflects an overall peraluminous chemical signature compatible with derivation mainly from melts extracted from paraderived crustal sources (Sa1 association). The Phase II, late to post-tectonic Robertson Pluton, reflects affinities to the Australian l-type granites (1a association). Despite the good structural constraints on the syn- and post-tectonic origin, the U---Pb ages point to a broadly synchronous crystallisation episode at 547±6 Ma and 536±5 Ma, respectively. In addition to U---Pb, Nd isotopic studies were also carried out for both plutons, as well as for the Riviera Granite, another phase II (1a association) pluton. The initial εNd (550 Ma) based on a depleted mantle model range from −3.5 (Darling), to −3.1 (Robertson) and to −2.6 (Riviera). The Nd mean crustal residence ages are 1559 Ma for Darling, 1626 Ma for Robertson and 1243 Ma for Riviera. Despite the small databank, a dominant Mesoproterozoic ( 1600 Ma) crust may be seen as the best candidate to explain the model TDM ages obtained. All the data largely overlap with others recently obtained for other plutons within the Cape Granite Suite and cast doubts on the current correlation between Saldania and the southeastern Brazilian, Dom Feliciano Belts. 相似文献
734.
Sunspots have an obvious direct effect upon the visible radiant energy falling upon the Earth. We show how to estimate this effect and compare it quantitatively with recent observations of the solar total irradiance (Willson et al., 1981). The sunspots explain about half of the total observed variance of one-day averages. Since the sunspot effect on irradiance produces an asymmetry of the solar radiation, rather than (necessarily) a variation of the total luminosity, we have also estimated the sunspot population on the invisible hemisphere. This extrapolation allows us to estimate the true luminosity deficit produced by sunspots, in a manner that tends toward the correct long-term average value. We find no evidence for instantaneous global re-emission to compensate for the sunspot flux deficit. 相似文献
735.
A brief summary about the composition and origins of the U deposit is present. The mineralization is composed by secondary uranium phosphates (saleeite and meta-saleeite). The precipitation was probably the main responsible factor for U retention within the quartz veins leading to the uranium phosphate mineralization of Vale de Abrutiga. 相似文献
736.
Paula Galego Fernandes Paula Carreira Manuel Oliveira da Silva 《Mathematical Geology》2006,38(6):765-780
The Sines coastal sedimentary basin, a tectonic trough with a NE-SW orientation filled with Mesozoic and Cenozoic deposits,
has two hydrogeological systems: the Mio-Pliocene and the Jurassic. Both systems are supplying water to the entire region
with highly populated and industrialized areas. The aquifers are recharged in the outcrop areas, although the Jurassic aquifer
also receives some contribution from the overlying Miocene rocks. The main groundwater flow direction in the Jurassic aquifer
is E to W towards the Atlantic Ocean.
In order to understand the influence of anthropogenic activities on the water quality, a statistical principal components
analysis (PCA) was performed on the physical–chemical data from groundwater samples in both aquifers. Four components were
obtained in the Jurassic and three in the Miocene. The principal components analyses indicate water–rock interactions as the
major mechanism responsible for the groundwater solutes (mainly calcium-bicarbonate type), from the calcareous and dolomitic
units. Anthropogenic contamination was identified in the influence of the water compositions, corresponding to local polluting
inputs. These were magnesium, sulfate, nitrate, iron and copper for PC 3 in the Jurassic and sodium, chloride, nitrate and
manganese for PC 2 in the Miocene. These account for about 13% of the system total variance in the Jurassic aquifer and near
23% in the Miocene one. 相似文献
737.
Cabral Victor Carvalho Reis Fábio Augusto Gomes Vieira D’Affonseca Fernando Mazo Lucía Ana dos Santos Corrêa Claudia Vanessa Veloso Vinicius Gramani Marcelo Fischer Ogura Agostinho Tadashi Lazaretti Andrea Fregolente Vemado Felipe Pereira Filho Augusto José dos Santos Claudia Cristina Lopes Eymar Silva Sampaio Rabaco Lis Maria Reoni do Carmo Giordano Lucilia Zarfl Christiane 《Natural Hazards》2021,108(3):3021-3043
Natural Hazards - Debris flows represent great hazard to humans due to their high destructive power. Understanding their hydrogeomorphic dynamics is fundamental in hazard assessment studies,... 相似文献
738.
Efflorescent nanophases(NPs)are found as a transitory accumulation of potentially hazardous elements(PHEs),particularly in tropical climates.The central objective of this study was to investigate the distribution of PHEs with NPs through the evaporative formation structures(EFS)of enormously PHEs-rich coal-mine drainages(CMD).The EFS were studied in natural coal mine drainage for five months in order to determine their geochemical and ecological structures and to assess their position in the reduction of PHEs in nature.The largest coal-fired power plant in South America,located in south Brazil,is used as an example of such a problem.In this work,a novel methodology for the analysis of PHEs in CMD precipitates is proposed for this affected coal area.The analytical method,combining X-Ray Diffraction(XRD)and advanced electron microscopies,shows the importance of nanomineralogy in understanding different circumstances of coal contamination.Several ultrafine-nanoparticles(UNPs)were identified in the sampled soils and river sediments together with the PHEs.A decrease in PHEs was identified in association with UNPs.However,further investigations are required with regard to the mobility of PHEs in water,atmosphere,soils,and sediments.The EPS was thoroughly studied,acquiring suitable understanding with investigational facts for Ca and Fe-sulphates,pickeringite,and several amorphous phases. 相似文献
739.
Hamza Valiya M. Vieira Fabio P. Silva Raquel T. A. 《International Journal of Earth Sciences》2018,107(1):19-33
International Journal of Earth Sciences - A comprehensive analysis of thermal gradient and heat flow data was carried out for sedimentary basins situated in the continental margin of Brazil (CMB).... 相似文献
740.
Ludmila de Freitas Marcílio Vieira Martins Filho José Carlos Casagrande Ivanildo Amorim de Oliveira Luiz Gabriel da Silva 《Environmental Earth Sciences》2018,77(18):642
The evaluation of soil quality is an important tool for degradation monitoring and sustainable management implementation. The objective of this study was to measure physical and chemical soil properties to set soil quality and validate a model of soil quality indicator in latosols (oxisols) under sugarcane cropping and native forest. The study was carried out in the cities of Araras, Santa Ernestina, and Guariba in São Paulo State, Brazil. We collected 24 samples of disturbed and undisturbed soil at 0.0–0.10 m layer from three areas grown with sugarcane and neighboring locations under native woodland. We assessed the following soil properties: (a) chemical—pH in CaCl2, organic matter (OM), phosphorus (P), potassium (K+), calcium (Ca2+), magnesium (Mg2+), potential acidity (H?+?Al), aluminum (Al3+), and sulfur (S); (b) physical—macro- and microporosity, soil bulk density (Ds), aggregate stability, mean weight diameter (MWD), rill (Kr) and interrill (Ki) global erodibility, shear stress (τc), and magnetic susceptibility (MS). Data underwent multivariate statistics to identify the properties that denote soil quality and to set their weights within the functions of soil quality indicator (SQI). This study showed that the multivariate analysis was efficient in determining which physical and chemical properties were most sensitive, of which we can mention total sand, MS, clay, microporosity, Mg, Ca, pH, and OM. We can therefore conclude that the quality indicators of soils grown with sugarcane were lower than those under forest were, showing the need for adoption of conservation management practices. 相似文献