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81.
L. M. B. C. Campos 《地球物理与天体物理流体动力学》2013,107(4):193-215
Abstract We deduce the dissipative Alfvén wave equation in a medium stratified in one direction, with a transverse magnetic field, in the presence of dissipation by fluid viscosity and electrical resistance; the dissipative Alfvén wave equation generalizes earlier results for homogeneous (Cowling, 1960) and inhomogeneous (Campos, 1983a) media, and corrects an error in the literature (Heyvaerts and Priest, 1983). The wave equation is solved exactly in two cases: a uniform magnetic field, and a magnetic field decreasing with height. In both cases the mean state is assumed to be isothermal, with a constant rate of ionization, so that the magnetic diffusivity is constant, but the dynamic viscosity increases with height. There are therefore two regions, a low- (high-) altitude region where electrical resistance dominates fluid viscosity (or vice versa), and an asymptotic regime relevant to the uppermost (lowermost) layers. The two regions are separated by a transition layer, across which the wave field is continuous and whose structure is expressible by hypergeometric functions, with different arguments in the low- and high-altitude regions, and over the whole altitude range. These exact solutions allow the amplitude and phase of the wave field to be plotted as a function of height for a variety of magnetoatmospheric mean states. They show that wave dissipation is more localized and intense when the magnetic field decreases with height than when it is uniform. 相似文献
82.
Julio Cezar Mendes Silvia Regina de Medeiros Ian McReath Cristina Maria Pinheiro de Campos 《Gondwana Research》2005,8(3):337-345
In the central-southern region of Espírito Santo State, southeastern Brazil, several granitoids with a variable composition intruded high-grade metamorphic rocks, in the northern segment of the Ribeira fold belt. A close relationship between hydrous and anhydrous facies is present in some of the plutons, including the Varzea Alegre Igneous Complex, which has an inner domain formed by gabbro, diorite and granite, and an irregular outer ring of charnockitic rocks. These green megaporphyritic charnockites have primary anhydrous mineral assemblage, I-type and metaluminous character, and high-K calc-alkaline signature. U-Pb zircon single crystal ages obtained by TIMS indicate crystallization at about 500 Ma, similar to other late tectonic plutons of this part of the Ribeira belt. Sr and Nd isotopic ratios ranging from 0.7078 to 0.7096 and 0.5114 to 0.5116 respectively, are interpreted to be indicative of a hybrid origin from crustal and mantle-derived magmas. A binary diagram using Sr isotope ratios also demonstrates that the genesis of the charnockites probably included both magma mixing and fractional crystallization processes. 相似文献
83.
Ismar de Souza Carvalho Antonio de Celso Arruda Campos Pedro Henrique Nobre 《Gondwana Research》2005,8(1):11-30
Baurusuchus salgadoensis is a new baurusuchid crocodylomorph from Bauru Basin (Cretaceous), Brazil, partially preserved through a complete skull. The fossil comes from a fine sandstone sequence of Adamantina Formation, General Salgado County, São Paulo State. The sedimentary sequence where it was found, located in Fazenda Buriti, is considered Turonian-Santonian in age. The described species _Baurusuchus salgadoensis sp. nov. _ is a baurusuchid with an antorbital fenestra, double external nares with a bony septum, two well-fused supraorbitals, the supratemporal fenestrae larger than the orbits and a quadrangular-shaped laterotemporal fenestra. The position of the external nares, located on anterior and terminal portion of the rostrum together with the theropod-like lateral compression of the snout and teeth are indicators that Baurusuchus salgadoensis was a terrestrial crocodyliform. This was a carnivorous species and the lateral compression of the rostrum could be interpreted as a mechanism to increase the skull resistance forces during biting. The pointed, conical teeth, some with crenulated borders, could be used to perforate and to carve the prey. The geological context of Baurusuchus salgadoensis indicates that it probably lived in a hot and arid climate. 相似文献
84.
Maria da Glria Motta Garcia Mrio da Costa Campos Neto 《Journal of South American Earth Sciences》2003,15(8):853-870
Metamorphic conditions are described for three major tectonic entities on the basis of geothermobarometry in a huge Neoproterozoic nappe complex that verges toward the southern border of the São Francisco craton. The uppermost Socorro-Guaxupé Nappe, represented by its granulite facies basal portion, yields a maximum temperature and pressure of 890 °C and 11 kbar. Its metamorphic evolution is consistent with heating at the base of the crust as a result of an abnormally high geothermal gradient, probably due to underplating by the lithospheric mantle. The underlying Três Pontas-Varginha Nappe yields two somewhat distinct P–T paths, both characterized by peak assemblages in the kyanite stability field. The basal kyanite-bearing granulites show higher peak pressure values (15 kbar at 840 °C) and a trajectory that continues in the kyanite stability field, whereas the upper sillimanite granulites show higher temperatures (880 °C at 13 kbar) and a steeper path toward the sillimanite stability field. Data for the Carmo da Cachoeira nappe reveal a steep trajectory, in which the elevated maximum pressure (18.5 kbar at 820 °C) was obtained from a garnet amphibolite that lies along its basal contact. The inverted metamorphic pattern previously observed across these sequences is confirmed by our thermobarometric data, which reveal that the highest temperatures were attained toward the top of the pile. 相似文献
85.
The ‘algarrobo’Prosopis flexuosais an important food resource in the Monte Desert of Argentina. Native, domestic, and exotic mammals consume the fruit of this legume and disperse the seed through faeces. In the present study we analyse the effect that different dispersal agents (cattle, horse, European wild boar, rodents, gray fox) have on seed damage, viability, and germination. Cattle increase germination at the expense of reduced viability, whereas horses maintain viability but do not contribute to a prompt germination response. Among native mammals, the gray fox maintains seed viability without increasing germination, whereas rodents affect seed viability but enhance germination rates. The European wild boar, however, damages all of the seeds it consumes. 相似文献
86.
Jos Carlos Sales Campos Maurício Antnio Carneiro 《Journal of South American Earth Sciences》2008,26(4):463-484
The sialic crust of the southern São Francisco craton along the Jeceaba-Bom Sucesso lineament, central-southern part of Minas Gerais (Brazil), encompasses, among other rock types, Neoarchean and Paleoproterozoic granitoids. These granitoids, according to their petrographic, lithogeochemical and geochronologic characteristics, were grouped into two Neoarchean suites (Samambaia-Bom Sucesso and Salto Paraopeba-Babilônia) and three Paleoproterozoic suites (Cassiterita-Tabuões, Ritápolis and São Tiago). Varied processes and tectonic environments were involved in the genesis of these suites. In particular, the lithogeochemistry of the (Archean and Paleoproterozoic) TTG-type granitoids indicates an origin by partial melting of hydrated basaltic crust in a subduction environment. In the Neoarchean, between 2780 and 2703 Ma, a dominant TTG granitoid genesis related to an active continental margin was followed by another granite genesis related to crustal anatexis processes at 2612–2550 Ma. In the Paleoproterozoic, the generation of TTG and granites s.s. occurred at three distinct times: 2162, 2127 and 1887 Ma. This fact, plus the rock-type diversity produced by this granite genesis, indicates that the continental margin of the southern portion of the São Francisco craton was affected by more than one consumption episode of oceanic crust, involving different island arc segments, and the late Neoarchean consolidate continent. A Paleoproterozoic tectonic evolution in three stages is proposed in this work. 相似文献
87.
Andre Salvaro Furtado Luis Otavio Campos Alvares Nikos Pelekis Yannis Theodoridis Vania Bogorny 《International journal of geographical information science》2018,32(1):140-168
Trajectory data analysis and mining require distance and similarity measures, and the quality of their results is directly related to those measures. Several similarity measures originally proposed for time-series were adapted to work with trajectory data, but these approaches were developed for well-behaved data that usually do not have the uncertainty and heterogeneity introduced by the sampling process to obtain trajectories. More recently, similarity measures were proposed specifically for trajectory data, but they rely on simplistic movement uncertainty representations, such as linear interpolation. In this article, we propose a new distance function, and a new similarity measure that uses an elliptical representation of trajectories, being more robust to the movement uncertainty caused by the sampling rate and the heterogeneity of this kind of data. Experiments using real data show that our proposal is more accurate and robust than related work. 相似文献
88.
Leandro Duarte Campos Sulsiene Machado de Souza Diogo Alves de Sordi Felipe Mattos Tavares Evandro Luiz Klein Elem Cristina dos Santos Lopes 《Natural Resources Research》2017,26(4):509-534
The Gurupi Belt hosts a Paleoproterozoic gold province located in north–northeastern Brazil, at the borders of Pará and Maranhão states. It is considered to be an extension of the prolific West African Craton’s Birimian gold province into South America. Additionally, the belt has been the object of recent mineral exploration programs with significant resource discoveries. This study presents the results of predictive mapping using up-to-date mineral system concepts and recently finished regional-scale geological mapping, stream sediment and airborne geophysical surveys conducted by the Geological Survey of Brazil. We relate gold mineralization to an initially enriched crust, metamorphism, deep fluid pathways, structurally controlled damage zones and hydrothermal alteration. Prospective targets were generated using only regional public datasets and knowledge-driven targeting technique. This work did not incorporate any known gold deposits, yet it predicted the largest known deposits and their satellite targets. Besides, high prospective targets mapped almost 40% of known primary gold occurrences within 7% of the project area. This work allowed considerable search area reduction and identification of new target areas, thus collaborating on reducing costs, time and risk of mineral exploration. Results indicate that we achieved an efficient understanding of the geological processes related to the Gurupi Belt mineral system. 相似文献
89.
Gervasio Degrazia Domenico Anfossi Haroldo Fraga De Campos Velho Enrico Ferrero 《Boundary-Layer Meteorology》1998,86(3):525-534
A new method for deriving the Lagrangian decorrelation time scales for inhomogeneous turbulence is described. The expression for the time scales here derived for the convective boundary layer is compared to those estimated by Hanna during the Phoenix experiment. Then the values of C0, the Lagrangian velocity structure function constant, and of Bi, the Lagrangian velocity spectrum constant, were evaluated from the Eulerian velocity spectra and from the Lagrangian time scales derived, under unstable conditions, from Taylor's statistical diffusion theory. The numerical coefficient of the lateral and vertical Lagrangian spectra in the inertial subrange was found equal to 0.21, in good agreement with previous experimental estimates. 相似文献
90.
Caio A. S. Coelho Cristiano Prestrelo de Oliveira Tércio Ambrizzi Michelle Simões Reboita Camila Bertoletti Carpenedo José Leandro Pereira Silveira Campos Ana Carolina Nóbile Tomaziello Luana Albertani Pampuch Maria de Souza Custódio Lívia Marcia Mosso Dutra Rosmeri P. Da Rocha Amanda Rehbein 《Climate Dynamics》2016,46(11-12):3737-3752