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51.
M. C. Lima e Cunha V. P. Pereira E. Menegotto A. C. Bastos Neto L. D. Oliveira M. L. L. Formoso 《Environmental Geology》2008,55(6):1355-1362
The vegetal species Ampelozizyphus amazonicus Ducke (Rhamnaceae Family) was chosen as a sampling medium for the lateritic surfaces of the Pitinga Mine in the Amazon region,
in order to study the biogeochemical behavior of this species and compare it with the chemical composition of a reference
plant. The Pitinga mining district is one of the largest producers of tin in the world. This district contains unique deposits
of cryolite and rare metals such as Zr, Nb, Ta, Y and REEs related to granitic bodies that intrude into the volcanic and acid
pyroclastic rocks. The results showed that the species A. amazonicus predominantly concentrates significant levels of Zr, Nb, Ta, Th, Be, Sc over U, Hf, Ga and In. These elements are characteristic
of the mineral paragenesis for the region, suggesting that this plant can provide a representative sampling medium future
geochemical exploration programs in the region. 相似文献
52.
Carlos J. P. Rosa Jocelyn McPhie Jorge M. R. S. Relvas Zélia Pereira Tomás Oliveira Nelson Pacheco 《Mineralium Deposita》2008,43(4):449-466
In the Iberian Pyrite Belt, volcanic rocks are relatively scarce, accounting for approximately only 25% of the geologic record,
with the remaining 75% consisting of sedimentary units. This association is very clear in the host succession to the Neves
Corvo massive sulfide deposit in Portugal. The Neves Corvo host succession comprises the products of explosive and effusive
rhyolitic eruptions intercalated with mudstone that records a submarine below-wave-base environment and provides precise biostratigraphic
age constraints. The first and second volcanic events involved eruptions at local intrabasinal vents. The first event generated
thick beds of fiamme breccia that are late Famennian in age. The fiamme were originally pumice clasts produced by explosive
eruptions and were subsequently compacted. The second event was the late Strunian (latest Famennian) effusion of rhyolitic
lava that was pervasively quench-fragmented. The third and final event is younger than the massive sulfide deposits poorly
represented in the mine area and minor compared with the two other events. The integration of biostratigraphic data with the
volcanic facies architecture indicates that the Neves Corvo ore deposits are similar in age to the late Strunian rhyolitic
lava. Although regionally the Iberian Pyrite Belt is essentially a sedimentary succession, ore formation at Neves Corvo can
be closely linked to discrete volcanic events that produced a relatively narrow range of volcanic facies. 相似文献
53.
J. J. Pereira J. Ziskowski R. Mercaldo-Allen C. Kuropat D. Luedke E. Gould 《Estuaries and Coasts》1992,15(3):289-297
Vitellogenin is an egg-yolk precursor protein in teleosts which is crucial to the survival of larvae. Manufactured in the liver, where pollutants are known to accumulate, and transported to the ovary by the blood, its synthesis by the liver or uptake by the gonad can be compromised by accumulation of xenobiotics. In three studies, winter flounder (Pleuronectes americanus) blood samples were taken to determine normal levels of vitellogenin during the reproductive cycle, and to learn how its production might be affected in degraded environments. Specifically, these studies followed the seasonal cycle of vitellogenin production in winter flounder through monthly sampling at relatively clean (Shoreham, New York) and degraded areas (Black Rock and New Haven harbors, Connecticut) in Long Island Sound; examined the relationship between parental vitellogenin levels and survival of offspring by sampling fish that had been spawned at the Milford Laboratory for a reproductive success study; and determined the effect of gross liver lesions on vitellogenin production by sampling flounder from Boston Harbor, Massachusetts, which have been reported to have a high prevalence of liver tumors. Blood vitellogenin levels were determined by measuring alkali-labile phosphate (ALP). Large fish (>30 cm) from the two degraded sites had elevated serum ALP levels relative to those from the clean area. Lowered total ovarian lipid levels in large fish from Black Rock Harbor suggested impaired vitellogenin uptake. There were no significant differences in serum ALP among the small (≤30 cm) fish from the three sampling sites. Boston Harbor flounder with gross liver lesions had lower ALP values than fish without such lesions. There were no significant differences in ALP values among the spawned fish. 相似文献
54.
Claudio Bastos Pereira 《Astrophysics and Space Science》1996,240(1):1-11
EG And is a S-type symbiotic star. Presented are UV observations made by IUE from 1978 to 1991. From these observations the electron density and the electron temperature were obtained. The size of the Heii emitting region was estimated as 7.3R. Line and continuum variations confirm the binary nature of EG And. 相似文献
55.
A two-surface plasticity model for stiff clay 总被引:1,自引:1,他引:0
This paper presents a constitutive model for describing some important features of the behavior of natural stiff clay evidenced experimentally such as the limited elastic zone, the presence of strain hardening and softening, and the smooth transition from elastic behavior to a plastic one. The model, namely ACC-2, is an adapted Modified Cam Clay model with two yield surfaces: similarly to bounding surface plasticity theory, an additional yield surface—namely Inner yield surface—was adopted to account for the plastic behavior inside the conventional yield surface. A progressive plastic hardening mechanism was introduced with a combined volumetric-deviatoric hardening law associated with the Inner yield surface, enabling the plastic modulus to vary smoothly during loading paths. The main feature of the proposed model is that its constitutive equations can be simply formulated based on the consistency condition for the Inner yield surface, so that it can be efficiently implemented in a finite element code using a stress integration scheme similar to that of the Modified Cam Clay model. Furthermore, it is proved to be an appropriate model for natural stiff clay: the simulations of a set of tests along different mechanical loading paths on natural Boom Clay show good agreement with the experimental results. 相似文献
56.
57.
Andre Frossard Pereira de Lucena Roberto Schaeffer Alexandre Salem Szklo 《Global Environmental Change》2010,20(2):342-350
Global climate change induced by the emission of greenhouse gases may pose challenges to energy security. The vulnerability of energy sources, in particular of renewable sources, to climate change raises the need to identify adaptation measures. This paper applies an integrated resource planning approach to calculate least-cost adaptation measures to a set of projected climate impacts on the Brazilian power sector. The methodology used has the advantage of finding optimal solutions that take into consideration the whole energy chain and the interactions between energy supply and demand. Results point in the direction of an increased installed capacity based, mostly, on natural gas, but also sugarcane bagasse, wind power and coal/nuclear plants, to compensate for a lower reliability of hydroelectric production, amongst other impacts. The indirect effect of these results is the displacement of natural gas from other consuming sectors, such as industry, in favor of its use for power generation. Results obtained are, however, based on the techno-economic premises used in the simulation, which may vary in the long term. 相似文献
58.
The model proposed in this article relates permeability to porosity measurements that can easily be performed in the laboratory. The pore size distribution (PSD) curve is updated with strains and damage. The updated volumetric fractions of natural pores and cracks are introduced in the expression of permeability. Contrary to classical permeability models based on PSD integrations, the model proposed in this article accounts for possible changes in the porosity modes: one mode for undamaged samples and two modes for cracked samples. The proposed approach also accounts for varying states of damage, as opposed to classical fracture network models, in which the cracks pattern is fixed. The only material parameters that are required to describe the microstructure are the lower and upper bounds of the pores size for both natural pores and cracks. All the other PSD parameters involved in the model are related to macroscopic parameters that can easily be determined in the laboratory, such as the initial void ratio. The framework proposed in this article can be used in any damage constitutive model to determine the permeability of a brittle porous medium. Drained triaxial compression tests have been simulated. Before cracks initiation, permeability decreases while the larger natural pores are getting squeezed. After the occurrence of damage, permeability grows due to the increase of cracks density. The model performs well to represent the influence of the confining pressure on damage evolution and permeability variations. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
59.
de Luna Rejane Maria Rodrigues dos Anjos Garnés Silvio Jacks da Silva Pereira Cabral Jaime Joaquim dos Santos Sylvana Melo 《Natural Hazards》2021,106(3):1821-1837
Natural Hazards - Recife Metropolitan Region, in the northeast of Brazil, is formed by a coastal plain bounded by hills and by the Atlantic Ocean. Recife Metropolitan Region has about 4 million... 相似文献
60.
Pereira E Abreu SN Coelho JP Lopes CB Pardal MA Vale C Duarte AC 《Marine pollution bulletin》2006,52(11):1450-1457
The main objective was to study the seasonal variation of mercury concentrations in different tissues (muscle, hepatopancreas and gills) of Carcinus maenas from low and high Hg contaminated areas, a valuable resource in temperate estuaries and a possible pathway for human uptake. Individuals of two size classes (around 35 and 55 mm cephalothorax wide) were captured monthly between March 1999 and May 2000 in two areas of Ria de Aveiro: in the main navigation channel that connects the lagoon to the sea, and in the inner lagoon area heavily contaminated by mercury (maximum Hg in sediments of 5.4 microg g(-1)). Pronounced decreases in salinity and temperature and reduced food availability in winter seemed to be the responsible for the decline of the crab condition index (0.75-0.45) in larger individuals. Muscle and hepatopancreas exhibited higher mercury concentrations than gills, with concentrations in the contaminated site ranging from 0.03 to 0.63 microg g(-1) and 0.02 to 0.34 microg g(-1), respectively. Linear regressions between muscle and hepatopancreas (r=0.94, p<0.001) and muscle and gills (r=0.97, p<0.001) suggested a rapid redistribution of mercury inside the organism. During winter, a rapid elimination of mercury was found in the three analysed tissues followed by uptake. Larger crabs presented elimination rates from 18 to 34 ng g(-1) per week, while the smaller crabs showed lower elimination rates (10-24 ng g(-1) per week). The uptake was similar in both size classes (11-15 ng g(-1) and 8.1-15 ng g(-1) per week, respectively for large and small crabs). Our results suggest that C. maenas harvested in the contaminated areas must be considered with caution, since Hg concentrations were found to exceed the threshold concentration allowed for human consumption (0.5 microg g(-1)). 相似文献