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71.
Geochemistry of granites and metasediments of the urban area of Vila Real (northern Portugal) and correlative radon risk 总被引:2,自引:2,他引:0
M. E. P. Gomes L. J. P. F. Neves F. Coelho A. Carvalho M. Sousa A. J. S. C. Pereira 《Environmental Earth Sciences》2011,64(2):497-502
Radon concentration was evaluated in dwellings of the urban area of Vila Real (Northern Portugal). The area is mainly composed
of Hercynian granites and Cambrian metasediments, and CR-39 passive detectors (n = 112) were used for the purpose. The results obtained in winter conditions suggest that the most productive geological unit
is the Hercynian granite G1 (geometric mean of 364 Bq/m3), while Cambrian metasediments of the Douro Group show the lowest average indoor radon concentration (236 Bq/m3). The geological, geochemical and radiological data obtained suggest that the most effective control on the radon concentrations
of the area is related with the uranium content of the rocks; indeed, the highest contents were observed in granite G1 (21 ppm)
and the lowest in the metasediments (3 ppm). This is also confirmed by the results obtained for groundwater, where granites
present the highest concentrations of dissolved radon (up to 938 Bq/l), uranium (5–18 ppb) and gross α activities (0.47–0.92 Bq/l). No important radiometric anomalies were found in relation with geological structures such as
faults, veins and contacts, but a moderate increase of the uranium content can occur locally in such structures. Petrographic
observations and SEM studies show that uranium is mainly contained within the rock in heavy accessory minerals (apatite, zircon,
monazite, xenotime), which reduces radon emanation. Notwithstanding, due to the high U contents granites show a significant
potential to induce indoor radon concentrations in dwellings in excess of the recommended value of 400 Bq/m3. Overall, we can conclude that the region of Vila Real presents a moderate to high radon risk in dwellings and groundwater. 相似文献
72.
Mário André Trindade Dantas Rodrigo Parisi Dutra Alexander Cherkinsky Daniel Costa Fortier Luciana Hiromi Yoshino Kamino Mario Alberto Cozzuol Adauto de Souza Ribeiro Fabiana Silva Vieira 《Quaternary Research》2013,79(1):61-65
During the Pleistocene a fauna composed of large (biomass > 44 kg) and giant mammals (biomass > 1000 kg) that are usually associated with open environments lived in the Brazilian Intertropical Region. We present here new information concerning the paleoecology and chronology of some species of this megafauna. Carbon isotope analyses were performed for a better understanding of the paleoecology of the species Eremotherium laurillardi (Lund, 1842), Notiomastodon platensis (Ameghino, 1888) and Toxodon platensis (Owen, 1849). The δ13C data allow attributing a generalist diet to these species, which varied according to the kind of habitat in which they lived. In more open habitats all species were grazers; in mixed habitats E. laurillardi and T. platensis were mixed feeders, and N. platensis was grazer; and in more closed habitats all species were mixed feeders. 相似文献
73.
In this work, the Bader’s topological analysis of the electron density, coupled with Thom’s catastrophe theory, was used to characterize the pressure-induced transformations in α-quartz. In particular, ab initio calculations of the α-quartz structures in the range 0–105 Gpa have been performed at the HF/DFT exchange–correlation terms level, using Hamiltonians based on a WC1LYP hybrid scheme. The electron densities calculated throughout the ab initio wave functions have been analysed by means of the Bader’s theory, seeking for some catastrophic mechanism in the sense of Thom’s theory. The analysis mainly showed that there is a typical fold catastrophe feature involving an O–O interaction at the quartz–coesite transition pressure, while the amorphization of α-quartz is coincident with an average distribution of the gradient field of the electron density around the oxygen atom which is typically observed in the free atoms. This approach is addressed to depict a phase transition from a novel viewpoint, particularly useful in predicting the stability of a compound at extreme conditions, especially in the absence of experimental data. 相似文献
74.
Giovanni Dolif Andre Engelbrecht Alessandro Jatobá Antônio José Dias da Silva José Orlando Gomes Marcos R. S. Borges Carlos A. Nobre Paulo Victor R. de Carvalho 《Natural Hazards》2013,65(3):1831-1847
Natural disasters, particularly those triggered by heavy rainfall, may cause major damage and death. However, if an accurate early warning is issued, the damage can be mitigated. In Latin America and Brazil, characteristics of socioeconomic development often lead to a disorderly growth of cities and, consequently, occupation and irregular construction in risk areas. Therefore, forecasts of heavy rainfall, as well as preventative and mitigatory actions based on meteorological data/alerts, are essential to saving lives and minimizing material loss. An event that would have benefited from such actions is that which occurred in the mountainous region of Rio de Janeiro in January 2011, when over 800 people lost their lives. This work describes the first research initiative on resilience engineering domain in systems to forecast heavy rains in Rio de Janeiro. The results indicate important sources of brittleness in the system that supports the work of meteorologists, mainly related to the technical and organizational framework, and suggests that the main source of resilience in dealing with critical situations is the tacit knowledge of experts. 相似文献
75.
David Valença Dantas Mario Barletta Jonas de Assis Almeida Ramos André Ricardo Araújo Lima Monica Ferreira da Costa 《Estuaries and Coasts》2013,36(2):237-256
This study describes the seasonal feeding habits of different size classes of Cathorops spixii and Cathorops agassizii along an estuarine ecocline and the food overlap when different size classes occur together. These species were essentially zoobenthivorous, feeding mainly on Polychaeta Nereis sp., Copepoda Pseudodiaptomus acutus, Ostracoda Asterope sp., Gastropoda: Littorinidae, and Bivalvia Mytilus sp. and Anomalocardia brasiliana. However, during their life cycle and between different habitats and seasons, their trophic guild can change to zooplanktivore. The competition for resources was observed among C. spixii and C. agassizii, but was significantly reduced due to the seasonal diference in habitat use by different ontogenetic phases in the main channel of the estuary. The food niche separation was strongly influenced by environmental fluctuations, principally of salinity, resulting from rainfall and river inflow. High abundance of some preys, such as P. acutus (all estuary), Asterope sp. (upper and middle estuary), and Littorinidae (upper and lower estuary), could influence the significant diet overlap, principally during the rainy season, and call for more detailed studies of the benthic community structure. Moreover, dietary overlap was observed mainly between smaller sizes (intraspecific and/or interspecific) or between corresponding ontogenetic phases (interspecific), suggesting some differentiation in the diet in relation to the size class. Differences in prey type and size between the different ontogenetic phases of these ariids, principally among juveniles and adults, could be related to the size of the mouth, since adults are able to successfully capture larger preys or larger quantities of particular items. 相似文献
76.
77.
Reinaldo L. Bozelli Adriano Caliman Rafael D. Guariento Luciana S. Carneiro Jayme M. Santangelo Marcos P. Figueiredo-Barros Joo J.F. Leal Adriana M. Rocha Letícia B. Quesado Paloma M. Lopes Vinicius F. Farjalla Claudio C. Marinho Fabio Roland Francisco A. Esteves 《Limnologica》2009,39(4):306-313
Human activities are exposing freshwater ecosystems to a wide range of stressors, whose direct and indirect effects can be alleviated or exacerbated through interactive effects with dynamic environmental drivers. This study used long-term data from two Neotropical lacustrine freshwater systems (Batata Lake, an Amazonian floodplain lake and Imboassica lagoon, an Atlantic coastal lagoon) subjected to different kinds of environmental fluctuations (i.e., flood pulse and sandbar opening) and anthropogenic impacts (i.e., siltation and eutrophication). Our objective was to determine whether the effects of human perturbations are contingent on modifications of important biotic and abiotic characteristics through environmental variability. For both ecosystems, environmental variability consistently interacted with anthropogenic perturbations to alter most of the variables analyzed, such as nutrient dynamics, chlorophyll-a concentration, zooplankton and benthic invertebrate species richness, and temporal community stability, which indicates that interactive effects between environmental variability and anthropogenic perturbations may impact a myriad of ecosystem properties. Furthermore, the nature of these interactive effects was highly dependent on the variable considered and on the ecosystem analyzed. For example, at Imboassica lagoon, sandbar openings interacted synergistically with trophic state to increase the phosphorus concentration in the water column. At Batata Lake, flooding generally alleviated the negative effects of siltation on species richness by both diluting inorganic suspended material concentration and by promoting local recruitment from the regional species pool. Such results indicate that our ability to understand and predict the outcome of anthropogenic impacts on inland aquatic systems can be hampered if we consider human stressors as “static” phenomena disconnected from dynamic interactions with major local environmental drivers. 相似文献
78.
New limits on the cosmic equation of state are derived from age measurements of three recently reported old high-redshift galaxies (OHRG). The results are based on a flat Friedmann–Robertson–Walker (FRW) type cosmological model driven by non-relativistic matter plus a smooth component parametrized by its equation of state p x ωρ x ( ω −1). The range of ω is strongly dependent on the matter density parameter. For ΩM ∼0.3, as indicated from dynamical measurements, the age estimates of the OHRG restrict the cosmic parameter to ω −0.27. However, if ΩM is the one suggested by some studies of field galaxies, i.e., ΩM ≃0.5, only a cosmological constant ( ω =−1) may be compatible with these data. 相似文献
79.
It is known that stellar winds from late type stars are of mixed thermal and magnetic origin. The stellar wind model presented in this work uses the hydrodynamic equations of mass and momentum conservation and closes the system of equations with a detailed energy equation. Both momentum and energy equations have terms due to the effects of Alfvén waves. A smooth transition between the two regimes for Alfvén wave propagation, the undamped and the damped modes, is achieved by considering the geometrical mean of both wave amplitudes. It will be shown that the initial push on the plasma is provided by the mechanical heating input, and that further out the Alfvén waves take over energetically. 相似文献
80.
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