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Jesus Berrocal Yara Marangoni Nelsí C. de S Reinhardt Fuck Jos E.P. Soares E. Dantas Fbio Perosi Celia Fernandes 《Tectonophysics》2004,388(1-4):187
Interpretation of seismic refraction data in the central sector of Tocantins Province, Central Brazil, has produced a seismic crustal model with well-defined upper, intermediate, and lower crust layers having smooth velocity gradient in each layer. The depths to Moho vary from 32 to 43 km, and mean crustal P velocity varies from 6.3 km/s, beneath Goiás magmatic arc on the western side, to 6.4 km/s, below Goiás massif in the central portion and the foreland fold-and-thrust belt on the eastern side. The behaviour of the lower crust layer allows an improved understanding of regional gravimetric features of the central and northern sectors of Tocantins Province and suggests subduction of the Amazon plate in Central Brazil. In the southeastern sector, the refraction experiment resulted in the detection of a thinner crust (38 km) below Brasília fold belt and a thicker crust (41 km) below Paraná basin and São Francisco craton (42 km). The upper crust beneath Paraná Basin is around 20 km thick, whereas it is less than 10 km thick below the craton. These results bring new insights into the geological history of the central and southeastern sectors of Tocantins Province.Gravimetric measurements in the central sector of Tocantins Province delineate a high and a low anomaly separated by a steep gradient with a NE direction. The axis of the gradient seems to bend still further to NE in the northern sector of that province, whereas the gravimetric high continues northwards, defining a separation between them. This suggests that those features belong to different tectonic processes that occurred during Tocantins Province orogenesis. The gravimetric model, which incorporates seismically resolved structure beneath Tocantins Province, better matches the observed gravimetric data.Although tectonic movements have only been monitored with high-precision GPS for short time interval (1999–2001), the results suggest observable deformations. The main seismicity of Central Brazil, the Goiás–Tocantins seismic belt, seems to be spatially associated with the large gravimetric high anomaly and with the observed tectonic deformation. 相似文献
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Edgardo D. Cerqueira Alicia M. Senz Celia M. Rabotnikof 《Journal of Arid Environments》2004,59(4):645-656
This study assessed the nutritive value of the most important forage species of the Calden forest (central semi-arid La Pampa, Argentina), for samples collected in fall, winter and spring, under grazing conditions and during two successive years, for ranges of good and fair conditions. The crude protein concentration (CP) of short-winter grasses (Piptochaetium napostaense, Poa ligularis, Stipa clarazii and Hordeum stenostachys) was about 10%. Mid-winter grasses (S. tenuissima and S. gynerioides) never reached 6% CP. Summer grasses (Digitaria californica and Trichloris crinita) ranged from 7% to 9% CP. In vitro dry matter digestibility (IVDMD) was similar among short-winter and summer grasses (40–50%). Mid-winter grasses had the lowest IVDMD for all seasons (<40%). Effects of sampling year and range condition on CP were consistently significant only for short-winter grasses. Good condition ranges provide a more acceptable forage supply than fair condition ranges. 相似文献
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Orthogonal collocation and alternating-direction procedures for unsaturated flow problems 总被引：2，自引：0，他引：2
The alternating-direction collocation method has recently been developed for general parabolic equations. In order to test the applicability of the procedure to highly nonlinear problems, an alternating-direction collocation algorithm is developed to simulate two-dimensional flow in unsaturated porous media. The algorithm employs an alternating-direction solution procedure within the framework of a modified Picard iteration scheme. Numerical behaviour of the new procedure is compared to the behaviour of a standard two-dimensional collocation formulation. The new method is also tested on several infiltration problems of practical interest, including a layered and sloping soil. Results demonstrate the method to be accurate and highly mass conservative. The algorithm also produces significant savings in both execution time and storage. 相似文献
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Geochemical reaction rate laws are often measured using crushed minerals in well-mixed laboratory systems that are designed to eliminate mass transport limitations. Such rate laws are often used directly in reactive transport models to predict the reaction and transport of chemical species in consolidated porous media found in subsurface environments. Due to the inherent heterogeneities of porous media, such use of lab-measured rate laws may introduce errors, leading to a need to develop methods for upscaling reaction rates. In this work, we present a methodology for using pore-scale network modeling to investigate scaling effects in geochemical reaction rates. The reactive transport processes are simulated at the pore scale, accounting for heterogeneities of both physical and mineral properties. Mass balance principles are then used to calculate reaction rates at the continuum scale. To examine the scaling behavior of reaction kinetics, these continuum-scale rates from the network model are compared to the rates calculated by directly using laboratory-measured reaction rate laws and ignoring pore-scale heterogeneities. In this work, this methodology is demonstrated by upscaling anorthite and kaolinite reaction rates under simulation conditions relevant to geological CO2 sequestration. Simulation results show that under conditions with CO2 present at high concentrations, pore-scale concentrations of reactive species and reaction rates vary spatially by orders of magnitude, and the scaling effect is significant. With a much smaller CO2 concentration, the scaling effect is relatively small. These results indicate that the increased acidity associated with geological sequestration can generate conditions for which proper scaling tools are yet to be developed. This work demonstrates the use of pore-scale network modeling as a valuable research tool for examining upscaling of geochemical kinetics. The pore-scale model allows the effects of pore-scale heterogeneities to be integrated into system behavior at multiple scales, thereby identifying important factors that contribute to the scaling effect. 相似文献
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Fragmentation as a Strategy for Caulerpa Species: Fates of Fragments and Implications for Management of an Invasive Weed 总被引：7，自引：0，他引：7
Abstract. The successful growth of fragments to full size macroalgal clones is well known for many taxa in mariculture. From an ecological context, however, few studies relate success by invasive species to the ability to fragment readily, disperse widely or re-attach rapidly - obvious hallmarks of weedy species. This study compares morphologically and ecologically distinct species of the green alga Caulerpa : in the Mediterranean, Caulerpa taxifolia is well known as an invasive weed; Caulerpa prolifera grows around or inside seagrass beds and is not apparently invasive; Caulerpa verticillata is among the most diminutive species, with potentially the most restricted reef distribution. We tested three hypotheses: (i) fragment success is independent of size, (ii) fragment success is independent of position within the plant and (iii) fragments from all species will be equally successful in establishing rhizoids, the first step to re-attachment. The success of small fragments (5–40 mm lengths) cut from distinct locations within replicate plants was scored for survival and establishment of rhizoids in bioassays. Additionally, for C. taxifolia , estimates were made of the force needed to puncture upright and prostrate axes, thereby estimating forces required to generate fragments from these two sources. Among the three species, only upright axes of C. taxifolia readily recovered from fragmentation stress for fragment sizes > 10 mm. The forces required to fragment upright axes were substantially less than for comparable rhizome portions. Fragments of C. prolifera were viable only for rhizome portions; fragments of C. verticillata were not viable at any size examined in this study. Estimates of viable fragment size, origin and force required to fragment axes for C. taxifolia support existing field data suggesting that fragmentation is the effective propagation mechanism underlying the spread of this invasive weed. 相似文献
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Celia Olabarria Iván F. Rodil Mónica Incera Jesús S. Troncoso 《Marine environmental research》2009,67(3):153-158
Invasive species represent a serious threat to natural ecosystems through a range of negative effects on native species in the region invaded. The invasive species Sargassum muticum has invaded several temperate regions worldwide including the Galician rocky shoreline (northwestern Spain) in Western Europe. The main aim of this study was to assess if colonization by S. muticum has any effect on native algal assemblages by experimental removal of S. muticum. We predicted that in those plots where S. muticum plants were removed, the structure of native algal assemblages would differ from that in plots where S. muticum plants were untouched. In addition, we predicted that the effect of Sargassum removal would be more important than other causes of variability at the small scale investigated. Results indicated limited impact of S. muticum on native assemblages. The impact was only evident on the total number of native taxa and two understory morpho-functional groups, filamentous and foliose algae, rather than on the entire macroalgal assemblages. 相似文献
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Francesca Rossi Celia Olabarria Mónica Incera Josefina Garrido 《Journal of Sea Research》2010,63(1):52-61
Native and exotic seaweeds frequently lie on the beach and sustain part of the benthic food web. However, the role of exotic seaweeds as food sources for beach consumers has been poorly studied. We studied the temporal and spatial variability in the trophic significance of the invasive brown seaweed Sargassum muticum on sandy beaches. We measured the stable isotopes (δ13C and δ15N) in the tissues of S. muticum and of invertebrate consumers and estimated the dietary biomass proportion of S. muticum during four sampling dates at two beaches and heights on the shore. Samples were collected from eight pitfall traps placed at a distance of 2 m from each other. Detrital macroalgae and seagrasses were also collected by hand within an area of 30 cm around each pitfall trap. We measured the spatial and temporal variability in the isotope composition of the beach consumers and of S. muticum using different models of analyses of variance. We then calculated the biomass proportion of S. muticum to the animal diet with a two-isotopic mixing model. The invasive alga S. muticum seemed to be one of the main food sources for the amphipod Talitrus saltator and, to a less extent, for the isopod Tylos europaeus. The importance of S. muticum was however temporally variable and decreased during spring (in March and May), probably due to the availability of native macrophytes. The supply of invasive wrack to beach food webs thus deserves more attention if we want to understand their role in influencing food web dynamics. 相似文献
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Large-scale implementation of geological CO2 sequestration requires quantification of risk and leakage potential. One potentially important leakage pathway for the injected
CO2 involves existing oil and gas wells. Wells are particularly important in North America, where more than a century of drilling
has created millions of oil and gas wells. Models of CO2 injection and leakage will involve large uncertainties in parameters associated with wells, and therefore a probabilistic
framework is required. These models must be able to capture both the large-scale CO2 plume associated with the injection and the small-scale leakage problem associated with localized flow along wells. Within
a typical simulation domain, many hundreds of wells may exist. One effective modeling strategy combines both numerical and
analytical models with a specific set of simplifying assumptions to produce an efficient numerical–analytical hybrid model.
The model solves a set of governing equations derived by vertical averaging with assumptions of a macroscopic sharp interface
and vertical equilibrium. These equations are solved numerically on a relatively coarse grid, with an analytical model embedded
to solve for wellbore flow occurring at the sub-gridblock scale. This vertical equilibrium with sub-scale analytical method
(VESA) combines the flexibility of a numerical method, allowing for heterogeneous and geologically complex systems, with the
efficiency and accuracy of an analytical method, thereby eliminating expensive grid refinement for sub-scale features. Through
a series of benchmark problems, we show that VESA compares well with traditional numerical simulations and to a semi-analytical
model which applies to appropriately simple systems. We believe that the VESA model provides the necessary accuracy and efficiency
for applications of risk analysis in many CO2 sequestration problems. 相似文献