A prefetching technique for prediction of porous media flows     

V. Ginting  F. Pereira  A. Rahunanthan 《Computational Geosciences》2014,18(5):661-675

In many applications in flows through porous media, one needs to determine the properties of subsurface to detect, monitor, or predict the actions of natural or induced forces. Here, we focus on two important subsurface properties: rock permeability and porosity. A Bayesian approach using a Markov Chain Monte Carlo (MCMC) algorithm is well suited for reconstructing the spatial distribution of permeability and porosity, and quantifying associated uncertainty in these properties. A crucial step in this approach is the computation of a likelihood function, which involves solving a possibly nonlinear system of partial differential equations. The computation time for the likelihood function limits the number of MCMC iterations that can be performed in a practical period of time. This affects the consistency of the posterior distribution of permeability and porosity obtained by MCMC exploration. To speed-up the posterior exploration, we can use a prefetching technique, which relies on the fact that multiple likelihoods of possible states into the future in an MCMC chain can be computed ahead of time. In this paper, we show that the prefetching technique implemented on multiple processors can make the Bayesian approach computationally tractable for subsurface characterization and prediction of porous media flows.  相似文献   

Total mercury in sediments from mud volcanoes in Gulf of Cadiz     

Mieiro CL  Pato P  Pereira E  Mirante F  Coutinho JA  Pinheiro LM  Magalhães VH  Duarte AC 《Marine pollution bulletin》2007,54(9):1539-1544

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An easy, non-destructive, probabilistic method to evaluate the imposex response of gastropod populations     

Fernandez MA  Pinheiro FM  de Quadros JP  Camillo E 《Marine environmental research》2007,63(1):41-54

Endocrine disruption in marine populations is a growing concern. One of the best documented examples is imposex, the development of male characteristics in female gastropods, including the development of a penis and/or vas deferens, by exposure to organotins, mainly tributyltin. This syndrome has been an effective and widely used biomarker of organic tin contamination for almost 20 years. However, established imposex evaluation protocols sacrifice all the animals and repeated assessments can result in depletion of populations. To preserve animal lives as much as possible and to have a fast screening of areas subjected to organotin impacts, a non-destructive approach was tested. This approach uses reversible narcotization and a statistical criterion to evaluate the extent of imposex in the populations, instead of imposex indexes, which are based on evaluation of sacrificed, fixed animals. The data consist of two categories: males plus masculinized females in one category and normal females in another. The probability is then calculated that this sample could have been drawn from a normal population. This new method was tested in two contrasting areas of Brazil and with two different species, and the results compared to the conventional evaluation. Narcotization was completely reversed with a survival rate of 98%. Impacted sites could be identified with this technique in the same way as with the conventional one. The only limitation was that female sterility could not be verified. This disadvantage could well be compensated by the minimal mortality in the studied populations.  相似文献   

Mercury contamination in invertebrate biota in a temperate coastal lagoon (Ria de Aveiro, Portugal)     

Coelho JP  Policarpo E  Pardal MA  Millward GE  Pereira ME  Duarte AC 《Marine pollution bulletin》2007,54(4):475-480

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Long-Term Trends in Intertidal and Subtidal Benthic Communities in Response to Water Quality Improvement Measures     

Paula Chainho  Gilda Silva  Michael F. Lane  José L. Costa  Tadeu Pereira  Carla Azeda  Pedro R. Almeida  Inês Metelo  Maria J. Costa 《Estuaries and Coasts》2010,33(6):1314-1326

Long-term monitoring studies are needed to understand changes in ecosystem status when restoration measures are implemented. A long-term data series (1996–2007) of the Tagus estuary (Portugal) intertidal and subtidal benthic communities was collected in a degraded area where mitigation measures were implemented. Multivariate analysis was used to analyze spatial and temporal patterns in benthic community composition and trends in five benthic community metrics (i.e., taxonomic richness, density, biomass, Shannon–Wiener diversity and the AMBI index) were also examined. The results revealed a clear separation between intertidal and subtidal assemblages, although they had 50% of taxa in common, including the most abundant. Significant positive trends were found for all metrics showing that both intertidal and subtidal communities responded to the restoration measures implemented. Nevertheless, biotic indices need some adaptation before being universally applied to intertidal and subtidal habitats.  相似文献   

Mercury fluxes between an impacted coastal lagoon and the Atlantic Ocean   总被引：1，自引：1，他引：0  

P. Pato  C. Lopes  M. Vlega  A.I. Lilleb  J.M. Dias  E. Pereira  A.C. Duarte 《Estuarine, Coastal and Shelf Science》2008,76(4):787-796

The objective was to estimate the seasonal and inter-tidal variability of dissolved and particulate mercury fluxes between the Ria de Aveiro (Portugal) and the Atlantic Ocean. The mercury fluxes were estimated by means of a two-dimensional vertically integrated hydrodynamic model. Results showed that the particulate fraction plays an important role in the transport of mercury while the contribution of the seston fraction to the transport of mercury was always <0.5%. During spring tides, in summer, about 2% of mercury transported in seston was present in an organic form. The mass balance for the mercury fractions revealed that the mercury export to the Atlantic Ocean varied with season and tidal regime, mainly in terms of the relative importance of the dissolved and particulate fractions. An approximate range of values for the annual mass balance between 42 and 77 kg shows that the export of dissolved and particulate mercury makes little impact on the near shore region of the Atlantic Ocean and that the recovery of the lagoon from mercury contamination is likely to remain a long-term issue.  相似文献   

The Solar Irradiance Spectrum at Solar Activity Minimum Between Solar Cycles 23 and 24     

G. Thuillier  D. Bolsée  G. Schmidtke  T. Foujols  B. Nikutowski  A. I. Shapiro  R. Brunner  M. Weber  C. Erhardt  M. Hersé  D. Gillotay  W. Peetermans  W. Decuyper  N. Pereira  M. Haberreiter  H. Mandel  W. Schmutz 《Solar physics》2014,289(6):1931-1958

On 7 February 2008, the SOLAR payload was placed onboard the International Space Station. It is composed of three instruments, two spectrometers and a radiometer. The two spectrometers allow us to cover the 16?–?2900 nm spectral range. In this article, we first briefly present the instrumentation, its calibration and its performance in orbit. Second, the solar spectrum measured during the transition between Solar Cycles 23 to 24 at the time of the minimum is shown and compared with other data sets. Its accuracy is estimated as a function of wavelength and the solar atmosphere brightness-temperature is calculated and compared with those derived from two theoretical models.  相似文献   

Ground-based measurements of local cloud cover     

Abel Antônio Silva  Mariza Pereira de Souza Echer 《Meteorology and Atmospheric Physics》2013,120(3-4):201-212

Clouds are believed to reflect temporal climate changes through variations in their amounts, characteristics, and occurrence. In addition, they reflect both weather and climate in a region. In this work, a methodology to determine the local cloud cover (LCC) is proposed using sky images obtained from a ground-based instrument. Three years of sky images from an urban, tropical site were obtained and analyzed through that methodology. Monthly average LCC varied from 3 to 96 %, while seasonal average values were 68 % for summer, 54 % for spring, 46 % for fall, and 23 % for winter. LCC results show a clear seasonal dependence and a fair agreement (r ² = 0.72) with satellite data, which typically underestimate the cloud cover in relation to LCC. Our analysis also suggests the possibility of a measurable link between LCC and natural events like the El Niño Southern Oscillation.  相似文献   

Vegetation patterns in South America associated with rising CO2: uncertainties related to sea surface temperatures     

Marcos Paulo Santos Pereira  Marcos Heil Costa  Ana Cláudia Mendes Malhado 《Theoretical and Applied Climatology》2013,111(3-4):569-576

Spatially precise forecasts of the impacts of climate change on the distribution of major vegetation types are essential for the implementation of effective conservation and land use policy. However, existing studies frequently omit major sources of climate variability that can significantly increase the uncertainty of projections. In this study we demonstrate how different predictions for sea surface temperature (SST) for the first half of the twenty-first century increase the uncertainty associated with forecasts of the future distribution of major ecosystems in South America. This is demonstrated through a numerical experiment using a coupled climate–vegetation model (CCM3-IBIS) for IPCC emission scenario A2 that incorporates the SST data from ten different models. The study reveals an increasing uncertainty in the ability to forecast future vegetation patterns, such that by 2050 the simulation is unable to robustly forecast the vegetation cover in an area equivalent to 28 % in South America (5?×?10⁶ km²). The future of the central and northeastern regions of Brazil is especially uncertain, with outcomes, ranging from savanna, and open shrubland to grassland. Recognizing and managing such uncertainty should be a priority for decision makers.  相似文献   

Straw Blankets Sewn With Recycled Plastic Threads for Erosion and Urban Sediments Control     

Terezinha Cássia de Brito Galvão  Aloisio Rodrigues Pereira  Arnaldo Teixeira Coelho  Paula Rodrigues Pereira  Joaquim Fernandes Teixeira Coelho 《Geotechnical and Geological Engineering》2011,29(1):49-55

Soil erosion, transport and deposition of sediments represent invisible threats that along time can affect negatively the existing infrastructure of roads and dams, and the quality of air and water resources. In the last decades, a great number of researches were devoted to study erosion and sediments transportation processes. However, they addressed mostly areas of agriculture, water impoundments for dams, and land conservation. A lack of studies for erosion processes in urban areas is evident, in special those aiming to diminish the deposition of sediments originated from urban areas into the rivers and air, in special as airborne particulate. Traditionally, the costs associated in controlling erosion and sediments in urban areas are high and in some case, out of the range for most developing countries. Factors responsible for those high prices are the use of heavy equipments for soil grading and transportation, the use of costly building materials, and the need for employing more specialized personnel. In the case of gullies in urban areas, another concern is to ensure proper equipment access to the area for remediation operations. Hereby, it is presented a cost-effective method to recover an extensive gully erosion area of about 11,000 m² located in urban area. Estimated sediments released from this area to the water resources and air were estimated on about 66,000,000 tons. In this study area, bioengineering works were performed in 60 days, with hardly any sediment generated outside the work area resulting from bioengineering operations. A combination of bioengineering techniques were chosen for this study area, which was a mixture of rigid and biological products including biologs, silt fence, biodegradable straw blankets sewn with plastic threads derived from recycled PET bottles, among others. An efficient drainage system was implemented for preventing upland flow, sub-seepage and seepage. Biologs were used aiming to fulfill a double role, the first as barrier to soil sediments flow, and the second as filler for empty spaces, avoiding expensive grading operations. All engineering works were concluded in about 60 days at a cost of US0.89/m < sup > 2 < /sup > . This price is cost-effective if compared with the traditional engineering cost of approximately US 0.89/m². This price is cost-effective if compared with the traditional engineering cost of approximately US 2.92/m² because it includes extensive use of grading and soil transportation. An environmental advantage of the bioengineering method is the immediate reduction of airborne particulates. Furthermore, the overall visual aesthetics improved shortly after the implementation of the works because the bare ground was substituted by native vegetation. After 6 months the vegetation in the gully erosion area was totally established. Monitoring was performed after 12 months and no erosion and sediment transport was visually noticed. The ease implementation of this technique without the need for specialized workers in combination with low prices makes this method a model for developing countries.  相似文献