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Search Results: 1 - 10 of 342463 matches for " D. V.;Silva "
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Simulations of incompressible fluid flows by a least squares finite element method
Pereira, V. D.;Campos Silva, J. B.;
Journal of the Brazilian Society of Mechanical Sciences and Engineering , 2005, DOI: 10.1590/S1678-58782005000300009
Abstract: in this work simulations of incompressible fluid flows have been done by a least squares finite element method (lsfem) using velocity-pressure-vorticity and velocity-pressure-stress formulations, named u-p-w and u-p-t formulations respectively. these formulations are preferred because the resulting equations are partial differential equations of first order, which is convenient for implementation by lsfem. the main purposes of this work are the numerical computation of laminar, transitional and turbulent fluid flows through the application of large eddy simulation (les) methodology using the lsfem. the navier-stokes equations in u-p-w and u-p-t formulations are filtered and the eddy viscosity model of smagorinsky is used for modeling the sub-grid-scale stresses. some benchmark problems are solved for validate the numerical code and the preliminary results are presented and compared with available results from the literature.
Coefficient modules and Rees polynomials of arbitrary modules
V. H. Jorge Perez,M. D. Silva
International Journal of Algebra , 2012,
Abstract:
Simulations of incompressible fluid flows by a least squares finite element method
Pereira V. D.,Campos Silva J. B.
Journal of the Brazilian Society of Mechanical Sciences and Engineering , 2005,
Abstract: In this work simulations of incompressible fluid flows have been done by a Least Squares Finite Element Method (LSFEM) using velocity-pressure-vorticity and velocity-pressure-stress formulations, named u-p-omega and u-p-tau formulations respectively. These formulations are preferred because the resulting equations are partial differential equations of first order, which is convenient for implementation by LSFEM. The main purposes of this work are the numerical computation of laminar, transitional and turbulent fluid flows through the application of large eddy simulation (LES) methodology using the LSFEM. The Navier-Stokes equations in u-p-omega and u-p-tau formulations are filtered and the eddy viscosity model of Smagorinsky is used for modeling the sub-grid-scale stresses. Some benchmark problems are solved for validate the numerical code and the preliminary results are presented and compared with available results from the literature.
Runaway and hypervelocity stars. The supernova connection
Ralf Napiwotzki,Manuel D. V. Silva
Physics , 2011,
Abstract: We present an investigation of the known sample of runaway stars. The orbits of these stars are traced back to their origin in the Galactic disc. The velocity distribution of these stars is compared to theoretical predictions. We conclude that the majority of stars is well explained by the standard binary ejection mechanism (BEM) and the dynamical ejection mechanism (DEM). However, we find a sample of ten stars which has ejection velocities in excess of those predicted by standard scenarios. We discuss how these can be explained by a variant of the BEM. This mechanism can create runaway stars exceeding the Galactic escape velocity (known as hypervelocity stars). The number of runaway stars in our Galaxy is estimated and compared to the known sample of high mass X-ray binaries, whose formation is linked to the BEM channel.
High Galactic latitude runaway stars as tracers of the spiral arms
M. D. V. Silva,R. Napiwotzki
Physics , 2013, DOI: 10.1093/mnras/stt177
Abstract: A direct observation of the spiral structure of the Galaxy is hindered by our position in the middle of the Galactic plane. We propose a method based on the analysis of the birthplaces of high Galactic latitude runaway stars to map the spiral arms and determine their dynamics. As a proof of concept, the method is applied to a local sample of early-type stars and a sample of runaways stars to obtain estimates of the pattern speed and the spiral arm's phase angle. We also estimate the performance of this method once the data gathered by Gaia, in particular for runaway stars observed on the other side of the Galaxy, is available.
Ejection velocities of high Galactic latitude runaway stars
M. D. V. Silva,R. Napiwotzki
Physics , 2010, DOI: 10.1111/j.1365-2966.2010.17864.x
Abstract: We estimate the distribution of ejection velocities for the known population of high galactic latitude runaway stars. The initial sample is a collection of 174 early-type stars selected from the literature. The stars are first classified according to their evolutionary status in order to obtain a homogeneous sample of 96 genuine main sequence stars. Their present velocities and flight times are then estimated using proper motion data from various astrometric catalogues (including Tycho-2, UCAC2, and USNO-B) and the ejection velocities are computed by tracing their orbits back in time, based on a galactic potential. The potential used is constructed from a mass density model chosen to fit the most recent observational constraints. We find evidence for two different populations of runaway stars: a "high" velocity population, with a maximum ejection velocity of about 400 - 500 km/s, and a "low" velocity population, with a maximum ejection velocity of about 300 km/s. We argue that the observed limit of 500 km/s and the bimodality of the observed ejection velocity distribution are natural consequences of the so-called Binary Ejection Mechanism. We discuss the connection between the "high" velocity population and the so-called hypervelocity stars, showing how previously studied hypervelocity stars are consistent with the results obtained. We also find that some stars that were once thought to be best explained as being formed in the Halo are compatible with a runaway hypothesis once proper motions are included in the analysis. However, three stars in the selected sample appear to be inconsistent with ejection from the galactic disc. Possible scenarios are discussed, including a possible formation in the galactic halo.
Characterization of Meloidogyne incognita populations from S?o Paulo and Minas Gerais state and their pathogenicity on coffee plants
Oliveira, Dagoberto S.;Oliveira, Rosangela D'Arc Lima;Silva, Débora G.;Silva, Rodrigo V.;
Tropical Plant Pathology , 2011, DOI: 10.1590/S1982-56762011000300008
Abstract: meloidogyne incognita is one of the most aggressive and harmful plant-parasitic nematodes attacking coffee plantations in brazil. however, populations from minas gerais state (mg) do not incite disease on coffee plants as strongly as populations from s?o paulo state (sp). this study aimed to compare the capacity to incite disease on coffee plants from sp and mg-populations based on penetration and post-infective development of second-stage juveniles (j2) stage. both populations were confirmed as m. incognita by using esterase phenotype i1 and species-specific pcr. physiologically they were classified as race 2 by differential host test. susceptible (c. arabica 'catuaí vermelho iac 44') and resistant coffee seedlings (c. canephora 'apoat? iac 2258') were inoculated with j2 and assessed for penetration and development from 2nd to 40th day after inoculation. although the penetration rate of the j2 from both populations was higher in susceptible than in resistant seedlings, the sp-population showed a higher penetration than the mg-population for both variables. post-infective development proceeded only in individuals of the sp-population in susceptible seedlings. the incompatibility between the mg-population and coffee seedlings was evident at the penetration phase, which was also followed by post-penetration resistance factors leading to significant j2 emigration, impeding nematode establishment.
The drying of sewage sludge by immersion frying
Silva, D. P.;Rudolph, V.;Taranto, O. P.;
Brazilian Journal of Chemical Engineering , 2005, DOI: 10.1590/S0104-66322005000200015
Abstract: the objective of this work was to dry sewage sludge using a fry-drying process. the frying experiments were carried out in commercial fryers modified by adding thermocouples to the setup. during frying, typical drying curves were obtained and it was verified that, in relation to the parameters: oil temperature, oil type and shape of the sample, the shape factor the most effect on the drying rate, at least within the range chosen for the variables studied. oil uptake and calorific value were also analyzed. the calorific value of the samples increased with frying time, reaching values around 24mj/kg after 600s of frying (comparable to biocombustibles such as wood and sugarcane bagasse). the process of immersion frying showed great potential for drying materials, especially sewage sludge, obtaining a product with a high energy content, thereby increasing its value as a combustible.
Estudo da intercala??o de compostos organicos em caulins na forma ácida
Fernandes, M. V. da S.;Silva, L. R. D. da;
Ceramica , 2011, DOI: 10.1590/S0366-69132011000200014
Abstract: the feasibility of using major clays such as kaolin in the adsorption processes, can occur through chemical modification by intercalation in their structures phyllite. samples of kaolin in the region of northeast brazil, one white and one gray of a portion of the region borborema-served in the state of paraiba, were interspersed with dimethylsulfoxide, oxalic acid and citric acid. the characterization natural and modified techniques were used x-ray diffraction, thermal analysis and absorption spectroscopy in the infrared.
Controle químico de Typha subulata em dois estádios de desenvolvimento
Silva, J.R.V.;Martins, D.;
Planta Daninha , 2004, DOI: 10.1590/S0100-83582004000300014
Abstract: the aim of this research was to evaluate cattail chemical control in two growth stages: full vegetative development (0.50-0.70 m) and full flowering. the herbicide rates applied were: imazapyr at 250, 500 and 750 g ha-1 plus aterbane at 0.5%; imazapyr at 250, 500 and 750 g ha-1 plus 0.01% of silwet; glyphosate at 3,360 and 4,320 g ha-1 plus aterbane at 0.5%; glyphosate at 3,360 and 4,320 g ha-1 plus 0.01% of silwet, and a check without herbicide treatment. the experiment was arranged in a completely randomized design, with four replications. treatments were sprayed using a co2 backpack sprayer at 220 kpa, with two xr teejet 8002s nozzle tips, with a spray volume of 200 l ha-1. at the end of the experiment, cattail plants at full vegetative development stage were more susceptible to the herbicides than at full flowering, with acceptable control being observed either by imazapyr or glyphosate, except at the rate of 250 g ha-1 of imazapyr with 0.5% of aterbane. at the full vegetative development stage, aterbane was less effective than silwet when added to the lowest rate of imazapyr.
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