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Search Results: 1 - 10 of 203936 matches for " Tavares P. "
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Relevant Factors to a Statistical Analysis of Overvoltages - Application to Three-Phase Reclosing of Compensated Transmission Lines  [PDF]
P. Mestas, M.C. Tavares
Energy and Power Engineering (EPE) , 2013, DOI: 10.4236/epe.2013.54B221
Abstract: This paper describes the statistical study of important factors that influences transient over voltages resulting from three-phase reclosing of shunt compensated transmission lines. These factors include the model used for transmission line representation and the influence of line transposition. Additionally, the over voltages reduction to proper levels depending on the type of control technique are illustrated and analyzed in statistical terms. The evaluation covers three shunt compensation degrees. The digital simulations were performed using the PSCAD/EMTDC software.
Structural Changes in Macroinvertebrate Communities Associated with Reduction in the Management of Coastal Saltpans
P. C. Tavares,D. Alves,M. Shapouri
Journal of Marine Biology , 2009, DOI: 10.1155/2009/629310
Abstract: Saltpans with different management levels were studied for macroinvertebrate community and abiotic variables like water depth, water conductivity, and organic matter in sediments. Significant variation was observed between saltpans, between ponds within saltpans, and between periods within ponds for abundance, and also between saltpans for biomass. Environmental variables varied significantly between saltpans and between ponds. Significant positive correlations occurred between depth and total abundance, between depth and Corixidae abundance, and also between organic matter in sediments and diversity. Significant negative correlations were observed between depth and diversity and between organic matter in sediments and total abundance. Multidimensional Scaling and Canonical Correspondence Analysis confirmed results of analysis of variance and correlations. Invertebrate communities were numerically dominant as also revealed by ABC method. Abandoned saltpan ponds show the largest changes in water depth, with communities dominated by some opportunist species, varying within short temporal scales, which is typical from highly disturbed systems.
Fissility of actinide nuclei by 60-130 MeV photons
Morcelle, Viviane;Tavares, Odilon A. P.;
Brazilian Journal of Physics , 2006, DOI: 10.1590/S0103-97332006000800011
Abstract: nuclear fissilities obtained from recent photofission reaction cross section measurements carried out at saskatchewan accelerator laboratory (saskatoon, canada) in the energy range 60-130 mev for 232th, 233u, 235u, 238u, and 237np nuclei have been analysed in a systematic way. to this aim, a semiempirical approach has been developed based on the quasi-deuteron nuclear photoabsorption model followed by the process of competition between neutron evaporation and fission for the excited nucleus. the study reproduces satisfactorily well the increasing trend of nuclear fissility with parameter z2/a.
The Pirabas Formation (Early Miocene from Brazil) and the Tropical Western Central Atlantic Subprovince
Orangel Aguilera Socorro,Eduardo Tavares Páes
Boletim do Museu Paraense Emílio Goeldi : Ciências Naturais , 2012,
Abstract: The Neogene Tropical Western Central Atlantic-South American faunal assemblage from the Pirabas Formation (Early Miocene) has specific and unique features, which distinguishes it from the rest of the Proto-Caribbean Subprovince in diversity, paleoceanographic condition and ecosystems. Principal component analysis (PCA) distinguished three groups of localities with similar faunas (Group A: Ilha de Fortaleza, Col nia Pedro Teixeira and Praia de Fortalezinha; Group B: Esta o Agron mica, Ilha de Marajó, Turiacu, Baixo Parnaíba, Aricuru and Salinópolis; Group C: Capanema B-17 Mine) and five different depositional facies (surf zone, beach, lagoons, tidal channel and tidal delta), in agreement with previous geological studies showing heterogeneous paleoenvironments among the outcrops. These heterogeneous lithostratigraphic sequences suggest different members, and may be related to different ages along the Pirabas sequence. The Neogene Northwestern Atlantic Subprovince is erected to encompass this entire geographical area.
Thermodynamics of quantum spin chains with competing interactions
T. S. Tavares,G. A. P. Ribeiro
Statistics , 2013, DOI: 10.1088/1742-5468/2013/09/P09007
Abstract: We consider integrable quantum spin chains with competing interactions. We apply the quantum transfer matrix approach to these spin chains. This allowed us to derive a set of non-linear integral equations for the thermodynamics of these spin chains. We provide numerical solution of these integral equations for the entropy as function of magnetic field, temperature and the coupling constant. This allow us to assess, at low but finite temperature, the picture describing the ground state diagram for high spin chain and longer range interchain interactions.
Magnetocaloric effect in the spin-$1/2$ chain with competing interactions
T. S. Tavares,G. A. P. Ribeiro
Statistics , 2014, DOI: 10.1088/1742-5468/2014/11/P11026
Abstract: We study the magnetocaloric effect for the integrable antiferromagnetic Heisenberg spin chain with competing interactions. We computed the Gr\"uneisen parameter, which is closely related to the magnetocaloric effect, for the quantum spin chain in the thermodynamical limit. This is obtained by means of the solution of a set of non-linear integral equations, which describes the thermodynamics of the model. We also provide results for the entropy $S$ and the isentropes in the $(H,T)$ plane.
Quality of Electroless Ni-P (Nickel-Phosphorus) Coatings Applied in Oil Production Equipment with Salinity  [PDF]
Fernando B. Mainier, Maria P. Cindra Fonseca, Sérgio S. M. Tavares, Juan M. Pardal
Journal of Materials Science and Chemical Engineering (MSCE) , 2013, DOI: 10.4236/msce.2013.16001
Abstract:

The corrosion resistance of nickel-phosphorus (Ni-P) coatings and their mechanical properties in seawater have led inestigations into the development of new technologies and the replacement of some special alloys in equipment used in oil production, such as valves, tubing, sucker rod joints, pumps, riser, manifolds and subsea Christmas trees. These studies began with Brenner and Riddel who developed, in the 1940s, formulations for Ni-P deposition on carbon steel without using an electric current. Joint deposition of nickel and phosphorus on a metallic surface (carbon steel) without applying an external current is accomplished using cathodic reduction with hydrogen (H) from a reducing agent (sodium hypophosphite) and nickel salts. To assure good performance of a Ni-P coating, the deposit quality must be inspected and evaluated during the chemical deposition process or in the end product. The recommended test parameters are: thickness, layer uniformity, hardness, adhesion, porosity, corrosion resistance and chemical composition of the nickel-phosphorus coating. The purpose of this paper was to investigate the Ni-P coating process, to evaluate the b haviour of Ni-P in a saline environment using aqueous brine (3.5% - 30% sodium chloride by mass) and to present possible defects that could compromise the coating.

Application of NMR Relaxometry to Study Nanostructured Poly(vinyl alcohol)/MMT/Cephalexin Materials for Use in Drug Delivery Systems  [PDF]
Antonio de Pádua Castelo Branco Cunha, Maria Inês Bruno Tavares, Emerson Oliveira da Silva
Materials Sciences and Applications (MSA) , 2016, DOI: 10.4236/msa.2016.77034
Abstract: Polymers containing nanoparticles dispersed and distributed in the matrix can be used for control of drug release. In this work, hydrophilic matrix systems were prepared using poly(vinyl alcohol) and unmodified clay containing the same amount of cephalexin. The materials were obtained through in situ polymerization and were characterized by the conventional technique of FTIR and NMR relaxometry, through determination of proton spin-lattice relaxation time, in order to understand the molecular behavior of the new materials. The NMR relaxometry data showed that the new materials containing low quantities of clay (0.25% and 0.75%) and the same amount of cephalexin (0.5 g) had very good dispersion and distribution of the clay and drug in the polymer matrix. The combination of clay and cephalexin formed a more homogenous material with a narrow domain curve and low relaxation values. The material containing 0.25% clay presented a mixed morphology, with part exfoliated and part intercalated, as could be seen from the relaxation domain distribution, which was larger than that for material with 0.75% clay.
Streptococcus Gallolyticus Bacteraemia associated with colonic adenomatous polyps
A. Murinello,P. Mendon?a,C. Ho,P. Tavares
Jornal Português de Gastrenterologia , 2006,
Abstract: Bacteraemia due to Streptococcus gallolyticus is frequently associated with colorectal carcinoma, making evaluation of the gastrointestinal tract by colonoscopy obligatory in such cases. Bacterial endocarditis and purulent arthritis are also common in patients with these bacteraemias. Intestinal bacteria could behave as promoters of aberrant hyperproliferative behaviour in preneoplastic colorectal lesions, apparently due to chronic inflammatory processes and production of carcinogenic metabolites. The authors treated a patient with several tubular adenomatous polyps of the right colon, two of which showed areas of high-grade dysplasia adjacent to areas of infectious bacterial colitis associated with Streptococcus gallolyticus bacteraemia and unilateral ankle arthritis. A bacteriémia por Streptococcus gallolyticus associa-se frequentemente ao carcinoma colorrectal, tornando obrigatória a colonoscopia nestas situa es. A endocardite bacteriana e a artrite séptica s o também comuns neste tipo de bacteriémias. Tem sido levantada a hipótese das bactérias intestinais poderem ter um papel promotor de hiperprolifera o celular aberrante em les es cólicas pré-neoplásicas, aparentemente devido a processos inflamatórios crónicos e produ o de metabolitos carcinogénicos. Os autores apresentam o caso dum doente com vários pólipos adenomatosos tubulares do cólon direito, em dois dos quais se demonstrou uma área de displasia de alto grau adjacente a zona de colite infecciosa bacteriana, associados a quadro clínico de infec o sistémica por Streptococcus gallolyticus e artrite do tornozelo.
Longitudinal dynamics with RF phase modulation in the LNLS electron storage ring
N. P. Abreu,P. F. Tavares,R. H. A. Farias
Physics , 2006, DOI: 10.1103/PhysRevSTAB.9.1433
Abstract: In the Brazilian synchrotron light source, we observed that modulating the phase of the accelerating fields at approximately twice the synchrotron frequency suppressed remarkably well a longitudinal coupled-bunch mode of the beam driven by a higher order mode (HOM) in one of the radiofrequency (RF) cavities. In this work, we present the results of a set of systematic measurements, in single and multibunch mode, aimed at characterizing the effects of RF phase modulation on the beam. We compare those experiments with the results of tracking simulations and of a theoretical model in which Landau damping is the stabilizing mechanism that explains the suppression of the longitudinal coupled bunch instability. We also measure the frequency of the stable islands created in longitudinal phase space by phase modulation and the longitudinal beam transfer function (BTF) as a function of the modulation frequency and amplitude. The experimental results are in good agreement with theoretical expectations.
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