171 resultados para Minimal surfaces.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
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Purpose: To evaluate the effect of finishing and polishing techniques on surface roughness of resin-based composites (RBCs). Materials and Methods: Forty specimens of each material were cured under Mylar strips and immersed in artificial saliva for 1 wk. Samples were tested with a profilometer to obtain baseline average surface roughness (Ra). Specimens of both RBCs were then finished and polished according to four techniques: (1) Sof-Lex disks; (2) Sof-Lex disks followed by Prisma Gloss; (3) Enhance points; (4) Enhance points followed by Prisma Gloss application. New readings of the roughness pattern were carried out and the difference of post-polishing and baseline values were analyzed. Results: ANOVA test (alpha= 0.05) did not show differences between materials (P= 0.9393) nor interaction effects (P= 0.3094), but significant difference among the finishing/polishing techniques were detected (P= 0.0157). Tukey's test showed that the smoothest surface was obtained when the specimens were treated by Sof-Lex followed by Prosma Gloss polishing paste; and the worst results were obtained after using Enhance points alone.
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
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Red blood cells (RBCs) from most vertebrates restore volume upon hypertonic shrinkage and the mechanisms underlying this regulatory volume increase (RVI) have been studied extensively in these cells. Despite the phylogenetically interesting position of reptiles, very little is known about their red cell function. The present study demonstrates that oxygenated RBCs in all major groups of reptiles exhibit no or a very reduced RVI upon -25% calculated hyperosmotic shrinkage. Thus, RBCs from the snakes Crotalus durissus and Python regius, the turtle Trachemys scripta and the alligator Alligator mississippiensis showed no statistically significant RVI within 120 min after shrinkage, while the lizard Tupinambis merianae showed 22% volume recovery after 120 min. Amiloride (10(-4) M) and bumetanide (10(-5) M) had no effect on the RVI in T merianae, indicating no involvement of the Na(+)/H(+) exchanger (NHE) or the Na(+)/K(+)/2Cl(-) co-transporter (NKCC) or insentive transporters. Deoxygenation of RBCs from A. mississippiensis and T merianae did not significantly affect RVI upon shrinkage. Deoxygenation per se of red blood cells from T merianae elicited a slow volume increase, but the mechanism was not characterized. It seems, therefore, that the RVI response based on NHE activation was lost among the early sauropsids that gave rise to modern reptiles and birds, while it was retained in mammals. An RVI response has then reappeared in birds, but based on activation of the NKCC. Alternatively, the absence of the RVI response may represent the most ancient condition, and could have evolved several times within vertebrates. (C) 2008 Elsevier B.V. All rights reserved.
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
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The recent experimental results on neutrino oscillation and on muonium-antimuonium conversion require extension of the minimal 3-3-1 model. We review the constraints imposed on the model by these measurements and suggest a pattern of leptonic mixing, with charged leptons in a non-diagonal basis, which accounts for the neutrino physics and circumvents the tight muonium-antimuonium bounds on the model. We also illustrate a scenario where this pattern could be realized.
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In the minimal 3-3-1 model charged leptons come in a nondiagonal basis. Moreover, the Yukawa interactions of the model lead to a non-hermitian charged lepton mass matrix. In other words, the minimal 3-3-1 model presents a very complex lepton mixing. In view of this we check rigorously if the possible textures of the lepton mass matrices allowed by the minimal 3-3-1 model can lead or not to the neutrino mixing required by the recent experiments in neutrino oscillation.
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The measurability of the non-minimal coupling is discussed by considering the correction to the Newtonian static potential in the semiclassical approach. The coefficient of the gravitational Darwin term (GDT) gets redefined by the non-minimal torsion scalar couplings. Based on a similar analysis of the GDT in the effective field theory approach to non-minimal scalar, we conclude that for reasonable values of the couplings the correction is very small.
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)