Ambipolar diffusion : self-similar solutions and MHD code testing. Cylindrical symmetry

Funding: This research has been supported by the Spanish Ministry of Science, Innovation and Universities through projects AYA2014-55078-P and PGC2018-095832-B-I00. The authors are also grateful to the European Research Council for support through the Synergy Grant number 810218 (ERC-2018-SyG). DNS acknowledges support by the Research Council of Norway through its Centres of Excellence scheme, project number 262622, and through grants of computing time from the Programme for Supercomputing. AWH gratefully acknowledges the financial support of STFC through the Consolidated grant, ST/S000402/1, to the University of St Andrews.Ambipolar diffusion is a process occurring in partially ionised astrophysical systems that imparts a complicated mathematical and physical nature to Ohm's law. The numerical codes that solve the magnetohydrodynamic (MHD) equations have to be able to deal with the singularities that are naturally created in the system by the ambipolar diffusion term. The global aim is to calculate a set of theoretical self-similar solutions to the nonlinear diffusion equation with cylindrical symmetry that can be used as tests for MHD codes which include the ambipolar diffusion term. First, following the general methods developed in the applied mathematics literature, we obtained the theoretical solutions as eigenfunctions of a nonlinear ordinary differential equation. Phase-plane techniques were used to integrate through the singularities at the locations of the nulls, which correspond to infinitely sharp current sheets. In the second half of the paper, we consider the use of these solutions as tests for MHD codes. To that end, we used the Bifrost code, thereby testing the capabilities of these solutions as tests as well as (inversely) the accuracy of Bifrost's recently developed ambipolar diffusion module. The obtained solutions are shown to constitute a demanding, but nonetheless viable, test for MHD codes that incorporate ambipolar diffusion. The Bifrost code is able to reproduce the theoretical solutions with sufficient accuracy up to very advanced diffusive times. Using the code, we also explored the asymptotic properties of our theoretical solutions in time when initially perturbed with either small or finite perturbations. The functions obtained in this paper are relevant as physical solutions and also as tests for general MHD codes. They provide a more stringent and general test than the simple Zeldovich-Kompaneets-Barenblatt-Pattle solution.PostprintPeer reviewe

Especiação redox de cromo em solo acidentalmente contaminado com solução sulfocrômica.

Determination of Cr(VI) and Cr(III) was studied in soil samples accidentally contaminated with sulphochromic solution. Molecular absorption spectrophotometry based on the diphenylcarbazide method was used for the determination of Cr(VI) after its alkaline extraction. The total chromium concentration was determined using ICP OES. The quantification of Cr(III) was accomplished by subtracting the Cr(VI) concentration from the total chromium concentration. Regardless of the known contamination of the soil samples by sulphochromic solution, concentrations of Cr(VI) were below the detection limit. Addition and recovery experiments for Cr(VI) in soil samples with and without organic matter indicated its influence on the reduction of Cr(VI) to Cr(III)

Rotavirus Genotypes Circulating in Brazil Before and After the National Rotavirus Vaccine Program: A Review.

We describe the rotavirus genotypes before and after rotavirus vaccine introduction in Brazil. 86 studies reported 6,884 (15.2%) rotavirus-episodes among 45,305 children. Rotavirus caused 22.4% and 11.6% of cases before and after vaccine introduction. G1P[8] and G9P[8], and G2P[4] and heterotypic-strains were most common before and after vaccine introduction. The vaccines may have selected heterotypic strains in this highly-vaccinated population

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Suplemento. Edição dos Trabalhos do 49 Congresso Brasileiro de Olericultura, Águas de Lindóia, ago. 200

Superluminal X-shaped beams propagating without distortion along a coaxial guide

In a previous paper [Phys. Rev. E64 (2001) 066603; e-print physics/0001039], we showed that localized Superluminal solutions to the Maxwell equations exist, which propagate down (non-evanescence) regions of a metallic cylindrical waveguide. In this paper we construct analogous non-dispersive waves propagating along coaxial cables. Such new solutions, in general, consist in trains of (undistorted) Superluminal "X-shaped" pulses. Particular attention is paid to the construction of finite total energy solutions. Any results of this kind may find application in the other fields in which an essential role is played by a wave-equation (like acoustics, geophysics, etc.). [PACS nos.: 03.50.De; 41.20;Jb; 83.50.Vr; 62.30.+d; 43.60.+d; 91.30.Fn; 04.30.Nk; 42.25.Bs; 46.40.Cd; 52.35.Lv. Keywords: Wave equations; Wave propagation; Localized beams; Superluminal waves; Coaxial cables; Bidirectional decomposition; Bessel beams; X-shaped waves; Maxwell equations; Microwaves; Optics; Special relativity; Coaxial metallic waveguides; Acoustics; Seismology; Mechanical waves; Elastic waves; Guided gravitational waves.]Comment: plain LaTeX file (22 pages), plus 15 figures; in press in Phys. Rev.

Metodologias para análise de isoenzimas e extração de DNA de Fusarium oxysporum f. sp. vasinfectum.

bitstream/CNPA/19696/1/COMTEC175.PD

Melhoria da germinação das sementes de mamoneira (Ricinus comunis L.) in vitro, através da quebra de dormência e desinfestação.

bitstream/CNPA-2009-09/22597/1/COMTEC125.pd